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This article was published in 1940
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
OESOPHAGOSTOMIAS1S - NODULE WORM INFESTATION OF SHEEP
By HUGH McL. GORDON, B.V.Sc.
McMaster Animal Health Laboratory.
Council for Scientific and Industrial Research.
THE CAUSE.
The casual parasite is Oesophagostomum columbianum (Curtice 1890), referred to as nodule worm, nodular worm, white worm, back gut worm, knotty gut worm,etc.
HABITAT.
The adult worms are found in the colon, extending backwards from a point some inches below the junction of the small and large intestines through the coiled portion of the colon (crown). The nodules produced by the larval stages are found in both the small and large intestines, extending from pylorus to anus.
ANIMALS AFFECTED.
Oe. columbianum has been recorded from sheep, goats and some wild ruminants,e.g. deer, antelopes, but not from cattle. (In cattle Oe. radiatum produces a similar disease). Another species, Oe. venulosum, occurs in the caecum of sheep but does not lead to nodule formation. In pigs several species of Oesophagostomum occur and lead to nodular disease. In man Oe. apiostomum, Oe. brumpti and Oe. stephanostomum occur and in parts of Africa cause nodular disease.
GEOGRAPHICAL DISTRIBUTION OF OE.COLUMBIANUM.
This parasite has been recorded from most countries where sheep husbandry is practised. It is the cause of serious disease conditions of sheep in Australia, South Africa, U.S.A., and Canada.
DISTRIBUTION OF OE. COLUMBIANUM IN AUSTRALIA.
The parasite is commonest and the disease produced is most severe in areas of high summer rainfall. In Queensland, the Darling Downs, the area between the Downs and the N.S.W. border, and portions of central Queensland are regions where oesophagostomiasis is a serious disease. In New South Wales the disease is of greatest importance in the Northern Tablelands, near north-west slopes, Barraba region, upper Hunter Valley, the portion of the Central Tablelands immediately west of the Blue' Mountains, and on the tablelands of the Moss Vale-Bowral-Mittagong region. The parasite has been observed and appears to be established in portions of the following districts: Braidwood, Oberon, Kanimbla Valley, County of Cumberland, Coolah, Gilgandra.
There have been isolated outbreaks in other areas,e.g. Jugiong, Cootamundra, which normally receive a prevailing winter rainfall, but which in the years of the occurrence of the outbreak received abnormal summer rains. In these outbreaks it is almost certain that sheep introduced from districts where oesophagostomiasis is endemic were responsible.
In a sequence of "wet" years this parasite is likely to become of importance in north-western plains areas. Irrigated pastures in almost any part of the State are potential danger areas. The extension of sheep raising into such regions as the Dorrigo is likely to be followed by severe outbreaks of oesophagostomiasis.
LIFE-HISTORY OF OE.COLUMBIANUM.
The eggs are passed in the faeces in an early stage of development. Within 12 to 24 hours a larva is formed and the egg hatches—the first stage larva emerges, feeds actively, rests, moults and a second stage larva emerges. This stage feeds, rests and moults, but does not shed its skin. The result is the third stage, infective larva enclosed in the old second stage skin. The infective stage is reached in about seven days under conditions of adequate moisture and temperature. When ingested by a sheep the infective larva soon sheds the old second stage skin and burrows into the mucous membrane of the small or large intestine. Here the larva may remain for varying periods—a few days to a few months—growing meanwhile, and finally returns to the lumen of the large bowel where it grows to the adult stage in about three weeks. In young and non-resistant sheep the time spent in the mucous membrane is shorter than in older, resistant animals.
PATHOGENIC EFFECTS.
The infective larvae invade the mucous membrane and burrow in it, setting up inflammatory changes which may end in nodule formation. In sheep which have no resistance to the disease, i.e. young sheep in areas where the disease is endemic or sheep of any age introduced to endemic areas from areas where the disease does not occur, the inflammatory reaction appears to be very slight and nodule formation is not marked—it may even be almost entirely absent. Thus, in endemic areas, it is usual to find young sheep—up to the weaner stage—showing few nodules and many worms. This is also seen in sheep of varying ages introduced from areas where Oe. columbianum does not occur,e.g. far west, south, and south-west. In endemic areas, as sheep become older, nodule formation continues and the number of nodules is increased each year.
It has been suggested that nodule formation is related to the presence of resistance on the part of the sheep—the greater the resistance the more marked the reaction of the larvae in the mucosa. A marked reaction probably results in larvae being walled off in fibrous tissue and eventually destroyed. However, the nodule remains and finally becomes calcified. In time, the presence of a large number of nodules leads to interference with bowel movements. It appears then that in oesophagostomiasis, resistance is effective in preventing the development of larvae to adult worms, but in doing so leaves a permanent lesion of a very undesirable nature.
In massive infestations the burrowing of larvae in the bowel wall leads to a severe inflammatory reaction and even an ulcerative colitis. At times, nodules rupture into the lumen of the colon and produce ulcers. Sometimes a nodule will rupture on to the peritoneal surface of the intestine and may then be followed by fatal peritonitis, or in less severe cases, by adhesions and calcification of lesions.
The adult worms appear to produce a secretion which causes a great outpouring of mucus from the mucous membrane. The mucous membrane also shows inflammatory changes and the wall of the colon is thickened.
This parasite probably does not directly kill a high proportion of sheep, but is responsible for more chronic effects in the form of great debility, loss of condition, and failure to thrive, grow, fatten and produce wool. The chronic effects are often seen in cases harbouring relatively few adult worms, but in which enormous numbers of nodules are present. It is probable that the effects of nodule worm infestation, both the effects of the adult worms and the effects of marked nodule formation, are largely responsible for the "tail" of flocks in areas where the condition is endemic. It has been observed that aged sheep which have been running on endemic areas for some years are difficult to fatten even when removed to other areas and ample feed.
Cases have been seen in which marked nodule formation appears to have been responsible for telescoping of the bowel (intussusception) and death.
The soft faeces passed frequently lead to soiling of the breach region, with consequent attraction of flies and development of fly strike. The soft faeces also lead to formation of "dags" which reduces the value of the wool from this region.
The presence of nodules in the bowel wall render it unsuitable for use as sausage casings or tennis racket strings, and is therefore of considerable economic importance.
DIAGNOSIS.
Ante-Mortem:
The occurrence of debilitated sheep, showing humped back, characteristic stiff action of the hind legs, tail frequently held up at an angle from the body, and passing soft faeces containing much mucus and sometimes streaks of blood, is almost diagnostic. When these symptons are seen in the late autumn and winter in endemic areas, one can be certain of the diagnosis. Examination of faeces for eggs of the parasite may be misleading. In the first place the worms are not very vigorous egg producers and one usually finds only a few eggs in egg counts. The eggs appear to be passed rather irregularly, possibly because they are mixed with the mucus in which the worms are lying and this is not intimately mixed with the faeces, but passes out intermittently. The eggs closely resemble those of Haemonchus contortus, the large stomach worm, and unless one sees a number of them, say about 50, it is unwise to try to differentiate them. In routine diagnostic work, faecal cultures should be made in order to obtain the third stage larvae which can be readily differentiated from those of Haemonchus and Trichostrongylus. Faecal examinations may also be misleading in cases where symptoms are due to heavy infestations with larvae or very marked nodule formation—for there may be very few adult worms present. Rectal exploration will reveal the presence of nodules in many cases but it must be remembered that in young sheep there may be no nodule formation.
Infestation with Chabertia ovina (the large-mouthed bowel worm) also leads to the passage of soft, unformed faeces containing mucus and often blood streaks. The geographical distribution of the outbreak will usually give a clue to the diagnosis, but it should be remembered that in an intermediate zone one may have outbreaks of Oesophagostomum columbianum infestation one year, and Chabertia ovina infestation the next (e.g. in the Coolah-Merriwa area both conditions have been seen).
The characteristic lesions are readily observed—nodules occur in the small and large intestines, and the adult worms, when present, are found in the colon. They are creamy white in colour, about half an inch long, and one end is usually bent into a hook-like structure. They are not attached to the mucous membrane, but are frequentry lying in mucus. The only other worm inhabiting this portion of the intestine is Chabertia ovina and this parasite is rarely seen in areas where Oesophagostomum columbianum commonly occurs. Chabertia ovina is a stouter worm and is usually firmly attached by its mouth capsule to the mucous membrane. Considerable force is necessary to detach these worms. It should be remembered that in the winter rainfall regions Oesophagostomum venulosum is found in the caecum. These worms are usually mixed up with the contents of the blind gut, are larger than the nodule worm and do not have one end bent into a hook. They do not lead to nodule formation.
EPIDEMIOLOGY.
In areas where nodule worm infestation is endemic, infestation is acquired during spring, summer and autumn months, but unless infestation are very severe, symptoms may not appear until late autumn or winter. It is usually during the winter months, when pastures have deteriorated, that the characteristic symptoms appear.
"Wet" summers with repeated rains and warm, humid weather present ideal conditions for the development and survival of larvae on pastures. Dryness and cold are very unfavourable for development of larvae. Frosts are fatal for the developing stages, but the third stage larvae are more resistant. In tableland areas it is probable that little, if any, infection with this parasite is picked up from mid-May to mid-September. Any plan of control should take advantage of this absence of resistance to cold.
In areas where this disease is not endemic, occasional outbreaks occur and are usually related to abnormal rainfall and the introduction of infested sheep, often grown sheep, which later leads to heavy infestations of young, highly susceptible animals.
CONTROL.
Control measures against this parasite present a number of special features. These are related to the nature of the disease produced and the life-cycle of the parasite. The parasite may produce disease conditions throughout the life of the sheep, the young animal suffering the effects of the mature worms, the older sheep suffering the effects of progressively increasing numbers of nodules. Control measures which simply lead to resolution of an outbreak of disease caused by the mature worm and have no long-lasting effects are not as valuable in oesophagostomiasis as in most other parasitic diseases. The object should be to reduce the degree of infestation very considerably, and then maintain it at such a low level that nodule formation will not be severe enough to produce ill-effects. Once nodules are formed, nothing can be done to remove them and provision of a high plane of nutrition is the only measure one can adopt.
This indicates that treatment should be highly efficient, but owing to the location of the worm in the large intestine, drugs given by mouth have, until the advent of phenothiazine, proved inefficient.
TREATMENT.
Treatment against the adult worms has been a difficult problem for many years in Australia, South Africa, U.S.A. and Canada. A great number of drugs have been tested and discarded. In South Africa, it was found that an enema of sodium arsenite and copper sulphate was an effective treatment. In Australia, enemas of sodium arsenite (two grains per quart) administered by means of a modified drenching gun or special syringe have been found to possess a very high degree of efficiency. This treatment, however, must be applied carefully and thoroughly in order to obtain satisfactory results and avoid deaths through damage to the bowel wall. The method is also tedious and time-consuming, but when once it has been demonstrated it loses most of those qualities of novelty and apparent impracticability which seem to disquiet the grazier. It is certainly not an easy, rapid method of treatment, but it is not much more trouble to carry out than jetting or cradling, for example.
In South Africa, a mixture of the insoluble drugs, copper arsenate and copper tartrate was compounded with lime to make a powder, which, administered after a dose of copper sulphate (to ensure swallowing into the abomasm), was claimed to be efficient against Oesophagostomum columbianum. This powder was widely tested in Australia but the results were not considered sufficiently promising to warrant a general recommendation of its use. It was thought at one stage that drastic purgation may remove these worms from the colon, but experiments showed that such drugs as sodium sulphate, magnesium sulphate, croton oil and Lentin (Merck), while producing marked purgation, did not lead to the removal of more than a few worms. In cases where nodule formation is severe it is probable that drastic purgation is dangerous as it may lead to rupture of the bowel in areas weakened by nodule formation, or may initiate intussusception. The drug which produced very marked pur- gative effects, Lentin, was found to be very toxic for sheep, especially those in poor condition.
During the last twelve months, work in U.S.A., Australia, Canada and South Africa has shown that phenothiazine is highly efficient against this parasite. This remarkable drug, being highly efficient against the three most important worm parasites of sheep (Oesophagostomum, Haemonchus and Trichostrongylus), marks a wonderful advance in the control of parasitic diseases of this animal. At the present time, however, it is not available in large quantities at a reasonable price and can only be recommended for the "tail" in severe outbreaks. When this drug finally becomes available for general use, the importance of nodule worm disease should progressively decline, and in some tableland areas, where winter conditions are severe, it may be possible to eventually either eradicate the parasite altogether, or so reduce its numbers that it is not likely to become of serious importance again for many years.
The time to treat is based on the epidemiology of the condition. In endemic areas, young sheep are likely to be suffering from infestation by autumn, and these effects will go on throughout winter. Treatment in the autumn will, therefore, reduce the infestation before the young sheep face the privations of winter and a lowered plane of nutrition. A second treatment in winter will remove adult worms which have developed since the autumn treatment and, as little or no further infection is likely to be acquired during the cold weather, sheep should enter the spring with very light infestations only.
A plan of control will depend eventually on the cost and availability of phenothiazine. In any plan, however, there are certain points for consideration. Advantage should be taken of the lack of resistance of the eggs and larvae to cold and dryness to spell country from sheep during the coldest winter months or dryest summer months, with the object of preparing it for treated young sheep or breeding ewes. The fact that cattle do not carry this parasite can be taken advantage of by using these stocks on country being spelled for sheep.
Ewes which are to lamb in spring should be treated in the late winter months and moved to a paddock which has been spelled for about a month. In this way the risks of the lambs becoming heavily infested will be considerably reduced. Young sheep should be treated in autumn and again in winter. If a plan of attempted eradication is adopted, all sheep should be treated during the winter months and moved to paddocks which have been spelled.
The provision of an adequate nutritional standard is a very essential part of any plan for the control of the nodule worm. In endemic areas, the winter months are usually periods of relative scarcity of feed, and at the same time are periods when the parasite is producing severe effects. Supplementary feeding of any kind is of value, and green, freshly-growing feeds,e.g. oats, improved pastures,etc., are especially valuable for heavily infested sheep.
Where a property has become heavily contaminated with the eggs and larvae of this parasite and sheep have suffered severely from the disease, it is advisable to consider disposal of all the sheep, resting on the property during winter months, and replacement of stock by animals from areas where Oe. columbianum does not occur.
SUMMARY.
Oesophagostomurn columbianum, the nodule worm of sheep, is an extremely important parasite for a number of reasons:-
1. It produces ill-effects throughout the life of the sheep.
2. The presence of resistance is not necessarily an advantage, because it apparently leads to severe nodule formation.
3. It produces ill-effects during periods when the general health and well-being of sheep are depressed by inadequate nutritional conditions.
4. It is not readily attacked by treatment (except by phenothiazine) and unless treatment is highly efficient it plays very little part in controlling the disease from year to year.
5. It leads to lasting ill-effects which may militate against the fattening of aged sheep from endemic areas.
6. Its presence gives country a "bad name" and sheep from such country are likely to be discriminated against in the market.
Other important facts are:-
7. It is commonest, and produces serious disease conditions, in areas receiving a predominantly summer rainfall.
8. The eggs and larvae are not resistant to cold or dryness and such unfavourable climatic conditions can be used to advantage plan of control.
9. The parasite is not carried by cattle or horses and these stock can be used on country which is being spelled for sheep.
10. The only treatments which are highly efficient against this parasite are (a) enemas of sodium arsenite and (b) phenothiazine administered by mouth.