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

BRUCELLOSIS 47ceptible animals accumulates—either heifers from the same herd or newly introducedanimals—a second outbreak can occur. In large herds, there are alwaysenough susceptible animals to maintain the infection, and abortions continue.Trading and movement of animals also help maintain active infection.SWINE: The main etiologic agent of brucellosis in swine is B. suis. In LatinAmerica, only biovar 1 infection has been confirmed, while in the United States both1 and 3 have been involved. Biovar 2 is found only in Europe. Infection by biovars1 and 3 is spread directly or indirectly from pig to pig. In contrast, biovar 2 (orDanish biovar) is transmitted to pigs when they ingest European hares (Lepuseuropaeus). Pigs can also be infected by B. abortus, although it is less pathogenicfor pigs and apparently not transmitted from one animal to another; the infection isgenerally asymptomatic, with the affected organisms limited to the lymph nodes ofthe head and neck.When brucellosis is introduced into a previously healthy herd, the symptoms arethose of acute disease: abortions, infertility, birth of weak piglets, orchitis, epididymitis,and arthritis. In small herds, the infection tends to die out or decrease inseverity because of a lack of susceptible animals owing to the normal sale of somepigs and to the spontaneous recovery of others. In large herds, the infection is persistentand transmitted from one generation to the next.Early abortions, which occur when the female is infected during coitus, generallygo unnoticed under free-range conditions. The aborted fetuses are eaten by the pigs,and the only abnormality that may be noted by the owner is the sows’ repeatedestrus. Abortions occur in the second half of gestation when the females are infectedafter one or two months of pregnancy. Affected sows rarely have a second abortion,and females infected before sexual maturity rarely abort.Infection is usually temporary in suckling pigs. However, a few may retain theinfection and become carriers. It rarely results in recognizable clinical symptoms.Occasionally, arthritis is observed, but transient bacteremia and low agglutinationtiters may be found.In infected pigs, abscesses of different sizes frequently occur in organs and tissues.Spondylitis is often found.Infection of the genital organs lasts for a shorter period of time in the female thanin the male. In the latter it may last for the life of the animal.GOATS: The main etiologic agent of brucellosis in goats is B. melitensis with itsthree biovars. All types of goats are susceptible to infection by B. melitensis.Infection by B. suis and B. abortus has occasionally been found.The symptomatology is similar to that observed in other species of animals and themain symptom is abortion, which occurs most frequently in the third or fourth monthof pregnancy. In natural infections occurring in the field, other symptoms, such asarthritis, mastitis, spondylitis, and orchitis, are rarely found. These symptoms can beseen when the animals are inoculated experimentally with large doses of the agent.Sexually mature female goats that are not pregnant are susceptible and suffer from achronic infection that may have no clinical symptoms, but that represents a risk forthe other animals in the flock. Infection of the mammary gland is common (Alton,1985). In chronically infected flocks, the signs of the disease are generally not veryapparent. Gross pathological lesions are also not usually evident, though thepathogen can frequently be isolated from a large number of tissues and organs.