A five-year study of tetanus in the Cayo Santiago rhesus monkey colony: Behavioral description and epizootiology

Tetanus is a major cause of death in the free-ranging rhesus moonkey colony on the island of Cayo Santiago, Puerto Rico. During the five-year period of observation (July 1, 1976 through June 30, 1981), the mean annual tetanus mortality rate (± 1 SD) was 1.74% (±0.15). The mean annual total mortality rate was 6.77% (±0.78). The tetanus mortality rate varied sigificantly (P < 0.005) among the six troops on the island. Clinically confirmed tetanus accounted for 24.68% of the 231 deaths which occurred on the island during the study. Although the base population increassed from 479 to 914 monkeys or 90.8% in five years, there were no significant changes in either the total or the tetanus mortality rates. The mean age of tetanus deaths was 6.9 years (±3.9) in the males and 7.1 years (±5.4) in females. The mean age-specific tetanus mortality rate increased with age. Of the 67 confirmed tetanus cases, 57 proved fatal (26 males, 31 females) for a case fatality rate of 85.1%. There was no significant sex difference in the tetanus mortality rate. No confirmed cases of neonatal tetanus were observed. Infection of juveniles and adults of both sexes occurred chiefly through septic wounds, but postpartum infection of females was also noted. The peak incidence of tetanus deaths for both sexes occurred during the mating season of the annual reproductive cycle, as a consequence of increased levels of aggression and subsequent wounding. The diagnosis of tetanus was based solely on the clinicla signs and was characterized by early behavioural abnormalities consisting of torpor, reluctance to interact with other animals, inability to prehend food, inordinate thirst, difficulty in swallowing, progressive stiffening and adduction of the pectorla limbs, bipedeal running, "kangaroo hopping," "toppling over," and pilo-erection. As the disease advanced, severely affected individuals developed the classic human triad of tetanus symptomatology:trismus (lockjaw), extensor rigidity, and opisthotonus, which progressed in most cases to status epilepticus and death from respiratory paralysis or physical exhaustion. The course of the disease in fatal cases ranged in duration from 24 hours to ten dyas. Obese monkeys with mild cases of tetanus were the most likely to recover with some taking as long as a month to return to normal condition and regain body weight. Of ten recoveries, six were female and four male. Multiple cases were observed in one adult male, indicating that previous infections do not necessarily confer immunity to future attacks. Survivous did not have demonstrable antitoxin titers to Clostridium tetani toxin, thus confirming that tetanus is a nonimmunizing disease. One half of an annual birth crop of thesus monkeys inoculated with tetanus toxoid at the age of one year had protective levels of tetanus antitoxin seven years postinoculation. However, the immunization program had no significant effect on either the total or tetanus motality rates during the study.