Venezuelan equine encephalitis virus: horse virulence of P-676 and MF-8 small and minute plaques.

The P-676 and MF-8 epizootic strains of Venezuelan equine encephalitis (VEE) virus were found to contain a minute plaque (MP), different from the predominant small plaque (SP) present in these virus strains. The MP and SP were stable after passages in Vero cells, mice, or horses. Equines were inoculated with the SP or MP of the P-676 and MF-8 strains. Inoculation of either P-676 SP or MP into horses induced high fever and viremia but no signs of encephalitis or death. Four horses infected with MF-8 SP became very ill, with high fever and viremia; three of the inoculated animals died. Four horses were infected with MF-8 MP; only showed viremia but appeared asymptomatic and afebrile. Neutralization tests with immune sera from the infected equines showed that the P-676 SP and MP appear distinct, while a clear difference cannot be observed with MF-8 SP and MP.

Viruses isolated from Aedeomyia squamipennis mosquitoes collected in Panama, Ecuador, and Argentina: establishment of the Gamboa serogroup.

Twenty-four virus strains were isolated from Aedeomyia squamipennis mosquitoes collected in Ecuador. One additional strain each was isolated from this species from Panama and ARgentina. All 26 isolates were shown to be related serologically to prototype Gamboa virus, originally isolated from Ad. squamipennis mosquitoes collected in Panama. Antigenic comparisons of eight strains, including prototype Gamboa virus, indicated the existence of four distinct viruses. Neutralization tests with sera from a variety of mammalian and avian species from Argentina provided further evidence that Gamboa serogroup viruses are transmitted between Ad. squamipennis and birds.

Presencia de anticuerpos contra la rubeola en comunidades urbanas y rurales de Panama, y evaluacion de los resultados de pruebas de neutralizacion e inhibicion de la hemaglutinacion. / Presence of rubella antibodies in urban and rural communities of Panama and evaluation of the results of neutralization and hemagglutination inhibition tests

Empleando la prueba de neutralizacion por reduccion de placas se encontro que en la poblacion de Coclesito, una comunidad rural de Panama, habia un 83% de mujeres susceptibles al virus rubeola mientras que en el area urbana de San Miguelito solo el 30% de las mujeres eran susceptibles. Una comparacion entre las pruebas de inhibicion de la hemaglutinacion y la de neutralizacion revelo que la prueba de inhibicion de la hemaglutinacion es tan sensible y confiable como la de neutralizacion, por lo cual se recomienda como metodo para la determinacion de anticuerpos en los laboratorios clinicos

Transplacental transmission of Venezuelan equine encephalitis virus in horses.

Transplacental passage of Venezuelan equine encephalitis virus, epizootic strain P-676, occurred in four of nine fetuses studied. The mares were infected near term. Virus was recovered in high titer from fetal blood and organs, while no virus was detected in maternal blood but neutralizing antibodies were present. No evidence of in utero infection was found in two fetuses from mares infected with MF-8, another epizootic strain of Venezuelan equine encephalitis virus.

Survival of arboviruses in trypanosome-infected triatomines.

The potential of triatomines to maintain arboviruses was demonstrated by the ability of Rhodinius prolixus with experimentally punctured abdomen to harbor Venezuelan equine encephalitis (VEE) virus for at least 4 months and St. Louis encephalitis virus for 1 month. At 30 days after infection VEE virus was found at low titers in Trypanosoma cruzi-infected R. prolixus and at moderate titers in T. rangeli-infected R. neglectus. Transmission of VEE virus by bite of punctured bugs was successful 2 weeks after virus ingestion; attempts at 30 days failed.

Infection of wild and laboratory animals with Machupo and Latino viruses.

Natural infection with Machupo and Latino viruses occurs only in the cricetine rodent Calomys callosus. Machupo virus induces fatal infection in suckling mice and hamsters, and in adult guinea-pigs, marmosets, and rhesus monkeys. Latino virus kills only suckling hamsters; it produces chronic but non-viraemic infection in Calomys rodents.Machupo virus, in contrast, induces a viraemic immunotolerant infection in suckling Calomys, and a split response in animals more than 9 days of age. Tolerant infection is associated with haemolytic anaemia and splenomegaly, lesions not observed in animals able to clear viraemia and produce circulating neutralizing antibodies. Experimental increase in the fraction of tolerant response was obtained by decreasing the virus dose or by phenotypic inbreeding of rodents. Long-term effects of tolerant infection included mild runting, decreased survival time, and almost total sterility among females, largely caused by fatal virus infection of embryos.