Bovine brucellosis

Pashu Sandesh, 08 October 2018

DR. Rakesh Kumar Gupta

Brucellosis is a highly contagious bacterial disease worldwide which can also be transmitted to humans. Bovine brucellosis is caused by the Brucella abortus which is gram-negative, non-mobile, non-spore-forming, rod-shaped bacteria and characterised by abortion during late gestation in bovines. Farmers, vets, abattoir workers and other people handling livestock are in a high-risk group for contracting brucellosis. In India, about 80% of people live within close contact to domestic livestock animals or wildlife, a critical risk factor for zoonotic disease transmission such as brucellosis. The infected cow also periodically secretes bacteria in her milk during the entire lactation period, and in some cows this may persist for the duration of its life. Cattle can also get infection by inhaling airborne bacteria when an infected cow urinates or through wounds or the mucous membrane of the eye. 

Sources and transmission

• Cattle normally become infected by eating contaminated fodder, drinking contaminated water, or licking the afterbirth or vaginal mucous secretion of an infected cow that has aborted or calved.
• Aborted foetuses, foetal membranes and uterine secretions are the most important sources of infection. The disease can also be transmitted in utero and via infected milk. 
• Once born, the calf continues the chain of transmission and infection and continues spreading the disease through successive calving.
• Artificial insemination with Brucella-infected semen continues the chain of disease when the semen is deposited in the uterus during AI. However, sexual transmission from infected bulls to susceptible cows or heifers is apparently very rare. 
• Lush vegetation in wet and muddy calving camps plays an important role in the transmission and spread of brucellosis.
• Consumption of contaminated unpasteurised raw milk and dairy products and the half-cooked meat of infected animals.
• Direct contact with the excretions and secretions of infected animals can also cause brucellosis.

Impact on health and economy

The worldwide economic losses due to brucellosis are not only in terms of animal production but also in terms of human health.  It causes significant economic losses including abortion, loss in milk production, reduced fertility, poor weight gain, lost draught power, low fertility rates, and cost of replacement of animals. The losses in livestock productivity compromise food security and lead to shifts in the cognitive competency of the working generation, influence the propagation of gender inequality, and cause profound emotional suffering in farmers whose herds are affected. The occurrence of the disease is usually high in organised farms (50%) compared to the marginal herds (10%) and this primarily associated with intensive farming practices in large organised animal farms. It is estimated that the infection causes a 20% to 25% loss in milk production as a result of interrupted lactation due to abortion and delayed conception. 

Symptoms 

• Abortion storm at 5-9 months of pregnancy.
• Still births.
• Some cows will give birth to weak calves.
• Drop in milk production.
• Infertility.
• Weight loss.
• Retained placenta.
• Enlarged arthritic joints.
• Orchitis (inflammation of the testicles) in bulls.

Diagnosis

Brucellosis in cows is very difficult to diagnose. The best indicators are abortion or the birth of weak calves and a drop in milk production.The microorganism can be identified by direct culture of the microorganism from infected tissues in selective medium, or direct stained smears. Diagnosis is made serologically by tests as standard tube agglutination test (STAT) and milk ring test (suspect animal serum or milk is tested for the presence of specific anti-brucella antibodies).

Treatment

There is no specific treatment in confirmed infected animals.The disease is managed in human.

Prevention and control

• Brucellosis is prevented through vaccination. Heifer calves should be vaccinated with S19 vaccine between 4-8 months of age (Calf hood vaccination scheme).
• To completely eradicate brucellosis from a herd, there is need to test the animals and eliminate those that test positive.
• Any new bull that is meant for serving cows should be tested for brucellosis.
• Any new animal introduced into the herd should be from a brucellosis free herd and should be isolated for 30 days before joining the herd.
• Humans should not consume undercooked meat or unpasteurised dairy products like milk and ice cream.
• People who handle animal tissues should protect themselves by using rubber gloves, gowns or aprons.
• There is no vaccine for humans, and high rates of initial treatment failure and relapse rates make clinical management particularly difficult. Hence, prevention of human brucellosis depends on management of the animal reservoir.

DR. Rakesh Kumar Gupta

PG Scholar (Department of Veterinary Pathology)

College of Veterinary Science and Animal Husbandry

NDUAT, Faizabad, Uttarpradesh-224229

Corresponding author:rakesh.jaiswal50@gmail.com

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