RESUMO
The ability of Simulium mexicanum and Simulium metallicum to serve as biological or mechanical vectors of an enzootic and an epizootic strain of Venezuelan equine encephalitis (VEE) virus was examined. Guinea pigs were inoculated with the epizootic Cordoba strain or the enzootic RPVP407 strain of VEE virus. Wild-caught adult Simuliidae were fed on the viremic guinea pigs and the virus content of groups of flies was determined at daily intervals post-engorgement to test for viral replication. Flies were refed on suckling mice at greater than or equal to 8 days post-engorgement to test for biological transmission. Other flies were interrupted while feeding on viremic guinea pigs and refed on suckling mice to test for mechanical transmission. Neither S. mexicanum nor S. metallicum appear to be efficient vectors of either strain of VEE virus, although occasional mechanical transmission was obtained. Titers of virus in flies decreased rapidly after engorgement and from 3-12 days post-engorgement virus was detected only in 5%-25% of both species of flies. Although earlier field evidence implicated both S. mexicanum and S. metallicum as vectors of epizootic VEE, we conclude that it is highly unlikely that they play an important role as vectors of the virus in nature.
Assuntos
Encefalomielite Equina/transmissão , Encefalomielite Equina Venezuelana/transmissão , Simuliidae/microbiologia , Animais , Colômbia , Vírus da Encefalite Equina Venezuelana/fisiologia , Encefalomielite Equina Venezuelana/microbiologia , Comportamento Alimentar , Cobaias , Masculino , Camundongos , Simuliidae/fisiologiaRESUMO
This study was conducted at Carimagua Research Centre in a well-drained savanna area in the eastern plains of Colombia. The objectives were to note the effect of ecological factors on tick burdens, principally the effect of the environment given by four grasses on the seasonal variations of tick populations. Adult female tick counts were carried out on heifers grazing four pastures and tick larvae on the grass detected by cloth dragging. Tick counts were significantly higher on animals grazing Brachiaria decumbens than those grazing Andropogon gayanus, Melinis minutiflora or native pastures. Tick larvae counts on the grass showed a similar tendency. Introduced grasses and intensification of production will require greater care to control tick infestations since increases in stocking rate and ground coverage could augment tick populations.