[Behavior of Argentine lymphocytic choriomeningitis virus strains in rodents]. / Comportamiento de cepas argentinas del virus de la coriomeningitis linfocitaria en roedores.

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.

Comportamiento de cepas argentinas del virus de la Coriomeningitis Linfocitaria en roedores / Behavior of Argentine lymphocytic choriomeningitis virus strains in rodents

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.

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.

Immune response to vaccination against Argentine hemorrhagic Fever in an area where different arenaviruses coexist.

Neutralizing antibody (NT Ab) titers to Candid #1 (C#1) vaccine against Argentine hemorrhagic fever were studied for 2 years post-vaccination in 330 volunteers, to assess whether the kinetics and/or magnitude of this immune response is modified by previous infection with the arena viruses Junin (JUN) and lymphocytic choriomeningitis (LCM). A total of 160 volunteers received C#1, distributed as follows: without detectable pre-infection with arenaviruses (n = 54); with pre-existing antibodies to JUN (n = 55); with pre-existing antibodies to LCM (n = 51). The remaining 170 individuals received placebo. Levels of anti-JUN NT Ab displayed a trend in which titers increased with the virulence of the infecting strain, from C#1 (X = 49), through subclinical JUN infection (X = 229), vaccination following subclinical infection (X = 367) to JUN clinical infection (X =773). It was also found that the mean titer of NT Ab to C#1 did not vary significantly during 2 years of study and was: a) significantly lower than that elicited by wild strains of JUN, both clinical and subclinical infections (p < 0.01); b) significantly increased the titers of pre-existing anti-JUN Ab (p < 0.01); and c) was not modified by pre-existing anti-LCM Ab (p > 0.05). These data indicate that the immune response to C#1 boosts pre-existing immunity to JUN virus and is not changed by previous experience with LCM virus.

Gene flow among Calomys musculinus (Rodentia, Muridae) populations in Argentina.

Calomys musculinus is a Sigmodontinae rodent inhabiting periodically disturbed habitats in the central eastern plains of Argentina. It is the natural reservoir host of Junin virus, the etiological agent of Argentine Hemorrhagic Fever (AHF). In order to analyze the levels of gene flow among populations of this species, allozymic variability at 26 loci was studied in 291 individuals from the endemic zone of AHF and localities outside it. All populations showed high levels of polymorphism (He between 0.107 and 0.144; P95% between 38 and 54%). Individual loci f values were in most cases negative, although not significantly different from zero. Mean genetic differentiation among populations was low, but statistically significant (theta = 0.020; P < 0.01). There was no correlation between genetic and geographic distances between pairs of populations, and scatter of the pairwise points suggests that, at the regional scale, genetic drift is more influential than gene flow. This result can be interpreted as indicative of a relatively recent expansion of C. musculinus habitat and restricted on-going gene flow, which would be compatible with a relatively slow expansion rate of AHF.

Evaluation of an enzyme-linked immunosorbent assay for detection of antibodies to Junin virus in rodents.

Junin virus is the etiological agent of Argentine hemorrhagic fever, a serious rodent-borne disease. An enzyme-linked immunosorbent assay (ELISA) to detect Junin virus IgG antibodies in rodents was evaluated using sera from 27 Calomys musculinus and five Calomys laucha, inoculated experimentally with a live attenuated strain of this arenavirus. The test performance was compared against an indirect immunofluorescence assay (IFA). The ELISA had a sensitivity and specificity of 100% and a reproducibility of 87.9% for samples with titers above the selected cut-off value. IFA had lower sensitivity (53%) with the same specificity. The ELISA results were similar, whether carried out on whole blood or serum samples, thus eliminating the need for serum separation. A high correlation (K=0.86) between ELISA and IFA results was obtained from 1011 wild sigmodontine and murine rodents collected within and outside of the Argentine hemorrhagic fever endemic area. These results indicate that Junin virus IgG ELISA is the most suitable assay for detection of Junin virus antibodies in rodent samples.

Respuestas serologicas secundarias en la epidemia de dengue de 1998 em Salta, Argentina, donde co-circulan otros flavivirus / Secondary serologic responses to dengue epidemic in 1998 in Salta, Argentina, where other flavivirus co-circulate

En 1998, ocurrió una epidemia de dengue (serotipo 2) en la provincia de Salta, Norte de Argentina, después de la primera detección de dengue en esa zona en 1997. En este trabajo se clasificaron las respuestas serológicas de los casos ocurridos en 1998 como primarios o secundarios, dado que riesgo de la enfermadad severa es mayor en los casos secundarios. Se estudiaron 154 casos por las pruebas de neutralización (NT) e inhibición de la hemoaglutinación. Se clasificaron 38 casos ( 25 porciento) como respuestas primarias y 84 casos (54 porciento) como respuestas secundarias. Los restantes 32 casos (21 porciento) con títulos de IgG en el límite no pudieron ser clasificados. Se analizó la exposición previa a otros flavivirus (Encefalitis de San Luis [SLE] y Fiebre Amarilla [YF]) que pueden cruzar serológicamente, como posible causa de los patrones secundarios. Nuestros resultados indican que el 83 porciento de los casos clasificados como respuesta a dengue secundaria, podrían atribuirse a exposiciones previas a los virus SLE o YF, o a reacciones serológicas cruzadas. La vacunación contra YF fue un factor menor contribuyente al patrón de respuesta secundaria encontrado. El hallazgo de serología positiva para YF en personas que no reconocen vacunación previa debe alertar acerca de la posible circulación silenciosa del virus de la YF, en una área que puede soportar tantos ciclos urbanos como selváticos. Otros casos que mostraron respuesta secundarias permanecen sin explicación, surgirindo la ocurrencia de infecciones previas por otros serotipos de dengue o por otro flavivirus distintos a SLE o YF.

Estimation of genetic divergence and gene flow between Culex pipiens and Culex quinquefasciatus (Diptera: Culicidae) in Argentina

Allele frequencies at seven polymorphic loci controlling the synthesis of enzymes were analysed 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, 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 reciprocal crosses. Hatching ranged from 76.5 to 100 per cent. The hybrid progenies were fertile through two subsequent generations.

Historical, Epidemiological and Ecological Aspects of Arboviruses in Argentina: Flaviviridae, Bunyaviridae and Rhabdoviridae

This is a review of the arboviruses in Argentina belonging to families Flaviviridae, Bunyaviridae and Rhabdoviridae. Of the many viruses beloging to these families, the flavivirus St. Louis encephalitis (SLE), has been most intensively studies. SLE virus strains have been recovered from three sources: 2 strains from humans with an undifferentiated, febrile disease; 6 from mosquitoes; and 2 from rodents. The viruses recovered from rodents are attenuated and those from mosquitoes are virulent based on a neuroinvasiveness test in mice; the degree of virulence of the mosquito strains remain to be analyzed. Serological surveys indicate a wide distribution and endemicity of SLE virus in the temperate and subtropical areas (central and northern Argentina), but no data are available from the Andean region or from the South. The virulent SLE virus strains appear to be transmitted between Culex (Cx.) spp., from which they were isolated, and wild birds, based on antibody prevalence. A urban cycle may involve Cx. quinquefasciatus (source of a viral isolate and a competent experimental vector) and abundant birds (house sparrows, doves, and/or chickens), chickens are experimentally competent host species. Despite similarities in the ecology of SLE between Argentina and North America, urban outbreaks of SLE have not recognized. Possible explanations for this discrepancy include virus strain differences in virulence, ecologic factors determining the rate os virus transmission, and the lack of disease recognition and specific laboratory diagnosisof human meningoencephalitis. The transmission cycle of attenuated SLE virus strains isolated from rodents has not been studied. Ilheus virus has been isolated only once from a human being. The available serological data are difficult to interpret due to cross-reactivity with other flaviviruses, and the ecology and medical importance of this agent remain uncertain. Dengue has not been recognized in Argentina since 1916, although its vector, Aedes aegypti, was not eradicated until 1963. Dengue was previously present in coastal localities of Chaco, Corrientes and Misiones Provinces. Within the last few years, Argentina was reinfested by Ae. aegypti. Although no human cases have yet been reported, outbreaks of dengue in bordering countries (Brazil, Paraguay, Bolovia) since 1986, clearly signal that the country in once again at risk of importation and spread of the viruse

Historical, epidemiological and ecological aspects of arboviruses in Argentina: Togaviridae, Alphavirus

This is a review of the arboviruses in Argentina belonging to families Flaviridae, Bunyaviridae and Rhabdoviridae. Of the many viruses belonging to these families, the flavivirus St. Louis encephalitis (SLE), has been most intensively studied. SLE virus strains have been recovered from three sources: 2 strains from humans with an undifferentiated, febrile disease; 6 from mosquitoes; and 2 from rodents. The viruses recovered from rodents are attenuated and those from mosquitoes are virulent based on a neuroinvasiveness test in mice; the degree of virulence of the mosquito strains remain to be analyzed. Serological surveys indicate a wide distribution and endemicity of SLE virus in the temperate and subtropical areas (central and northern Argentina), but no data are available from the andean region or from the South. The virulent SLE virus strains appear to be transmitted between Culex (Cx.)spp. from which they were isolated, and wild birds, based on antobody prevalence. A urban cycle may involve Cx. quinquefasciatus (source of a viral isolate and a competent experimental vector) and abundant birds (house sparrows, doves, and/or chickens), chickens are experimentally competent host species. Despite similarities in the ecology of SLE between Argentina and North America, urban outbreaks of SLE have not been recognized. Possible explanations for this discrepancy include virus strain differences in virulenc, ecologic factors determining the rate of virus transmission, and the lack of disease recognition and specific laboratory diagnosis of human meningoencephalitis. The transmission cycle of attenuated SLE virus strains isolated from rodentshas not been studied. Ilheus virus has isolated only once from a human being. The available serological data are difficult to interpret due to cross-reactivity with other flaviviruses, and the ecologyand medical importance of this agent remain uncertain. Dengue has not been recognized in Argentina since 1916, although is vector, Aedes aegypti, was not erradicated until 1963. Dengue was previously present in coastal localities of Chaco. Corrientes and Misiones Provinces. Within the last few years, Argentina was reinfested by Ae. aegypti. Although no human cases have vet been reported, outbreaks of dengue in bordering countries (Brazil, Paraguay, Bolivia) since 1986, cleary signal that the country in once againat risk of importantion ans spread of the virus

Detección retrospectiva de infecciones clínicas por hantavirus en la Argentina / Retrospective detection of hantavirus clinical infections in Argentina

La actividad de los hantavirus en la Argentina en roedores y humanos ya era conocida desde la década de 1980. En este trabajo, se investigó retrospectivamente la infección por hantavirus entre los pacientes notificados para Fiebre Hemorrágica Argentina (FHA) entre 1987 y 1994, sin confirmación virológica. La detección de anticuerpos IgG e IgM antihantavirus se realizó por técnica de ELISA. Entre 1028 pacientes estudiados se encontraron 13 infecciones recientes (1,26 por ciento) y 13 remotas (l,26 por ciento). Entre 745 personas sanas procedentes de las mismas localidades de los casos de infección reciente, sólo se encontraron anticuerpos IgG en una (O,13 por ciento). De las 13 infecciones recientes, 9 se presentaron como FHSR y 4 como SPH. Se realizó una comparación clínica y epidemiológica entre los 9 pacientes con FHSR y dos grupos control apareados: uno de casos de FHA y otros considerados Síndrome febril de etiología indeterminada (SFEI), que fueron negativos para Hantaan, Junín y Linfocoriomeningits (LCM). No se encontraron diferencias entre los signos y sintomas clínicos. Para el diagnóstico diferencial resulto sugerente la presencia de leucocitos normales o aumentados, con plaquetopenia, hemoconcentración, creatininemia aumentada y proteinuria en las FHSR. Estos resultados muestran la coexistência dentro del área endémica de FHA de virus Junín y hantavirus, e indican la necesidad de incluir a las infecciones por estos virus en el diagnóstico diferencial de las Fiebres Hemorrágicas y de los Síndromes de Distrés Respiratorio de etiología desconocida. La variabilidad clínica encontrada sugiere la presencia de más de un serotipo de hantavirus en nuestro país.

Localized Eastern equine encephalitis in Santiago del Estero province, Argentina, without human infection

Se documenta una epizootia de encefalitis equina del este (EEE) localizada en una zona irrigada de cuatro departamentos de la Privincia de Santiago del Estero, Argentina, en 1981. La incidencia de casos equinos fue estimada en 17% con una tasa de casos fatales del 61% y una relación de infección inaparente: aparente de < ou = 2,9:1. El diagnóstico para el virus EEE fue confirmado por pruebas serológicas y no se encontró evidencia de casos por virus de las encefalitis del oeste o Venezuela. Esta es la primera epizootia circunscripta a una pequeña área geográfica que se ha definido en Argentina y la primera en que el virus EEE se ha encontrado como único arbovirus etiológico. Su reconocimiento brindo la posibilidad de buscar la infección humana, pero no se encontró clara evidencia de enfermedad o infección. Esto se atribuyó a la baja densidad de población humana rural, aunque no se descartaron otros factores ecológicos. La serología en otros animales no permitió determinar los huéspedes vertebrados y no se estudiaron los vectores por lo cual el ciclo de transmisión continúa desconocido, impidiendo especular sobre el riesgo potencial del virus EEE para el hombre en Argentina

Peroral susceptibility of Aedes alblifasciatus and Culex pipiens complex mosquitoes (Diptera: Culicidae) from Argentina to western equine encephalitis virus

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 mosquitoes 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 cicle in Argentina

Geographic patterns of allele frequencies in Calomys musculinus reservoir-host of junin virus

Con el propósito de obtener información sobre el grado de contacto entre poblaciones de C. musculinus, se analizaron las frecuencias alélicas en tres loci polimórficos en muestras de seis diferentes localidades de la provincia de Córdoba ubicadas en el área endémica de fiebre hemorrágica argentina (FHA) y en regiones marginales, libres de virus Junín. Dichas localidades están situadas sobre una línea sur-noreste (250km de longitud) y otra sur-noreste (50km) que siguen el sentido en el cual progresó la endemia desde su aparición en Córdoba, hace más de veinte años. En el locus Aat-1 la frecuencia del alelo b osciló entre 0,95 y 0,99 en las diferentes localidades analizadas. En cinco de las seis muestras, las frecuencias génicas fueron muy similares en el locus Es-4 y en el Es-6. En la sexta localidad, los alelos a de ambos loci presentaron menor frecuencia. Esta población mostraba una característica particular: era la única con predominio de individuos de peso mayor a 16g, los cuales corresponderían a ejemplares adultos y viejos. Si se comparan las frecuencias alélicas de las diferentes muestras agrupando los ejemplares con menos de 16g (¿jóvenes?) y los adultos más los viejos, se observa una notable homogeneidad geográfica. Algunas características ecológicas conocidas para C. musculinus, tales como su gran capacidad de adaptación a ambientes inestables, su alta actividad ambulatoria y la ausencia de barreras naturales en el área estudiada, apoyarían la presunción de que existe un importante flujo génico entre poblaciones contiguas. Por otro lado, la observación de que los alelos a en los loci Es-4 y Es-6 se presentan con mayor frecuencia entre los individuos de menor peso, sugiere que los portadores del alelo b deben poseer mayor tasa de supervivencia, lo cual estaría determinado por fuerzas selectivas similares en toda el área analizada. La FHA se ha expandido lenta pero sostenidamente desde la aparición de los primeros casos humanos. Tal progresión es consecuencia de la transmisión del virus de Calomys infectados de la zona endémica a los de las zonas marginales. La ...