CONTROL OF FLUKE

Hawke's Bay Herald-Tribune, Volume 81, Issue 70, 15 December 1937, Page 13

CONTROL OF FLUKE

Incidence in Hawke's Bay Flocks RESULTS OF RESEARCK Important factors conneeted with the incidence of liver-fluke and blaek disease among the sheep flocks of H.B. have been revealed as a result of researeh carried out in this district during the past 18 months by Mr W * V. Macfarlane, of the Veterinary Laboratory, of the Department of Agriculture, at Wallaceville. During the course of his investigations, Mr MacfarlanC was able to definitely identify one type of water-snail as responsible for acting as intermediary host to the fluke, to confirm the believed association between fluke and black disease, and to ■ present much information which will be of value in controlling this serious disease in the future. Sporadic outbreaks of black disease in sheep have occurred since the first investigation of the trouble in the years 1924 to 1928, "in spite of the e£forts that have been made to control the factors causing mortality, stated Mr Macfarlane in outlining the results of his research. It was shown at that time that the larval liver-fiuke entered the liver and burrowed through the tissues to stimulate the growth of the bacillus, the toxin produced causing the death of the animal. During the first half of 1937 the death of at least 500 breeding ewes from this cause came under the notice of the Department of Agriculture, while in addition there was a large number of rejections Of livers at the meat works because of the presence of fluke. The direct losS of sheep through the presence of large numbers of adult fluke in the bile-ducts was now negligible, however, owing to the regular drenching with carbon tetrachloride which was carried out in the district. It was formerly thought that the intermediate host of the parasite was the small black mollusc which is common in streams and lakes throughout the country. The investigations carried out by Mr Macfarlane, however, proved lliat this was not responsible for the liver-fluke, thcugh it harbours the immature forms of at least 14 other flukes whose adults live in flsh, birds or mammals. An examination of 5200 speeimens of this snail failed to provide one sample of the liver-fluke which was sought, while this observation was supported by the fact that the miracidium hatched from fluke eggs would not penetrate the tissues of this snail. Intermediate Host. In Hawke's Bay an^ Poverty Bay the only intermediate host of the fluke was discovered to be a snail which had been named myxas amulla. This snail grows to a length of one centimeter, is a broad shelled mollusc of a grey or greenish colour and has four whorls to the shell. The first three apcal whorls are small and the fourth is large, forming the shelter for the greater part of the. animal. Exammations of 2300 specimens of this snail from various parts of the district was made, and fluke infection was found to vary from complete absence to 43 per cent. In a normal fluke-infected pasture about five per cent. of the myxas will be found to be carrying parasites. The dentity of the parasite was established by feeding the cysts to laboratory-fed rabbits, from which mature fluke were recovered after 50 days. The habits of the myxas are well defined and limited, a factor which will assist greatly in effecting the control of both fluke and black disease in Hawke's Bay. The snail is an a»breathing animal adapted for life on muddy areas. Accordingly, it is not i'ound in deep or fast-runnlng waters with clearly cut banks. 'The characteristic locality in which myxas lives is a seepage from the hillside where the flow of water is imperceptibly slow but is constant throughout the year. Stagnant water is totally unsuitable, well aerated water being required. The Best Habitat. A short, green rush, ltnown as juncus lampocarpus, grows in such seepages, and when it is growing sparsely with extensive patches of bare mud on the association it provides the best habitat. Only fine, silty loains form a suitable substratum for myxas, which may be found either moving over the soft mud or mating in the water-filled hoofmarks of the swamp. Much information regarding the breeding habits of the enail, the periods of the year when it can best be tackled, and the methods which will prove most effective", was gathered during the course of the research, and this will ,be dealt with in a further a.rticle on the subject on Monday. Of particular importance will be the results of research into the use of blueetone, the investigations having indicated that in the past a great deal of bluestono used has been put t'o an incffective use and has been virtually wasted.