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

182 BACTERIOSESvae and nymphs found on these small wild mammals, as well as their high rate ofinfection by B. burgdorferi. The adult tick has a predilection for deer (Odocoileusvirginianus) in the foci along the eastern coast of the US. This cycle is repeated inother areas of the world, with different animal species whose blood feeds the stagesof various tick species. The biotope where these cycles develop is wooded areas orareas of dense vegetation that retain the moisture that is favorable to ticks (Madiganand Tleitler, 1988).Adult ticks are abundant in spring and fall; nymphs, in spring and early summer;and larvae, in late summer and early fall. All stages in the development of ticks areparasitic in humans, but the nymph stage is primarily responsible for the transmissionof B. burgdorferi to man (Anderson, 1989; Steere, 1990).Role of Animals in the Epidemiology of the Disease: On the basis of currentinformation, it can be asserted that wild animals are primarily responsible for maintainingthe infection in natural foci. Dogs and birds may spread ticks and increaseendemic areas. Man is an accidental host.Diagnosis: Until recently, diagnosis was based exclusively on the clinical picture,especially a history of EM, and on epidemiological information.Although now possible, isolation of the infective agent by culture is still not verypractical. In 1983, Steere et al. isolated the agent in only three patients, using a totalof 142 clinical samples taken from 56 patients. Barbour, Stoener, Kelly (BSK)medium is used for isolation and is incubated at 33°C; it is easier to isolate the agentfrom cutaneous lesions than from blood. The indirect immunofluorescence test withconjugated IgM and IgG sera was widely used. Patients with EM had elevated IgMantibody titers only between the EM phase and convalescence two to three weekslater. Patients with late manifestations of the disease (arthritis, cardiac, or neurologicalanomalies) had elevated IgG antibody titers (Steere et al., 1983). It was latershown that indirect ELISA was more sensitive and specific than immunofluorescence(Steere, 1990). In serological tests, there may be cross-reactions with otherspirochetes. Given that all serological tests have limited specificity and sensibility,their use is not recommended for asymptomatic individuals.Diagnosis in animals is similar to that in humans. Early treatment with antibioticsshortens the duration of EM and may prevent or lessen late manifestations of the disease;it may also have an effect on reducing the level of antibodies.Control: The only methods of prevention consist of avoiding endemic areas andtick bites. Persons entering natural foci should use protective footwear and clothing,though this is not always possible. Insect repellents may provide some protection. Itis advisable to check the body frequently and remove attached ticks by pulling gentlywith tweezers pressed as closely as possible to the skin. It is recommended thatgloves be used during this operation.Dogs should be checked frequently and ticks should be removed as carefully aswith humans. The use of tickicides in powder form or collars is a good preventivemeasure. There is currently an inactivated commercial vaccine available for dogs. Itis administered in two doses at three week intervals and annually thereafter (Chu etal., 1992). Widespread and indiscriminate use of this vaccine is a matter of discussion,although it is recognized that the bacterin has no side effects (Kazmierczak andSorhage, 1993).