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

62 BACTERIOSESAs goats are generally raised in marginal areas where socioeconomic conditionsare very poor, it is difficult to carry out eradication programs. In these areas, reinfectionoccurs constantly, flocks are often nomadic, and animal-raising practicesmake sanitary control difficult. Another important factor is that diagnostic methodsfor small ruminants are deficient. Experience with Rev. 1 vaccine in Italy, Turkey,Iran, Mongolia, Peru, and the Caucasian Republics of the former Soviet Union hasproven it to be an excellent means of control. In Mongolia, 6 million animals werevaccinated between 1974 and 1977; as a result, the prevalence of from 3 to 4 per10,000 animals was reduced by half or more, as was the incidence of human cases.In Malta, after seven years of vaccination of small ruminants with Rev. 1, the numberof human cases per year fell from 260 to 29. The same thing happened in Italy,although there are no reference data (Alton, 1987). However, the control procedureof diagnosing and sacrificing reactor animals has produced satisfactory results inareas of low prevalence.Rev. 1 vaccine has some limitations, such as residual virulence, the possibility ofabortions when pregnant females are vaccinated, and the limited stability of the vaccine,which necessitates constant monitoring. These disadvantages should not eliminateuse of the vaccine as the basis for control of brucellosis in small ruminants, atleast until there is a better vaccine. A Chinese strain of B. suis biovar 1, known as B.suis strain 2, is considered reliable. This strain was isolated from a swine fetus andits virulence was attenuated by continuous and repeated replications in culturemedia over years, reaching an attenuation that remains stable. Vaccine B. suis strain2 has been used in China with very good results for more than 20 years, not only insmall ruminants but in cattle and swine as well. Its use began in the semiarid regionsof northern China, where vaccination operations were very difficult due to the lackof fetters and traps, and thus the vaccine was administered in the drinking water(Xin, 1986). Various research institutes have conducted tests on conjunctive, oral(with syringes of the type used to administer antiparasitic agents), and subcutaneousvaccines in small ruminants; it has generally been possible to confirm the resultsobtained in China. Elimination of the vaccine strain in milk or through the vaginahas not been confirmed and studies continue on this vaccine.Ram epididymitis can be successfully controlled by a combination of the followingmeasures: elimination of rams with clinically recognizable lesions, eliminationof clinically normal rams positive to the gel diffusion or the complement fixationtest, and separation of young rams (those not yet used for breeding) from adultmales. In some countries, such as New Zealand and the US, a bacterin prepared fromB. ovis and adjuvants is used. Animals are vaccinated when weaned, revaccinatedone or two months later and annually thereafter. This vaccine produces antibodiesagainst B. ovis but not B. abortus. The B. melitensis Rev. 1 vaccine is effectiveagainst epididymitis, but also produces B. abortus antibodies, which could be confusedwith infection by B. melitensis. The B. suis strain 2 vaccine does not provideprotection against ram epididymitis.Brucellosis caused by B. canis in dog kennels can be controlled by repeated serologictests and blood cultures, followed by elimination of reactor animals. No vaccinesare available yet. Veterinary clinics should advise owners of the risk of keepinga dog with brucellosis and should recommend that the dog be put to sleep.