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This article was published in 1961
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.

Liver Fluke Infestation in Sheep in the Riverina

E. P. BUCKLEY, B.V.Sc., Veterinary Inspector, Corowa

Although Liver Fluke infestation has been the subject of considerable investigation in the areas apparently more suited to the intermediate host snail, Lymnaea tomentosa, only very limited study has been reported of the special factors influencing the epidemiology of Fluke and Black Disease in the drier Western Plains. (According to recent studies by J. C. Boray. D.V.M. (unpublished) Lymnaea tomentosa (Pfeiffer) 1885 is the correct name for the host snail of Fasciola hepatica in Eastern Australia and New Zealand. L. brazieri, L. launcestonensis, L. huonensis, S. subaquatilis, et cetera are only local variants of the same species.) It has been thought advantageous to record observations over the past few years in Corowa, Jerilderie and Urana districts, of the distribution and activity of the intermediate host snail, and to discuss the above two disease conditions in sheep likely to result from this activity.

In the Eastern Riverina distribution is mainly influenced by irrigation and flooding, although occasional apparently permanent habitats have been found. It may be best to discuss these two types of habitats separately, although the conditions under which snails thrive are very similar.

(a) Irrigation. The commonest use of pasture irrigation in this area is to extend and assure the normal Winter rainfall. This entails flooding the pasture at 10 or 15-day intervals from late February until May, and from mid-August until about October. At these times water temperature is very suitable for rapid breeding and growth of L. tomentosa. Snails are not seen frequently in irrigation channels, however, but become very numerous in drainage areas and swamps. The supply channels only contain much water while irrigation is in progress, but drainage water may take a week or more to reach the swamps in which it collects, and water may be running into these swamps continuously during the watering programme. Once water has been directed into the main canal, it must be used by the farmer who ordered it. A farmer usually starts using water on a 10-day cycle and has to continue on this or a 15-day cycle till the end of the season regardless of rainfall. In wet seasons this can result in heavy flooding, particularly of drainage areas, and extension of the snail habitat.

The importance of drainage swamps as a habitat for the snails also influences their distribution to a marked degree. Snails were first seen by me in a drainage swamp about 5 miles east of Tocumwal, and several days later in another about 3 miles south of Berrigan, about 20 miles distant. It was learnt later that these were the ends of a chain of swamps, and that on occasions water ran through the whole chain (e.g. 1956 floods). L. tomentosa occurs right along this chain, but apparently is absent from similar swamps, sometimes only a mile from infested swamps. Some swamps to the East of this line also carry numerous fluke snails, but they have not been seen West of the chain, apart from an area West of Tocumwal on Tuppal Creek. Distribution in the irrigated country shows no obvious relationship to supply channels.

It has been proved that L. tomentosa can survive for long periods in drying mud, and, although these swamps dry out for considerable periods, they are filled twice yearly during the most suitable breeding seasons for these snails. The temperature range most suitable for growth of the desired pasture species is also apparently within the range most suited to snail development. During Autumn watering snails usually start to become obvious by mid-March, and are numerous in April and May. Numerous snails were seen on a Berrigan holding on 1st June, 1960, but L. tomentosa has not been seen further into the Winter in this area. (Local Bullinoid type snails, however, have been noticed moving round under ice in mid-Winter). In the Spring they were seen first in mid-August, 1953, following heavy rain, but usually do not become active and numerous till mid-September. Activity usually ceases by the end of November, but renewed activity was seen in mid-December, 1960, where storm rains had brought a flow of fresh water. The local Bullinoid snails are also more active in summer and appear more acclimatised to stagnant water.

(b) Effect of Flooding. Apart from the irrigated area, L. tomentosa is mainly an inhabitant of the major watercourses in the area, the Murray and Murrumbidgee Rivers and Billabong Creek. It is not known how far westward the snail can normally be found in these streams, but no doubt some swamps and backwaters provide suitable environments in many seasons.

When Spring flooding occurs, snails are spread from these streams over a wide area, some of the widest spread in this area being from Billabong Creek. When this creek floods it usually leaves its banks West of Rand, and may run 4 to 5 miles wide, from 3 inches to 18 inches deep, and finally reach Lake Urana, about 15 miles North of the creek. During 1960, flood waters also left the South bank near Rand, and flowed through Daysdale to Wangamong Creek and along this watercourse to Jerilderie. Snails were found in large numbers in streams and swamps filled by this water, and in some water further upstream. In one road drain they appeared to have travelled up at least one mile from Wangamong Creek. In other places snails were found from five to twenty miles above the entry point of Billabong Creek water, but that they had been carried to these swamps on the feet of waterfowl, which were very widespread in the area last Spring. It appears, however, that permanent suitable habitats for L. tomentosa are uncommon in this area. They have been found adapted to the overflow of a tank on the shore of Lake Urana, which is kept moist by a mill, but similar habitats with snails able to gain access would be uncommon. This particular tank is only & storage for a sheep-dip.

Further investigation is necessary into the survival of snails in these various temporary habitats. They may not last one Summer. It is not likely that they would remain long enough to support any heavy fluke infestation on the areas involved, but in many cases where snails are washed onto a property, they carry sufficient fluke to cause light infestation.

Disease Conditions. The above indicates that fluke infestation can reach serious levels on irrigation areas when L. tomentosa gains entry, but is not likely to be serious on dry areas subject to occasional flooding. Black Disease on the other hand can result in quite unexpected losses in these latter areas. Its occurrence depends also on the presence in the soil of Clostridium novyi of course. Once diagnosed, vaccination after Spring floods is all that is necessary.

Where snails have become established on irrigated country, control measures must be much more effective. There is the advantage over other fluke areas that the provision of snail habitats is regulated by application of irrigation water. Control measures can thus be applied to more advantage. Due to the rapid repopulation of treated areas by snails, attack on these intermediate hosts is probably uneconomic, and the best point to break the life cycle of the fluke is in the final host.

Drenching prior to placing stock on Autumn irrigated pasture, and again when snails are inactive in mid-Winter appears to be all that is necessary practically to eliminate this parasite from infested properties. On three properties which were suffering heavy losses three years ago, this approach has been effective to the extent that livers of ration sheep have been it for human consumption for the past 18 months. It must be realised, of course, that hosts other than sheep must be considered in this programme. Facilities for handling cattle are not good on many properties in this area, and some graziers require very forceful warning of the danger of running untreated cattle on snail infested country, particularly if this may be used later by sheep. Pigs, horses, kangaroos, rabbits and humans can also spread the parasite, the importance of the rabbit in such a control programme not yet having been studied. I hope the opportunity does not arise.

To summarise, the important points in disease control are:—

Vaccinate on flooded country following Spring floods and annually on irrigated country.
Drench for fluke before Autumn watering and during mid-Winter on infested irrigated country.
Do not allow untreated cattle onto snail infested irrigation country.