On the transmission of leishmania Mexicana to man - abstract

It has been established that the phlebotomine sandfly Lutzomyia flaviscutellat is the vector of leishmaniasis among forest-dwelling rodents in British Honduras; between 1964 and 1969, 0.65 per cent, of females of this species of fly were found infected with the leptomonads of Leishmania mexicana. Such infections have not been dissected. But Lu. flaviscutella bites man so rarely that it is difficult to understand how this fly could be responsible for the transfer of L. mexicana from rats to man. Nevertheless, a crude analysis of collections of phlebotomine sandflies made between 1963 and 1969 shows that the epidemiology of dermal leishmaniasis in British Honduras can be explained on the basis that, in nature, Lu. flaviscutellata is the only insect host for L. mexicana. Over a period of 3 1/2 years (1963-67), collectors sat in forest, waiting for phlebotomine sandflies to land on them; Lu. flaviscutellata accounted for 0.29 per cent of the female phlebotomines that landed on human skin, the density of this species being 0.06 flies per 10 hours of collecting. But when the leaf litter is disturbed soon after dawn, the density of Lu. flaviscutellata rest under dead leaves on the forest floor, and this fact was used in collections made over a period of one year (1967-1968). The forest leaf litter was periodically distributed in collections made in the early hours of darkness; Lu. flaviscutellata accounted for 0.51 per cent of the flies landing on man, the density increasing to 0.30 flies per 10 hours of collecting. But when the leaf litter is disturbed soon after dawn the density of Lu. flaviscutellata is increased 91.5 times; between August, 1968 and February, 1969, in early morning collections, Lu. flaviscutellata accounted for 8.46 per cent of the phlebotomines taken on man, the density of the species being 5.49 flies per 10 hours of collecting. Thus, although Lu. flaviscutellata is not normally attracted to man, there is quite a high degree of contact between the fly and man in the hour or so after dawn (AU)

The biting rhythms of some anthropophilic phlebotomine sandflies in British Honduras

Further observations are needed on the biting rhythms of phlebotomine sandflies in British Honduras. From the information now available, it seeems that only Lutzomyia panamensis, Lu. cruciata, Lu. olmeca and Lu. ovallesi can be reasonably suspected of transmitting Leishmania mexicana to man by day, though Lu. olmeca and Lu. cruciata are more probably the vectors of infection. Although dermal leishmaniasis can be transmitted by day, man is more likely to become infected during the hours of darkness, especially between dusk and midnight when anthropophilic sandflies are most active. Parous flies may be most numerous at dusk or soon afterwards; sandflies with natural leptomonad infections can, therefore, be expected to be collected between 18.00 and 19.59 hours.(Summary)

The epidemiology of dermal leishmaniasis in British Honduras. 3. The transmission of Leishmania mexicana to man by Phlebotomus pessoanus with observations on the development of the parasite in different species of Phlebotomus

During 1960-62 a study on the epidemiology of dermal leishmaniasis due to Leishmania mexicana in British Honduras revealed 18 species of Phlebotomus in the enzootic forest areas. In addition, 7 other sandflies remain to be identified and may represent new species. 9 species of Phlebotomus were found commonly to bite man. All were predominantly nocturnal in their feeding habits and, as they were readily infected with L. mexicana, all must be regarded as potential vectors in nature. The infection rates for sandflies fed directly on hamster lesions, at the periphery, and on normal adjacent skin were 95 percent, 48 percent and 0 percent respectively. Maintenance of wild-caught Phlebotomus species is discussed. Best results were obtained by keeping single flies in corked tubes containing a fresh green leaf. The corks had a groove cut throughout their length, to allow air exchange, and all tubes were kept in constant light and at approximately 100 percent relative humidity. 332 sandflies, including all the known man-biting species from British Honduras, were fed on the lesions of hamsters and mice infected with both human and rodent strains of L. mexicana. 52 flies were induced to re-feed on volunteers (8 fed a second time and 1 a third time), in all inflicting a total of 90 probes. Transmission of L. mexicana to man was achieved, by Phlebotomus pessoanus, on one occasion. This insect had fed on the infected hamster only 3 days and 23 hours previously. The development of L.mexicana in the insect host has been followed by a study of the gut contents and sections of entire sandflies which were fixed at 3, 6, 12, 24, 36, and 48 hours and 3-5 days after their infective feed. The development is to an anterior station, the leptomonads reaching the proboscis as early as 4 days after the infecting blood meal. 439 wild-caught female sandflies were dissected in an attempt to find insects naturally infected with L. mexicana. Flagellates were seen in the hind-gut of one specimen of P. ovallesi and others in the crushed gut from a single P. cruciatus (exact position in the gut uncertain). In the absence of animal inoculation the nature of these flagellates remains uncertain, but they are not thought to be leptomonads of L. mexicana. Attempts to demonstrate mechanical transmission of L.mexicana were made by interrupting sandflies feeding on hamster lesions and immediately allowing such insects to renew feeding on volunteers. No transmission was achieved and it is felt that such a mode of transfer plays little or no part in the transmission of the parasite in nature. On the contrary, the killing and squashing of infected sandflies feeding on human skin may well facilitate entry of the parasite. Although sandflies were successfully infected with L. mexicana after feeding on a newly acquired and non-ulcerative human lesion, man-to-man transmission is considered most unlikely in nature. (AU)

Observations on the phlebotomine sandflies of British Honduras

An account is given of the numbers of phlebotomine sandflies collected in British Honduras (a) on man, (b) in rat-baited fly-traps and (c) from resting places. Twelve species of Phlebotomus were taken on man, 11 species (including three never taken on man) were obtained in rat-baited traps, and 16 species (including three not taken on man or in fly traps) were collected from resting-places. Evidence of the geographical distribution and relative abundance of the different species is insufficient to establish which is the vector of Leishmania mexicana in British Honduras, but a comparison of the man-biting and rat-biting populations suggests P. apicalis and P. cruciatus as the probable vectors of the infection. Further investigations on the phlebotomines of British Honduras are required to discover flies with natural leptomonad infections. (AU)

Dermal leishmaniasis in British Honduras - the vector

Flies of genus Phlebotomus, analogous to those which are vectors of leishmaniasis in the Old World, were studied in forest areas in British Honduras in order to determine whether they also were vectors of leishmaniasis. The disease was transmitted from an infected hamster to a human volunteer by a phlebotomus sandfly. It was also found possible to infect hamsters by injections of suspensions of triturated wild-caught man-biting Phlebotomes (AU)

Dermal leishmaniasis in British Honduras - the parasite

This disease is largely restricted to forest workers and is manifested by localised sores which often causes considerable disfigurement. The causative organism, Leishmania braziliensis mexiccura, is readily demonstrable in stained smears of early lesions, but this becomes increasingly difficult as the infection becomes chronic. Culture in NNN medium supplements microscopic examination. The ear is most commonly involved and lesions there tend to become chronic. Active infection may protect against re-infection but the possibility of long-term immunity is not yet classified. Infected Phlebotomine sand flies and infected rodents were found to co-exist in a selected area of forest where numerous human cases of proven leishmaniasis were found. It is suggested that the disease in British Honduras is a zoonosis. The parasites is maintained in certain rodent populations which act as intermediaries for the Phlebotomes which prey on these rodents and on man. The infected rodents found to date include the Tree-rat (Ototylomus Sp.) White-footed rat (Peromyscus Sp.) and the Spiny-ocket mouse (Heteromys Sp.) (AU)