On-line version ISSN 1678-9946
Rev. Inst. Med. trop. S. Paulo vol.45 no.2 São Paulo Mar./Apr. 2003
UNA virus: first report of human infection in Argentina
Virus UNA: primeiro registro de infecção em humanos na República Argentina
Luis Adrián DiazI, II; Lorena Ivana SpinsantiI; Walter Ricardo AlmironII; Marta Silvia ContigianiI
IInstituto de Virología "Dr. J. M. Vanella", Facultad de Ciencias Médicas, Universidad Nacional de Córdoba, Córdoba, Argentina
IICentro de Investigaciones Entomológicas de Córdoba, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Argentina
Una virus (UNAV), Togaviridae family, is widely distributed in South America, where infections have been detected in mosquitoes and vertebrate hosts (humans, birds and horses). We analyzed human sera from Córdoba inhabitants aged 44 to 89 years and using a neutralization test, we found a prevalence of UNAV antibodies of 3.8% (3/79). The low titers detected suggest past infections probably acquired in rural areas of the Province of Córdoba (central Argentina). None sera were found positive for MAYV neutralizing antibodies. This is the first report of human infections by UNAV in Argentina.
Keywords: Una virus; Togaviridae; Seroprevalence; Neutralizing Antibodies.
O virus Una (Togaviridae) tem ampla distribuição na América do Sul, detectando-se infecções até hoje em mosquitos e hospedeiros vertebrados (humanos, aves e cavalos).
Mediante a realização do teste de neutralização em soros humanos provenientes de indivíduos entre 44 e 89 anos, da cidade de Córdoba, foi detectada uma prevalência de 3,8% (3/79) de anticorpos para o vírus UNA. Nenhum soro apresentou anticorpos para o vírus Mayaro.
Os títulos foram baixos demonstrando-se a presença de infecção passada. Dados epidemiológicos indicam que a infecção ocorreu em áreas rurais da província de Córdoba (centro da Argentina).
Os dados aqui expostos representam o primeiro registro de infecção de humanos por vírus Una na República Argentina.
Una virus (UNAV), Togaviridae family, is a member of the Semliki Forest virus (SFV) complex, and a subtype of Mayaro virus (MAYV)4. UNAV was isolated for the first time from Psorophora ferox mosquitoes in the state of Pará, Brazil11. However, it is widely distributed in tropical and subtropical regions of Central and South America (Brazil, Colombia, French Guiana, Panama, Surinam, Trinidad, Venezuela) where it has a low seroprevalence4,10,12. Even though human infections by UNAV have been previously reported, they have not been associated with any specific type of disease4,8.
Currently, UNAV is the only member of the SFV complex with activity reported in Argentina8. In central Argentina, two strains of this virus (Cba An 979 and Cba An 995) have been isolated from febrile or dead equines at Río Segundo and Colonia Videla two villages located in the province of Córdoba3; and antibodies against UNAV were detected in birds and horses from other areas of this province8,9. Several strains of arbovirus (not UNAV) have been isolated from mosquitoes collected in different provinces of Argentina: Chaco, Corrientes, Río Negro and Santa Fe between 1977 and 19846,7. Human sera from the provinces of Buenos Aires, Mendoza and Tucumán (Argentina) were also tested for UNAV antigens with negative results5.
The purpose of our study was to detect the presence of neutralizing antibodies for UNAV in human sera from Córdoba, a province located in the central area of Argentina.
MATERIALS AND METHODS
The Instituto Nacional de Previsión Social (PAMI) provided human sera from Córdoba citizens (males and females) aged 44 to 89 years. The specimens were obtained randomly between May and June, 2001. Afterwards, sera were inactivated at 56 ºC during 30 min, centrifuged at 10 000 rpm for 30 min, and stored at -20 ºC until assayed.
Seventy-nine samples of sera were tested by neutralization assay, estimating the sample with Epi Info software1. The plaque reduction neutralization test was performed with an 80% plaque reduction endpoint in Vero cell line under agar2.
The suspensions of Cba An 979 UNAV and Be Ar 20290 MAYV strains were prepared from a 10% dilution of infected suckling-mice brain in Minimum Essential Medium (MEM) with Earle's salts and L-glutamine, 10% fetal calf sera (FCS) and 1% antibiotics, centrifuged at 10 000 rpm for 30 min. A 1:5 dilution of each serum in MEM containing 2% FCS and 1% antibiotics was used for the screening procedure.
Three out of 79 sera analyzed were positive for UNAV neutralizing antibodies, representing a prevalence of 3.8% (Table 1).
Two of these 3 infected subjects were interviewed and revealed a history of residency in rural areas of the province of Córdoba (Río Primero and Sobremonte), farming activities, and recent moving to the city of Córdoba. Unfortunately, the third infected person could not be interviewed.
None sera were found positive for MAYV neutralizing antibodies (data not shown).
Our results could indicate the circulation of UNAV, at least in rural areas of the province of Córdoba. This event could have happened years ago according to the low titers of neutralizing antibodies detected and the available information of viral isolation in the province3. It is important to remark that the towns of Río Segundo and Colonia Videla, where UNAV strains were first isolated from equines in the province of Córdoba, are towns located approximately 60 and 180 km southern from Río Primero and Sobremonte, respectively (Fig. 1). Therefore, our results suggest a larger area of distribution and circulation range of UNAV in Córdoba.
This is the first report of human infection by UNAV in Argentina, demonstrating an enlargement of its southern limit of distribution. However, infections by related alphavirus belonging to SFV complex cannot be excluded in the exam of UNAV positive sera.
These preliminary data contribute to the knowledge of UNAV distribution in Argentina. It would be necessary to carry out more studies regarding human infection, associated symptoms and physiopathology, spatial and temporary patterns of virus activity, transmission cycle, vertebrate hosts involved, and vector incrimination.
The authors are specially grateful to Dr. Luiz T. M. Figueiredo for his recommendations; to Natalia Alvarez Oliveira, Luciana Nicola and Sergio Grutadauria for translating the manuscript and to the personal of the Instituto Nacional de Previsión Social (PAMI) for providing the human sera. This study was supported by grants of the Agencia Córdoba Ciencia S. E. and the Programa VIGI+A Ministerio de Salud de la Nación Argentina.
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Luis Adrián Diaz
Instituto de Virología "Dr.. J. M. Vanella", Facultad de Ciencias Médicas, Universidad Nacional de Córdoba
Enfermera Gordillo Gómez s/n
CP: 5016, Ciudad Universitaria, Córdoba, Argentina
Received: 20 August 2002
Accepted: 3 April 2003