VECTORIAL TRANSMISSION OF STRAINS OF ST. LOUIS ENCEPHALITIS VIRUS IN

DIAZ LA; FLORES FS; BERANEK M; RIVAROLA ME; CONTIGIANI MS

Buenos Aires

Encuentro; III Encuentro Internacional Sobre Enfermedades Olvidadas; 2012

Mundo Sano

St. Louis encephalitis virus (SLEV, Flavivirus, Flaviviridae), a reemerging human pathogen, is widely distributed in the American continent. Along its geographic distribution SLEV strains show biological variation according to its capacity to cause neuroinvasion in monkeys and rodents and viremia in birds. Although it is not completely understood, its transmission network would include Culex quinquefasciatus mosquitoes vectors and columbidae species as hosts. In 2005, a human encephalitis outbreak by SLEV took place in Cordoba Province (central region of Argentina). In order to evaluate the susceptibility of local Cx. quinquefasciatus populations to the infection/transmission by three different native SLEV viral strains, competence vector studies were carried out. Differences in infection rate among viral strains were observed. Viral strain 78V-6507 produced the highest infection rate observed (90.8%). After re-feeding on non-viremic chicks, mosquitoes were able to transmit the virus. Non-viremic chicks developed viremias ranged between 3 to 5 log PFU/mL. Our findings indicate local Cx. quinquefasciatus populations are susceptible and able to transmit different SLEV strains. The variation observed in the transmission rate among SLEV strains should be considered as a result of an ability-infection strain dependent. Pursuant to previous evidence, there should exist a strong adaptation among Argentinean viral strains and local mosquitoes vector populations. To be considered a vector, mosquito species must comply with a list of several criteria, including intrinsic and extrinsic factors. In Argentina, Cx. quinquefasciatus natural populations were detected infected by SLEV in several locations and they were associated with human encephalitis cases during outbreak scenario. Its susceptibility to infection and ability to transmit the virus were pointed out by Mitchell et al. (1980a, 1983) and Flores et al. (2010). On the other hand, Cx. quinquefasciatus populations are abundant during February and March where SLEV human cases often increase. So, we can conclude that autochthonous Cx. quinquefasciatus mosquito populations are the main urban vectors for SLEV infection in the central area of Argentina.