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

COLIBACILLOSIS 93K99). Although F4 (K88) and 987P have also been isolated, they are not believed toplay a role in ETEC virulence in these animals. The pili associated with enterotoxigeniccolibacillosis in suckling pigs are F4 (K88), F5 (K99), F41, and 987P.In the developing countries, the enterotoxigenic E. coli group primarily affectschildren under 2 or 3 years of age. In unhygienic homes, children may frequently sufferfrom ETEC. The incidence of the disease declines after the age of 4 and remainslow. In addition, ETEC is the most common cause of “traveller’s diarrhea” in adultswho visit endemic countries. This epidemiological characteristic suggests that thepopulation in endemic countries acquires immunity, while in industrialized countriesthe population is little exposed to these agents and does not acquire immunity.The disease in man produces symptoms that closely resemble those caused byVibrio cholerae. After an incubation period of 12 to 72 hours, there is profuse,watery diarrhea; abdominal colic; vomiting; acidosis; and dehydration. The feces donot contain mucus or blood and there may be fever. The duration of the illness isshort and the symptoms generally disappear in two to five days.ETEC can be diagnosed in man by demonstrating the presence of enterotoxin TL,TS, or both through an enzyme immunoassay. DNA probes can also be used to identifythe genes in the bacteria that encode the toxins.Man is the main reservoir and source of infection is the feces of patients and carriers.The route of transmission is fecal-oral. The vehicle of infection may be foodand water contaminated by human feces.ETEC is the cause of some outbreaks that affected many people in the developedcountries. Some occurred in children’s hospitals in Great Britain and the US,although the source of infection was not definitively determined. There have beenoutbreaks among adults that affected hundreds of people and were attributed to specificfoods and contaminated water. One of the largest outbreaks, affecting morethan 2,000 people, occurred in 1975 in a national park in Oregon (USA). Other outbreakswere due to imported Brie cheese that caused enterocolitis in several USstates as well as in Denmark, the Netherlands, and Sweden. A large outbreak affecting400 people occurred among diners at a restaurant in Wisconsin (USA). In thiscase, the source of infection was believed to be an employee who had diarrhea twoweeks prior to the outbreak. A passenger on a cruise ship suffered two episodes ofgastroenteritis caused by ETEC, one of them due to the ship’s contaminated water(Doyle and Padhye, 1989).c) Enteroinvasive E. coli (EIEC). This category represents a small group of E.coli. Many components are nonmotile (lacking the H antigen) and they are slow toferment lactose or are nonlactose fermenting. The disease they cause is very similarto bacillary dysentery caused by Shigella. Their somatic antigens may cross-reactwith those of Shigella. Enteroinvasive E. coli can invade and multiply in the cells ofthe intestinal mucosa, especially in the colon.EIEC colitis begins with strong abdominal pains, fever, malaise, myalgia,headache, and watery feces containing mucus and blood. The incubation period isfrom 10 to 18 hours. If diarrhea is severe, the patient can be treated with ampicillin.The reservoir seems to be man and the source of infection contaminated water orfood. However, the source of infection is not always definitively identified.EIEC is endemic in the developing countries and accounts for 1% to 5% of allpatients with diarrhea who see a doctor (Benenson, 1990). Studies conducted with