Absence of naturally acquired tetanus antitoxin in the free-ranging Cayo Santiago rhesus monkeys (Macaca mulatta).

Tetanus is enzootic in the free-ranging rhesus monkey colony on Cayo Santiago. The disease accounts for 25% of all mortalities in the population. The high prevalence of tetanus provided a unique opportunity to study the potential roles of geophagia, wounding, and clinical tetanus infections on the development of naturally acquired tetanus antitoxin in rhesus macaques. Eighty-six unvaccinated monkeys, including six that recovered from tetanus, were serosurveyed using a mouse toxin neutralization test. None of the animals had detectable antitoxin titers (less than 0.001 AU/ml), suggesting that natural immunity to tetanus is either rare or nonexistent in the Cayo Santiago colony.