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

LEPTOSPIROSIS 165Control: In man, control measures include: (a) personal hygiene; (b) use of protectiveclothes during farm work; (c) drainage of lowlands whenever possible; (d)rodent-proof structures; (e) food protection and correct garbage disposal; (f) controlof infection in domestic animals; (g) avoidance of swimming in streams and otherfresh watercourses that may be contaminated, and (h) chemoprophylaxis of highriskoccupational groups (sugarcane harvesters, rice-paddy workers, or soldiers).Human immunization has not been widely applied. It has been used with promisingresults in Italy, Poland, and the former Soviet Union. However, because of secondary,mainly allergic effects, its use did not spread. Tests of a vaccine made in achemically defined, protein-free medium are under way (Shenberg and Torten,1973). In China, a similar vaccine is being used on a wide scale.The use of antibiotics in prophylaxis and treatment of human leptospirosis hasyielded contradictory results. One study (Takafuji et al., 1984) showed that doxycyclineis effective in chemoprophylaxis; the same drug is probably also effective intreatment. Because leptospirosis caused many cases of disease among American soldierstraining in Panama, a double-blind field test was undertaken to determine theefficacy of doxycycline in preventing the infection. Nine hundred forty soldier volunteerswere randomly divided into two groups. One group was given an oral doseof 200 mg of doxycycline each week for three weeks, and the other group was givena placebo. After remaining in the jungle for three weeks, 20 cases of leptospirosiswere diagnosed in the placebo group (attack rate of 4.2%) and only one case wasdiagnosed in the doxycycline group (attack rate of 0.2%), i.e., the drug was 95%effective (Takafuji et al., 1984). It has been suggested (Sanford, 1984) that chemoprophylaxiswould be justified in areas where incidence is 5% or higher.Mechanization of farm work has resulted in a decrease of outbreaks, for example,among rice-paddy workers.Among domesticated animals, vaccination of pigs, cattle, and dogs is effective inpreventing the disease, but it does not protect completely against infection.Vaccinated animals may become infected without showing clinical symptoms; theymay have leptospiruria, although to a lesser degree and for a shorter time thanunvaccinated animals. A few known human cases of leptospirosis were contractedfrom vaccinated dogs. There are bacterins to protect against the pomona, hardjo, andgrippotyphosa serovars in cattle; against pomona in swine; and against canicola andicterohaemorrhagiae in dogs. Immunity is predominantly serovar-specific, and theserovar or serovars active in a focus must be known in order to correctly immunizethe animals. Females should be vaccinated before the reproductive period to protectthem during pregnancy. Young animals can be immunized after 3 or 4 months of age.Bacterins now in use require annual revaccination. For herds to which outside animalsare being introduced, it is recommended that vaccination be repeated every sixmonths. An effective measure is to combine vaccination with antibiotic treatment(Thiermann, 1984).Vaccination against hardjo is not very satisfactory, not even if the prevalent genotypehardjo-bovis is used in combined vaccines (Bolin et al., 1989b) or in monovalentvaccines (Bolin et al., 1991).It has been demonstrated that vaccination with bacterins initially stimulates theproduction of IgM antibodies, which disappear after a few months and are replacedby IgG antibodies. Vaccination generally does not interfere with diagnosis becauseof the quick disappearance of IgM antibodies, which are active in agglutination. IgG