Brucellosis Other names: Bang’s disease, contagious abortion; undulant fever (humans); may be a cause of suppurative bursitis (fistulous withers/poll evil) in horses Cause: Brucella abortus (also caused by Brucella melitensis in some countries, especially in goats; B. melitensis is not present in the US) Species: cattle, alpacas, other ruminants and camelids, horses, humans Note: The brucellosis of dogs is caused by a different organism, and is unlikely to cause illness in humans or livestock. The brucellosis of swine is also caused by a different organism; it causes illness in humans and dogs, but typically not other livestock species. Signs: Cattle – Abortion, usually at ~5-6 months gestation (cow typically only aborts once after exposure; subsequent pregnancies normal) and temporary infertility; usually many cows in herd affected at a time (~40-80% of pregnant cows). In some cases the calves survive pregnancy but are weak and die soon after birth. Also can cause reduced milk yield and retained placentas, which leads to metritis. Hygromas, especially of the carpal joints, may develop in animals with chronic infections. Infected bulls typically asymptomatic, but sometimes develop testicular abscesses, orchitis, epididymitis, and/or seminal vesiculitis; may be either unilateral or bilateral. Horses – Most common sign is fistulous withers or poll evil (The supraspinous or supra-atlantal bursa distends with a clear, straw-colored, viscous exudate. Secondary infection with purulent discharge and fistula formation occurs when bursa wall ruptures. If left untreated, the ligament and the dorsal vertebral spines are also affected, and may become necrotic). Lameness due to infection of the joints and late abortions occur rarely. Humans – recurrent (undulant) fever, sweats; prolonged or recurrent malaise, anorexia, headache, pain in muscles, joints, and/or back; chronic fatigue, arthritis, orchitis, endocarditis, neurological signs (5% of cases), depression, swelling of liver and spleen. Death occurs in up to 2% of cases. Often mistaken for malaria in areas where both diseases are endemic. Transmission: Cattle – Organisms are shed in milk and secretions from non-lactating udders (typically for life), uterine discharges (typically resolves after abortion/parturition, but not always), and are present in the aborted fetus, placenta, and other fetal membranes. Infection occurs when an uninfected animal ingests feed or water contaminated with bacteria or licks the genitals of infected herdmates. Venereal transmission is rare, but can occur. Transmission can also occur via artificial insemination with infected semen. Horses – History of exposure to infected cattle or grazing in a pasture previously occupied by infected cattle. Humans – Consuming unpasteurized/raw dairy products most common mode of transmission; inhaling aerosolized bacteria or bacterial contamination of wounds or mucous membranes (risk of this mode of transmission is greatest for slaughterhouse workers, hunters, farmers, and veterinarians). Direct transmission between humans is very rare, but can occur via breast milk, sexual intercourse, tissue transplantation or blood transfusions. **Accidental exposure to brucellosis vaccine via needle stick or by getting vaccine splashed in an eye or wound can lead to symptoms of brucellosis. ** In ideal conditions (cool, out of direct sunlight) the bacteria can remain infective in the environment for over 2 months. Diagnosis: Requires laboratory testing. Cattle – Many options available: culturing samples from the placenta, or from the stomach or lungs of the aborted fetus; milk or serum ELISA tests; serum agglutination test (standard); complement fixation, rivanol precipitation, and acidified antigen procedures. Brucella milk ring test (BRT), the brucellosis card (or rose bengal) test and plate test are useful for screening but due to high numbers of false positives, further testing is required for a definitive diagnosis. Horses – Serum agglutination titers or isolation of B. abortus from bursa fluid. Humans – Isolation of bacteria from blood, bone marrow, or other body fluids. Serum antibody test. Treatment: Cattle – None. Cull infected animals and retest herdmates at regular intervals until two or three successive tests are all negative. Horses – Complete surgical removal of the infected bursa. Earlier treatment results in a better prognosis; treatment of chronic cases often cost-prohibitive. Sodium iodide therapy is usually unhelpful. Humans – Antibiotics (usually doxycyxline or rifampin) for a minimum of 6-8 weeks. Recovery can take up to several months. Prevention: Cattle – Protect brucellosis-free herds!! Any replacement animals from outside the herd should be vaccinated calves or adults that originate from brucellosis-free areas or herds and be seronegative. Replacements should be isolated for ~30 days and retested before being added to the herd. Vaccination, especially of calves, with B. abortus Strain RB51. Vaccination increases resistance but some vaccinated cattle may still become infected. For this reason, avoid vaccination with B. abortus Strain 19 if possible, as this vaccine may cause persistent antibodies that confuse diagnostic tests (not an issue with B. abortus Strain RB51 vaccine). Strain 19 may also cause orchitis or hygromas. Practice good environmental management, including cleaning and disinfecting all cattle premises which may be contaminated with B. abortus and burning/burying all contaminated fetuses, fetal membranes, etc. Horses – Do not graze with cattle or on pastures previously used to graze cattle. Vaccination ineffective. Humans – Do not consume raw/unpasteurized dairy products! Wear PPE when handling animal tissues or infected animals (rubber gloves, goggles, gowns or aprons). **If accidental exposure to the vaccine occurs, follow CDC guidelines here https://www.cdc.gov/brucellosis/veterinarians/rb51-reduce-risk.html ** Note: This is a reportable disease! Brucellosis has been eradicated from cattle herds in the USA, but brucellosis is endemic in some nondomesticated bison and elk herds in the USA. While transmission of Brucellosis from wild ruminants to domestic cattle is rare, it has occurred in the area around Yellowstone Park. Brucellosis remains endemic in cattle in most other countries. Sources: Blackwell's Five-Minute Veterinary Consult: Canine and Feline, Merck Veterinary Manual, horsedvm.com (image of horse), CDC, Purdue University, African Veterinary Information Portal (images of fetus and higromas), Infonet-Biovision (image of retained placenta)
