What is Brucellosis and its Controlling Measures
Brucellosis is one of the major bacterial zoonoses, and in humans is also known as Undulent fever, Malta fever or Mediterranean fever. It is occasionally transmitted to man by direct or indirect contact with infected animals. It is caused by different species of the brucella group of organisms and characterised by intermittent or irregular febrile attacks, with profuse sweating, arthritis and an enlarged spleen. The disease may last for several days, months or occasionally years. Brucellosis is both a severe human disease and a disease of animals with serious economic consequences.
Problem Statement:
Brucellosis is a recognized public health problem with worldwide distribution. It is endemic wherever cattle, pigs, goats and sheep are raised in large numbers. Important endemic areas for brucellosis exist in Mediterranean Zones, Europe, Central Asia, Mexico and South America. Eastern Mediterranean countries have experienced an increase in the most European countries and in North America and Australia. Majority of cases are reported from Middle East countries.
Animal brucellosis is reported from particularly every State in India. However no statistical information is available about extent of infection in man in various parts of the country.
The prevalence of human brucellosis is difficult to estimate. Many cases remain undiagnosed either because they are unapparent or because physicians in many countries are unfamiliar with the disease.
Epidemiological Determinants:
Agent Factors:
a) AGENT: The agents are small, Gram negative rod shaped, non-sporing and intracellular coccobacilli of the genus Brucella. Four species infect man : B melitensis, B. abortus, B. suis, and B. canis. B. melitensis is the most virulent and invasive species; it usually infects goats and occasionally sheep. B. abortus is less virulent and is primarily a disease of cattle. B. Suis is of intermediate virulence and chiefly infects pigs. B. canis is a parasite of dogs.
b) RESERVOIR OF INFECTION: Main reservoirs of human infection are cattle, sheep, goats, swine, buffaloes, horses and dogs. in animals the disease can cause abortion, premature expulsion of the foetus or death. Cross infections can often occur between animal species. The infected animals excrete Brucella in the urine, milk, placenta, uterine and vaginal discharges particularly during a birth or abortion. The animals may remain for life.
Host Factors: Human Brucellosis is predominantly a disease of adult males. Farmers, shepherds, butchers and abattoir workers, veterinarians and laboratory workers particularly at special risk because of occupational exposure. Immunity follows infection,
Environmental Factors: Brucellosis is most prevalent under conditions of advanced domestication of animals in the absence of correspondingly advanced standards of hygiene, Overcrowding of herds, high rainfall, lack of exposure to sunlight, unhygienic practices in milk and meat production all favor the spread of brucellosis. the infection can travel long distances in milk and dust. The environment of a cowshed may be heavily infected. The organism can survive for weeks or months in favorable conditions of water, urine, feces, damp soil and manure.
Mode of Transmission: Transmission is usually from infected animals to man. There is no evidence of transmission from man to man. The routes of spread are :
a) 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. This type of spread is largely occupational and occurs in persons involved in handling livestock and slaughter house workers.
b) Food-Borne infection: Infection may take place indirectly by the ingestion of raw milk or dairy products 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.
c) Air-borne infection: The environment of a cowshed may be heavily infected. Few people living in such an environment can escape inhalation of infected dust or aerosols. Brucellae may be inhaled in aerosol form in slaughter houses and laboratories, so these infections are notified as occupational.
* incubation Period is Highly variable, usually 1-3 weeks, but may be as long as 6 months or more.
Pattern of Disease:
Brucella infection in man can vary from an acute febrile disease to a chronic low grade ill defined disease lasting for several days, months or occasionally years.
The acute phase is characterized by a sudden or insidious onset of illness with
a) Swinging pyrexia, rigors and sweating.
b) Arthalgia/arthritis involving larger joints such as hip, knee, shoulder and ankle.
c) low back pain.
d) headache, insomnia.
e) Small firm splenomegaly and hepatomegaly.
f) leucopenia with relative lymphocytes. The most striking aspect of the clinical picture is the severity of the illness and the absence of clinical signs.The acute phase subsides with in 2-3 weeks. If the patient is treated with tetracyline, the symptoms may disappear quickly but the infection being intracellular may persist giving rise to sub acute or relapsing disease.
In a few patients symptoms recur for prolonged periods. Diagnosis is established by isolation of the organism from cultures of blood, bone marrow, exudate’s and biopsy specimens during the acute phase of the disease and by serological tests.
Control of Brucellosis:
(a) IN THE ANIMALS: The most rational approach for preventing human brucellosis is the control and eradication of the infection from animal reservoirs which is based on the combination of the following measures:
(1) Test and Slaughter: Case finding is done by 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.
(2) Vaccination: Vaccine of B, abortus strain 19 is commonly used for young animals. A compulsory vaccination programme for all heifers in a given community on a yearly basis can considerably reduce the rate of infection. Systematic vaccination for a period of 7 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.
(3) Hygienic Measures: these comprise provision of a clean sanitary environment for animals, sanitary disposal of urine and feces, veterinary care of animals and health education of all those who are occupationally involved.
(b) IN THE HUMANS:
(1) 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 6 hours for about 3 weeks. In patients with skeletal or other complications intramuscular streptomycin 1 g daily in addition to tetracycline usually achieves a cure.
(2) 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.
(3) Protective measures: The aim is to prevent direct contact with infected animals. Persons at risk such as farmers, shepherds, milkmen, abattoir workers 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.
(4) Vaccination: Human live vaccine of 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 reference center, Indian Veterinary Research Institute, Izatnagar.
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