Complement fixation test in experimental clinical and subclinical melioidosis.

Nigg, Clara (University of California, Berkeley), and Margaret M. Johnston. Complement fixation test in experimental clinical and subclinical melioidosis. J. Bacteriol. 82:159-168. 1961.-Soluble stable antigens prepared from Pseudomonas pseudomallei gave 4+ complement fixation reactions in a dilution of 1 to 8,000 when tested with specific rabbit antiserum diluted 1 to 10,000. The complement fixation reaction was positive in 100% of experimentally infected rabbits 9 to 11 days postinfection. Infected guinea pigs and monkeys showed similar results. Monkeys inoculated with very small infecting doses of P. pseudomallei developed positive complement fixation reactions in the absence of clinical manifestation of infection. An anamnestic complement-fixing antibody response could be induced in such monkeys, after the titer had dropped to approximately the preinfection level, by inoculating very small doses of viable P. pseudomallei or larger doses of killed melioidosis vaccine. The complement fixation test described appeared to be both sensitive and specific, and should be of value in human melioidosis which cannot be diagnosed on the basis of clinical manifestations alone. It is suggested that subclinical infections may play a role in the epidemiology of human meliodosis. The potential application of the complement fixation test to serological surveys in areas where melioidosis occurs endemically is discussed.