Unheard-of Numbers and Invitations on the Web

Abstract

This referred to the mechanical transmission of pathogenic trypanosomes in sub-Saharan Africa, discussed here at length and quite vigorously for several weeks at the beginning of the year when Burkhard Bauer (Vector Control Unit, Burkina Faso) argued that ‘the presence of trypanosomosis in these areas is ESSENTIALLY related to the presence of tsetse’. However, Gerrit Uilenberg, from Corsica, clear that mechanical transmission of Trypanosoma vivax and T. evansi outside Africa is no myth, preferred MAINLY to ‘ESSENTIALLY’. But Steve Mihok agreed with Bauer, who believes that field and lab results differ, and understood why the subject was often viewed as ‘the ‘cold fusion’ of trypanosomosis epidemiology in Africa. The disease may exist where (1) densities of tsetse are low, or (2) tsetse are ‘nearby’ – ‘eg. tens or hundreds of kilometres away’ or (3) undetectable, ‘probably associated with rainy seasons and the emergence of large numbers of biting flies’. Movements of animals already infected, or of tsetse, may explain some observations –‘courtroom’ evidence is needed. While situation (3) applies outside Africa, he wondered about the Sudan where ‘many Sudanese scientists/veterinarians accept mechanical transmission as a normal fact of life’. Ian Maudlin (University of Glasgow, UK) said, like cold fusion, the onus is on the proponents of mechanical transmission to demonstrate it. It should be established that tsetse have been properly monitored and whether or not infected animals are immigrants; ‘where tsetse have been successfully eradicated in Africa we no longer find trypanosomiasis – not even T. vivax … certainly the case in N. Nigeria where an abundance of biting flies remained after tsetse were eradicated’. Burkhard Bauer gave another example: ‘in the pastoral zone of Sideradougou, Burkina Faso … 18 months after termination of releases of sterile males … incidence of trypanosomosis was negligible in spite of numerous … biting flies. Two important outbreaks of T. vivax … one was due to transhumance [seasonal movement of livestock to regions of different climate] … in adjacent tsetse-infested areas, the other … from a peripheral reinvasion of Glossina tachinoides’. Similarly, Brian Hursey (FAO, Rome, Italy) said that eradication of tsetse from Ugunja Island, Zanzibar ‘eliminated tryps whilst the adjoining island of Pemba where no tsetse have ever been recorded is also free of trypanosomiasis despite the presence of biting flies’. Other places where eradication of tsetse resulted in elimination of the disease are Zimbabwe, Uganda (South west), Kenya (Western region), Zanzibar, Nigeria, Principe and Somalia.