Brucellosis is a bacterial infection that causes reproductive failure in buffalo, most notably late-term abortions, stillbirths, and sharp drops in milk production. It is caused by Brucella abortus, a pathogen that targets the reproductive tract and can spread to humans through unpasteurized dairy products and direct contact with infected animals. Globally, about 14% of buffalo test positive for the disease, making it one of the most economically significant livestock infections in regions where buffalo are raised.
How Brucella Infects Buffalo
Brucella bacteria enter the body through the mouth, nose, or eyes, typically after a buffalo ingests contaminated feed or water. Within minutes of contacting the lining of the mouth or digestive tract, the bacteria trigger the host cells to pull them inside, essentially hijacking the cell’s own machinery to gain entry. Once inside, fewer than 10% of the bacteria are actually destroyed by immune cells. The rest survive by hiding within specialized compartments inside the cell, blocking the normal process that would break them down.
This ability to live and multiply inside immune cells is what makes brucellosis so persistent. The bacteria suppress the immune system in multiple ways: they prevent infected cells from self-destructing (a normal defense mechanism), they block immune cells from maturing and alerting the rest of the immune system, and they redirect their transport compartments away from the cell’s digestive machinery. From there, the bacteria travel through the bloodstream to their preferred tissues, particularly the uterus in pregnant females, the udder, and the reproductive organs of bulls.
Symptoms in Buffalo
The hallmark sign is abortion during the last trimester of pregnancy. An infected buffalo may also deliver stillborn calves or calves too weak to survive. Retained placenta, where the afterbirth fails to pass normally, is common after these abortions. Even when a pregnant buffalo doesn’t abort, visible swelling of the mammary gland down to the navel and vaginal bleeding can occur.
Milk production drops significantly. Studies estimate around a 10% loss of total milk output over the full lactation period in infected animals. Perhaps more damaging in the long run, brucellosis extends the time between pregnancies. In buffalo, an abortion-related delay adds roughly 190 extra days to the calving interval, meaning nearly an additional six months before the animal can calve again. This compounds the economic damage because the buffalo is neither producing milk at full capacity nor producing offspring during that gap.
In bulls, the infection causes inflammation and swelling of the testicles and surrounding structures. Severe cases can lead to abscesses, and the resulting damage often causes permanent infertility. Fever accompanies the disease in both sexes.
How It Spreads Between Animals
The primary source of environmental contamination is an abortion event. The aborted fetus, placental membranes, and uterine fluids contain extremely high concentrations of bacteria. Other buffalo become infected by sniffing, licking, or stepping through this material, then ingesting the bacteria. Brucella organisms survive for months in the environment, especially in cold, damp conditions, persisting in soil, water, dung, and slurry.
Infected buffalo also shed bacteria in their milk and urine, creating ongoing exposure for herd mates and nursing calves. Shared water sources are one of the most important routes of spread between herds. Infected bulls can transmit the disease through natural mating or artificial insemination, serving as lifelong carriers once infected. Inhalation of contaminated dust or aerosols in confined spaces is another route, though less common than ingestion.
Risk to Humans
Brucellosis is a zoonotic disease, meaning it passes from animals to people. The infectious dose is very low, so even brief exposure can be enough. The three main routes of human infection are consuming unpasteurized milk or dairy products (fresh cheese, yogurt, or raw liver from infected animals), direct skin contact with abortion materials or reproductive fluids, and inhaling contaminated particles.
In people, brucellosis causes undulant fever (a wave-like pattern of high and low temperatures), general fatigue, joint pain, and arthritis. It is considered an occupational hazard for farmers, veterinarians, slaughterhouse workers, and lab personnel. Pasteurization reliably kills the bacteria in milk, making this the single most effective step for protecting consumers.
Where It Is Most Common
Brucellosis in buffalo is concentrated in South Asia, Sub-Saharan Africa, and parts of the Middle East. A global meta-analysis found an overall seroprevalence of 9.7% in water buffalo worldwide. India, which has the world’s largest buffalo population, reports prevalence between 12% and 14.2% depending on the study, with herd-level rates ranging from roughly 13% to 35% in some regions of India and Pakistan. These numbers translate to enormous economic losses. In India alone, brucellosis-related losses in livestock are estimated at $3.4 billion annually, driven by abortions, reduced milk, extended calving intervals, and infertility. In Sub-Saharan Africa, where both water buffalo and African buffalo (a wild species) are affected, prevalence in domestic ruminants ranges from 8% to 46%.
How It Is Diagnosed
Because brucellosis symptoms overlap with other reproductive diseases, diagnosis relies on blood tests that detect antibodies against Brucella. The Rose Bengal Test is the most widely used screening tool. It is fast, inexpensive, and highly accurate, with an estimated sensitivity of about 99% and specificity above 99%. This means it catches nearly all infected animals and rarely flags healthy ones as positive.
A second test called the complement fixation test offers similarly high specificity and is often used to confirm positive results. ELISA-based tests are also available and work well in large-scale surveillance programs, though they are slightly less specific (around 87%) than the Rose Bengal or complement fixation tests. Bacterial culture from tissue samples (spleen, lymph nodes) remains the definitive confirmation, but it is slow, expensive, and requires specialized laboratory facilities.
Vaccination and Control
Two vaccines are used globally to prevent brucellosis in cattle and buffalo. The S19 vaccine, a live weakened strain developed decades ago, is the reference standard. It produces a strong immune response and is administered to young female calves, typically around five months of age. Its main drawback is that vaccinated animals can test positive on standard blood tests, complicating disease surveillance because it becomes difficult to distinguish vaccinated animals from naturally infected ones.
The RB51 vaccine was developed partly to solve this problem. Animals vaccinated with RB51 do not produce antibodies detectable by the Rose Bengal or complement fixation tests, making it easier to identify truly infected animals in a vaccinated herd. RB51 has become the official vaccine in several countries for cattle. However, studies in water buffalo have raised questions about its effectiveness in this species. In one controlled trial, buffalo given RB51 at three times the standard cattle dose, with a booster, still showed Brucella bacteria in the spleen and lymph nodes after being exposed to a virulent strain. The immune response in buffalo vaccinated with S19 was stronger by comparison.
Beyond vaccination, control programs rely on test-and-slaughter strategies (identifying and removing infected animals from herds), quarantine of new animals before introduction to a herd, proper disposal of abortion materials, and hygiene at calving areas. In many developing countries where buffalo farming is concentrated, limited veterinary infrastructure makes these measures difficult to implement consistently, which is why prevalence remains stubbornly high.