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

BRUCELLOSIS 61resistant to brucellosis, so that eradication of the disease may then begin. It is estimatedthat 7 to 10 years of systematic vaccination are necessary to achieve thisobjective.In regions or countries with a low prevalence of the disease, an eradication programcan be carried out by repeated serologic diagnostic tests applied to the entireherd, and elimination of reactors until all foci of infection have disappeared. Thisprocedure can be used alone (in countries with a low prevalence) or in combinationwith the vaccination of calves. Epidemiological surveillance and control of animaltransport are very important in such programs. Countries that are close to eradicationmay suspend vaccination with strain 19 or any other vaccine.Until a few years ago, the vaccination of adult cows with strain 19 was inadvisablebecause of the prolonged resistance of antibodies that could interfere withdiagnosis. In the 1950s, several researchers proved that vaccination of adult animalswith a smaller dose could impart an immunity comparable to that of a full dose,while at the same time agglutination titers stayed lower and disappeared faster. In1975, Nicoletti (1976) began a series of studies in the US using a reduced dose inhighly infected herds; he concluded that vaccination decreases the spread of theinfection within the herd, that antibodies disappear approximately six months aftervaccination, and that less than 1% of the females remained infected by the vaccinestrain from three to six months after vaccination. Complementary tests were veryuseful in distinguishing between reactions due to infection and those due to vaccination.Other studies, done under both controlled and natural conditions, confirmedthese findings (Nicoletti et al., 1978; Alton et al., 1980; Viana et al., 1982; Alton etal., 1983). Vaccination of adult females may be considered in herds suffering acutebrucellosis characterized by abortions and rapidly spreading infections, as well as inlarge herds where chronic brucellosis has proven hard to eradicate. The recommendeddose is one to three billion cells of strain 19 Brucella administered subcutaneously.Only animals testing negative should be vaccinated and they should beindelibly marked under government supervision. At the beginning of the operation,reactors should be eliminated immediately. Vaccinated animals should be examinedserologically 6 months later, using tests such as rivanol, mercaptoethanol, and complementfixation, and those that have become infected should be slaughtered. Usingperiodic serologic examination, it is estimated that a problem herd can be free ofinfection in 18 to 24 months (Barton and Lomme, 1980).The control of swine brucellosis consists of identifying and certifying brucellosisfreeherds. If infection is diagnosed in an establishment where pigs are raised formarket, it is advisable to send the entire herd to the abattoir and reestablish it withanimals from a brucellosis-free herd. If the infected pigs are valuable for breedingor research, suckling pigs should be weaned at 4 weeks and raised in facilities separatefrom the main herd. Periodic serologic tests (such as rose bengal) are recommendedto eliminate any reactor. Finally, when no brucellosis is found in the newherd and it is well established, the original herd should be sent to slaughter. Thereare no effective vaccines for swine.Control of the infection caused by B. melitensis in goats and sheep is basedmainly on vaccination. The preferred vaccine is B. melitensis Rev. 1, which isadministered to 3- to 6-month-old females. Adult females can receive a smaller dose(20,000 times fewer bacterial cells than in the dose for young females) of the samevaccine (Alton et al., 1972).