Studies on the fate of Taenia hydatigena and Taenia ovis larvae in rabbits, and cross immunity with Taenia pisiformis larvae

Lethal cysticercosis in a pet rabbit

A one-year-old neutered female crossbreed rabbit died unexpectedly after initially responding to symptomatic treatment over a three-month period for recurrent gut stasis, inappetence and lethargy. Postmortem examination revealed numerous fibrous tracks within the liver from which flattish ovoid parasites could be extruded. Parasites were also found in large numbers throughout the peritoneal cavity. Histopathology confirmed verminous hepatitis with numerous parasitic granulomas within the parenchyma of the liver containing intact and degenerate parasites. The severity of the parasitic burden and associated liver damage was the presumed cause of death. Intact parasites showed morphological features consistent with Taenia pisiformis at 6–15 days postinfection. Species identification was confirmed by PCR sequence analysis. The rabbit was fed on hay sourced from a local farm, commercially available nuggets and washed vegetables. It did not graze outside. Hay contaminated with dog or fox faeces was the presumed source of infection.

Heterologous antagonistic and synergistic interactions between helminths and between helminths and protozoans in concurrent experimental infection of mammalian hosts

Experimental concurrent infection with two or more parasite species in mammalian host models may result in heterologous antagonistic and synergistic interactions ranging in magnitude from reduced/enhanced growth and fecundity to blockage/enhancement of establishment/expulsion. With some exceptions only, there is a reasonable correlation between the levels of interaction monitored by parasitological and by clinico-pathological parameters. Heterologous antagonistic interactions mediated by functional and specific immunological cross-reactivity occur between closely related parasite species exhibiting a marked immunobiological similarity. In contrast, antagonistic interactions between antigenetically more remote species of helminths, protozoan-induced resistance to helminth infection and helminth-induced suppression of concurrent protozoan infection generally appear mediated by immunologically non-specific factors like macrophage activation and inflammatory reactions. Synergistic heterologous interactions between helminths, helminth-induced enhancement of concurrent protozoan infection and interference with the development and maintenance of resistance to helminth infection in response to concurrent protozoan infection are generally thought to be mediated by non-specific parasite-induced immunosuppression. Concurrent experimental infection is very complex. There are problems and limitations in extrapolating from experimental studies on concurrent infection in laboratory animals to natural polyparasitism. This fact, coupled with the complex influence of ecological factors on the pattern and frequency of concurrent natural infection means that major consequences of natural concurrent parasite infection have not been definitively demonstrated. Appropriately planned and controlled field studies and further laboratory experiments on primate and domestic animal models are imperative for elucidation of the importance of heterologous interactions in concurrent parasite infection for the disease pattern in man and domestic stock. Experimental studies hitherto conducted on concurrent parasite infection pointing to natural heterologous interactions may be a valuable starting point for further studies.

Hydatid disease: research and control in Turkana. II. The role of immunological techniques for the diagnosis of hydatid disease

Immunological studies have been applied to the immunodiagnosis of human hydatidosis in Turkana and for the specific identification of Echinococcus eggs, particularly in regard to their potential for the assessment of a hydatid control programme in the north-west of the District. A high rate of false negatives has been obtained with sensitive antibody tests for proven hydatid patients in Turkana and presents problems for prevalence estimation in the population. A seroepidemiological study using specific antibody detection indicated a 2.17% seropositive rate, and by using a portable ultrasound 67% of antibody positives were confirmed as having liver/abdominal cysts. An enzyme immunoassay test for specific circulating antigen, often associated with circulating immune complexes, was positive in sera in 75% of hydatid patients who were antibody-negative. The formation of specific circulating immune complexes may contribute directly to the production of a state of false negativity. These studies indicate that by combining tests for antibodies and antigens together with ultrasound, the true prevalence of human hydatidosis in Turkana is at least 5%. Characterization of Echinococcus antigens recognized by human antisera from Turkana and British hydatid patients indicates that both groups recognize the same major protein antigens in cyst fluid and protoscoleces. The results of assaying anti-oncospheral antibodies in people living in the high prevalence area of north-west Turkana compared to people in areas of low prevalence indicates that most of the people in the high prevalence area are probably infected (challenged) with Echinococcus eggs. This observation suggests that there may be a high level of acquired resistance. A species-specific immunofluorescence test using an anti-Echinococcus monoclonal antibody has been developed which can specifically identify oncospheres artificially hatched from Echinococcus eggs. This test will be applied to the problem of identification of Echinococcus eggs in the environment and in dog faeces, with a view to studying the epidemiology of the disease and for use in assessment of the hydatid control programme.

Immunisation of mice against Taenia taeniaeformis using antigens prepared from T. pisiformis and T. hydatigena eggs or oncospheres

Experiments were carried out to investigation the degree of immunity stimulated against Taenia taeniaeformis infection in mice by prior administration of eggs or ultrasonically disrupted oncospheres of T. pisiformis or T. hydatigena. Sonicated oncospheral antigens were given either orally or by subcutaneous injection in Freund's complete adjuvant, and eggs were given orally. Three inbred strains of mice with varying degrees of innate resistance to initial infection with T. taeniaeformis were used in the experiments. These were the moderately resistant BALB/c, moderately susceptible CBA/H, and highly susceptible C3H/He strains. It was found that BALB/c mice developed high levels of immunity when immunised with either T. pisiformis or T. hydatigena eggs, or with sonicated oncospheres administered orally or parenterally. CBA/H mice developed moderate immunity, and C3H/He mice generally did not develop a satisfactory level of resistance. the implication of these findings with respect to immunisation of outbred animals against natural infection with larval cestodes using antigen prepared from the oncospheres of heterologous parasite species is discussed.

Attempts to immunise rats and mice against infection with fasciola hepatica using antigens prepared from taenia hydatigena

Attempts were made to immunise rats and mice against infection with F. hepatica by oral dosing with T. hydatigena eggs, or by vaccination with various T. hydatigena antigen preparations. These antigens included extracts from T. hydatigena cysticerci and cyst fluid, and antigens collected during short-term (48 h) and long-term (14 days) in vitro cultivation of larvae. Immunity was assessed by the numbers of F. hepatica recovered from the challenge infection in rats, and the mortality rates of infected mice. None of the immunisation regimes with T. hydatigena antigens induced consistent, significant immunity. This was in contrast to the high level of immunity shown by rats dosed orally with F. hepatica metacercariae four weeks prior to challenge infection.

Evidence that a hydatid cyst is seldom "as old as the patient"

Human hydatid disease caused by the strain of Echinococcus granulosus endemic in Australia and New Zeland has been regarded as a very lonstanding condition, and most cysts diagnosed in adults were believed to have resulted from infection in childhood. A significant drop in the number of new cases among people and 25 and over (P less than 0.05) in two hydatid-control programmes makes it necessary to revise this view. In both Tasmania (P greater than 0.50) and New Zealand (0.50 greater than P greater than 0.10) the incidence was halved without significantly altering the age-distribution. These findings indicate that adults are relatively susceptible and that the latent period between infection and diagnosis in many cases is only a few years.

Vaccination of lambs against infection with Taenia ovis using antigens collected during short-term in vitro incubation of activated T. ovis oncospheres

Activated oncospheres of Taenia ovis were incubated for 24 h or 48 h at 37-5 degress C in Medium 858 alone or in Medium 858 enriched with 20% lamb serum or foetal calf serum. Antigens contained in the supernatant medium from these incubations were concentrated, emulsified in Freund's incomplete adjuvant and injected intramuscularly into lambs. These lambs developed a very high level of immunity to subsequent challenge infection with T. ovis eggs.