C.M. Monzón; A.M. Russo*
* National Council for Scientific and Technical Research (CONCITEC), Argentina. Veterinary Diagnostic and Research Centre Formosa (CEDIVEF): P.O. Box 292 (3600) Formosa, Argentina.
References
Horse trypanosomosis in Argentina is caused by the haemoflagellate Trypanosoma evansi; occasionally also known by the synonym T. equiperdum. The disease in horses is known as "Mal de Cadeiras ". The course may be acute or chronic. Infected animals demonstrate fever, anaemia, loss of body weight, maintain their appetite, occasionally show paralysis of the hind quarters and frequently die (Monzón et al., 1984; Monzón, 1986; Monzón et al., 1991). Mules have inapparent clinical symtoms and it is suggested that they may be a possible reservoir (Monzón et al., 1994).
T. evansi is sporadically found in dogs (Mayer and Marder, 1978) and also in Capibara (Hidrochoerus) (Boero, 1974).
Using the haematocrit centrifuge technique and/or inoculation of blood into mice, we were not able to detect T. evansi in 567 blood samples taken from beef cattle in Formosa (Monzón et al., 1993).
Parasites isolated from naturally infected animals usually have no more than 3% with kinetoplasts, however strains maintained in mice showed between 3% and 20% of the organisms with kinetoplasts (Monzón et al., 1995).
Bakos (1982) reports the serological diagnosis of T. cruzi in horses (l), but the parasites have not yet been isolated from these animals. Both parasites, T. cruzi and T. evansi, demonstrate shared common antigens (Monzón, 1986; Monzón and Colman, 1988).
Tabanus sp is responsible for the mechanical transmission of T. evansi from host to host. These horseflies multiply in the hot season, however horse trypanosomosis usually appears in winter when the animals frequently suffer stress (Monzón et al., 1995).
Desmodus rotundus, may also be a biological vector (Boero, 1974; Clarkson, 1976; Greehall and Schmidt, 1988) for T. evansi. The distribuition of this vampire bat in Argentina coincides with the region where "Mal de Cadeiras" is enzootic (Mendez, 1972). Reports of Mal de Cadeiras in Argentina go back over a long time. In 1897, Joaquín Zabala performed experimental trials using infected animals (Gelormini, 1954).
T. evansi infections in horses, occur in the northern region, situated above parallel 30°, where there are approximately 1.000.000 horses. This large land area (900.000 Km2) has a subtropical climate and is divided in to three sub-regions: the east region is humid and furrowed by important rivers; the center region is subhumid and the west region is arid with some humid valleys. The large populations of tabanids that swarm in the hot season (autumn and summer), especially in the wet areas, provide favorable ecological conditions for T. evansi transmission.
Using an immunofluorescence antibody test (IFI), Bakos and Bustamante (1989) studied 800 horse sera from 9 provinces in the north of Argentina. The prevalence was: in Jujuy 35%, Corrientes 33%, Formosa 29%, Chaco 22%, Salta 12%, Santa Fé 10% and Santiago del Estero 8%.
Twelve outbreaks of T. evansi were detected in Formosa between 1983-1985, all from 45 farms that sent blood samples to CEDIVEF for parasitological diagnosis (Monzón and Mancebo, 1986). The prevalence of the disease in Formosa for the years 1983 to 1985 and as determined by IFI, was 19.3% (Monzón and Colman, 1988). More, recently 8 outbreaks of Mal de Cadeiras appeared in 1993 (Monzón et al., 1995a; Monzón et al., 1995b), and 2 new ones in 1995.
This epidemiological picture of horse Trypanosomosis in Argentina shows that the disease is widespread in the subtropical area, where horses are very important for field work.
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