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

BRUCELLOSIS 51In arctic and subarctic regions, there have been confirmed cases that resulted fromeating bone marrow or raw meat from reindeer or caribou infected with B. suis biovar4. Brucellae are resistant to pickling and smoke curing, therefore some meatproducts thus prepared could possibly cause human infection; however, this mode oftransmission has never been verified.It is also possible for raw vegetables and water contaminated with the excreta ofinfected animals to serve as sources of infection.Transmission by contact predominates in areas where bovine and porcine brucellosisare enzootic. Human brucellosis is, for the most part, an occupational diseaseof stockyard and slaughterhouse workers, butchers, and veterinarians. The infectionis usually contracted by handling fetuses and afterbirth, or by contact with vaginalsecretions, excreta, and carcasses of infected animals. The microorganism entersthrough skin abrasions as well as through the conjunctiva by way of the hands. Inslaughterhouses, prevalence of the disease is higher among recently employed staff.The practice in some companies of employing workers with negative serology ismisguided, since an individual who is asymptomatic but has a positive serology isless likely to become sick.In areas where goat and sheep brucellosis is enzootic, transmission by contact alsooccurs when shepherds handle newborn animals or fetuses. In some countries withhard winters, goats share the beds of goatherds and their families for protectionagainst the cold, which results in infection of the whole family (Elberg, 1981).Airborne transmission has been proved by experimentation and research. In laboratories,centrifugation of brucellosis suspensions poses a special risk when done incentrifuges that are not hermetically sealed. An epidemic outbreak of 45 casesoccurred among students at Michigan State University (USA) in 1938–1939. The 45students were attending classes on the second and third floors of a building thathoused a brucellosis research laboratory in the basement. In the ensuing investigation,it was shown that the only possible means of transmission was by aerosol particles.Subsequent epidemiological studies have supplied proof that airborne transmissionin meat lockers and slaughterhouses plays an important role, and perhaps ismore frequent than transmission by direct contact with infected tissue. When air inthe killing area is allowed to disperse, it leads to high rates of infection among workersin adjoining areas. The minimum infective dose for man by way of the respiratorypassages seems to be small. When the killing area is completely separate, ormaintained at a negative air pressure, the risk to surrounding areas is reduced(Kaufmann et al., 1980; Buchanan et al., 1974).Some cases of possible human-to-human transmission of brucellosis have beendescribed. One of them occurred in Kuwait due to transmission of B. melitensis to a30-day-old girl through her mother’s milk. The mother had experienced fever, discomfort,and arthralgia for at least two weeks prior to the child’s becoming sick. B.melitensis biovar 1 was repeatedly isolated from the blood of both mother and child(Lubani et al., 1988). In a hospital laboratory in the US, eight microbiologists wereexposed to accidental dispersion of a clinical specimen in aerosol and B. melitensisbiovar 3 was isolated from five of them. The spouse of one of the patients becameill six months after her husband had been admitted to the hospital and B. melitensisof the same biovar was isolated from her blood; it is suspected that the infection wassexually transmitted (Ruben et al., 1991). A probable case of transmission duringchildbirth occurred in Israel. The mother had a fever on the first day postpartum and