The epidemiology of Sarcocystis spp. in cattle of Western Australia

Oesophagus samples from 714 cattle from Western Australia were examined by artificial digestion to detect the presence of Sarcocystis spp. The overall prevalence of infection was 52%. The prevalence of infection increased with age and was highest in the entire males (92%). The prevalence was lower in cattle which originated from arid and semiarid regions (9 and 31% respectively) than those from tropical (87%) and temperate (60%) regions. possible reasons for these differences are discussed and it is concluded that environmental and management factors as well as host age and sex influence the prevalence of infection with Sarcocystis spp. in cattle

Climate and the distribution of intestinal Trichostrongylus spp. of Sheep

The relative prevalences of Trichostrongylus vitrinus, T. colubriformis and T. rugatus in sheep in south-west Western Australia were examined for evidence of associations with climatic conditions in different localities. The region has a mediterranean-type climate with hot, dry summers and cool, wet winters. The intestinal Trichostrongylus spp. populations in sheep sampled comprised 50% T. vitrinus, 38% T. colubriformis and 12% T. rugatus. The prevalence of T. vitrinus was negatively correlated with mean autumn, winter and spring temperatures of a locality. The prevalence of T. colubriformis was positively correlated with mean autumn, winter and spring temperatures. The prevalence of T. rugatus was not correlated with temperature of any season, but was negatively correlated with mean annual rainfall and length of growing season of a locality. There were suggestions of association of amount of rainfall of a locality and prevalence of T. colubriformis and of differences in seasonal prevalence of T. vitrinus, but the significance of these was obscured by confounding of some climatic factors. The differences in prevalence of the three Trichostrongylus spp. at different locations was attributed to differences in preferred ambient conditions for development and survival of the freeliving stages

Viability of the sporocysts of Sarcocystis cruzi after exposure to different temperatures and relative humidities

The effect of temperature and relative humidity (RH) on the survival of sporocysts of S. cruzi were investigated in vitro. Under all experimental conditions (temperature of 4°C, 37°C or room temperature; RH of 18%, 75%, or 100%) some sporozoites retained their viability to excyst for at least 90 days. The best conditions for survival were 4°C at 100% RH (more than 240 days) and 37°C at 18% RH (more than 180 days). Sporocysts maintained at room temperature at all humidities had the lowest level of survival. It is concluded that sporocysts of S. cruzi are able to survive in most environments for several months and that the fluctuation of the daily ambient temperature is likely to influence the viability of the sporocysts

The accumulation of Toxocara canis larvae in the brains of mice

In a series of experiments it has been shown that larvae of Toxocara canis continue to accumulate in the brains of mice for many weeks after infection. This implies that the larvae, as long as they live, continue to circulate in the body until they reach the brain. Unlike other sites where they may be sequestered, in the brain they are not subject to encapsulation by a host reaction. The further implications of larval survival in the brain are discussed

Comparative strobilar development of Echinococcus granulosus of sheep origin from different geographical areas of Australia in vivo and in vitro

Consistent differences in the growth, segmentation and maturation of Echinococcus granulosus in dogs were demonstrated between the parasite of Tasmanian sheep origin and that of Eastern and Western Australian sheep origin. These results were complemented by in vitro studies which found that Tasmanian E. granulosus produced eggs approx. 7 days earlier than the parasite of Eastern and Western Australian origin. These results support the suggestion that at least two distinct strains of E. granulosus of domestic animal origin exist in Australia. The significance of the differences in development demonstrated in this study is discussed

Class-specific antibody responses in cattle following experimental challenge with sporocysts or merozoites of Sarcocystis cruzi

An ELISA using antigen produced from merozoites of Sarcocystis cruzi was developed to monitor specific IgM and IgG antibody, following challenge of cattle with either merozoites or sporocysts of S. cruzi. This assay was compared with an ELISA using antigen produced from the cystozoite stage of the parasite. Both ELISAs were able to detect significant increases in levels of circulating IgM and IgG antibodies against Sarcocystis in all challenged cows; however, the magnitude of the titres was greater in the ELISA which used the antigen derived from the merozoites. This immunoassay also detected increases in the levels of IgG earlier than did the assay using antigen derived from cystozoites of S. cruzi. Since this rise coincided with the presence of clinical signs, and was persistent for several weeks, the IgG-ELISA using antigen derived from merozoites appears to be suitable for the diagnosis of acute sarcocystiosis in cattle. Furthermore, since significant increases in the levels of circulating IgM and IgG antibodies against Sarcocystis were detected in the cows infected with merozoites of S. cruzi, it is evident that merozoites of S. cruzi cultured in vitro maintain their capability to replicate in the natural intermediate host

Echinococcus granulosus: Secretory activity of the rostellum of the adult cestode in situ in the dog

Secretary activities associated with the rostellum of adult Echinococcus granulosus were studied using histological, histochemical, and ultrastructural techniques, following rapid fixation of the cestodes in situ in the small intestine of the anaesthetised dog. Studies concentrated on the host-parasite interface from 30 to 35 days postinfection. At this time, contraction of the muscular rostellar pad appeared to be associated with extension of the apical rostellum into a crypt of Lieberkühn. Crypt invasion by the apical rostellum coincided with morphological changes and secretory activity in a group of modified tegumental cells, previously referred to as the rostellar gland. Secretory material, a cystine-rich protein, was observed in the nuclei and cytoplasm of the rostellar gland cells. Release of this material into the interface was seen only following crypt invasion by the apical rostellum. Although the mechanism of release is not clear, it may be analagous to holocrine secretory mechanisms, since apparent degeneration of the rostellar gland region was associated with secretion. Possible functional activities of the secretion associated with hook formation, nutrition, regulation, adhesion, and protection are discussed

Excystation rates and infectivity of sporocysts of Sarcocystis cruzi exposed to different treatments and storages

The effect of some chemical and anatomical factors on the excystability and infectivity in cell culture of sporocysts of Sarcocystis cruzi was investigated. A significantly (P < 0.001) higher excystation rate (ER) occurred when sodium bicarbonate was added to the excysting fluid at concentrations between 0.075 and 0.3 M. Sporocysts collected from different dogs had different ER. In contrast, although not uniformly distributed along the intestinal lumen, the sporocysts collected from the different tracts of the intestine showed similar ER. The period of storage did not affect the excystability of the sporocysts; however, it influenced the pattern of growth of the sporozoites in cell culture. Sporozoites excysted from sporocysts stored for approximately 2 years grew slower and produced significantly fewer merozoites compared to those excysted from sporocysts stored for 5-7 months