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Biomedical subjects

M D Rickard

Publications and source records attributed to M D Rickard.

At least 109 records · Page 6Linked to original sources
PubMed1976

Vaccination of lambs against infection with Taenia ovis.

A trial was designed to test the efficacy of vaccination of lambs against field challenge with T. ovis eggs using 3 different levels of pasture contamination. Three concentric paddocks (1.62 hectares each) were used and the inner paddock was heavily contaminated with T. ovis eggs by tethering 2 dogs, experimentally infected with T. ovis, at 5 different points in the paddock over a period of 1 month. Four groups of lambs were used. Sixty lambs, from a property known to be free of T. ovis for 2 years previously, were divided into 2 groups of 30 each; one group was vaccinated with T. ovis culture antigen (vaccinated group=V) while the other was vaccinated with culture medium without antigen (sham-vaccinated group=SV). Thirty mature sheep were obtained from a property with a recent record of T. ovis infection (previous natural exposure to infection group=PNE) and 15 lambs were artificially reared from birth under cestode-egg-free conditions (artificially reared groups= AR). Ten animals from groups V, SV, and PNE, and 5 AR lambs were grazed on each of the 3 concentric paddocks for 6 weeks, and then all animals were slaughtered and their total muscle mass (including heart, diaphragm, tongue and masseters) examined, by slicing, for T. ovis cysticerci. The mean total numbers of T. ovis cysticerci recovered were as follows: Inner paddock, PNE 45.5, AR 47.6, SV 107.8, V 6.5; Middle paddock, PNE 5.2, AR 9.0, SV 8.2, V 0.3; Outer paddock, PNE 2.9, AR 2.8, SV 2.3, V 0.2. There were 4 major conclusions from this study. Firstly, vaccination was more effective than previous natural exposure to infection in preventing establishment of new cysticerci. Secondly, although vaccination effectively reduced the numbers of cysticerci, those that became established were mostly viable at the time of slaughter. In contrast, PNE sheep had greater numbers of cysticerci but the majority were degenerating. Vaccination, therefore, did not seem to stimulate a complete immunological response. Thirdly, the presence of T. hydatigena in lambs did not prevent subsequent infection with T. ovis. Fourthly, T. ovis eggs were dispersed from the inner paddock to the outer paddock.

Animals↗
PubMed1975

The location of Taenia pisiformis, Taenia ovis and Taenia hydatigena in the gut of the dog and its effect on net environmental contamination with ova.

Autopsy of dogs 56 days after infection with either T. pisiformis, T. ovis or T. hydatigena showed that these worms could be found attached at any point along the length of the small intestine, but were most commonly in the anterior half. The mean relaxed lengths of T. pisiformis, T. ovis and T. hydatigena were 107 cm, 156 cm and 177 cm respectively. Attached gravid proglottides contained a mean of 41 000 eggs each in T. pisiformis, 31 000 eggs in T. hydatigena and 95000 eggs in T. ovis, whereas proglottides free in the gut contained means of only 1370, 500 and 1400 eggs respectively; therefore, the majority of eggs were released into the gut before segments passed out into the faeces. It was shown that eggs of all 3 species of worms hatched and activated in the small intestine of the dog, especially in the anterior half. Eggs of T. pisiformis which had been passaged through the intestine of the dog and stored in the faeces for 5 days were poorly infective for rabbits compared with eggs only stored in faeces. It was concluded, therefore, that during taeniid infections of dogs the point of apolysis in the gut plays a significant role in determining environmental contamination with eggs. Puppies which had been fed 10000 T. ovis eggs daily for 6 weeks prior to infection with T. ovis cysticerci showed no difference in susceptibility to the infection when compared with untreated puppies.

Animals↗
PubMed1975

The developmental cycle of a species of Sarcocystis occurring in dogs and sheep, with observations on pathogenicity in the intermediate host.

Twelve dogs were fed mutton containing small sarcocysts, and killed 1, 3, 4, 6, 7, 10, 15, 16, 17 days after infection (DAI). Beginning 13-15 DAI sporocysts 14.7 times 9.0 mum were passed in the faeces of the dogs killed 15-17 DAI. Histological examination showed that developing stages were most numerous in the subepithelial tissue at the tips of villi in the proximal third of the small intestine. Macrogametes containing tiny PAS + granules, and microgametocytes with peripheral developing microgametes were present 1 DAI. By 4 DAI oocysts, with a small nucleus and vacuolate cytoplasm were seen. Sporulation was observed 7-10 DAI. The first nuclear division resulted in 2 polar nuclei which divided laterally, resulting in 2 sporocysts each with 2 polar nuclei. This process was repeated once more to produce 4 nucleated sporozoites in each of 2 sporocysts. PAS + granules were seen at the periphery of sporulating oocysts and sporocysts. There was a large PAS + granule in the mid zone of sporozoites, with a smaller granule at one tip. Numerous sporulated sporocyst pairs were present beneath the epithelium at the tips of villi in dogs killed during patency. Four lambs were inoculated orally with sporocysts passed by dogs following feeding of infected mutton. Fifteen DAI schizonts were seen in the endothelium of arteries and arterioles in many organs, but not brain. Twenty-four DAI, smaller schizonts were seen in capillary endothelium in many organs, including brain. The two other lambs died 42 and 104 DAI, after an illness characterized by anaemia and ill-thrift. Mature schizonts were found in cells in the brain 42 DAI, associated with nonsuppurative meningoencephalitis. Developing sarcocysts were found in muscle, associated with myositis. Sarcocysts in muscle 104 DAI were mature. In the brain there were degenerate cysts and mature sarcocysts, and nonsuppirative meningoencephalitis.

Animals↗
PubMed1975

Prenatal infection with Fasciola Hepatica in calves.

The livers from 16,776 calves 1 to 3 weeks of age slaughtered at Shepparton abattoirs were examined for gross evidence of infection with Fasciola hepatica. Those livers with thickened bile ducts were examined for the presence of liver fluke by slicing. One hundred and eight F. hepatica were collected from 84 of these livers, giving a minimum prevalence rate of prenatal infection of calves of 0.5%. These results are discussed in context with reports from other countries.

Animals↗
PubMed1975

Toxoplasmosis in dasyurid marsupials.

During a histopathologic survey of 240 dasyurid marsupials a high prevalence of infection of Toxoplasma gondii was found in eight of thenine species examined. Amongst the infected species, endemic infection in field animals was proved in Dasyuroides byrnei, but there was also good evidence of laboratory infection probably derived from raw sheep tissues in their diet. Infection was never demonstrated in animals less than six months of age. The 21 Antechinus stuartii examined remained free from infection despited a lengthy stay in the laboratory and a similar diet. This freedom from infection may indicate a particular resistance to Toxoplasma infection by this species.

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