Brucellosis

Organism is a Gram-negative bacillus, Brucella melitensis, B. abortus, B. suis and B. canis. B. melitensis causes the disease in goats that was first investigated in Malta (Melita was the Roman name for the island). B. abortus, as its name implies, causes abortion in cattle. B. suis is an infection of pigs. Both pigs and sheep are often infected with B. melitensis and B. abortus. B. canis is restricted to dogs.

The organism is killed by heating at 60°C for 10min and by 1% phenol for 15 min. It survives well in milk and cream cheeses that have not fermented or gone hard. In places contaminated by the faeces and urine of infected animals, survival can be for months and even years, especially at lower temperatures. With temperatures above 25°C, survival time is reduced.

Clinical features The severity and duration of the disease is very variable and may go undiagnosed for a considerable period of time. Characteristically, there are intermittent or irregular fevers (undulant fever) with generalized aches and pains. The patient is unduly weak and tired, often retiring in the second half of the day. There may be depression, a cough, lymphadenopathy and splenomegaly. Recovery may occur spontaneously, or the disease become chronic, with the undulant pattern of fever and fatigue more pronounced. If not treated, this can continue for 6 months to 1 year, after which 80% of patients fully recover. Abortion is more frequent in women with the disease.

Diagnosis is difficult, but isolation of the organism from blood, bone marrow or urine should be attempted. Serum agglutination tests can be used, but a rise in titre is required.

Transmission Humans are infected by drinking raw milk or milk produce. B. melitensis is mainly spread by unpasteurized goat's milk or the consumption of cream cheeses prepared from it. B. abortus has less invasive power and virulence when consumed in cow's milk and so asymptomatic infection from drinking cow's milk can occur. In people whose occupations bring them in close proximity to animals, infection can occur through the skin, probably via an abrasion, the mucous membrane, the conjunctiva or as an aerosol through the respiratory tract. Such persons as farmers, shepherd, goat herds, vets and abattoir workers are at greater risk. Animal handlers can contract the much rarer B. canis infection from dogs.

Incubation period is 5-60 days, but may be up to 7 months.

Period of communicability Not transmitted from person to person.

Occurrence and distribution The disease is mainly one of animals, resulting in economic losses to the society and ill health to those involved in looking after animals. Brucellosis is common in South and Central America, Africa, the Mediterranean, South, Southwest and Central Asia. It is often not recognized, being found in a large number of animals if looked for. In Sudan and Nigeria, 60% of cattle were found to be infected.

Cattle become infected from eating placentae, licking a dead fetus or close contact with contaminated surroundings, such as cattle paddocks, barns or shelters. The young can obtain infection through the milk of their mothers.

Control and prevention is by pasteurization or boiling of cow and goat milk. Where pasteurization is not a legal requirement, people should be told of the risks of drinking raw milk and advised to boil it.

Anybody working with animals, especially those concerned with slaughter of animals, or coming into contact with products of abortion, should wear overalls and gloves that are frequently washed and sterilized. Proper animal husbandry reduces areas of contaminated pastureland that perpetuates infection.

Where facilities permit, herds or flocks can be rendered Brucella-free by diagnosis and slaughter of infected animals. A useful test for this purpose is the milk-ring test on cow's milk. Haematoxylin-stained Brucella antigen is added to a sample of cow's milk and if positive, a blue ring appears at the interface. By removing infected animals from a herd and preventing them from coming into contact with others, whole areas of land, and even complete countries, have been made Brucella-free. This is a large and expensive undertaking and beyond the means of many developing countries. An alternative is to vaccinate herds. The live, attenuated vaccine Rev-1 or recombinant RB51 can be given to calves at 6-8 months. Vaccination can also be given to adult animals, but should not be administered if an eradication programme is envisaged as it then becomes impossible to tell whether an animal is infected or not.

Treatment is with doxycycline 100 mg every 12 h combined with either rifampicin 600 mg daily, or streptomycin 1 g daily, for 6 weeks.

Surveillance of cattle using the milk-ring test (see above). Brucellosis is a notifiable disease in countries in which it has been eliminated, such as in northern Europe, USA and Japan.

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