Observations on a zoonosis: leishmaniasis in British Honduras.
This paper reports the results of field studies carried out between February 1964 and February 1966 on the rodent and insect hosts of Leishmania mexicana in British Honduras [belize].
A cheaply constructed live trap for small mammals is described, and the success and efficiency of the apparatus are assessed. Altogether, 1695 mammals were examined for cutaneous lesions, 369 specimens of 37 species other than rodents (with negative results) and 1326 specimens of 17 species of rodents. Leishmanial lesions were found on the tails of 12 Ototylomys phyllotis (infection rate 2.8%) and of one Sigmodon hispidus (0.2%), and on the ears of one Heteromys desmarestianus (1.0%). No lesions were found on Nyctomys sumichrasti, which had previously been found infected with L. mexicana in British Honduras [this Bulletin, 1964, v. 61, 1021]. One Oryzomys couesi was infected with L. mexicana in the laboratory, but no wild-caught specimens had lesions.
Baited oil traps [ibid., 1966, v. 63, 1189] were used to collect phlebotomine sandflies attracted to small mammals. With 15 different mammalian species as bait, 12 species of phlebotomine sandflies were caught; reference is also made to other blood-feeding insects-Simuliidae, Ceratopogonidae, Culicidae- taken in the traps. In searching for the insect host of L. mexicana, 2074 female phlebotomines were dissected and examined individually for flagellate infections. Promastigotes capable of producing L. mexicana lesions when inoculated intradermally into hamsters were found in the digestive tracts of 0.5% of Lutzomyia flaviscutellata, the species of phlebotomine most frequently captured in oil traps set within 8 metres of the ground. Flagellates which failed to produce leishmanial lesions on hamsters were found in one specimen of each of Lu. cruciata, Lu. beltrani, IM. permira and Lu. trinidadensis.
The greater part of the paper is devoted to ecological observations on the hosts of the parasite. The habitats investigated are divided into forest, developed land, pine savanna and buildings. Immature, low, medium and high bush are defined on the basis of a " bush index ". For both rodent and sandfly hosts of L. mexicana, consideration is given to distribution in relation to habitat, vertical zonation, activity and the clock, density and fluctuations in numbers, resting and breeding places, feeding requirements and preferences of sandflies, and reproduction and growth of rodents. Some predators of rodents are noted and reference is made to the diets of H. desmarestianus and S. hispidus. [The original should be consulted for a wealth of ecological data on rodents and phlebotomine sandflies in British Honduras.]
It is concluded that the prime mammalian host of L. mexicana is O. phyllotis and that H. desmarestianus is a host of secondary importance; other mammals, including man, are accidental hosts. The principal insect host is Lu. flaviscutellata, without which a focus of leishmaniasis could not be maintained, although other phlebotomine species may be hosts of secondary importance. O. phyllotis is the most abundant rodent species in the forests of British Honduras; because of its scansorial habits, it is more exposed than most rats to sandflies seeking blood meals and is, most probably, the main source of supply for Lu. flaviscutellata. This phlebotomine is a wet season fly which passes the dry season as a quiescent egg. Duration and dryness of the dry season influence the numbers of Lu. flaviscutellata and, therefore, the incidence of L. mexicana infections in O. phyllotis.
[Recent studies have shown that Lu. flaviscutellata is a South American sandfly and the species found in British Honduras should be called Lu. olmeca. Lu. steatopyga should be substituted for specimens referred to as Lu. beltrani. The word ' shannoni' has been omitted after Lutzomyia in line 24, p. 23; in two places on p. 27, Oryzomys melanotis is incorrectly named Ototylomys melanotis.] Paul Williams.
- breeding places
- developmental stages
- disease prevalence
- dry season
- human diseases
- natural enemies
- protozoal infections
- small mammals
- wet season