Isfahan virus, a new vesiculovirus infecting humans, gerbils, and sandflies in Iran

The characteristics and ecology of Isfahan virus, a new vesicular stomatitis virus (VSV) serotype, are described. Two strains of the agent were isolated from pools of Phlebotomus papatasi collected in Iran in 1975. Its animal pathogenicity, growth rate, cytopathic effect, and plaque morphology are similar to those of the other VSV serotypes. Electron microscopic examination of the virus demonstrated a bullet shape, the presence of truncated particles and maturation at plasma membranes. Antigenic relationships between Isfahan virus and three other VSV serotypes (Cocal, Piry, and Chandipura) were demonstrated by complement fixation or neutralization tests. A high prevalence of Isfahan neutralizing antibodies was found in human sera from several regions of Iran, suggesting that the virus may be of some public health importance. All of the residents over 5 years of age in the village where the virus was isolated had been infected. Neutralizing antibodies to Isfahan virus were also found in sera of Iranian gerbils but not in domestic animals. Results of this study suggest that the ecology of Isfahan virus is distinct from the other VSV serotypes and involves chiefly humans, gerbils, and sandflies, a pattern also observed with cutaneous leishmaniasis and sandfly fever in Iran.