Seasonal variation in prevalence of antibody to hantaviruses in rodents from southern Argentina

Abstract

SummaryWe conducted a small mammal trapping study to investigate temporal variation in prevalence of infection in hantavirus reservoir populations in the Patagonian Andes mountain range, Rio Negro province, Argentina. Rodent blood samples collected in natural and periurban habitats and at the home of an hantavirus pulmonary syndrome (HPS) case patient were analysed by enzyme-linked immunosorbent assay. Organ tissue samples were tested by polymerase chain reaction (PCR) and nucleotide sequence analysis. Eight species of 1032 rodents were captured in 15 551 trap nights, giving an overall trap success of 6.6%. Hantavirus antibody was detected in 30 of 555 Oligoryzomys longicaudatus (reservoir of Andes virus), three of 411 Abrothrix longipilis, and one of 10 Loxodontomys micropus. Antibody prevalences in O. longicaudatus were 13.7% in spring 1996, 59.3% in summer 1996, 2.1% in autumn 1997, 12.4% in winter 1997 and 3.1% in spring 1997. A much higher antibody prevalence (33%) was found during trapping around the residence of an HPS case patient. Higher prevalences were found in older male O. longicaudatus. There was no apparent correlation of antibody prevalence with rodent population density, or of rodent population density or antibody prevalence with numbers of human cases. For an HPS case that occurred in our study area in 1997, we identi®ed the probable rodent reservoir and likely site of exposure by matching the genetic sequences of virus obtained from a rodent and the HPS case patient.

Prevalence of infection with hantavirus in rodent populations of central Argentina

“…The higher rates of hantavirus seroprevalence found in larger and reproductively active (i.e., older) individuals of A. azarae, and specially in males, is in agreement with that observed in O. longicaudatus in Southern Argentina by Cantoni et al (2001), in C. laucha in Paraguay by Yahnke et al (2001) in species of Peromyscus in the United States (Abbott et al 1999, Kuenzi et al 1999, and in C. musculinus infected with Junín virus (Mills et al 1994). Differences in seroprevalence among age classes and sexes have been related to horizontal transmission that involves a higher chance of older individuals of being infected, since they have a longer period of exposition to the virus (i.e., the "age factor").…”

“…Strong variations in seroprevalences are not only evident when comparing studies conducted by different authors, but also within habitats and times (Abbott et al 1999. In Argentina and other areas of the Americas seroprevalence range between 3-14% (Calderón et al 1999, Cantoni et al 2001, Yahnke et al 2001. However, the difference in seroprevalence could also be attributed to the different type of antigen used to estimate seroprevalence in each study (Sin Nombre and AND antigens for Calderón et al's and our study, respectively), although Toro et al (1998) did not find differences in serologic results obtained with these two types of antigen.…”

“…Previous studies of rodent hantavirus reservoirs in US (Abbott et al 1999 and Argentina (Cantoni et al 2001) suggest that the prevalence of infection is higher for adult males than for females and juveniles. Differences among demographic groups have been related to behavioral factors as agonistic interactions, to home range size, and to the age effect that increase the probability of being infected, suggesting that horizontal transmission is the main mechanism of maintaining the virus in nature (Abbott et al 1999.…”

“…Nowadays, the occurrence of cases is concentrated in three geographically isolated areas: North (Salta and Jujuy provinces), Center (Buenos Aires, Santa Fe and Entre Ríos provinces), and Southwest (Neuquén and Río Negro provinces). In an extensive study conducted in sites were HPS cases occurred, many sigmodontine species were found infected with hantavirus, with seroprevalences which varied between 1.5 and 10.2%, depending on the area and species (Calderón et al 1999, Cantoni et al 2001. López et al (1996López et al ( , 1997 described the virus associated to HPS cases in Argentina, Andes virus (AND), as a new type of hantavirus.…”

“…Differences among demographic groups have been related to behavioral factors as agonistic interactions, to home range size, and to the age effect that increase the probability of being infected, suggesting that horizontal transmission is the main mechanism of maintaining the virus in nature (Abbott et al 1999. Although seroprevalence variations according to changes in population density and structure have been described (Graham & Chomel 1997, Kuenzi et al 1999, Biggs et al 2000, Cantoni et al 2001, there is still not a clear pattern of variation of seroprevalence with density. When higher density is accompanied with an increase in the proportion of juveniles in the population, a lower seroprevalence have been related to a dilution effect .…”