This is a sub-acute or chronic infection manifested by abortion, sterility, high piglet mortality and orchitis in pigs. Br. suis causes brucellosis among pigs. It is morphologically similar to other brucellae but is serologically distinct. Br. suis is more resistant and can live for up to 6 weeks outside the animal body. The organism is also pathogenic to man, cattle and horses. Many infected pigs may not show any clinical sign.
Transmission: The disease is often introduced by an infected boar in a herd. The major routes of transmission are ingestion and coitus, and sometimes via respiratory tract and conjunctiva. Nursing pigs become infected as a result of ingesting contaminated milk from diseased sows. The organism can also enter the body through the intact skin.
Symptoms: The clinical signs vary and are often absent even though the infection is present in the herd. Lameness, in coordination of gait and posterior paralysis are seen when the infection of lower spine takes place. The incidence of abortion is low, but small litters, stillbirths and weak piglets are common. Infertility may result from infection of genital tract. Abortion may occur early or in late pregnancy. In young pigs swollen joints and lameness is common. Unlike cattle , the infected sows may eliminate the infection but are susceptible to reinfection.
Lesions: Focal abscess formation is common in affected organs. In boar, the abscesses are found in the testes or seminal vesicles. In the sow catarrhal metritis and abscesses are common in the bones of spine, spleen, liver, kidneys, lymphnodes and occasionally in joint capsules.
Diagnosis: Due to chronic nature and variability of symptoms of the disease, it is difficult to diagnose the disease on symptoms alone. Suspicion is based on symptoms if they are associated with undulant fever (Mediterranean fever) [e.g. intermittent or recurring fever] in human contacts. The confirmatory diagnosis can be arrived at by laboratory investigation. Seroagglutination test and isolation of organisms from infected tissues are confirmatory for the diagnosis.
Treatment: No effective treatment is available.
Control: No suitable vaccine is available in India. The vaccine currently used is the combination of attenuated Br. abortus organisms and a lipopolysaccharide prepared from heat-killed Br. abortus. The control depends on good sanitation and good herd management. Removal of infected animals from the herd followed by the serological testing of animals at 30 day intervals is recommended. The rectors are separated from the herd. Vaccination is not practiced in India.