Transmission is usually from infected animals to humans. There is no evidence of transmission of the disease from humans to humans. The routes of spread are:
Contact Infection Most commonly, infection occurs by direct contact with infected tissues, blood, urine, vaginal discharge, aborted fetuses and especially, placenta infection takes place through abraded skin, mucosa or conjunctiva (mucocutaneous route). This type of spread is largely occupational and occurs in persons involved in handling livestock and slaughterhouse workers.
Food–borne Infection Infection may take place indirectly by the ingestion of raw milk or dairy products (cheese) from infected animals. Fresh raw vegetables can also carry infection if grown on soil containing manure from infected farms. Water contaminated with the excreta of infected animals may also serve as a source of infection.
Air–borne Infection The environment of a cowshed may be heavily infected. Few people living in such an environment can possibly escape inhalation of infected dust or aerosols. Brucellae may be inhaled in aerosol form in slaughterhouses and laboratories. Hence, these infections are notified as occupational.
Incubation Period It is highly variable. It could last anywhere between one to three weeks, but may also be as long as six months or more.
Control In Animals The most rational approach towards preventing human Brucellosis, is the control and eradication of the infection from animal reservoirs which is based on a combination of the following measures:
- Tests and Slaughter :- Case finding is done in mass surveys. Skin tests are available. The complement fixation test is also recommended. Those animals infected with Brucellosis are slaughtered, with full compensation paid to farmers. This is the only satisfactory solution aimed at eradication of the disease.
- Vaccination :- The vaccine of B Abortus strain 19 is commonly used for young animals. A compulsory vaccination program for all heifers in a given community on a yearly basis can considerably reduce the rate of infection. Systematic vaccination for a period of seven to 10 years may result in the elimination of the disease. Control of the infection caused by B melitensis in goats and sheep has to be based mainly on vaccination.
- Hygienic Measures :- These include provision of a clean, sanitary environment for animals, sanitary disposal of urine and feces, veterinary care of animals and health education for all those who are occupationally involved.
- Early Diagnosis and Treatment :- In uncomplicated cases, the antibiotic of choice is tetracycline. For adults in the acute stage, the dose is 500 mg every six hours for about three weeks. In patients with skeletal or other complications, intramuscular streptomycin 1g daily, in addition to tetracycline usually achieves a cure.
- Pasteurization of Milk :- This is a useful preventive measure which will render milk and milk products safe for consumption. Boiling of milk is effective when pasteurization is not possible.
- Protective Measures :- The aim is to prevent direct contact with infected animals. Persons at risk, such at farmers, shepherds, milkmen and abattoir workers should observe high standards of personal hygiene. They should exercise care in handling and disposal of placenta, discharges and fetuses from an aborted animal. They should wear protective clothing when handling carcasses. Exposed areas of the skin should be washed and soiled clothing renewed.
- Vaccination :- Human live vaccine of the B abortus strain 19–BA is available.
Brucellosis would disappear if it were eradicated from animals. The national and international center for Brucellosis is located at FAO/WHO Brucella Center, Indian Veterinary Research Institute, Izatnagar, Uttar Pradesh.