Transmission study of Andes hantavirus infection in wild sigmodontine rodents

Abstract

Our study was designed to contribute to an understanding of the timing and conditions under which transmission of Andes hantavirus in Oligoryzomys longicaudatus reservoir populations takes place. Mice were caged in test habitats consisting of steel drums containing holding cages, where seronegative rodents were exposed to wild seropositive individuals by freely sharing the same cage or being separated by a wire mesh. Tests were also performed for potential viral transmission to mice from excrement-tainted bedding in the cages. Andes virus transmitted efficiently; from 130 attempts with direct contact, 12.3% resulted in virus transmission. However, if we consider only those rodents that proved to be infectious, from 93 attempts we obtained 16 infected animals (17.2%). Twelve of them resulted from intraspecies O. longicaudatus encounters where male mice were differentially affected and 4 resulted from O. longicaudatus to Abrothrix olivaceus. Experiments using Abrothrix longipilis as receptors were not successful. Transmission was not observed between wire mesh-separated animals, and mice were not infected from excrement-tainted bedding. Bites seemed not to be a requisite for oral transmission. Genomic viral RNA was amplified in two out of three saliva samples from seropositive rodents, but it was not detected in urine samples obtained by vesicle puncture from two other infected rodents. Immunohistochemistry, using antibodies against Andes (AND) hantavirus proteins, revealed strong reactions in the lung and salivary glands, supporting the possibility of oral transmission. Our study suggests that AND hantavirus may be principally transmitted via saliva or saliva aerosols rather than via feces and urine.

FIG. 1.

Anti-N-AND IgG responses in sera from rodents infected experimentally. Blood samples were collected at the indicated days postencounter and were examined for reactivity to the N-AND antigen by ELISA. Data are presented in IgG units, in which the OD of each test sample was divided by the OD of the positive control sample run on the same microtiter plate. Samples with titers less than 0.2 IgG units (indicated with dashed line) were considered negative.

FIG. 2.

Intracage experiments indicating positive transmission chains related to the date of 24-h encounter. Distribution of AND viral antigen and detection of viral RNA in tissues are shown. IHC was performed on tissues from the salivary glands of infectious rodents. Δt, interval between date of first positive serology of donor rodent and date of viral transmission from donor to susceptible rodent; Olm, O. longicaudatus male; Olf, O. longicaudatus female; Aom, A. olivaceus male; Aof, A. olivaceus female; *, estimate by linear regression of IgG OD values for each rodent; ^#, unique serum sample; +, positive transmission.

FIG. 3.

Timeline (in weeks) of intracage experiments with intra- and interspecies direct contacts between susceptible and infectious donor rodents. Ol, O. longicaudatus; Ao, A. olivaceus; Al, A. longipilis; *, rodent infected in experimental encounter. Filled blocks indicate rodents who tested positive; underlining indicates male rodents.

FIG. 4.

Hantavirus immunoreactivity is localized in epithelial cells (arrows) lining the alveolar lumen (AL) and in macrophages (M). Paraffin sections of the lung of an infectious (A) and an experimentally infected (B) rodent are shown. For the infectious rodent used as the control, a section (C) was processed for IHC but was not incubated with antibodies against AND virus proteins.