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

278 BACTERIOSESthe tick Dermacentor andersoni, which during outbreaks is found in great numbersat the base of the sheep’s ears and on the neck. Sick animals separate themselvesfrom the flock and manifest fever, rigid gait, diarrhea, frequent urination, and respiratorydifficulty. Most deaths occur among young animals. Pregnant ewes mayabort. Reactions to serologic tests indicate that many animals have an inapparentinfection. Sheep can be classified in group 2 based on their susceptibility to theinfection. Autopsy reveals infarcts of the regional lymph nodes, mainly those of thehead and neck, as well as pneumonic foci. In this species, tularemia is a seasonaldisease, coinciding with tick infestations.The disease has been confirmed on occasion in horses, with symptoms thatinclude lack of coordination, fever, and depression. The animals were parasitized bya large number of ticks. Infected young swine can manifest fever, dyspnea, anddepression. Cattle seem to be resistant (Rohrbach, 1988).Cats can become infected and fall ill when hunting rodents in endemic areas or byconsuming dead lagomorphs. Cats can, in turn, transmit the infection to man. In acase that occurred in Georgia (USA), a young man who contracted ulceroglandulartularemia had three Siamese cats that had fallen ill two weeks earlier. The cats hadfever, anorexia, and apathy; the veterinarian prescribed streptomycin and penicillin.The animals were cared for by their owner, who developed a necrotic ulcerous lesionthat started with a wound on his finger, although he did not recall having beenscratched or bitten. The three cats died despite treatment. On autopsy, necrotic fociwere found in the liver and spleen that contained coccobacilli positive for F. tularensiswith immunofluorescence.Another case was described in New Mexico (USA). The patient found his catunder the bed eating a dead wild rabbit. He tried to remove the cat and was bitten;four days later he fell ill with tularemia. The cat fell ill one day earlier, with apathy,anorexia, and fever, but no other symptoms. The veterinarian did not prescribe anytreatment and the animal was found to be healthy when examined a week later.Serum agglutination yielded a titer of 1/160. The owner also recovered, after beingtreated with streptomycin (CDC, 1982). In Oklahoma (USA), a state consideredendemic, a case of acute tularemia in three cats was diagnosed clinically and thenconfirmed by culture and immunofluorescence. The three animals showed signs ofdepression, lethargy, ulcerated tongue and palate, moderate lymphadenomegaly,hepatosplenomegaly, and panleukopenia, with a severe toxic change in the neutrophils.Upon necropsy, multiple necrotic foci were found in the lymph nodes, liver,and spleen, as well as severe enterocolitis. The diagnosis was confirmed byimmunofluorescence and culture (Baldwin et al., 1991). Although tularemia is rarein cats, it should be kept in mind in enzootic areas. Since 1928, only 51 human caseshave been described that involve exposure to infected cats (Capellan andFong, 1993).Source of Infection and Mode of Transmission (Figure 19): In natural foci, theinfection circulates among wild vertebrates, independently of man and domestic animals.Ticks are biological vectors of F. tularensis; not only do they transmit the etiologicagent from donor animals to other animals, they also constitute an importantinterepizootic reservoir. They are also responsible for transtadial and transovarialtransmission of the bacteria. Each enzootic region has one or more species of vertebrateanimals and of ticks that play the primary roles of transmitting and maintain-