Application of enzyme linked immunosorbent assays to the diagnosis of the pathogenic animal trypanosomoses

The pathogenic animal trypanosomoses comprise a number of diseases caused by different species of vector borne trypanosomes. In Africa, trypanosomes transmitted by tsetse flies (Glossina spp.) constitute a major constraint on socioeconomic development; over ten million km2 of sub-Saharan Africa are infested by the fly and 400 million livestock are at risk from infection with Trypanosoma congolense, T. vivax and T. brucei. Diseases caused by trypanosomes also occur outside the tsetse belt. Two trypanosome species are transmitted mechanically by haematophagous biting flies, mainly tabanids, and thereby have achieved a wider geographical distribution; T. evansi occurs in North Africa, Asia and South America, while a non-tsetse-transmitted form of T. vivax is found in South America. Animal trypanosomoses are difficult to diagnose: there are no pathognomonic signs, and detection of parasites is problematic. Therefore, considerable effort has been expended to develop serological assays with improved diagnostic sensitivity for use in obtaining information on the incidence and prevalence of infection and in the management of disease in the individual animal. Many different tests have been used over the past 70 years, but it is only recently that attention has been paid to test standardization, principally because of the introduction of enzyme linked immunosorbent assays (ELISAs) for the detection of trypanosomal antibodies and antigens. Although a variety of serological diagnostic techniques have been available for many years, there is still a lack of reliable data on trypanosomosis prevalence that makes economic justification and planning of control difficult to support. Clearly, enzyme immunoassays could provide this basic information. Additionally, as the emphasis moves from eradication to control of the tsetse transmitted trypanosomoses, there will be a greater need for surveillance and diagnosis of infection in individual animals. Both antigen and antibody assays can fulfil these roles, but differences in the biology of tsetse transmitted and mechanically transmitted trypanosomoses, as well as the different approaches to their control, are likely to be a major consideration in determining which is most appropriate. (author)