Comparative susceptibility of mosquito species and strains to oral and parenteral infection with dengue and Japanese encephalitis viruses.

Thirty-four strains of Asian and Pacific mosquitoes belonging to 22 species of 7 genera were compared for oral and/or parenteral susceptibility to infection with 1 or more strains of each of the 4 dengue serotypes. Surprisingly, several species of common man-biting Aedes were much more susceptible to oral infection with each of the 4 dengue serotypes than was Aedes aegypti. These species included Aedes albopictus and members of the scutellaris group of the subgenus Stegomyia found on South Pacific islands. Mosquito strains and species relatively susceptible to 1 dengue serotype usually were relatively susceptible to the others also. Almost all species of Aedes tested were uniformly susceptible to parenteral infection with the dengue viruses but, with the exception of a species of Tripteroides, species of all other genera were comparatively resistant to that mode of infection. Dengue viruses usually replicated to about the same extent in orally-infected mosquitoes as they did in parenterally-infected specimens of the same species. Seventeen species of mosquitoes of 7 genera also were tested for parenteral susceptibility to infection with Japanese encephalitis virus. With the possible exception of 2 species of Anopheles, the virus replicated to about the same degree in all species tested and achieved levels considerably higher than did any of the dengue viruses in the same mosquito strain and species held under the same conditions.

Evaluation of personal protection methods against phlebotomine sand flies including vectors of leishmaniasis in Panama.

Three personal protection methods were evaluated against phlebotomine sand flies in Panama. Skin applications of five selected repellents including deet (N,N-diethyl-m-toluamide) provided a mean coefficient of protection (CP) of 99.2% against the attack of at least three sand fly species. Deet-treated net jackets also provided good protection, but it was concluded that an additional application of repellent to the unprotected face was necessary for maximum protection. Permethrin-treated clothing did not provide the protection expected. Apparently sand fly behavior and resistance to quick knock-down were responsible for the numbers of bites recorded, and therefore maximum protection from bites would require application of deet or another suitable repellent to the exposed skin when wearing permethrin-treated clothing.

Palm trees and Chagas' disease in Panama.

An ecological survey of triatomines in the sylvan ecosystem of the Canal Zone and selected sites in Panama disclosed for the first time a close association of Rhodnius pullescens and Triatoma dimidiata, the two most important vector species of Chagas' disease in Panama, with a single species of a widely distributed palm tree, Scheelea zonensis. This association may explain why Chagas' disease is prevalent in certain rural communities in Central Panama and rare in others. An immense focus of zoonotic Trypanosoma cruzi infection exists in the forests of the Canal Zone with presence of large populations of triatomines, associated with scheelea zonensis and other yet undescribed microhabitats, and high (50--60%) trypanosome infections in all of the major triatomine species. Common opossums, anteaters, and spiny rats seem to be the principal animal reservoirs of T. cruzi in this complex and relatively undisturbed ecosystem.

Antigenic relationships among phlebotomus fever group arboviruses and their implication for the epidemiology of sandfly fever.

The antigenic relationships of 21 known or presumed Phlebotomus fever group serotypes and of 2 ungrouped, solvent sensitive, sandfly-associated arboviruses (Pacui and Charleville) were studied by complement fixation, plaque neutralization, and hemagglutination-inhibition methods. Results of complement fixation and neutralization tests were specific, allowing clear separation of the various serotypes, while those of the hemagglutination-inhibition test showed broader crossing and lack of specificity. Pacui virus was shown to be a member of the Phlebotomus fever serogroup. Six new Phlebotomus fever group serotypes are also described, increasing the known members of the group to 22. The implications of these and other recent data about the epidemiology of sandfly fever are discussed.

Vesicular stomatitis virus (Indiana serotype): transovarial transmission by phlebotomine sandlies.

Transovarial transmission of vesicular stomatitis virus (Indiana serotype) by experimentally infected Lutzomyia trapidoi and Lutzomyia ylephiletrix to their progeny was demonstrated. Virus was recovered from all developmental stages; mean virus titers from egg to first generation adult showed a four-log increase, indicating that virus multiplication occurred during development of the sandflies. Virus titers in first generation adult females were comparable to those found in their parents. These infected female sandflies transmitted vesicular stomatitus virus Indiana by bite to susceptible animals and transmitted the virus transovarially to their offspring (second generation). Results demonstrate a possible mechanism for transmission and maintenance of this virus in nature without a vertebrate (heat) host reservoir.