The activity of LCM virus was first reported in Argentina at the beginning of the seventies and only five strains have been isolated from rodents Mus domesticus and two from humans. The objective of this paper was to find differential biological characteristics of Argentine strains of LCM virus comparing them in relation to the historical strains WE and Armstrong. Regarding the results obtained in tissue culture, when L 929 cells were used, plaque forming units (PFU) were obtained with human and mouse strains, whilst on Vero cells only human strains developed PFU. Differentials characteristics of historical and Argentine strain's plates were not found, neither differences related to the strain's origin. Neither historical nor Argentine strains were lethal to new-born mice giving a persistent infection, that was demonstrated when we inoculated new-born mouse by intracranial route with different strains of LCM virus and virus was isolated from brains harvested at different days post inoculation. The only exception was Cba An 13065 strain that exhibited virulence in new-born mice, only with 0.026 PFU was obtained 1 DL50. All the strains resulted lethal to adult mice. The mouse strains were more virulent than human strains, being Cba An 13065 the most virulent. These results demonstrate a different behavior in tissue culture between human and mouse strains and allow the identification of virulence markers by intracranial inoculation into new-born or adult mice.

La actividad del virus LCM fue informada en Argentina a comienzos de la década del 70 y sólo han sido aisladas cinco cepas a partir del roedor Mus domesticus y dos de humanos. El objetivo de este trabajo consistió en investigar características biológicas de las cepas argentinas de virus LCM para compararlas entre sí y respecto a las cepas históricas WE y Armstrong. En células L 929 se obtuvieron placas bajo agarosa tanto con las cepas humanas como con las cepas de ratón, pero en células Vero sólo se obtuvieron placas con las cepas humanas. No se observó ninguna característica morfométrica de las placas que distinguiera nítidamente a las cepas históricas de las cepas argentinas, ni se observaron diferencias que se relacionen con las especies de origen de las cepas. Las cepas históricas y las cepas argentinas no fueron letales para ratón recién nacido (rrn) generando una infección persistente, según se comprobó al inocular ratones recién nacidos (rrn) por vía intracerebral con cepas de virus LCM y detectarse virus en los cerebros cosechados a diferentes días post inoculación. La única excepción fue la cepa Cba An 13065 que resultó virulenta para rrn ya que con sólo 0.026 UFP se logró 1 DL50. Todas las cepas resultaron letales en ratón adulto (rad), siendo las cepas de ratón más virulentas que las cepas de humanos. Estos resultados permitieron evidenciar el diferente comportamiento en cultivos celulares de las cepas de ratón con respecto a las cepas humanas, e identificar marcadores de virulencia mediante la respuesta a la inoculación por vía intracerebral del rad y del rrn.

We model potential distribution for three species of rodents known to be reservoirs of zoonotic diseases: Calomys musculinus, Oligoryzomys flavescens and O. longicaudatus. These models provide general distribution hypotheses obtained using environmental data from record localities. Satellite remote sensing is then used to extrapolate climatic and ecological features of potentially suitable habitats for these rodents. In the three species mapped, we found high overall correspondence between predicted (based on environmental data) and specimen based distributions. The maps proposed here provide several advantages over dot and shaded outline maps. First, the predictive maps incorporate geographically explicit predictions of potential distribution into the test. Second, the validity of the predictive map can be appreciated when localities of previous records of the studied species, not used as training sites or used as control sites, are overlaid on the map. In this approach, environmental factors, criteria and analytical techniques are explicit and can be easily verified. Hence, we can temporally fit data in more precise distribution maps.

Allele frequencies at seven polymorphic loci controlling the synthesis of enzymes were analyzed in six populations of Culex pipiens L. and Cx. quinquefasciatus Say. Sampling sites were situated along a north-south line of about 2,000 km in Argentina. The predominant alleles at Mdh, Idh, Gpdh and Gpi loci presented similar frequencies in all the samples. Frequencies at the Pgm locus were similar for populations pairs sharing the same geographic area. The loci Cat and Hk-1 presented significant geographic variation. The latter showed a marked latitudinal cline, with a frequency for allele b ranging from 0.99 in the northernmost point to 0.04 in the southernmost one, a pattern that may be explained by natural selection (FST = 0.46; p < 0.0001) on heat sensitive alleles. The average value of FST (0.088) and Nm (61.12) indicated a high gene flow between adjacent populations. A high correlation was found between genetic and geographic distance (r = 0.83; p < 0.001). The highest genetic identity (IN = 0.988) corresponded to the geographically closest samples from the central area. In one of these localities Cx. quinquefasciatus was predominant and hybrid individuals were detected, while in the other, almost all the specimens were identified as Cx. pipiens. To verify the fertility between Cx. pipiens and Cx. quinquefasciatus from the northern- and southernmost populations, experimental crosses were performed. Viable egg rafts were obtained from both reciprocal crosses. Hatching ranged from 76.5 to 100%. The hybrid progenies were fertile through two subsequent generations

Desconhece-se o ciclo de transmissão da encefalite eqüina tipo oeste (WEE) na América do Sul. Uma cepa do vírus foi isolada na Argentina, durante a epizootia de 1982-1983, a partir de Aedes albifasciatus. Sob o ponto de vista experimental, o Culex pipiens da Argentina revelou-se capaz de transmitir o vírus WEE, porém outros resultados têm indicado que o Cx. pipiens dos Estados Unidos é refratário a esse vírus. Assim, procurou-se determinar a suscetibilidade de cepas argentinas de Ae. albifasciatus e complexo Culex pipiens, à infecção do vírus WEE por via oral. As fêmeas adultas foram alimentadas em pintos infectados com cepa do vírus isolada na Província de Córdoba, Argentina, ou então alimentadas em suspensão do vírus e sangue. Cada mosquito ingeriu entre 10(1,6) e 10(6,4) unidades virais formadoras de placas de cultura de célula ("vero cell"). Cada um dos 28 Ae. albifasciatus mostrou-se a partir do quarto dia pós-prandial e houve evidência de replicação viral. Em contraposição, 0/44 Cx. p. quinquefasciatus e apenas 1/15 Cx. p. pipiens revelou-se positivo. Aedes albifasciatus é suscetível à infecção pelo vírus WEE e deveria ser considerado vetor potencial desse agente na Argentina. Ambas subespécies de Cx. pipiens são refratárias à infecção por via oral e provavelmente não desempenham papel do ciclo do vírus WEE na Argentina.

The transmission cycle of western equine encephalitis (WEE) virus in South America is unknown. A WEE virus strain was isolated from Aedes albifasciatus in Argentina during the WEE epizootic of 1982-83. Also, Culex pipiens from Argentina was reported to be able to transmit WEE virus experimentally, but other results indicate that Cx. pipiens from the USA is refractory to this virus. We determined the susceptibility of Argentina strains of Ae. albifasciatus and Culex pipiens complex mosquites to infection by WEE virus by the oral route. Adult females were fed on chicks infected with a WEE virus strain isolated in Cordoba Province, Argentina, or were fed on a blood/virus suspension. Each mosquito ingested between 10(1.6) to 10(6.4) vero cell plaque-forming units of virus. Each of 28 Ae. albifasciatus was positive for virus from the fourth day postfeeding, and there was evidence for virus replication. In contrast, 0/44 Cx. p. quinquefasciatus and only 1/15 Cx. p. pipiens was positive. Aedes albifasciatus is susceptible to infection by WEE virus and should be considered a potential vector of this virus in Argentina. Both subspecies of Cx. pipiens are refractory to peroral infection by WEE virus and probably do not play a role in the WEE virus cycle in Argentina.

Desconhece-se o ciclo de transmissão da encefalite eqüina tipo oeste (WEE) na América do Sul. Uma cepa do vírus foi isolada na Argentina, durante a epizootia de 1982-1983, a partir de Aedes albifasciatus. Sob o ponto de vista experimental, o Culex pipiens da Argentina revelou-se capaz de transmitir o vírus WEE, porém outros resultados têm indicado que o Cx. pipiens dos Estados Unidos é refratário a esse vírus. Assim, procurou-se determinar a suscetibilidade de cepas argentinas de Ae. albifasciatus e complexo Culex pipiens, à infecção do vírus WEE por via oral. As fêmeas adultas foram alimentadas em pintos infectados com cepa do vírus isolada na Província de Córdoba, Argentina, ou então alimentadas em suspensão do vírus e sangue. Cada mosquito ingeriu entre 10(1,6) e 10(6,4) unidades virais formadoras de placas de cultura de célula ("vero cell"). Cada um dos 28 Ae. albifasciatus mostrou-se a partir do quarto dia pós-prandial e houve evidência de replicação viral. Em contraposição, 0/44 Cx. p. quinquefasciatus e apenas 1/15 Cx. p. pipiens revelou-se positivo. Aedes albifasciatus é suscetível à infecção pelo vírus WEE e deveria ser considerado vetor potencial desse agente na Argentina. Ambas subespécies de Cx. pipiens são refratárias à infecção por via oral e provavelmente não desempenham papel do ciclo do vírus WEE na Argentina.

The transmission cycle of western equine encephalitis (WEE) virus in South America is unknown. A WEE virus strain was isolated from Aedes albifasciatus in Argentina during the WEE epizootic of 1982-83. Also, Culex pipiens from Argentina was reported to be able to transmit WEE virus experimentally, but other results indicate that Cx. pipiens from the USA is refractory to this virus. We determined the susceptibility of Argentina strains of Ae. albifasciatus and Culex pipiens complex mosquites to infection by WEE virus by the oral route. Adult females were fed on chicks infected with a WEE virus strain isolated in Cordoba Province, Argentina, or were fed on a blood/virus suspension. Each mosquito ingested between 10(1.6) to 10(6.4) vero cell plaque-forming units of virus. Each of 28 Ae. albifasciatus was positive for virus from the fourth day postfeeding, and there was evidence for virus replication. In contrast, 0/44 Cx. p. quinquefasciatus and only 1/15 Cx. p. pipiens was positive. Aedes albifasciatus is susceptible to infection by WEE virus and should be considered a potential vector of this virus in Argentina. Both subspecies of Cx. pipiens are refractory to peroral infection by WEE virus and probably do not play a role in the WEE virus cycle in Argentina.