Brucellosis, a zoonotic disease primarily affecting domestic animals like cattle, goat, sheep, buffaloes, pigs and other animals and transmitted to humans through close contact with infected animals and their products.Brucella is a non-motile bacteria that grow in the presence of oxygen. These are strict parasites of animals and capable of causing human infections.Brucella melitensis from goat milk, Brucella abortus from contagious abortion of cattle and Brucella suis from pigs are the main species that cause human infections.
Brucella suis strains that produce hydrogen sulfide are known as ‘American strains’ and those that do not produce as ‘Danish’ strains.Brucella can be grown artificially in the corioalantoic membrane (a membrane found inside of the bird's eggs, that helps in the exchange of gases) of chick embryo which leads to the death of the chick in a few days.
Brucella can be destroyed by acid, heating at 600C in 10 minutes, direct sunlight, and by 1% phenol in 15 minutes.They remain survive in the soil for several weeks, 10 days in refrigerated milk, one month in ice cream and 4 months in butter.Out of the 3 main human infecting strains, Brucella abortus is the most pathogenic one. The incubation period of the infection is 10-30 days.Brucellosis is an intracellular disease affecting the reticuloendothelial system (body’s defense system).
Brucella enters the human body through wounds, mouth, eyes, and respiratory and gastrointestinal (GI) tracts.The mode of transmission is through unpasteurized milk and meat products.The brucellae spread from the site of entry to the lymph glands in which they multiply. Dissemination into the bloodstream occurs followed by spreading to all parts of the body.
Human infection may be of three types;
1. Latent infection with serological and no clinical evidence; where the pathogen remains hidden inside the body and cause infection when the patient’s immunity goes down.
2. Acute or sub-acute brucellosis; Acute brucellosis is mainly due to Br. melitensis. It is often associated with prolonged bacteremia, irregular fever, muscle and joint pain, asthmatic attacks, drenching sweat at night, exhaustion, constipation, sleeplessness, chilling and nervous irritations.
3. Chronic brucellosis; Chronic brucellosis is non-bacteremic low grade infection with periodic exacerbations. Symptoms include hypersensitivity, sweating, joint pain, etc. the illness may last for years.
The most important substance that causes the spread is raw milk. Milk products, water contaminated with infected feces, through contact such as breast feeding, sexual contact, and through placenta also rarely transmit the infection.
Occupational hazard occurs in veterinarians, butchers, animal handlers, etc. Infection by inhalation is found in the lab personnel handling the organism.
Culturing of blood is the most important diagnostic method. The Castaneda method of culturing blood is recommended. Cultures are taken from lymph nodes, Cerebro-spinal fluid, sputum, breast milk, vaginal discharge and from seminal fluid. Serological methods like Standard Agglutination Test (SAT), complement fixation and ELISA are found to be more effective.
Certain methods for detection of brucellosis in herds also have been developed. Rapid plate agglutination test and Rose Bengal card test are examples. Milk is checked for the pathogen by ‘milk ring test’.
A combination of streptomycin with tetracycline or rifampicin with doxycycline for a period of not less than 3 weeks is usually prescribed. This finds to be effective in acute infections, but not acceptable in chronic cases.
Precautions:
1. Avoid the intake of raw milk, vegetables, etc.
2. Check the animals for brucellosis which provide milk to dairies.
3. Detection of infected animals and slaughtering them can prevent further spread.
4. Pasteurization of milk before use.
