Biology of Tacaribe-Complex Viruses

Summary

Tacaribe viruses have basic properties in common with LCM virus. Eight distinct serotypes, all found in the Western Hemisphere, have been collected as an antigenic complex because of extensive sharing of complement- fixing antigens, although there is a demonstrable immunological relationship, particularly as detected by immunofluorescent antibody, between members of the complex and the Old World arenaviruses LCM and Lassa.

Seven of the Tacaribe viruses are strongly rodent-associated, and accumulating evidence suggests that clinically silent, chronic infection of one or two rodent species with both horizontal and vertical intraspecific virus transmission represents the fundamental mechanism for natural maintenance of these agents. Experimental study of Machupo virus in its natural host, the field mouse Calomys callosus, disclosed many features in common with the behavior of LCM virus in Mus musculus. Salient differences also were documented. These included: 1) absence of acute disease in infected adult Calomys, 2) rapid development and longterm persistence of microcytic hypochromic anemia in animals infected shortly after birth, 3) major reduction in reproductive potential following neonatal infection, 4) definite but minimal evidence of formation of circulating and renal-bound virus-antibody complexes, and 5) two distinct response patterns among animals infected after the 8th day of life. About half of the Calomys had all the markers of newborn infection; the remainder developed neutralizing antibody and cleared virus from the blood.

Both Machupo and Junin viruses cause acute hemorrhagic fever in man, a disease characterized by fever, leukopenia, gastrointestinal hemorrhage, shock, and neurological signs. Mortality varies from 10 to 50%. Clinical and experimental evidence suggesting that virus infection in nonnatural hosts is immunosuppressive is reviewed, and progress toward development of vaccines suitable for use in man is reported.