Observations on a zoonosis: leishmaniasis in British Honduras.
The following is based largely on the author's partly hypothetical interpretation of existing data on the zoonosis caused by Leishmania mexicana in British Honduras, which he reviews and discusses in this paper on the basis of his observations between February 1964 and February 1966 [cf. RAE B 54 159], supported by extensive reference to the literature. He concludes that the principal reservoir host is Ototylomys phyllotis, that other forest rats, particularly Heteromys desmdrestianus, act as secondary reservoir hosts and that other mammals, including man, are accidental hosts. The prime importance of O. phyllotis appears to depend firstly on its abundance as a forest species and secondly on its climbing habits, which mean that it is exposed to potential insect vectors more frequently than other rats or other forest mammals. The principal vector is Lutzomyia olmeca Vargas & Diaz Nájera (flaviscutellata auct.), which has previously been referred to as Phlebotomus apicalis Floch & Abbonnenc [cf. 58 488]. Certain other species of Lutzomyia, possibly including L. cruciata (Coq.), L. permira (Fairchild & Hertig) and perhaps L. pana-mensis (Shannon), are secondary vectors but cannot maintain a focus of infection without L. olmeca. L. olmeca seeks blood-meals within 8 m of the ground. Adults are active in the wet season, the dry season being passed as a quiescent egg. Rainfall, but more particularly the duration and intensity of the dry season, influences the numbers of L. olmeca and therefore the incidence of infection in O. phyllotis. L. olmeca and O. phyllotis have similar but not coincident geographical ranges, and the principal source of blood for L. olmeca in any part of its range is probably determined to a great extent by the frequency of encounter between it and the various mammals present. Similarly, in a locality with a pool of infected mammals, the vectors are likely to be those species of Lutzomyia that have the highest chances of acquiring and passing on the infection. The part that a species of Lutzomyia plays in the transmission of Leishmania thus depends mainly on such factors as its abundance, distribution in time, height zonation and diurnal rhythms of activity.