LETTERS TO THE EDITOR HOST SPECIFICITY OF SARCOCYSTIS SPP IN SHEEP AND C A m L E A number of workers have demonstrated that Sarcocystis spp of domesticated animals have a preypredator type life-cycle. Particular cycles so far elucidated involve cat-sheep and dog-sheep (Sarcocystis tenella), cat-cattle, dog-cattle and man-cattle (Sarcocystis fusiformis) and man-pig (Sarcocystis miescheriana) (Rommel and Heydorn 1972; Ford 1974, 1975; Munday and Corbould 1974; Munday and Rickard 1974). It is apparent from these studies that sporocysts in the faeces of dogs fed either beef or mutton are equal in size (15 x 10 pm), as are sporocysts in the faeces of cats fed either type of meat ( 1 2 x 8 pm). Furthermore, the dog-transmitted form of each parasite is pathogenic in its intermediate host whereas no such pathogenicity has been reported for either of the cattransmitted forms. It is possible, therefore, that there may be a single species of Sarcocystis in the dog and a single species in the cat, each of which uses both sheep and cattle as intermediate hosts. The following experiments were carried out to clarify this point. Puppies and kittens were fed on proprietary canned foods from weaning. Two lambs and 3 calves were reared indoors on wire-mesh floor .cages away from contact with dogs and cats, and fed initially on a milk replacer ration and weaned onto pelleted feed. The 2 lambs and one of the calves were deprived of colostrum after birth. Serum samples collected from calves immediately prior to and at 4, 8, and 12 weeks after infection were tested for complement-fixing antibodies against Sarcocystis (Munday and Corbould 1974). Pure suspensions of sporocysts of the dog-transmitted and cat-transmitted forms of S. tenella of sheep were obtained from the faeces of puppies and kittens fed on mutton from sheep with pure infections of each “strain” (Munday and Rickard 1974). Experimental infections of lambs and calves were carried out when they were 6 and 4 weeks of age respectively. The colostrum-deprived calf was dosed with 0.5 x 1045 S. tenella sporocysts from dogs’ faeces and, in addition to serological observations, a muscle biopsy sample was examined 2 months after infection. This calf was not killed. A further calf was infected orally with 1 x 106 S. ienellu sporocysts from dogs’ faeces both at 5 and at 2 months prior to killing and the remaining calf was doqed with 0.5 x 100 S. tenella sporocysts from the faeces of cats and killed 5 months later. After killing, striated muscle from these two calves (including tongue, oesophagus, heart and diaphragm) was fed separately to each of 2 puppies and 2 kittens. Pieces of each type of muscle were fixed in 10% formalin for histological examination (haematoxylm and eosinstained section). The two control lambs were dosed with 1 x 10s sporocysts of either the dog-transmitted or cat-transmitted forms to confirm the viability of the sporocysts fed to calves. Faeces from the puppies and kittens fed meat from the calves were collected daily and examined for sporocysts for 4 weeks after the first feed by flotation on saturated sucrose or sodium nitrate solutions. They were then autopsied and the intestinal mucosa further examined for the presence of sporocysts by scraping or digestion in pepsinIHC1. Both of the calves which had had colostrum were serologically positive to Sarcocystis before infection

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(titres 1: 4 0 ) , but their titres declined until slaughter (titres 1 : 8 ) despite the large doses of dog- or cattransmitted S. tenella sporocysts administered to them; it was concluded that these antibodies must have been maternally derived. None of the puppies or kittens fed meat from these calves showed sporocysts in their faeces or in their intestinal mucosa, nor could sarcocysts be demonstrated histologically in the muscle of the calves. The colostrum-deprived calf fed dog-transmitted S. tenella sporocysts remained serologically negative and no sarcocysts could be found in muscle biopsies. The control lamb dosed with dog-transmitted S. tenella sporocysts died 29 days after infection and had Sarcocystis schizonts in all organs examined histologically a t autopsy. The lamb fed cat-transmitted S. tenella had numbers of Sarcocystis cysts in its muscle when killed 5 months after infection. The numbers of animals used in these experiments were small and this places limitations on interpretation of the data. However, none of the infections with S . t e n e h sporocysts were successful in the calves, although they produced infection in the lambs. It could be argued that the 2 calves with maternal antibody in their sera were passively protected against the experimental infection with S. tenella. Nevertheless, Munday and Rickard ( 1 9 7 4 ) were able to superinfect lambs which had been infected 4 weeks previously with S. tenella sporocysts, and which had high titres of antibody in their serum. The present results suggest that the dog and the cat-transmitted forms of S. tenella of sheep may be biologically distinct from the corresponding forms of S. fusiformis of cattle, as well as being distinct from each other (Munday and Rickard 1974). Further support for this suggestion is provided by the results of Gestrich et al ( 1 9 7 4 ) who showed that S. fusiformis sporocysts collected from the faeces of dogs fed beef were not infective for lambs. Because of the number of apparently distinct organisms in this genus of parasites that have emerged as a result of recent investigations, the whole genus is in urgent need of taxonomic revision. Invaluable assistance was provided by Messrs A. Corbould and G. Goodsall and G. Scott and G. Mares at Mt Pleasant Laboratories and the University of Melbourne respectively. References Ford, G. E. (1974)-Aust. vet. J . 50: 38. Ford, G. E. (1975)-Azrst. vet. J . 51: 407. Gestrich, R., Schmitt, M. and Heydorn, A. -0. ( 1 9 7 4 ) - B e d Munch. Tierarztl. Wschr. 87: 362. Munday, B. L. and Corbould, A. (1974)-Br. vet. J . 130: ix. Munday, B. L. and Rickard, M. D. (1974)-Actst. vet. J . 50: 558. Rommell, M. and Heydorn, A. -0. (1972)-Berl. Munch. Tierarztl. Wschr. 85: 143. M. D. RICKARD, B.V.Sc., Ph.D. University of Melbourne, Veterinarv Clinical Centre. Werribee,‘ Victoria, 3030 . B. L. MUNDAY, M.V.Sc. Mt Pleasant Laboratories, Launceston South, Tasmania, 7250 12 September 1975 Australian Veterinary Journol, Vol. 52, January, 1976