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

248 BACTERIOSESdren aged 1 to 5 years (WHO, 1987). Of 16,567 isolations done in the US during1987, 67.7% were S. sonnei, 22.2% were S. flexneri, 2.1% were S. boydii, 1.4% wereS. dysenteriae, and 6.6% were unidentified species (Keusch and Bennish, 1991).It is very difficult to calculate the number of cases worldwide, but they are estimatedat more than 200 million each year, 650,000 of whom die (WHO, 1991). Inthe US, there are an estimated 300,000 clinical cases (Bennett, cited in Wachsmuthand Morris, 1989).An outbreak affecting large numbers of people occurred in 1987 during a mass“Rainbow Family” gathering in a forest in North Carolina (USA). It is estimatedthat more than 50% of the 12,700 participants were affected. The location’s sanitaryinfrastructure was insufficient for so many people. The outbreak was causedby S. sonnei, which is resistant to many antibiotics (ampicillin, tetracycline, andtrimethoprim with sulfamethoxazole), and which contained a 90-kilobase plasmidnot found in strains not related to this epidemic. When the participants dispersed,they became the source of infection for outbreaks in three US states (Wharton etal., 1990).Those who suffer most from the disease are those who cannot follow personalhygiene rules, such as patients or residents confined in different institutions.Children are the principal victims of the disease in endemic areas. Resistance inadults is due to acquired immunity to the prevalent serotype. Adult travelers visitingendemic areas contract the disease because they have had no previous exposure.Similarly, when a new serotype is introduced into a susceptible population, the diseaseaffects all age groups (Levine and Lanata, 1983).Occurrence in Animals: It is common in captive nonhuman primates and rare inother animal species. All species of Shigella, including S. dysenteriae type 1 (Shigabacillus), which is considered the most pathogenic form for man, have been isolatedfrom nonhuman primates (L’Hote, 1980). In 1984, an epizootic caused by S. flexnerioccurred at the National Zoo in Washington, DC (USA), and since then, shigellosishas become endemic. The infected species were gibbons (Hylobates concolor andH. syndactylies), macaques (Macaca silenus, M. nigra, and M. sylvanus), colobusmonkeys (Colobus guerzea), and gorillas (Gorilla gorilla). From 1984 to 1988, thetwo species of gibbons (species in danger of extinction) had a high rate of infectionand disease (Banish et al., 1993a). S. sonnei was isolated from mangabey monkeys(Cercocebus albigena) and spider monkeys (Ateles susciceps) in the same zoologicalcollection (Banish et al., 1993a).The Disease in Man: It is seen most often in preschool-aged children. When anew serotype is introduced in tropical areas in which the population is undernourished,the disease affects all age groups, particularly children, the elderly, and debilitatedindividuals. The incubation period is one to seven days, but usually four days.The clinical picture may vary from an asymptomatic infection to a serious andfatal disease. The disease begins with fever and abdominal pains, as well as diarrheathat may be watery at first and later dysenteric with blood and mucus. The rectumand colon are the parts of the intestine most affected. In the final stages, there is anintense tenesmus with frequent elimination of small amounts of feces consistingalmost entirely of blood and mucus. The disease is self-limiting in well-nourishedindividuals, but may last for weeks or months in undernourished persons (Keuschand Bennish, 1991). Convulsions are frequent in hospitalized children.