Background

Brucellosis is an infectious disease of animals having zoonotic potential. The disease got special attention because it can affect both the animal industry and human health. Bruce first described brucellosis in 1887 after the discovery of Brucella melitensis. Cattle, goat, sheep, pigs, horses, and dogs are responsible for human transmission of brucellosis, making a public health problem in many parts of the world. In India, brucellosis is endemic. Though Brucellosis is distributed worldwide, it is well controlled in most developed countries. It is commonly found in Asia, Africa, Middle East, South and Central America, the Mediterranean Basin, and the Caribbean. Brucella species differ in geographic distribution. B. abortus is distributed worldwide in cattle except in countries where it has been eradicated like Canada, Japan, Australia, European countries, New Zealand, Israel, and the USA. B. melitensis is commonly found in the Mediterranean and also in the Middle East, Central Asia, Africa, and India. Recently, there is an increase in human brucellosis cases due to B. melitensis, which causes brucellosis in small ruminants. A facultative Gram-negative coccobacillus or short rod shaped bacteria belonging to the family Brucellaceae, , genus Brucella cause the disease. Six different species are well known: Brucella abortus, Brucella melitensis, Brucella suis, Brucella canis, Brucella ovis, and Brucella neotomae. These species have a high preference for the host. B. abortus has a preference for cattle, B. melitensis for sheep and goats. The other species like B. suis, B. canis, B. ovis, and B. neotomae have a choice for swine, dogs, sheep, and rodents, respectively. Brucellosis is a chronic disease in cattle, sheep, goats, and pigs. Following infection, the initial phase is often not apparent. In mature animals, the disease is localized in the reproductive organs, causing placentitis leading to abortions in females and epididymitis and orchitis in the male. The diagnosis of the disease is performed by the presence of Brucella species by isolation, detection of antigen, specific antibody, or cell-mediated immune response. It is transmitted by direct contact from animals to human or by consumption of infected raw milk. Dairy workers, butchers, shepherds, abattoir workers, veterinarians, and animal husbandry personnel are at higher risk of infection. It is still an uncontrolled public health problem in developing countries. Different strategies to control brucellosis are immunization as well as stamping out of confirmed animal cases. Vaccination in female calves reduces the number of infections and helps in disease control. Vaccination is not recommended in male animals. It is because male animals secrete Brucella organinms through semen resulting it unfit for artificial insemination. In human, brucellosis is controlled by regulating infected animals. Raw or undercooked animal products and unpasteurized dairy products should be avoided.

Cause

A disease caused by a bacteria, Brucella abortus

Host Species

Cattle, buffalo, sheep, goat, pigs, dog and some wild animals

• Ingestion: The disease is transmitted by ingestion during grazing on infected pasture contaminated by discharges and fetal membranes from infected cow.
• Contact: Animals get infection when it comes in contact with aborted fetuses and infected newborn calves.
• Transmission is also possible through penetration of the intact skin and conjunctiva.
• Milking of contaminated udder may also result in disease transmission.
• Disease is transmitted to healthy animals through feeder and water troughs contaminated with infectious pathogen.
• Transmission may also occur by flies, dogs, rats, ticks, infected objects, fodder within and in between herds.
• Movement/ transportation of animal from an infected herd to a susceptible non-infected herd is a common route of transmission.
• Congenital infection may occur in calves born from infected dams but its frequency is low.
• Uterine discharges and milk: A cow's tail heavily contaminated with infected uterine discharges may be a source of infection if it comes in contact with the conjunctiva or the intact skin of other animals.
• Artificial insemination (AI): Semen from infected bull is a potential source of infection to healthy animals during Al.
• The carrier animals, recovered from brucellosis may also transmit disease intermittently through milk.

• Abortion: In highly susceptible non-vaccinated pregnant cattle, abortion occurs after the 5th month of pregnancy.
• Retention of placenta and metritis are common sequelae to abortion. Mixed infections are usually the cause of the metritis which may be acute with septicemia and death or chronic, leading to sterility.
• In vaccinated herd, abortion is much less common.
• Orchitis and epididymitis: The scrotal sac show acute & painful swelling (double in size) where testes will be of normal size.
• The seminal vesicles are enlarged that can be felt on rectal palpation.
• Affected bulls are usually sterile. Such bulls are neither recommended for natural service nor for semen collection for the purpose of Al.
• Synovitis: The joints become swollen. The hygromatous swellings of knee joints in adult whereas, arthritis of the stifle joints in young cattle are seen.

Management

• Screening and subsequent isolation of infected animals from healthy animals
• Screening of newly purchased animals for brucellosis from government recognized agencies will prevent the entry of infection to the farm.
• The newly purchased animals must be kept in quarantine. The time will usually range from 120 days to 1 year, or until all breeding animals have completed a gestation without test evidence of infection.
• If any animal found infected, they should be separated from herd or shifted to registered NGO or gaushala.
• Treatement with appropriate antibiotic therapy

Preventive measures

Vaccination is recommended to control the disease.

Type of vaccines

Inactivated oil adjuvant, alum precipitated and aluminum hydroxide gel adsorbed vaccines

Combined vaccine is also available

Vaccination schedule

First vaccination is done at 4-5 months of age followed by annually. The vaccination preferably before 2-3 weeks of monsoon season is recommended.

Dose: 3 mL I/M or S/C route or following manufacturer's instructions)

Note: Deworming is must at least 15 days before vaccination

Source/manufacturer of vaccine in India

Bio Vet. Pvt. Ltd., Karnataka

Indian Immunologicals Ltd, Hyderabad

Brilliant Bio Pharma Ltd., Hyderabad