CASE NOTES
Entry and establishment of QLD Cattle tick to the North Coast of NSW through saleyard purchasing: A risk analysis for an uncertain future
Matt Ball, Senior District Veterinarian, North Coast LHPA and Paul Freeman, Regional Veterinary Officer, NSW DPI
Posted Flock & Herd July 2012
Contents
I KEY FINDINGS
II Introduction
Why would the LHPA write a paper on cattle tick?
Why a risk analysis by the LHPA and what is its scope?
What is not covered in the risk analysis?
Relevant history of Cattle tick Control in NSW and QLD
III THE PATHWAY OF TICK INFECTION
IV HAZARD IDENTIFICATION - CATTLE TICK
Cattle tick life cycle and tick fever
Queensland Status
North Coast of NSW Status
Conclusion for hazard identification
V RISK ASSESSMENT
A Release Assessment
Do QLD cattle move from QLD saleyards to NSW North Coast farms?
What is the likelihood that QLD originated cattle would have been infected with cattle tick on their source farm?
What is the likelihood that cattle ticks on QLD saleyard originated cattle will survive any chemical treatments?
What is the likelihood that QLD cattle tick positive cattle will remain tick positive with transport to the North
Coast of NSW?
Conclusion for release assessment 20
B Exposure Assessment
Initial exposure
Extent of exposure
Conclusion for exposure assessment 24
C Consequence Assessment
Direct consequences
Indirect consequences
Outbreak scenarios
Conclusion for consequence assessment 27
D Risk Estimation
VI RISK MANAGEMENT
VII RISK COMMUNICATION
VIII CONCLUSION
I KEY FINDINGS
- The North Coast of NSW is easily within the natural habitat limit of the cattle tick in Australia.
- The regular detection of cattle tick on North Coast properties each year is the result of local NSW spread from pre-existing infections and also new QLD incursions.
- The introduction of QLD saleyard cattle to NSW does occur regularly and can pose significant risk for the entry of cattle tick to a North Coast property.
- Greater numbers of QLD saleyard cattle enter into the New England and North West LHPA regions.
- The risk estimation for QLD saleyard cattle and cattle tick to the North Coast is high.
- Producers are recommended to undertake risk management strategies when introducing cattle from interstate.
- If the LHPA was to be given greater responsibility in the Cattle Tick Program it would face significant challenges not just in terms of resources but also in changing risk.
II Introduction
Why would the LHPA write a paper on cattle tick?
In 2009 the independent consulting firm, Integrated Marketing Communications (IMC), completed a review of the NSW Rural Lands Protection Boards, the predecessor organisation of the current Livestock Health and Pest Authorities (LHPA). One of the recommendations of this review was for the organisation to consider taking over the NSW cattle tick program from the NSW Department of Primary Industries (NSW DPI). At the time the newly formed LHPA rejected the proposal (IMC, 2009).
The issue of cattle tick is resurfaced again in the 2011 review of the LHPA. The review issues paper and the LHPA submission to the review suggested that a ‘one stop shop’ for NSW biosecurity could be considered (Donges et al., 2011; Ryan, 2011). Weed, plant disease and cattle tick activities that are currently undertaken by other State agencies or local government could be undertaken by an expanded LHPA for administrative efficiency. The final review document released in 2012 also suggested a LHPA role in cattle tick (Ryan, 2012).
If the cattle tick program were to be linked to the LHPA the North Coast LHPA (NCLHPA) would be one of the most affected because most cattle tick activity is in the northeast of the State. To be prepared for any future debate on whether it is appropriate for the LHPA to be involved in the cattle tick program it is necessary for the livestock health manager of the NCLHPA to substantially improve his knowledge of the issues involved and where possible collect further information relevant to NCLHPA ratepayers. This risk analysis forms part of that process.
Why a risk analysis by the LHPA and what is its scope?
Cattle tick and associated tick fever are significant diseases in Australia (Sackett et al., 2006). Both QLD and NSW Governments have had a long and complex history of cattle tick control policies (West, 2005). Previous risk analysis has been done on the entry of cattle tick to NSW but none have focused on the movements of cattle from saleyard to farm.
Today Australian animal health policy makers are increasingly shifting away from a government dominated regulatory approach for disease control. Instead they promote policy that encourages risk-based systems where industry is supported to take greater responsibility to protect itself. Over the last ten years both NSW and QLD Governments have shifted towards industry having greater responsibility for cattle tick control. QLD has gone further down this pathway than NSW.
Since 2004 the two states have differed substantially in their status for cattle tick under the National Standard Definitions and Rules (SDRs). All NSW is a free zone while QLD continues to have infected, protected and free zones. This difference in zoning complicates decision making in NSW when QLD makes changes to its cattle tick policy.
In 2011 a number of media releases have drawn attention to outbreaks of cattle tick in the ‘tick free’ south-western and central regions of QLD. In late May 2011, cattle tick were detected on 12 cattle in Charleville after they had been inspected and treated at Roma. Other properties in the tick free Warwick area were also found to be infected. At least 15 properties in central QLD also had cattle tick incursions. Some of the explanations put forward for these outbreaks include improved conditions for ticks after the recent QLD flooding, increasing acaricide resistance, decreased resources in the QLD cattle tick program and lack of knowledge by ‘hobby farmers’. Any increase in the number of outbreaks of cattle tick in these regions is significant for NSW because, in contrast to cattle from the tick infected zone, cattle from the tick free zone can enter NSW without restriction.
NSW DPI has informed the NCLHPA that the QLD government is likely to further reduce its involvement in the management of cattle tick. The board of directors of the NCLHPA expressed concern on behalf of the NCLHPA ratepayers that the risk to cattle producers in the region may now be increasing. This risk analysis provides information which:
Qualitatively assesses the risk that QLD cattle purchased through the saleyard system and pastured on the North Coast of NSW will introduce and spread cattle tick.
The risk assessment assumes a hypothetical situation where QLD cattle tick control is limited perhaps, by current zoning, minimal regulation and supervision by government, the use of a voluntary cattle health statement and voluntary industry control and eradication. The risk analysis has taken this approach because growing acaracide resistance and decreasing government involvement may make this a reality in the near future. The risk analysis assumes that all current NSW livestock entry requirements stay in place.
What is not covered in the risk analysis?
Besides the purchase of cattle at saleyards, other pathways for the entry of QLD cattle tick to the North Coast of NSW could potentially include:
- QLD cattle sent direct to local North Coast abattoirs at Casino and Grafton;
- Cattle travelling to NSW North Coast agricultural shows;
- Legal private ‘property to property’ (P2P) purchases of QLD cattle i.e purchases not involving a saleyard;
- Illegal private ‘property to property’ (P2P) of QLD cattle;
- QLD horses entering NSW or NSW horses returning after a trip to QLD;
- Fomites such as hay, rugs and other stock equipment entering NSW; and
- QLD wild animals (that can be potential hosts) entering NSW.
The majority of QLD cattle entering NSW are doing so on a direct consignment to an abattoir. There is an exemption on movement requirements for these cattle. Over 100,000 of QLD cattle enter NSW abattoirs annually (Rabiee et al., 2006). Casino and Grafton abattoirs, on the North Coast of NSW, receive almost 60% of these cattle. Rabiee et al. (2006) have assessed the risk of cattle tick entry and establishment by QLD cattle travelling direct to the abattoirs. The risk was found to be ‘neglible’ from all zones of QLD under current QLD and NSW regulation. If current regulations were lifted in QLD the risk of entry of cattle tick by direct consignment to abattoir was considered ‘very high’ but the release of those cattle ticks to the environment was considered to be ‘low’.
There is inadequate data to assess the risk of entry from P2P. It is not possible to easily search the National Livestock Identification System (NLIS) database for movements of cattle for all individual QLD Property Identification Code (PIC) transfers to a NSW North Coast PIC. Local knowledge suggests that these movements would be limited and probably mainly involve the purchase of stud bulls. The risk in purchasing these bulls would be variable, depending on their origin and treatment history. At least one NSW North Coast tick outbreak in the last 5 years has come from the entry of a bull. Male cattle are also assumed to be more susceptible to cattle tick (Rabiee et al., 2006).
Horses, fomites and wild animals were also considered outside the scope of this risk analysis because data is difficult to collect. Of these, horses may be of increasing risk because registered products being used to treat horses before entry to NSW are likely to be increasingly ineffective as resistance to acaricides increases.
The risk of tick fever occurring from the entry of QLD cattle to the North Coast of NSW is not specifically addressed. The epidemiology of tick fever suggests that QLD cattle, without cattle ticks, but carrying tick fever organisms (either by vaccination or natural infection) have always entered NSW from QLD and are generally not considered a risk because tick fever cannot spread without the cattle tick vector. If anything, they are useful for improving herd immunity in case a cattle tick incursion occurs (Rabiee et al., 2006). However, because the population of North Coast cattle has minimal immunity to tick fever it can be assumed that a risk analysis on the entry of cattle tick is also relevant to assessing the risk of tick fever to the region because if there are more tick incursions there will also be more tick fever outbreaks. The main tick fever organism, Babesia bovis, is found in approximately 1 in every 5000 cattle ticks (Tick Fever Centre, 2010).
Relevant history of Cattle tick Control in NSW and QLD
NSW has been dealing with cattle ticks since their entry from QLD in 1906 and subsequent expansion through the state (Fiani, 2005). At one time in the 1930s cattle ticks and the NSW tick quarantine area had spread as far down the east coast to below Coffs Harbour. Government regulation of the disease was formally introduced in 1920. Zoning and eradication strategies over subsequent decades led to gradual shrinking of the quarantine area. This involved significant resources including at one stage a program that employed over 700 staff and had built more than 1600 cattle tick dip yards. By the late 1990s cattle ticks were rare in NSW and only a small ‘Cattle Tick Protected Area’ remained in the northeast corner of the State. In 2004 the whole of NSW was classified as Tick Free. A cattle tick program continues to protect this status.
Today NSW DPI, using treasury funds, runs a highly specialised program that annually costs approximately $3.5million. It employs 15 full time staff and, as required, 15-20 casual staff. The program includes both surveillance for cattle tick outbreaks and management of compulsory eradication programs for detected incursions. Surveillance includes activities such as electronic border surveillance, inspection of led and tractable stock at the border, saleyard inspections, investigation of reports by producers and abattoir inspections. For each infestation there is significant tracing and surveillance work. NSW DPI funds 75% of the cost of the chemical (moxidectin) used for eradication purposes, which totals approximately $500,000 a year (Freeman, 2011).
The area covered by the NCLHPA remains susceptible to cattle tick. This is where the vast majority of cattle tick infestations are found. The average number of new infestations over the past 10 years is 72. Because surrounding properties are quarantined as many as 500 properties can be under quarantine at any one time. The source of many of the cattle tick infestations is never found. Cattle ticks may be detected at local saleyards or at the abattoir and traced back to the last property the cattle were on but often how the cattle tick arrived at that property is hard to establish. A common assumption is that they are an incursion from QLD but in many cases infestations have probably arisen from local spread (Fiani, 2005). A single incursion from QLD probably leads to an ongoing cycle of local spread. As one cluster of local spread is controlled another starts up either from a QLD incursion or more likely by local cattle movements.
Wherever NSW cattle tick incursions originate, it is predicted that the annual number of cattle tick infestations will rise as cattle tick resistance to chemicals develops (Freeman, 2011). Only macroclyic lactones, such as moxidectin, and growth regulators, such as Flurazuron, can be relied upon. However there is also a strain of cattle tick in QLD developing resistance to these (Freeman, 2011).
QLD has had its own historic battle to restrict the spread of cattle tick, although to a certain extent climate and other factors have meant that eradication was not considered feasible in a large eastern area of the State. QLD has used considerable resources over the decades to maintain zones of Tick Free QLD, Tick Protected QLD and Tick Infected QLD. The tick protected and tick infected zones are often both described as Tick Infested QLD separated from Tick Free QLD by the ‘Tick Line’ (Map 1)
Map 1: Tick Free and Tick Infested Zones in QLD and Tick Free Zone in NSW
A varying system of permits, pre-movement treatment and inspection and dipping at clearance centres has and is still used to manage movements between the zones. Increasingly, QLD livestock clearing dips between the tick infected and tick free zones are run by outside contractors and most require livestock owners to book 48 hours in advance for dipping. The producer is also able to carry out pre-treatment of cattle on his farm with any registered product against cattle tick. However, many of these products will have a known resistance in the local cattle tick population.
Tick detections in the ‘tick free zone’ lead to movement restrictions and eradication programs but not in the tick infected zone. Movement restrictions mean animals to be moved for sale or slaughter must first be inspected and, if necessary, treated. Acaracide resistance and decreasing QLD resources increasingly make this process difficult. In comparison to NSW, eradication programs in QLD are largely producer funded and are relatively unsupervised. In 2009 a review of cattle tick management in QLD was undertaken but the results are still to be released.
Acaricide chemical resistance, occupational health and safety concerns, environmental issues and limited government resources have and will continue to be significant challenges for cattle tick control programs in QLD and NSW. For example, many registered acaricide products being used in QLD will have now developed resistance in the local tick populations. This decreases the value of the clearance centres. Environmental and health concerns have led to many dips being decommissioned. Other government priorities are a threat to the resourcing required for an effective cattle tick program.
III THE PATHWAY OF TICK INFECTION
NSW North Coast cattle producers may purchase QLD origin cattle for their herds from a variety of saleyards. The purchases may be deliberate by attending a saleyard in Queensland or by purchasing cattle that originated in QLD but were resold through a NSW saleyard. The QLD cattle sold at a NSW saleyard may have recently been purchased in QLD or may have been part of a NSW herd for some time.
Relevant saleyards in NSW include Casino, Lismore, Grafton and Murwillumbah. In QLD some of the relevant saleyards may include Warwick, Stanthorpe, Dalby, Toowoomba, Moreton, Beaudesert, Silverdale, Roma and Boonah.
Cattle purchased from QLD are subject to NSW cattle entry requirements in regards to cattle tick. Cattle require inspection and treatment if coming from Tick Infested QLD (Map 1). This includes both pre-treatment on farm and treatment at a clearance centre. Only led and tractable cattle can be inspected and treated at the Pacific Highway NSW border-crossing centre. All other cattle will need to be treated at a QLD clearance centre such as Helidon or Aratula, moved to Tick Free QLD and then into Tick Free NSW. Necessary paperwork is required but there are no restrictions for the movement of cattle from Tick Free QLD unless they are under quarantine for cattle tick. Quarantined properties in Tick Free QLD will need treatments similar to properties in Tick Infested QLD.
Purchased cattle are transported from the particular saleyard by truck to a North Coast producer's property. The property may or may not contain other cattle.
IV HAZARD IDENTIFICATION - CATTLE TICK
Cattle tick life cycle and tick fever.
The cattle tick, Boophilus microplus, is a notifiable disease in NSW. Cattle tick is the vector for the tick fever's Bovine Babesiosis and Bovine Anaplasmosis. These diseases are also notifiable in NSW and are listed diseases in the OIE Terrestrial Animal Health Code. Impacts resulting from the introduction and establishment of cattle ticks in a region are considered severe (Rabiee et al., 2006).
Cattle tick is an external parasite principally found on cattle but infestations also occur on buffaloes, deer, camels, horses and sheep. Cattle ticks may occasionally be seen on donkeys, goats and pigs. Animals in poor condition are especially vulnerable to infestation as are previously unexposed cattle. Cattle can build up varying resistance to cattle tick. Bos indicus and their crosses develop better resistance than Bos Taurus cattle (Newby et al., 1998).
The cattle tick has four stages in its life cycle - larvae, nymphs, adults and eggs. The larvae, nymphs and adults remain on the same host so the cattle tick is described as a one-host tick. The larvae (seed ticks) hatch from eggs and climb onto grass. They can survive here for up to 8.5 months before a suitable host is found. When they find a host the larvae attach, feed on blood for about a week and then turn into nymphs. Nymphs feed for a further week and then they moult and turn into adults. Adult female ticks feed slowly for a week before they drop onto pasture and lay up to 3000 eggs before they die. Adult male ticks feed only occasionally and wander over the host for 2 months or more, mating with females. Eggs laid by the adult females hatch into larvae after two to six months depending on seasonal conditions.
Although cattle ticks can be found at any time of the year they mainly occur from late spring to mid winter. The tick thrives in warm and humid conditions. They are rarely found in areas receiving less than 500mm of rain and an average temperature of less than 16 degrees. The rapid spread of cattle ticks between 1880 and 1906 across tropical Australia and down the warm humid east coast of QLD and into NSW, closely follows the limits of the natural habitat of the tick. Without a control program cattle tick would flourish on the North Coast of NSW. It is estimated that the tick could colonise an area several hundred kilometres south of the QLD-NSW border. McColloch and Lewis (1968) estimated that this could be as far south as Newcastle.
Susceptible cattle, infested with enough ticks, will lose condition because of ‘tick worry’ and loss of blood. Heavy infestations will kill calves and some adults. Hides become damaged from the ticks. Serious tick borne disease, such as tick fever, can be transmitted (Rabiee et al., 2006). In Australia there are three different organisms that cause tick fever. These are Babesia bovis, Babesia bigemina and Anaplasma marginale. Babesia bovis is responsible for 80% of tick fever outbreaks in Australia. Only a small number of cattle ticks carry tick fever organisms - for example, only 1 in 5000 cattle ticks transmit B. bovis. Morbidity and mortality rates with tick fever will depend on the level of ticks present, the organism involved and the susceptibility of the herd.
The tick fever organisms are parasites of the red blood cells. The disease caused by the two Babesias is very similar. The incubation period is 7-17 days. The severity of illness can range from a mild fever to rapid mortality. Clinical signs may include high fever, pale mucous membranes, milk drop, weight loss, abortion and red urine. Deaths can occur from three days to four weeks after clinical signs are observed. Surviving animals can have a prolonged recovery. In anaplasmosis, the incubation period is longer at approximately 3-6 weeks. This disease is also milder with mild fever and jaundice being common signs. Red urine and deaths do not tend to occur (Tick Fever Centre, 2010).
Eradication programs are possible for cattle tick if effective treatments occur at 21 day intervals to ensure no ticks mature to drop from the host and if the program runs for a minimum of 8.5 months to cover the period that larvae may survive on the pasture.
Queensland Status
Cattle tick is endemic in Tick Infested QLD. Outbreaks occur sporadically in Tick Free QLD, especially in the marginal areas adjacent to the infected areas. The frequency of outbreaks in more western areas of Tick Free QLD has increased in 2011. Annually, there are about 250 confirmed outbreaks of tick fever in QLD (Tick Fever Centre, 2010).
North Coast of NSW Status
The whole of NSW is a free zone for cattle tick. However on average 72 infestations do occur each year on the North Coast and are subject to eradication programs. The vast majority of over 6000 North Coast cattle properties are free from cattle tick. Tick fever is not endemic on the North Coast of NSW but sporadic outbreaks occur. Approximately 10 outbreaks of tick fever are known to have occurred in the last 20 years (NCLHPA, 2011).
Conclusion for hazard identification
Cattle tick and associated tick fever can be clearly identified as potential hazards to the North Coast of NSW from the introduction of QLD cattle. It is justified to continue a risk analysis.
V RISK ASSESSMENT
There are four processes to undertake a risk assessment. These include release assessment, exposure assessment, consequence assessment and risk estimation (MacDiarmid and Pharo 2003).
In a qualitative assessment the terms used to describe relative likelihoods need to be defined (Biosecurity Australia, 2001). The terminology outlined below has been used in this risk assessment.
| Likelihood | Descriptive definition |
|---|---|
| High | The event would be very likely to occur |
| Moderate | The event would occur with an even probability |
| Low | The event would be unlikely to occur |
| Very low | The event would be very unlikely to occur |
| Extremely low | The event would be extremely unlikely to occur |
| Negligible | The event would almost certainly not occur |
A Release Assessment
This process consists of estimating the likelihood of an imported commodity or pathway being infected or contaminated with an identified hazard and describing the pathway/s necessary for that hazard to be introduced ‘released’ into a particular environment (OIE, 2004).
Do QLD cattle move from QLD saleyards to NSW North Coast farms?
A small number of NSW North Coast cattle producers opportunistically purchase cattle from QLD saleyards. The numbers of cattle involved are relatively small when compared to the number of cattle entering the North Coast abattoirs. However over time significant numbers of QLD cattle can enter the North Coast population.
An analysis of data extracted from the National Livestock Information System (NLIS) regarding movements of cattle from 8 southeast QLD saleyards was undertaken and is summarised in Table 1. Data was not available for Roma saleyard, which is known to attract some North Coast cattle buyers. The data shows 186 cattle movements to North Coast farms over two months in 2011. Only 13 farms were involved. Annually at least 1000 QLD saleyard cattle would move to North Coast farms. This is in comparison to the over 100,000 cattle that would be moving direct to Grafton or Casino abattoirs in that time. 1321 cattle were moved to farms in other areas of NSW besides the North Coast. The majority of these were to Tenterfield (New England LHPA) or Warialda (North West LHPA).
Table 1: Movements to NSW farms from key QLD saleyards in Feb and Aug 2011
| QLD saleyard | Tick zone | Month in 2011 | No. cattle sold | No. cattle moved to a north coast farm | No. north coast farms receiving cattle | Other farm locations in NSW |
|---|---|---|---|---|---|---|
| Moreton | Tick infested QLD | Aug | 2105 | 0 | 0 | 0 |
| Moreton | Tick infested QLD | Feb | 3589 | 23 | 7 | Glenn Innes (4) Warialda (1) Narrabri (6) |
| Beaudesert | Tick infested QLD | Aug | 448 | 0 | 0 | 0 |
| Beaudesert | Tick infested QLD | Feb | 1780 | 15 | 1 | 0 |
| Boonah | Tick infested QLD | Aug | 335 | 39 | 1 | 0 |
| Boonah | Tick infested QLD | Feb | 864 | 0 | 0 | 0 |
| Toowoomba | Tick infested QLD | Aug | 1782 | 0 | 0 | Tenterfield (14) Merriwa (8) |
| Toowoomba | Tick infested QLD | Feb | 2286 | 0 | 0 | Warialda (60) |
| Silverdale | Tick infested QLD | Aug | 2014 | 0 | 0 | Tenterfield (22) |
| Silverdale | Tick infested QLD | Feb | 2317 | 0 | 0 | Warialda (59) |
| Warwick | Tick free QLD | Aug | 3535 | 14 | 1 | Tenterfield (470) |
| Warwick | Tick free QLD | Feb | 6297 | 18 | 1 | Tenterfield (85) Warialda (120) Molong (40) |
| Stanthorpe1 | Tick free QLD | Feb | 249 | 0 | 0 | Tenterfield (62) Warialda (24) |
| Dalby2 | Tick free QLD | Feb | 19546 | 75 | 2 | Warialda (340) Tamworth (6) |
| Total tick infested | 79 | 9 | 174 - Glenn Innes (4) Warialda (120) Narrabri (6) Merriwa (8) Tenterfield (36) | |||
| Total tick free | 107 | 4 | 1147 - Tenterfield (617) Warialda (484) Molong (40) Tamworth (6) |
The cattle bought at QLD saleyards may stay on one North Coast property or be spread through local saleyards. QLD cattle may be kept for a short time on one property before slaughter or be traded to multiple properties. Analysing data from local saleyards can allow further information to be gathered on QLD originated cattle on North Coast farms (Table2).
Table 2: Analysis of data from local NSW saleyards
| North coast saleyard | Month and year | No. cattle sold | No. QLD cattle at sale | No. QLD cattle offered for sale that move to another north coast farm |
|---|---|---|---|---|
| Casino | Feb 2011 | 5920 | 50 | 16 |
| Feb 2010 | 7799 | 70 | 23 | |
| Feb 2009 | 10867 | 295 | 120 | |
| Aug 2011 | 2733 | 62 | 28 | |
| Aug 2010 | 7079 | 58 | 26 | |
| Aug 2009 | 5817 | 150 | 59 | |
| Grafton | Feb 2011 | 3759 | 17 | 13 |
| Feb 2010 | 4680 | 15 | 3 | |
| Feb 2009 | 2707 | 14 | 10 | |
| Aug 2011 | 1406 | 17 | 15 | |
| Aug 2010 | 2646 | 13 | 10 | |
| Aug 2009 | 2306 | 4 | 1 | |
| Murwillumbah | Feb 2011 | 9981 | 3 | 9 |
| Feb 2010 | 950 | 1 | 1 | |
| Feb 2009 | 422 | 6 | 1 | |
| Aug 2011 | 297 | 0 | 0 | |
| Aug 2010 | 700 | 6 | 4 | |
| Aug 2009 | 614 | 0 | 0 | |
| Lismore | Feb 2011 | 4240 | 114 | 89 |
| Feb 2010 | 5218 | 542 | 8 | |
| Feb 2009 | 36261 | 120 | 90 | |
| Aug 2011 | 1858 | 5 | 4 | |
| Aug 2010 | 2877 | 10 | 6 | |
| Aug 2009 | 2396 | 5 | 1 | |
| Total | A=81915 | B=1099 | C=557 |
Approximately 1.5% of cattle offered for sale at North Coast saleyards originated in QLD (B/A in Table 2). Since the vast majority of cattle are marketed at some stage through a saleyard it would be a fair assumption that this figure would be close to the percentage of QLD origin cattle in the total North Coast herd. There are approximately 375,000 beef cattle on the North Coast of NSW, of which as many as 5000 may have been born in Queensland. At least 50% of QLD originated cattle that are moved initially to one farm on the North Coast of NSW are subsequently moved to a second farm (C/B in Table 2).
Local knowledge held by staff of the NCLHPA suggested a few individual producers that were suspected of regularly buying QLD cattle. An analysis of cattle transfers to their property on the NLIS database indicated that in most cases QLD cattle had been purchased (Table 3). Some of these cattle may also be from P2P and not only from saleyards.
Table 3: Analysis of cattle transfers
| Description of producer | Time period | Number of QLD cattle purchased | Total cattle purchased if known |
|---|---|---|---|
| Cattle trader 1 in Casino | 3 years | 220 | 1297 |
| Cattle trader 2 in Casino | 3 years | 247 | 6005 |
| Tweed Heads beef producer who buys cows in calf and then sells both | 5 years | 15 | - |
| A 300 cow dairy | 6 years | 3 | 60 |
| A 500 beef cattle herd near Casino | 6 years | 315 | - |
| Largest dairy farm on the north coast | 6 years | 0 | - |
| Third largest beef herd on north coast (1500 breeders) | 6 years | 10 (assumed to be bulls) | 29 (assumed to be bulls) |
Statements were also collected from key members of the local livestock industry. These industry members were asked what would motivate producers to purchase cattle from saleyards in QLD:
‘A lot of dealers are put off by the tick area’.there are always the hobby farmers who move a small number of pet cattle when they relocate from QLD to northern NSW. There is a trade of Tenterfield cattle into QLD and then out again (Biosecurity Queensland employee)
‘Is mainly just punters but there are producers who look for bulls.’ If prices are low in QLD it will attract NSW buyers. Things like drought in QLD will attract buyers from NSW (Stock and Station agent, Lismore)
‘There are a few local buyers who go up to QLD sales and purchase cattle that are then sold through our local saleyards’ (LHPA employee)
‘I wanted to get some Murray Grey cattle and bought them from a local saleyard. It was not until they arrived that I realised that they must have originated in QLD. I have had trouble with cattle tick in the past’ (Beef producer, North Coast NSW).
‘Many North Coast dairy farmers are interested in purchasing QLD cattle. Yes most would from time to time buy some for their herds. We need them. Price overrides any concerns about disease..Yes I have purchased cattle from the Tick infested area but would probably not do again because despite having been treated a tick was found and the cattle were held up for a week just eating poor quality feed, went off their milk and never that good. Can be some good cattle at better prices in QLD. Many farmers would not be turned off by distance. These days a cow can be worth $2500 so a bit of travel is nothing if get a good cow for a good price’ (North Coast dairy farmer).
NLIS data was used to generate a list of properties on the North Coast of NSW that had QLD saleyard cattle directly come onto them in the months of February or August 2011. The approximate location of these properties can be mapped (Map2). When the locations are compared to a NCLHPA map (Map3) it can be observed that cattle are moved to locations widespread throughout the Authority's region. QLD origin cattle are also being moved from local North Coast saleyards to farms. Map 4 and 5 indicate the approximate locations where in Feb or August 2011 properties added QLD origin cattle to their herd. There are a few clusters seen in Map 4 including ones around Ettrick and Tatham. It may be significant that over the last 10 years Ettrick has been prone to multiple cattle tick infestations. A likely scenario for a few regions on the North Coast is that some producers in that region do from time to time buy QLD cattle. At some stage a QLD animal brings in cattle tick. Climatic, husbandry and other factors favour survival of the tick and spread to other properties, often before detection. Eradicating the parasite from the area may take a few years because new properties keep appearing. In that time a new incursion could also occur from QLD or a property assumed to have been cleared may have re-emergence of infection.
Maps 2 and 3: Locations on the North Coast to which QLD saleyard cattle moved in February and August 2011 and NCLHPA map.
Map 3 and 4: Locations on NSW North Coast to where QLD originated cattle moved in Feb and August 2011 from local saleyards of Casino, Murwillumbah, Grafton and Lismore.
What is the likelihood that QLD originated cattle would have been infected with cattle tick on their source farm?
If cattle originate from Tick Infested QLD there is a very high likelihood that they were infected with cattle tick on their source farm. If cattle originate from Tick Free QLD there is a low likelihood that they were infected with cattle tick on their source farm.
The likelihood of QLD cattle being infected with cattle tick will depend on where they are coming from, the feeding system they were subjected to, the signalment of the cattle, level of stress and density of stocking rate (Rabiee et al., 2006). Table 4 provides the approximate proportion of farms in QLD estimated in 2006 to be cattle tick positive (Rabiee et al., 2006).
Table 4: Approximate proportion of tick positive farms in QLD in 2006
| Area of QLD | Approximate proportion of farms tick positive |
|---|---|
| Free zone | 150 / 15,000 = 1% |
| Protected zone | 350 / 2,000 = 17.5% |
| Infected zone | 18,000 / 25,000 = 72% |
It is assumed that in 2011 the number of farms tick positive would be higher because seasonal conditions have been more favourable for the parasite. In addition this risk analysis assumes a situation where movements of cattle from Tick Infested QLD to Tick Free QLD will be less regulated and chemicals more ineffective so the 2006 figure for the Free Zone may be too conservative. Although survivability of the tick is reduced in areas west of the ‘tick line’ it is assumed in this risk analysis that the proportion of farms tick positive in the Free Zone is closer to 2%.
Cattle that have been grazing on pasture are much more likely to have cattle tick than those that have been in a feedlot. It is assumed that nearly all cattle being marketed through saleyards will have been grazing.
Being older, male and of Bos taurus rather than Bos indicus breed will increase the likelihood of cattle carrying cattle tick. Many south eastern QLD farms have Bos indicus or Bos indicus cross cattle, which will reduce tick numbers. Farms with a higher stocking rate or other forms of stress may also have a higher rate of cattle tick in their herds. For example, the recent flooding throughout south eastern QLD will have increased stress on cattle and may have increased cattle tick numbers.
Rabiee et al. (2006) considered all these factors and using information from various sources estimated that in both the protected and free zones of QLD 50% of cattle in a tick positive herd would carry ticks while in the infected zone 75% of cattle in a tick positive herd would carry ticks. However, Freeman (2011) suggests that only 10-15% of cattle in a herd would carry ticks. Rabiee et al. (2006) also outlined that the number of ticks on each head of stock would vary significantly depending on whether they were Bos indicus or Bos taurus. Estimates for the infected zone included 144 cattle ticks on Bos taurus breeds compared to 3 cattle ticks on Bos indicus breeds. In the free zone Bos indicus were estimated to have at the most one tick compared to 14 ticks per head for Bos taurus.
What is the likelihood that cattle ticks on QLD saleyard originated cattle will survive any chemical treatments?
There is a moderate likelihood that cattle ticks will survive any chemical treatment. Cattle from Tick Free QLD are likely to have had no or minimal treatments against cattle tick before their purchase by a North Coast producer. Cattle from Tick Infested QLD should have had tick treatments and have been inspected before their entry to NSW. Tick treatments should have included both one on property and also at time of inspection. These treatments may or may not have been effective. There are a wide range of registered products against cattle tick including organophosphates (OP), synthetic pyrethroids (SP), amitraz, insect growth regulators and macrocyclic lactones (ML) (IVS, 2011). There is cattle tick resistance to OP, SP and amitraz chemicals. The Ultimo strain of cattle tick is resistant to OP, SP and amitraz and is common in southeast QLD (Kearney, 2011 and Tick Fever Centre, 2010). Flurazuron, an IGR, and moxidectin, a ML, are likely to still be effective for many ticks. However Freeman (2011) reports that flurazon resistance has been documented and that field experience suggests emerging ML resistance. There are of course regional differences intick resistance. Most of the reports of resistance come from SE QLD. Table 1 indicated that most of the cattle movements come from SE QLD. In general iot is likely that less effective chemicals are routinely used because of cost. MLs and Flurazuron are more expensive than other treatments. Cattle tick entry requirements simply require that a registered product be used.
The technique of applying chemicals will also change the effectiveness of the product. Traditionally, plunge dipping of cattle was the most effective method of treating against cattle tick. However, the number of cattle dips and spray races has decreased. Environmental concerns and health issues are some factors for the decrease in plunge dips. ML chemicals are not applied by dipping and experience shows that although the chemical is active against cattle tick the use of MLs are not as effective as a plunge dip with an effective chemical. MLs may not start working against cattle tick for 5 days (Kearney, 2011).
What is the likelihood that QLD cattle tick positive cattle will remain tick positive with transport to the North Coast of NSW?
There is a high likelihood that QLD tick positive cattle will remain tick positive once they reach NSW. The transport to the NSW North Coast will be by road. The average travel time between the QLD saleyards and main centres of the North Coast is 3 hours. The longest journey would be 9 hours to reach Coffs Harbour. It can be estimated that 5% of cattle ticks would fall off during transport. Considering the likely number of ticks from the source farm and the impact of any chemical treatments an estimate number of remaining ticks can be calculated. Many of the adult ticks would remain (Table 5). Figures in Table 5 are an average taking into account differences between breeds of cattle.
Table 5: Estimated number of ticks per head of cattle before and after transport
| Zone of origin in QLD | Estimated average adult ticks per head at start of journey | Estimated average adult ticks after transport |
|---|---|---|
| Infested | 10 | 9 |
| Free | 5 | 4 |
It is assumed that nearly all larvae and nymph cattle ticks present before the journey would still be on the host at the end of the journey.
Conclusion for release assessment
Biosecurity Australia (2001) provides a matrix to combine descriptive likelihoods (Table 6).
Table 6: Combining Descriptive Likelihoods
| High | Moderate | Low | Very low | Negligible | |
|---|---|---|---|---|---|
| High | High | Moderate | Low | Very low | Negligible |
| Moderate | Moderate | Low | Low | Very low | Negligible |
| Low | Low | Low | Very low | Very low | Negligible |
| Very low | Very low | Very low | Very low | Negligible | Negligible |
| Negligible | Negligible | Negligible | Negligible | Negligible | Negligible |
Using Table 6 and descriptive likelihoods described in the text it is calculated that:
There is a moderate likelihood that QLD cattle obtained through saleyards could be infected with cattle tick and that cattle tick could be released into the North Coast environment.
A moderate likelihood suggests an even probability that the event would occur.
The risk is higher for cattle that originated in Tick Infested QLD but the risk is increasing for those from Tick Free QLD. Cattle can easily move into Tick Free QLD after applications of a chemical that may have been ineffective.
To put the risk assessment into perspective it is estimated that on average three to four QLD saleyard cattle are moving to the North Coast every day of the year. One of these animals is likely to have originated from Tick Infested QLD. It is estimated in this risk analysis that every second or third day at least one cattle tick would survive on a single animal from the Tick Infested area and arrive on the North Coast of NSW. It is also estimated that once a month at least one cattle tick would survive on an animal from Tick Free QLD.
A scenario tree can be used to summarise the release pathways (figure 1)
Figure One: Release pathways for cattle tick QLD saleyard cattle
B Exposure Assessment
This process involves estimating the likelihood that a susceptible animal in NSW North Coast being exposed to an identified hazard and describing the pathways necessary for this to occur (OIE, 2004).
Initial exposure
There is a high likelihood that a susceptible North Coast animal will be exposed to cattle tick. The North Coast of NSW has widespread hosts for the cattle tick. There are 375,000 cattle in the region (FARMS, 2011). Over 6000 properties have cattle. The majority of these cattle have no or limited immunity to cattle tick. There are also a high number of Bos taurus cattle that are limited in their ability to develop tick resistance. Black and Hereford type cattle have remained popular.
Environmental conditions are ideal on the North Coast of NSW for the survival and spread of cattle tick. The known difficulties of eradicating the parasite from the region are evidence for this. The winter is not cold and long. The temperature in many areas is never much below 10 degrees so winter temperatures may never be fatal to larvae. McCulloch and Lewis (1968) showed that the non-parasitic stage of cattle ticks on the North Coast of NSW could survive in the environment for 7.5 months. Without eradication programs cattle tick would flourish on the North Coast of NSW.
Once cattle tick has arrived on a North Coast farm on a QLD animal, infection may spread quickly to a North Coast animal or it is also possible for eggs to be simply released into the environment and cause an infection at a later date.
Extent of exposure
Once a single North Coast cow is exposed to cattle tick and, possibly also tick fever, the spread of infection will easily occur within that herd. However, there will be variations in the attack rate and extent of herd infestation. Many cattle owners tolerate ‘bush’ tick burdens on their cattle and they are unlikely to notice the parasite until numbers are significant. The ability of producers to distinguish between tick types is also an issue.
The available data shows that cattle tick spreads easily within the North Coast of NSW once it has become established on a single property. Cattle straying between neighbours and private movements of cattle easily lead to new outbreaks. There have been some infestations with nine infested neighbours (Fiani, 2005). There is a high likelihood that, once cattle tick has occurred on one property from QLD cattle, subsequent cattle tick outbreaks will occur in the region. However, the same is not true for tick fever, as outbreaks once they occur tend to be restricted to individual properties. There is a high likelihood that if eradication programs did not occur then the parasite would become endemic in northern NSW.
Conclusion for exposure assessment
The overall exposure assessment is high. The event would be very likely to occur.
C Consequence Assessment
This process involves describing possible consequences following exposure to a hazard and estimating the likelihood and magnitude of these consequences occurring (OIE, 2004).
Direct consequences
- Few cattle in North Coast of NSW have good immunity to cattle ticks or tick fever. There is a high likelihood that the exposure of North Coast cattle to cattle ticks alone or cattle ticks and tick fever will lead to clinical disease and on some properties death.
- There is a high likelihood cattle tick would spread to other properties on the North Coast causing clinical disease and some deaths.
- There is a high likelihood that an outbreak of cattle tick alone or cattle tick and tick fever on the North Coast will cause moderate economic consequences to individual cattle producers. Under current policy they are placed under quarantine and need to meet 25% of eradication costs.
Indirect consequences
- Under current NSW policy the Government and producers would not allow cattle tick and tick fever to become endemic so considerable costs are needed to ensure control and eradication.
- There is a high likelihood that an outbreak of cattle tick alone or cattle tick and tick fever on a property or properties on the North Coast of NSW will cause moderate economic consequences to the NSW Government to undertake eradication.
Outbreak scenarios
It can be useful to identify and describe consequences by various ‘outbreak scenarios’. In these scenarios the potential impacts can be estimated at local, regional and national levels (Biosecurity Australia, 2001). For the scenarios in this risk analysis the impacts were considered at local ‘North Coast farm’ and ‘regional’ (NSW) levels. The following definitions were used to assess the impacts (Biosecurity Australia 2001):
- an ‘unlikely to be discernible’ impact is not usually distinguishable from normal day-to-day variation in the criterion
- an impact of ‘minor significance’ is not expected to threaten economic viability, but would lead to a minor increase in mortality/morbidity or a minor decrease in production. For non- commercial factors, the impact is not expected to threaten the intrinsic ‘value’ of the criterion though the value of the criterion would be considered as ‘disturbed’. Effects would generally be reversible
- a ‘significant’ impact would threaten economic viability through a moderate increase in mortality/morbidity, or a moderate decrease in production. For non-commercial factors, the intrinsic ‘value’ of the criterion would be considered as significantly diminished or threatened. Effects may not be reversible
- a ‘highly significant’ impact would threaten economic viability through a large increase in mortality/morbidity, or a large decrease in production. For non-commercial factors, the intrinsic ‘value’ of the criterion would be considered as severely or irreversibly damaged.
These four values were translated to a range (A-F) using the schema outlined below (Biosecurity Australia, 2001):
In this risk analysis only local (farm) and regional (NSW) are considered.
To calculate the overall consequence the impact scores for local and regional levels were combined according the following rules:
- Where any direct or indirect effect is ‘F’, the overall consequences associated with the outbreak scenario are considered to be ‘extreme’.
- Where more than one direct or indirect effect is ‘E’, the overall consequences associated with the outbreak scenario are considered to be ‘extreme’.
- Where a single direct or indirect effect is ‘E’ and each remaining direct or indirect effect is ‘D’,the overall consequences associated with the outbreak scenario are considered to be ‘extreme’.
- Where a single direct or indirect effect is ‘E’ and remaining direct and indirect effects are not unanimously ‘D’, the overall consequences associated with the outbreak scenario are considered to be ‘high’.
- Where all direct and indirect effects are ‘D’, the overall consequences associated with the outbreak scenario are considered to be ‘high’.
- Where one or more direct or indirect effect is ‘D’, the overall consequences associated with the outbreak scenario are considered to be ‘moderate’.
- Where all direct and indirect effects are ‘C’, the overall consequences associated with the outbreak scenario are considered to be ‘moderate’.
- Where one or more direct or indirect effect is ‘C’, the overall consequences associated with the outbreak scenario are considered to be ‘low’.
- Where all direct and indirect effects are ‘B’, the overall consequences associated with the outbreak scenario are considered to be ‘low’.
- Where one or more direct or indirect effect is ‘B’, the overall consequences associated with the outbreak scenario are considered to be ‘very low’.
- Where all direct and indirect effects are ‘A’, the overall consequences associated with the outbreak scenario are considered to be ‘negligible’.
Scenario One:
Cattle tick establishes in a North Coast property but is eradicated in standard time frame without spread.
At a farm level the consequences are minor while at a regional level they are unlikely to be discernible. Overall consequences are negligible.
Scenario Two:
Cattle tick establishes in a North coast property but eradication is prolonged due to a variety of herd and property factors. No spread occurs.
Farm level significant and regional level unlikely to be discernible. Overall consequences are very low.
Scenario Three:
Cattle tick establishes in a North Coast property and eradication occurs in standard time but before then spread occurs to one or a few other properties
Farm level minor significance and regional level is of minor significance. Overall consequences are low.
Scenario Four.
Cattle tick establishes in a North coast property, eradication is prolonged and for various factors spread occurs throughout the region.
Farm level significant and regional level significant. Overall consequences are moderate.
Scenario Five:
Cattle tick establishes and spreads in NSW and cannot be controlled with current resources.
Farm level significant and regional level highly significant. Overall consequences are high.
Conclusion for consequence assessment
Biosecurity Australia (2001) describes a number of rules that can be used to combine scenarios into one consequence:
For the scenarios in this risk assessment rule four applies. It can therefore be determined that the overall likely consequences are considered to be high.
D Risk Estimation
The final step in risk assessment consists of summarising and integrating the results from the release assessment, exposure assessment and consequence assessment to produce an overall idea of the risks associated with the identified hazards (OIE, 2004).
- As concluded from the release assessment the overall risk of introduction is moderate.
- As concluded from the exposure assessment the overall risk of exposure is high.
- These likelihoods can be combined as indicated in Table 6. Therefore the overall probability of establishment and spread is moderate.
- It was concluded in the consequence assessment that the overall consequences were high.
Biosecurity Australia (2001) also outline how the probability of establishment and spread can be combined with the consequence (Table 7)
Table 7: Combining consequence and release and exposure assessments
Therefore the:
THE RISK ESTIMATION FOR QLD SALEYARD CATTLE AND CATTLE TICK IS HIGH.
VI RISK MANAGEMENT
Because the risk estimation is greater than negligible, risk management strategies are justified. Some risk management strategies to consider include:
1. Maintain cattle tick surveillance and supervised eradication procedures in NSW.
2. Increase advisory messages to North Coast producers to:
- Decrease risk by preferred purchase of tick free zone cattle;
- Purchase Bos indicus or Bos indicus cross cattle;
- Initial on farm quarantine all QLD origin cattle on farm and give 2 ML treatments 3 weeks apart.
VII RISK COMMUNICATION
This risk analysis has been peer reviewed by an academic at Murdoch University and the North East Regional Veterinary Officer with NSW DPI. It is also proposed that the risk analysis will be reviewed by the scientific committee of the NSW District Veterinarians Association prior to online publication
As relevant the risk analysis will be discussed with other senior district veterinarians, local private veterinarians and managerial staff in both the LHPA and NSW DPI. A media release may be made regarding the risk analysis to NCLHPA ratepayers.
VIII CONCLUSION
The North Coast of NSW is easily within the natural habitat limit of the cattle tick in Australia. It is likely that the regular detection of cattle tick on North Coast properties each year is the result of local NSW spread from pre-existing infections and also new QLD incursions.
This risk analysis demonstrates that the introduction of QLD saleyard cattle to NSW does occur regularly and can pose significant risk for the entry of cattle tick to a North Coast property. Ongoing communication of this risk to both Government and Industry can assist policy decisions. It may be appropriate for industry leaders to take greater ownership of cattle tick control on the North Coast of NSW but it is unlikely that many producers are prepared to do so. For many producers the short term economic advantages of a ‘good deal’ will always outweigh any concept of biosecurity.
If the LHPA was to be given greater responsibility in the Cattle Tick Program it would face significant challenges not just in terms of resources but also in changing risk.
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