zoonoses and communicable diseases common to ... - PAHO/WHO

268 BACTERIOSEScheostomy. Simultaneously with these measures, human antitetanus immunoglobulinmust be administered (intramuscular administration of 500 IU). Administrationof penicillin or other antibiotics is recommended to reduce the toxin load(Cate, 1990).The Disease in Animals: Horses are very susceptible to tetanus and usuallyacquire it from shoeing nails. They may also contract it from any other wound contaminatedwith C. tetani if anaerobic conditions favor its multiplication. Their symptomsare similar to those of human tetanus. Localized rigidity appears first, due totonic convulsions of the masseter muscles, the neck muscles, and the hind legs, followedby generalized rigidity. Reflexes are increased and the animals are easily startledby noise, which causes general convulsions.Postpartum cases are seen in cows, especially if the placenta is retained. Cattlehave a high rate of neutralizing antibodies against the neurotoxin (tetanospasmin) ofC. tetani,but the antibody level drops markedly after parturition, leaving the animalvery susceptible to the disease. In calves and lambs, tetanus often follows castration,especially when rubber bands are used, since the necrotic tissue left by this operationfavors anaerobiosis.Dehorning, tail docking, and shearing may also give rise to the disease.Iatrogenic tetanus sometimes occurs after surgical operations and vaccinations.The incubation period lasts 2 to 14 days. The symptomatology is similar to thatin man. Death occurs in 4 to 10 days.Treatment consists of tranquilizers, curariform agents, and 300,000 IU of tetanusantitoxin every 12 hours. Good results can be obtained in horses if they are treatedat the onset of the disease. The wound must also be cleaned and drained, and broadspectrum antibiotics administered (Fraser et al., 1991).Source of Infection and Mode of Transmission: The reservoir and source ofinfection is soil containing C. tetani. The etiologic agent is found in many soils, particularlycultivated soil rich in organic matter. Areas where the exposure risk is highare referred to as “telluric foci” of C. tetani.The agent is commonly found in horse feces. It has also been found in otherspecies, such as cattle, sheep, dogs, rats, and chickens; similarly, man may harbor C.tetani in the intestinal tract.Transmission is effected through wounds. Scabs or crusts promote multiplicationof the etiologic agent. Some cases are due to dog bites. Tetanospasmin is producedafter the spores have germinated, i.e., by the vegetative form of the bacteria.In Paraguay, of 2,337 cases studied from 1946 to 1972, the portal of entry was theumbilical stump in 31.7%, small wounds in 38.7%, wounds caused by removal ofthe chigoe flea Tunga penetrans in 7.7%, and the remainder followed induced abortions,surgical interventions, burns, and injections without proper asepsis (VeraMartínez et al., 1976).Role of Animals in the Epidemiology of the Disease: Tetanus is a diseasecommon to man and animals, not a zoonosis. Some authors ascribe the role ofreservoir to animals (McComb, 1980; Benenson, 1990), but it is more likely thatthe disease agent derives from the soil, and that it is present in the digestive tract ofherbivores and omnivores only transitorily and does not multiply there (Wilson andMiles, 1975; Smith, 1975). Nevertheless, domesticated animals can disseminate