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

SHIGELLOSIS 249Shigellae rapidly acquire resistance to antimicrobials. The choice of an antimicrobialwill depend on the antibiogram of the strain isolated or local patterns of susceptibility.Fluids and electrolytes must be replaced if dehydration occurs.Antiperistaltics are contraindicated, both for intestinal infections caused by shigellaeand for other intestinal infections.In many countries, strains of Shigella resistant to sulfonamides and to severalantibiotics have been observed.The Disease in Animals: It occurs in monkeys, with a clinical picture similar tothat in man. In nonhuman primate colonies, strains resistant to many antibiotics arefrequently found. As in man, an antibiogram must be done to identify the mostappropriate antimicrobial. Enrofloxacine was used with good results at the NationalZoo in Washington, DC (Banish et al., 1993a).Source of Infection and Mode of Transmission: The principal reservoir of theinfection for man is other humans who are sick or carriers. The sources of infectionare feces and contaminated objects. The most common mode of transmission is thefecal-oral route. Outbreaks with numerous cases have had their origin in a commonsource of infection, such as foods contaminated by hands or feces of carrier individuals.Insects, particularly flies, can also play a role as mechanical vectors.There is a direct relationship between the frequency of shigellosis and a country’sdegree of economic development, as well as between poor and well-off classeswithin a country. Lack of health education, health infrastructure (potable water andsewer system), environmental hygiene, and personal hygiene habits are all factorsthat contribute to the spread of infection. Shigellosis is a disease of poverty.Bacillary dysentery is a serious disease with high mortality in nonhuman primatesin captivity, but there is doubt that monkeys can harbor the etiologic agent in theirnatural habitat. Monkeys probably contract the infection though contact withinfected humans. The infection spreads rapidly in nonhuman primate coloniesbecause the monkeys defecate on the cage floor and often throw their food there.Role of Animals in the Epidemiology of the Disease: Of little significance.Cases of human bacillary dysentery contracted from nonhuman primates are known.The victims are mainly children. In highly endemic areas, dogs may shed Shigella,at least temporarily.The etiologic agent has been isolated rarely from bats and rattlesnakes.Nevertheless, animals other than nonhuman primates play an insignificant role.Diagnosis: Definitive diagnosis depends on isolation of the etiologic agent by cultureof fecal material on selective media. There are several selective media, which arebased on the suppression of lactose fermenters. One of these is MacConkey agar withbile salts, xylose, lysine, and deoxycholate (XLD). Serologic identification and typing,at least of the serogroup, are important for diagnosis and for epidemiological research.Control: In man, control measures include: (a) environmental hygiene, especiallydisposal of human waste and provision of potable water; (b) personal hygiene; (c)education of the public and of food handlers about the sources of infection andmodes of transmission; (d) sanitary supervision of the production, preparation, andpreservation of foods; (e) control of flies; (f) reporting and isolation of cases andsanitary disposal of feces; and (g) search for contacts and the source of infection.