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

272 BACTERIOSESCanada (British Columbia), Mexico, Guatemala, Panama, Colombia, Venezuela,Ecuador, and Argentina.Although endemic relapsing fever is usually sporadic, at times group outbreaksoccur. In 1973, there was an outbreak with 62 cases (16 confirmed and 46 clinicallydiagnosed) among tourists at Grand Canyon National Park in Arizona (USA) whowere lodged in rustic wooden cabins infested by rodents and their ticks. In 1976, anoutbreak occurred under similar circumstances in California, with 6 cases among 11tourists (Harwood and James, 1979).A telephone and mail survey was conducted of 10,000 people who visited theGrand Canyon. The results showed that there were 14 cases of relapsing feveramong the tourists, and that 7 of these had to be hospitalized. There was laboratoryconfirmation of 4 cases and clinical diagnosis of 10 cases. Rodent nests were foundbeneath the ceilings and underneath the floors of the cabins where the tourists werelodged. These nests may have sheltered the vectors of the infection, as frequentlyhappens with Ornithodoros (CDC, 1991).Occurrence in Animals: In natural foci, many wild animal species are infected,among them rodents, armadillos, opossums, weasels, tree squirrels, and bats.The Disease in Man: Epidemic relapsing fever (transmitted by lice) and endemicrelapsing fever (transmitted by ticks) have similar clinical pictures. The averageincubation period is 7 days after the tick bite, but may vary from 4 to 18 days. Thedisease is characterized by an initial pyrexia that lasts three to four days and beginsand disappears suddenly. The fever, which may reach 41°C, is accompanied bychills, profuse sweating, vertigo, cephalalgia, myalgia, and vomiting. At times, erythemas,petechiae, epistaxis, and jaundice of varying degrees of severity may beobserved. After several days without fever, the attacks of fever recur several times,lasting longer than in the first episode. The primary characteristic of the disease isthe syndrome of periodic fevers. There are generally three to seven relapses of fever,with intervals of four to seven days (Barbour, 1990). Periodic recurrences are attributedto antigenic changes or mutations in the borreliae, against which the patientcannot develop immunity. Borreliae in the first attack are antigenically differentfrom those isolated in relapses and there is no protective immunity among theseserotypes. The variable antigens are proteins on the outer membrane and their variationis the result of a new DNA arrangement (Barbour, 1990).Treatment is based on tetracyclines. Complications consist of meningitis andsome other neurological disorders, but these occur in a small percentage of patients.Endemic fever is fatal in 2% to 5% of cases.The Disease in Animals: Little is known about the natural course of the infectionand its possible clinical manifestations in wild animals. As with many otherreservoirs of infectious agents in natural foci, the hosts and borreliae are probablywell adapted to each other, and the latter likely have little or no pathogenic effecton their hosts.Borreliosis (spirochetosis) of fowl is a serious disease in geese, ducks, and chickens.It is caused by B. anserina and transmitted by Argus persicus and A. miniatus.The bovine infection in South Africa produced by B. theileri and transmitted byMargaropus decoloratus and Rhipicephalus evertsi causes a benign disease. Theseborrelioses affect only animals and are not transmitted to man.