Measurement of Antibodies to Machupo Virus by the Indirect Fluorescent Technique

Abstract

Bolivian hemorrhagic fever (BHF) was first recognized in the Province of Beni, Bolivia, in 1959 (1), and cases have continued to occur since then. Recent outbreaks have confirmed the fact that clinical manifestations can be quite nonspecific. Laboratory diagnosis is handicapped by a scarcity of facilities in the endemic region, as well as by the hazard to nonimmune personnel of working with the causative agent, Machupo virus. These problems also apply in varying degree to two other diseases caused by members of the arenavirus group (2, 3): Argentine hemorrhagic fever (AHF) caused by Junin virus (4) and Lassa fever caused by Lassa virus (5). The early recognition of outbreaks of these diseases is important since rodent control, immune serum therapy, and isolation of patients are thought to be of some use in treatment and prevention.

A plaque-neutralization test for detection of Machupo virus antibodies has been developed and proved to be specific and sensitive (6). However, these advantages are posited on two special considerations: the regular production of the necessary cell cultures, and the presence of trained immune personnel working in facilities designed to allow efficient and safe handling of Machupo virus. If inactivated antigens are used, the complement-fixation (CF) test (7) can be done by nonimmune workers, but this technique requires careful standardization and is less specific and less sensitive than the neutralization test. False-positive reactions occur and anticomplementary activity is often a major problem.

Direct or indirect fluorescent antibody staining of Tacaribe complex viruses in tissue culture or infected animal tissues, has been successful in a number of laboratories (8-12) as well as our own (13-15). Furthermore, the indirect fluorescent antibody test (IFAT) with human and animal sera proved to be a broadly reactive and extremely sensitive tool capable of demonstrating an immunological relation between the Tacaribe viruses and lymphocytic choriomeningitis (LCM) virus (15).