Variation Between Strains of Hamsters in the Lethality of Pichinde Virus Infections

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Abstract
Infection by Pichinde virus, a member of the arenavirus group, was studied in Golden Syrian hamsters (Mesocricetus auratus) with regard to possible mechanisms of resistance to virus infection in adult hamsters. Two hamster strains were differed in their susceptibility to lethal Pichinde virus infection. LVG/Lak randomly bred hamsters were 100% susceptible to low doses of Pichinde virus during the first 6 days of life, but after 8 days of life mortality was uncommon. Peak virus titers in the serum of animals infected at 3 days of life were 4 logs greater than in animals infected at 12 days. MHA/Lak inbred hamsters, in contrast, were susceptible to lethal virus infection as newborns and as adults. Peak virus titers of greater than 108 plaque-forming units/ml were observed in serum 8 days after infection of adult MHA hamsters as compared with < 103 plaque-forming units/ml in the serum of adult LVG hamsters. Cultured primary kidney cells and peritoneal macrophages from either hamster strain supported Pichinde virus replication equally well in vitro. Antibodies to the complement-fixing antigens and to antigens at the surface of virus-infected cells were produced by both strains of hamsters. Cyclophosphamide immunosuppression rendered adult LVG animals susceptible to lethal infections, and virus grew to high titers in the treated animals. Immunological factors that appear early in life in LVG hamsters and are deficient in MHA hamsters may limit Pichinde virus infection. Unlike previously reported arenavirus diseases, death is probably produced by a direct viral effect and not through immunopathological mechanisms.