The use of an enzyme-linked immunosorbent assay for tropical theileriosis research in Morocco

Ticks and Tick-Borne Pathogens Abound in the Cattle Population of the Rabat-Sale Kenitra Region, Morocco

Tick-borne pathogens cause the majority of diseases in the cattle population in Morocco. In this study, ticks were collected from cattle in the Rabat-Sale-Kenitra region of Morocco and identified morphologically, while tick-borne pathogens were detected in cattle blood samples via polymerase chain reaction assay and sequencing. A total of 3394 adult ixodid ticks were collected from cattle and identified as eight different tick species representing two genera, Hyalomma and Rhipicephalus. The collected ticks consisted of Hyalomma marginatum, Hyalomma anatolicum excavatum, Rhipicephalus sanguineus sensu lato, Rhipicephalus bursa, Hyalomma detritum, Hyalomma lusitanicum, Hyalomma dromedarii, and Hyalomma impeltatum. The overall prevalence of tick-borne pathogens in blood samples was 63.8%, with 29.3% positive for Babesia/Theileria spp., 51.2% for Anaplasma/Ehrlichia spp., and none of the samples positive for Rickettsia spp. Sequencing results revealed the presence of Theileria annulata, Babesia bovis, Anaplasma marginale, Theileria buffeli, Theileria orientalis, Babesia occultans, Anaplasma phagocytophilum, Anaplasma capra, Anaplasma platys, Anaplasma bovis, Ehrlichia minasensis, and one isolate of an unknown bovine Anaplasma sp. Crossbreeds, females, older age, and high tick infestation were the most important risk factors for the abundance of tick-borne pathogens, which occurred most frequently in Jorf El Melha, Sidi Yahya Zaer, Ait Ichou, and Arbaoua locations.

A quantitative risk assessment of bovine theileriosis entering Luapula Province from Central Province in Zambia via live cattle imports from traditional and commercial production sectors

Theileriosis or East Coast Fever (ECF) is an important livestock disease widespread in Zambia except for some provinces such as Luapula. This freedom status has been achieved due to strict livestock movement regulations that only authorise cattle imports from commercial farms implementing strict ECF control regimens. Recent increases in both the demand and price of beef in Zambia are stimulating a policy change towards a more inclusive inter-provincial trade in live cattle. This may also encourage the introduction of breeding cattle from high production pastoral sectors such as Central Province to stimulate the beef industry in disease free low production areas such as the Luapula Province. To estimate and compare the risks linked with those potential introductions of cattle from the traditional or commercial production sectors of the Central Province, a quantitative risk assessment model was developed. This risk comparison was necessary because the traditional livestock production sector accounts for over 79% of breeding cattle trade in Central Province but is characterised by minimalistic tick-borne disease control and a higher prevalence of ECF. We estimate that should the importation of breeding cattle from Central into Luapula Province be permitted, we could expect to import ECF by the introduction of infected animals at a median rate (5th and 95th percentiles) of every 0.44 years (0.12, 2.60), from the traditional sector compared to every 3.57 years (0.37, 103.6) from the commercial sector. Infected ticks would be expected to enter every 3.46 (0.66, 43.8) years via traditional cattle imports. These risks are strongly influenced by the prevalence of infection, performance of pre-transport screening tests, and the effectiveness of pre-transport tick cleansing. This assessment is expected to provide a model for tick borne disease risk assessments in similar settings, as well as inform ECF control, cattle trade, and stock movement policies in Zambia.

Vaccination against tropical theileriosis

Theileria annulata, the cause of tropical theileriosis is propagated in cattle with stage-to-stage transmission by Hyalomma ticks. Three stages in the life cycle of the parasite--tick-derived sporozoites, intramononuclear schizonts, and erythrocytic merozoites--infect cattle. When cattle are inoculated with schizont-infected cells, the parasite is transferred from the donor cell to the recipient. The main pathological damage in cattle is induced by the schizont stage. Each development stage of T. annulata elicits a specific immune response. Schizont-infected lymphoid cells can be grown indefinitely in culture and prolonged cultivation results in loss of virulence. Blood-derived schizonts induce stronger immunity than culture-derived schizonts, which suggests that restrictions on the parasite population or antigenic variation occur during prolonged cultivation. The duration of immunity following sporozoite or schizont infections has not yet been determined, but does not appear to be lifelong. The attenuated, culture-derived anti-theileria vaccine proved to be safe and effective in prevention of field theileriosis in large enzootic areas.

Development of an indirect Tams1 enzyme-linked immunosorbent assay for diagnosis of Theileria annulata infection in cattle

An enzyme-linked immunosorbent assay (ELISA) was developed based on a recombinant major Theileria annulata merozoite surface antigen, Tams1. Four different recombinant proteins derived from two different Tams1 alleles, both in two different truncated forms, were tested for their performance in the ELISA. Furthermore, antigen concentration, various buffers, washing protocol, and the choice of anti-total-immunoglobulin G (IgG), anti-IgG1, or anti-IgG2 as second antibody were evaluated. The performance of the resulting ELISA was analyzed by measuring the coefficient of variation (CV). A total of 22 sera were analyzed over the measurement range, resulting in a CV of ca. 10%, whereas 30% variation is the maximum acceptable. The cutoff value was determined by the two-graph receiver operating characteristic (TG-ROC), using the indirect fluorescent antibody test (IFAT) as a reference. It was shown that up to 3 months postinfection (p.i.) IFAT is more sensitive and specific, whereas beyond 3 months p.i. ELISA performed as well as IFAT. The cutoff was determined at maximal sensitivity, based on the TG-ROC after 3 months p.i. Nine calves experimentally infected with four different T. annulata stocks remained positive in the ELISA for at least 1 year p.i. Finally, limited cross-reaction was found only with T. parva antisera, but not with any other Theileria or Babesia species. Since the T. parva endemic area hardly overlaps with T. annulata, the Tams1 ELISA has the potential to become a useful tool in the epidemiology of tropical theileriosis.

Theileria annulata: carrier state and immunity

Recovery from primary infection of Theileria annulata results in the development of a persistent carrier state in the vertebrate host. The carrier state is of great importance in the maintenance of the life cycle by alternate tick/cattle challenge and both contributes to and may be necessary for maintenance of immunity. Therefore, an accurate determination of carrier animals could be useful in determining immune status and may allow the necessary control measures to be implemented. Detailed information on the carrier state of animals following immunization with attenuated cell lines is lacking. In this study, relationship between immune response, persistence of the parasite, and the antibody response has been investigated. Calves were infected with T. annulata sporozoites, low passage (non-attenuated) or high passage (attenuated, vaccine) cell lines and later challenged with a lethal dose of heterologous sporozoites. The presence and persistence of the parasite were monitored by PCR using primers derived from genes coding for ssrRNA and a 30 kDa major merozoite surface protein, by Giemsa stained blood smears to detect the presence of piroplasms and also by attempting to establish infected mononuclear cell cultures from venous blood. Antibody responses were measured by indirect ELISA using a merozoite recombinant antigen and IFAT using piroplasm and macroschizont antigens. Results showed that there was an evident relationship between the persistence of carrier status, antibody response in ELISA and immune response to challenge.