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La encefalitis equina del oeste (WEEV, por su sigla en inglés, Western Equine Encephalitis) es una enfermedad reemergente en Argentina a partir del año 2023. La co-municación inicial fue en 1933, las últimas epizootias ocurrieron en 1983 y el último caso humano se registró en 1996. Se revisan las características del agente causal, la ecología con especial referencia a los vectores iden-tificados en el país, su competencia en la transmisión y el ciclo así como los factores de riesgo para adquirir la enfermedad. La situación epidemiológica en equinos y humanos desde noviembre 2023 hasta marzo 2024 es analizada. Se describen las formas clínicas de presen-tación de la enfermedad humana, las posibilidades evo-lutivas, los datos disponibles en los casos confirmados y el tratamiento. La metodología y algoritmo empleados para el diagnóstico etiológico en el Centro Nacional de Referencia son detallados. Las estrategias para la pre-vención y el control se basan en la vacunación de los equinos, el saneamiento ambiental y el control del foco ante la presentación de la enfermedad animal (vigilancia epidemiológica activa)

Western equine encephalitis (WEE) is a re-emerging dis-ease in Argentina starting in 2023. Since the initial notifi-cation in 1933, the last epizootics occurred in 1983, and the last human case was recorded in 1996.The charac-teristics of the causative agent, the ecology with special reference to vectors identified in the country, their compe-tence in transmission, and the cycle as well as the risks factors for acquiring the disease, are reviewed.The epidemiological situation in horses and humans from November 2023 to March 2024 is analyzed. The clinical presentation of the human disease, its evolutionary po-tential, available data in confirmed cases, and the treat-ment are described.The methodology and algorithm used for the etiological diagnosis at the National Reference Center are detailed. Strategies for prevention and control are based on vaccination of horses, environmental sani-tation and outbreak control in the presence of the animal disease (active epidemiological surveillance)

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In Argentina, many Flavivirus were recognised including West Nile virus (WNV). During 2009 several strains of Culex Flavivirus (CxFV), an insect-specific flavivirus, were isolated in the same region where circulation of WNV was detected. Hence, the objective of this study was to analyse the effect of co-infection in vitro assays using CxFV and WNV Argentinean strains in order to evaluate if CxFV could affect WNV replication. Our results showed that WNV replication was suppressed when multiplicity of infection (MOI) for CxFV was 10 or 100 times higher than WNV. Nevertheless, in vivo assays are necessary in order to evaluate the superinfection exclusion potential.

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In Argentina, many Flavivirus were recognised including West Nile virus (WNV). During 2009 several strains of Culex Flavivirus (CxFV), an insect-specific flavivirus, were isolated in the same region where circulation of WNV was detected. Hence, the objective of this study was to analyse the effect of co-infection in vitro assays using CxFV and WNV Argentinean strains in order to evaluate if CxFV could affect WNV replication. Our results showed that WNV replication was suppressed when multiplicity of infection (MOI) for CxFV was 10 or 100 times higher than WNV. Nevertheless, in vivo assays are necessary in order to evaluate the superinfection exclusion potential.

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The importance of Zika virus (ZIKV) has increased noticeably since the outbreak in the Americas in 2015, when the illness was associated with congenital disorders. Although there is evidence of sexual transmission of the virus, the mosquito Aedes aegypti is believed to be the main vector for transmission to humans. This species of mosquito has not only been found naturally infected with ZIKV, but also has been the subject of study in many vector competence assays that employ different strains of ZIKV around the world. In Argentina, the first case was reported in February 2016 and a total of 278 autochthonous cases have since been confirmed, however, ZIKV virus has not been isolated from any mosquito species yet in Argentina. In order to elucidate if Argentinian Ae. aegypti populations could be a possible vector of ZIKV, we conducted vector competence studies that involved a local strain of ZIKV from Chaco province, and a Venezuelan strain obtained from an imported case. For this purpose, Ae. aegypti adults from the temperate area of Argentina (Buenos Aires province) were fed with infected blood. Body, legs and saliva were harvested and tested by plaque titration on plates of Vero cells for ZIKV at 7, 11 and 14 days post infection (DPI) in order to calculate infection, transmission, and dissemination rates, respectively. Both strains were able to infect mosquitoes at all DPIs, whereas dissemination and transmission were observed at all DPIs for the Argentinian strain but only at 14 DPI for the Venezuelan strain. This study proves the ability of Ae. aegypti mosquitoes from Argentina to become infected with two different strains of ZIKV, both belonging to the Asian lineage, and that the virus can disseminate to the legs and salivary glands.

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BACKGROUND: The Argentine Hemorrhagic Fever (AHF) is a zoonotic disease endemic in a wide area of the humid pampa of Argentina. The etiologic agent is the Junin virus that is maintained in the wild by the rodent Calomys musculinus and transmitted to humans, mainly, through aerosols generated from secretions and excretions. AIMS: To characterize and compare the assemblages of small rodent composition and diversity inside the epidemic, historic and non-endemic zone of AHF and to register C. musculinus abundance in each zone and in each area within each zone, registering the prevalence of infection in rodent populations. METHOD: One central and two peripheral areas were delimited to sample rodents in each zone with different incidence of AHF. Thus, 18 localities were selected to do the sampling in two years. Host abundance between zones and among areas inside each zone and among nearby areas between zones were compared applying nested ANOVA's. RESULTS: In each zone, the rodent assemblage showed differences in composition, diversity and numeric representation of C. musculinus. The epidemic zone was the richest of the three, registering also great host abundance; meanwhile in the historic zone, A. azarae was the dominant numeric species with less number of other species. Regarding the non-endemic zone, the assemblage composition and C. musculinus abundance varied respect the sampled year. Junin virus infection was only detected in C. musculinus individuals corresponding to the epidemic zone, with a prevalence of 2.7 and 1.1% for the years 2007 and 2008, respectively. CONCLUSION: In this system, the abundance of C. musculinus could be impacting over the pathogen dynamic, rather than the assemblage diversity or the A. azarae presence.

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Resumen La fiebre hemorrágica argentina (FHA) es una enfermedad zoonótica endémica en una amplia zona de la pampa húmeda de Argentina. El agente etiológico es el virus Junin que es mantenido en la naturaleza por el roedor Calomys musculinus y transmitido, principalmente, al humano a través de aerosoles generados de las secreciones y excreciones. Objetivos: Caracterizar la composición y diversidad de los ensambles de pequeños roedores, determinar la abundancia del hospedador C. musculinus y la prevalencia del virus de la FHA en las zonas epidémica, histórica y no endémica de dicha enfermedad en Argentina. Métodos: Para el muestreo de roedores en cada una de las zonas se demarcaron un área central y dos periféricas para 18 localidades de la región central de Argentina (incluyendo las provincias de Córdoba, Buenos Aires y Santa Fe) muestreadas en dos años. Se comparó la abundancia de C. musculinus entre zonas y entre las áreas dentro de cada zona y áreas cercanas entre zonas, utilizando modelos de análisis de varianza anidados. Resultados. Dentro de cada zona, el ensamble de roedores mostró diferencia espacial en la composición específica, diversidad y abundancia de C. musculinus. La zona epidémica registró mayor número de especies y mayor abundancia del hospedador. En zona histórica se capturó el menor número de especies (de roedores) y Akodon azarae fue la más abundante. En zona no endémica la composición del ensamble y la abundancia de C. musculinus variaron entre los dos años. Sólo se detectó infección por virus Junin en C. musculinus correspondientes a la zona epidémica con una prevalencia de 2,7 y 1,1% para los años 2007 y 2008, respectivamente. Conclusión: En este sistema, la abundancia del hospedador estaría afectando la dinámica espacial de este virus, más que la diversidad del ensamble o la presencia de A. azarae.

Background. The Argentine Hemorrhagic Fever (AHF) is a zoonotic disease endemic in a wide area of the humid pampa of Argentina. The etiologic agent is the Junin virus that is maintained in the wild by the rodent Calomys musculinus and transmitted to humans, mainly, through aerosols generated from secretions and excretions. Aims: To characterize and compare the assemblages of small rodent composition and diversity inside the epidemic, historic and non-endemic zone of AHF and to register C. musculinus abundance in each zone and in each area within each zone, registering the prevalence of infection in rodent populations. Method: One central and two peripheral areas were delimited to sample rodents in each zone with different incidence of AHF. Thus, 18 localities were selected to do the sampling in two years. Host abundance between zones and among areas inside each zone and among nearby areas between zones were compared applying nested ANOVA's. Results: In each zone, the rodent assemblage showed differences in composition, diversity and numeric representation of C. musculinus. The epidemic zone was the richest of the three, registering also great host abundance; meanwhile in the historic zone, A. azarae was the dominant numeric species with less number of other species. Regarding the non-endemic zone, the assemblage composition and C. musculinus abundance varied respect the sampled year. Junin virus infection was only detected in C. musculinus individuals corresponding to the epidemic zone, with a prevalence of 2.7 and 1.1% for the years 2007 and 2008, respectively. Conclusion: In this system, the abundance of C. musculinus could be impacting over the pathogen dynamic, rather than the assemblage diversity or the A. azarae presence.

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We describe an outbreak of hantavirus pulmonary syndrome in the Burruyacú Department, Province of Tucumán. The detection in 2016 of a case of hantavirosis affecting a 23-year-old woman, considered at that time to be the first case occurred in that province, promoted a thorough epidemiological study. The investigation allowed the retrospective detection of another case occurred one month earlier in a 5-year-old child in the same Department. In both cases, the infection was confirmed by serology (case 1 at days 4 and 7 of disease onset, case 2 at day 4) and the viral genotype was characterized as HU39694. The contacts of both cases were serologically negative for hantavirus. The rodents captured in the area belonged to genus Akodon, genus Calomys and species Mus musculus. Oligoryzomys, the known reservoir for this viral genotype, was not found. Specific anti-hantavirus antibodies were not detected in the captured rodents. Given that the patients had not visited hantavirus endemic areas and their contacts were negative for hantavirus, we infer that the patients were locally exposed to fluids of infected rodents during their usual social or recreational outdoor activities. In conclusion, we demonstrate that hantavirus HU39694 -a genotype until now considered to be restricted to the Central Pampas of the country- is circulating in the North Western province of Tucumán. The endemic area of hantavirosis is thus expanded to this province but the viral reservoir in the area has not yet been identified.

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Se describe un brote de síndrome pulmonar por hantavirus en el departamento de Burruyacú, provincia de Tucumán. La detección en 2016 de un caso de hantavirosis en una joven de 23 años -en ese momento considerado el primero ocurrido en dicha provincia- promovió un estudio epidemiológico exhaustivo, que permitió detectar retrospectivamente otro caso ocurrido en un niño de 5 años, un mes antes, en el mismo departamento. La infección fue confirmada por serología en ambos casos (caso 1 en muestras de 4 y 7 días de evolución, caso 2 en muestra a los 4 días). En ambos casos el genotipo viral fue caracterizado como HU39694 y los contactos fueron serológicamente negativos. En las áreas fueron identificados roedores pertenecientes a los géneros Akodon y Calomys y a la especie Mus musculus, pero no a Oligoryzomys, el reservorio habitual del genotipo HU39694. Tampoco se detectaron anticuerpos anti-hantavirus en suero de los roedores capturados. La ausencia de registro de viajes a área endémica de este genotipo y los hábitos recreacionales de los pacientes, sumados a los resultados serológicos negativos para hantavirus en los contactos, permiten inferir la posible exposición de los pacientes a fluidos de roedores infectados durante actividades recreativas o sociales al aire libre en sus respectivas áreas de residencia. En conclusión, se demuestra la circulación en Tucumán del genotipo viral HU39694, hasta ahora considerado restringido a la región pampeana central. Se extiende así a Tucumán el área endémica de hantavirosis, pero no se identificó el reservorio en el área.

We describe an outbreak of hantavirus pulmonary syndrome in the Burruyacú Department, Province of Tucumán. The detection in 2016 of a case of hantavirosis affecting a 23-year-old woman, considered at that time to be the first case occurred in that province, promoted a thorough epidemiological study. The investigation allowed the retrospective detection of another case occurred one month earlier in a 5-year-old child in the same Department. In both cases, the infection was confirmed by serology (case 1 at days 4 and 7 of disease onset, case 2 at day 4) and the viral genotype was characterized as HU39694. The contacts of both cases were serologically negative for hantavirus. The rodents captured in the area belonged to genus Akodon, genus Calomys and species Mus musculus. Oligoryzomys, the known reservoir for this viral genotype, was not found. Specific anti-hantavirus antibodies were not detected in the captured rodents. Given that the patients had not visited hantavirus endemic areas and their contacts were negative for hantavirus, we infer that the patients were locally exposed to fluids of infected rodents during their usual social or recreational outdoor activities. In conclusion, we demonstrate that hantavirus HU39694 -a genotype until now considered to be restricted to the Central Pampas of the country- is circulating in the North Western province of Tucumán. The endemic area of hantavirosis is thus expanded to this province but the viral reservoir in the area has not yet been identified.

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