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

280 BACTERIOSESthe disease can be contracted through the respiratory system by inhaling aerosolscontaminated in the laboratory or dust from fodder, grain, or wool contaminatedwith rodent excreta.Some cases of human infection by cat scratches or bites have been described. It isassumed that these animals had recently hunted and captured sick rodents or hadeaten dead lagomorphs. Another case occurred in a person exposed to a cat with anulcer (CDC, 1982). The disease was also contracted by a Canadian zoo veterinarianwho was bitten on the finger when treating a sick primate (Sanguinus nigricollis). Inthis zoo, four primates in adjacent cages died from tularemia, possibly transmitted byfleas from squirrels that often came near the cages. F. tularensis was isolated fromone of the squirrels. The primate responsible for infecting the veterinarian had sialorrhea,ocular and nasal discharges, and ulcers on the tongue (Nayar et al., 1979).The highest incidence of cases occurs in the summer, when ticks are most active.Hunters are an especially vulnerable group, and the number of human casesincreases in hunting season.Role of Animals in the Epidemiology of the Disease: Human-to-human transmissionhas not been confirmed. Tularemia is a zoonosis that is transmitted to man(an accidental host) through contact with wild or domestic animals (of the latter,usually sheep), by a contaminated environment, or by such vectors as ticks, horseflies,and mosquitoes.Diagnosis: In man, clinical diagnosis is based on the symptomatology and priorcontact with a likely source of infection. Laboratory confirmation is based on: (a)isolation of the etiologic agent from the patient’s local lesion, lymph nodes, andsputum by means of direct culture or inoculation into laboratory animals; (b) theimmunofluorescence test on exudates, sputum, and other contaminated materials;(c) the skin test with bacterial allergen, which gives delayed hypersensitivity reactions(these reagents can give a diagnosis during the first week of illness); and (d)serologic tests, such as tube agglutination or microagglutination (Snyder, 1980;Sato et al., 1990). An enzyme-linked immunosorbent assay with sonicated antigenhas been perfected (Viljanen et al., 1983). This test has the advantage of permittingan early diagnosis, which is important for treatment; it can also detect IgM, IgA, orIgG antibodies. However, the microagglutination test is used more often due to itssimplicity and reliability; other tests are used only in case of doubt (Syrjälä et al.,1986). In the agglutination test, a four-fold increase in titer is significant.Antibodies appear in the second week of illness and may persist for years. Crossagglutination with Brucella antigen can occur, but at a lower level than with thehomologous antigen. Absorption of the patient’s serum with Brucella antigenremoves all doubt.In sheep, laboratory confirmation is obtained by isolating the causal agent or byserologic tests.Due to the risk to laboratory personnel, methods to isolate the causal agent shouldonly be used at reference laboratories that have the required safety measures.Control: To prevent the disease in man, general and individual protective measuresmay be taken. General measures include reducing the source of infection, controllingvectors, changing the environment, and educating the public. Except for thelast one, these control measures are costly and difficult to apply. In the former Soviet