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

84 BACTERIOSESType C causes hemorrhagic enterotoxemia (“struck”) in adult sheep in GreatBritain, as well as necrotic enteritis in calves, lambs, suckling pigs, and fowl inmany parts of the world (Timoney et al., 1988).Type D is the causal agent of enterotoxemia in sheep. It is distributed worldwideand attacks animals of all ages. The disease is associated with abundant consumptionof food, whether milk, pasture, or grains. Outbreaks have also been describedin goats and, more rarely, in cattle.Type E causes dysentery or enterotoxemia in calves and lambs, and has been confirmedin the US, England, and Australia (Timoney et al., 1988).Source of Infection and Mode of Transmission: The natural reservoir of C. perfringenstype A is the soil and the intestine of man and animals. Some studies(Torres-Anjel et al., 1977) have shown that man harbors higher numbers of C. perfringensthan fowl or cattle and that some people excrete great quantities of thesebacteria, making man the most important reservoir of clostridial food poisoning. Theamount of C. perfringens type A in the intestine varies with the animal species andlocation. C. perfringens is found in large numbers in the small intestine of pigs, insmall amounts in sheep, goats, and cattle, and is practically nonexistent in horses(Smith, 1965).Type A enterotoxemia is caused primarily by the alpha toxin, which forms in theintestine and is released during sporulation, for which the small intestine is a favorableenvironment. The source of poisoning for man is food contaminated by sporesthat survive cooking. Heat (heat shock) activates the spores, which then germinate.The vegetative forms multiply rapidly if the prepared food is left at room temperature,and can reach very high concentrations if the temperature is high for a sufficientamount of time (see the section on etiology). The vegetative forms carried tothe intestine by the food sporulate, releasing the enterotoxin in the process. The foodvehicle is almost always red meat or fowl, since they provide C. perfringens with theamino acids and vitamins it needs. Less frequently, other foods, such as pigeon peas,beans, mashed potatoes, cheeses, seafood, potato salad, noodles, and olives havegiven rise to the disease (Craven, 1980). Immersing meat in broth or cooking it inlarge pieces creates anaerobic conditions that favor the multiplication of the bacteriaduring cooling or storage. The foods that cause poisoning are usually prepared inlarge quantities by restaurants or dining halls and are served later that day or thenext. The spores of some strains of C. perfringens can be destroyed by adequatecooking, but other spores are heat-resistant. Reheating food before serving it canstimulate the multiplication of bacteria if the heating temperature is not highenough. It is now known that high concentrations of the vegetative form of C. perfringensin food cannot be destroyed by stomach acid, and thus pass into the intestine.The enterotoxin synthesized in the intestine when the bacteria sporulate isresistant to intestinal enzymes, has a cytotoxic effect on the intestinal epithelium,affects the electrolyte transport system, and thus causes diarrhea (Narayan, 1982).It should be borne in mind that not all strains of C. perfringens are toxigenic. Onestudy of strains implicated in food poisonings found that 86% were toxigenic, whileanother study found that 2 strains out of 174 isolated from other sources producedthe enterotoxin (Narayan, 1982).In lamb dysentery caused by C. perfringens type B, the animals are infected duringthe first days of life, apparently from the mother or the environment. Young