Ag-ELISA and PCR for monitoring the vaccination of cattle against Taenia saginata cysticercosis using an oncospheral adhesion protein (HP6) with surface and secreted localization.

A Taenia saginata oncosphere-derived adhesion protein (HP6) with surface and secreted localization was used to successfully vaccinate calves against oral challenge with T. saginata eggs. In contrast, vaccination using a combination of T. saginata oncosphere-derived peptides, selected on the basis of their antigenic index, and including three derived from the HP6 molecule (HP6-1, HP6-2 and HP6-3), was unsuccessful. This either indicated that the wrong peptides were selected or, in the case of the HP6 protein, that the protective epitope is conformational in nature. The protection experiments were monitored using a parasite antigen detection ELISA (HP10 Ag-ELISA), which allowed the early determination of the success of the vaccination protocol, subsequently confirmed at autopsy. PCR assays were used for the first time to confirm the presence of T. saginata DNA in lesions recovered at autopsy and thus verify the parasite origin of the lesions.

Control of Taenia saginata by post-mortem examination of carcasses.

BACKGROUND: A study to curb transmission cycle of a zoonotic Taenia cestodiasis between humans and cattle is presented. OBJECTIVE: To evaluate the reliability of meat inspection procedure in detecting carcasses of cattle with T. saginata cysticercosis. METHODS: A total of 55 cattle divided into two groups of artificially (n=30) and naturally (n= 25) infested animals were utilized. Total dissection method was used as a gold standard of validity. RESULTS: Meat inspection insensitively revealed cysticerci in 12 carcasses in each group compared with 24 and 23 carcasses revealed by total dissection in natural and artificial infestations, respectively. Sites of oncosphere invasion showed great variations with the two groups of cattle. In the predilection sites, most cysticerci were found in the heart, Triceps brachii, tongue and head muscles in that order. However, non-predilection sites (neck and back, hind limbs, chest, pelvic and lumbar regions, lungs and liver) considerably harboured high numbers of cysticerci. Observations indicated that except for the dead, degenerate or calcified cysticerci a careless meat inspector will most likely miss out quite a number of viable cysticerci, which blend the pinkish-red colour of the meat and be passed on for human consumption, becoming the source of bovine cysticercosis. CONCLUSIONS: The results confirmed that in spite of the time and efforts taken by meat inspectors looking for cysticerci at specified predilection sites of carcasses, this method is insensitive and inaccurate. To effectively improve meat inspection procedures, there is need to increase the area and number of predilection sites observed during inspection and vary them according to the nature of the animals, their husbandry history and the target human population for consumption. In addition, other control approaches such as vaccination, chemotherapy and immunodiagnosis should be developed and implemented to complement meat inspection procedures.

Taenia saginata derived synthetic peptides with potential for the diagnosis of bovine cysticercosis.

Immunity in Taeniids is predominantly antibody mediated and thus many serological immuno-determinants will have potential in both protection and diagnosis. The antigenicity of six peptides derived from four potentially protective molecules cloned from a Taenia saginata oncospheres cDNA library have been evaluated as targets for the specific diagnosis of bovine cysticercosis. The six peptides consist of: two peptides (HP6-2 and HP6-3) derived from the sequence of the 18 kDa surface/secreted oncospheral adhesion antigen identified by McAb-HP6, two peptides (Ts45W-1 and Ts45W-5) derived from the sequence of the T. saginata homologue of the T. ovis 45W protective gene family, one peptide (TS45S-10) derived from a T. saginata sequence with significant similarity to the T. ovis 45S protective antigen, and one peptide (TEG-1) derived from the sequence of the T. saginata homologue of Echinococcus spp. main surface protein. Longitudinal studies indicate that T. saginata infected cattle respond to all six peptides by 3-4 weeks post-infection and that the antibody levels remain high for at least 12 weeks post-infection. As protection against Taeniid parasites is predominantly antibody mediated, some of these six peptides may be of value as immuno-prophylactic tools and hence also in assays to determine resistance to infection with the parasite. For diagnosis, on the other hand, only three peptides (HP6-2, TEG-1 and Ts45S-10) performed with the necessary sensitivity and specificity to determine exposure to infection with T. saginata, and now merit an exhaustive evaluation prior to employment as routine diagnostic tools.

Serodiagnosis of bovine cysticercosis by detecting live Taenia saginata cysts using a monoclonal antibody-based antigen-ELISA.

An ante mortem antigen-ELISA-based diagnosis of Taenia saginata cysticercosis was studied in artificially (n = 24) and naturally (n = 25) infected cattle with the objective of further validating the assay as a field diagnostic test. Based on total dissection as the definitive method of validity, the assay minimally detected 14 live cysticerci in artificially infected calves and 2 in naturally infected steers. In natural infections, the minimum number of live cysticerci consistently detected by Ag-ELISA was 5 while in artificial infections it was above 14. However, other animals with 12 and 17 live cysticerci in artificially infected calves, and 1 and 2 live cysticerci in naturally infected steers, escaped detection for unknown reasons. Animals harbouring dead cysticerci gave negative reactions in the assay as was the case in non-infected experimental control calves. There was a statistically significant positive linear correlation between Ag-ELISA optical density values and burdens of live cysticerci as obtained by total dissection of both artificially infected calves (r = 0.798, n = 24; P < 0.05) and naturally infected steers (r = 0.631, n = 25; P < 0.05). These results clearly show the potential effectiveness of ante mortem monoclonal antibody-based antigen detection ELISA in the diagnosis of bovine cysticercosis in cattle. Its value lies in the diagnosis of infection in cattle as a screening test in a herd, rather than as a diagnostic test at the individual level, due to false positive and negative reactions. In a herd of heavily infected cattle, the assay may, however, provide for individual diagnosis. Nevertheless, more work is recommended to increase its sensitivity so as to be able to diagnose light infections consistently in the field.

Seroepidemiological survey of Taenia saginata cysticercosis in Kenya.

A sero-epidemiological study of Taenia saginata cysticercosis was carried out to determine the prevalence and distribution of the infection in three provinces of Kenya. Serum samples and meat inspection records were collected from cattle at slaughter at export and district abattoirs. Cattle origin and the presence of T. saginata cysticerci were noted as was the prevalence of other helminths such as Echinococcus granulosus and Fasciola gigantica. Serum samples were screened for circulating parasite antigen using a monoclonal antibody-based enzyme-linked immunosorbent assay (Ag-ELISA) and for ante-parasite antibody by indirect ELISA (Ab-ELISA). Eighty per cent of the sera were collected from cattle from the Rift Valley Province of Kenya. The prevalence of T. saginata cysticercosis and the other helminth infections varied between districts and was particularly high in Narok. Animal husbandry practices in arid areas such as Narok may be particularly conducive to transmission. The potential value of the Ag-ELISA for use in sero-epidemiological studies was verified by this study. It detected at least twice as many cases as T. saginata cysticercosis as meat inspection and, of the three methods investigated, was considered the most valuable.

Diagnosis of Taenia saginata cysticercosis in Kenyan cattle by antibody and antigen ELISA.

Sera from calves, either experimentally or naturally infected with Taenia saginata, were screened for an antibody response to T. saginata, and for parasite antigen, by enzyme-linked immunosorbent assays (ELISAs). An antibody response was detected by 3 weeks post infection (p.i.), rose to a peak at 10-12 weeks p.i., and was still in evidence 1 year p.i. Parasite antigen was first detected 4-7 weeks p.i. and persisted until the end of the experiment, over 1 year p.i. In the experimentally infected animals, cattle with 14 or more live cysticerci had detectable levels of parasite antigen in their sera at slaughter, while animals with live cyst burdens ranging from 0 to 4 were negative. Furthermore, levels of circulating antigen were positively correlated with live cysticercus burden in the experimental animals. In naturally infected cattle, 83% (5/6) of those with 30 or more live cysts, and 22% (5/23) of those with 1-29 live cysts, could be detected by the ELISA for parasite antigen, although no significant correlation between antigen level and live cyst burden could be detected. Antibody levels were not found to be associated with cyst burdens in either experimentally or naturally infected cattle. In slaughterhouse cattle, the antigen assay was almost three times as sensitive as meat inspection. However, there was no agreement between cattle found positive at meat inspection and those found positive by the antigen detection ELISA. One possible reason is that the ELISA only detects live cysts, while lesions left by dead cysts are more noticeable at meat inspection. The mouse monoclonal antibody-based antigen detection ELISA is of value for the diagnosis of naturally occurring, viable, T. saginata cysticercosis in live cattle and has an immediate application for field based epidemiological studies designed to determine prevalence.

Specific and shared antigenic components of Taenia saginata oncospheres.

Taenia saginata oncosphere components were analysed by double diffusion. Antigenic components in saline or detergent (Triton x-100) extracts of T saginata oncospheres were identified using a rabbit polyclonal serum directed against the oncosphere and compared with extracts prepared from the metacestodes and proglottids of T saginata and six other helminths commonly found in cattle. There were seven antigenic components found in the saline extract of the oncospheres, of which six were shared with the metacestodes and proglottids. None of these components was consistently different from those of the other six helminths. However, one of the four components in the detergent extract of the oncospheres was present in neither of the extracts of other stages of T saginata nor in extracts of other helminths. This may be of diagnostic significance.