Brucella melitensis

Brucella melitensis:

Before Brucella melitensis was recognized as the cause of Malta fever in man, a disease causing the same symptoms in countries bordering the Mediterranean was known as Fibris andulans. David Bruce, a British military medical officer stationed in Malta described the aetiology of the disease in man in 1884. The bacteriologist Zammit Themistocles, a member of the Mediterranean Fever Commission, isolated B. melitensis in 1897 from the milk of goats that had aborted. Zammit also discovered that drinking milk from these goats was the reason for outbreaks of Malta fever amongst British soldiers stationed in Malta. It soon became apparent that the disease is prevalent in Russia, the Balkans, Asia, Africa and other European countries, and that the organism also infects sheep.

Brucella melitensis primarily affects the reproductive tract of sheep and goats, and B. melitensis infection is characterized by abortion, retained placenta and, to a lesser extent, impaired fertility. Although B. melitensis infects mainly sheep and goats it is a zoonose that plays a significant role in the national economy and the public health of many developing countries.

Distribution:

Most Mediterranean countries have large numbers of flocks of sheep and goats infected with B. melitensis . Brucella melitensis is also prevalent in developing countries of South-West Asia, parts of Latin America and Africa where it constitutes a serious human health hazard.

In countries with organized brucellosis control some areas may be free from B. melitensis while other areas are still infected. This is because the geographic context and the methods of farming influence the spread of the infection. In mountainous areas grouping of flocks in valleys is common, as in the villages. This allows maintenance of brucellosis that may become enzootic. However, mountainous areas may also isolate infected from non-infected flocks and sporadic outbreaks of brucellosis may not spread to other areas. The data given in the geographic distribution table dates back 10-15 years and may reflect a situation resulting from geographical conditions. Most of the data is based on sero-epidemiological studies although it is generally accepted that only the isolation of Brucella confirms the presence of brucellosis. Therefore, the data must be looked upon as an indication for the presence of B. melitensis in an area or a country and not to what extend the area is infected.

Pathogenesis and disease:

The bacterium causes severe inflammation of the epididymis, with formation of spermatocoeles and fibrinous adhesions. This disease is known as ovine brucellosis, and is a reportable disease in the USA. In goats and sheep, B. melitensis can cause abortion, stillbirth, and weak offspring for the first gestation after the animal is infected. Mastitis can happen, but is uncommon. The infection can also reduce milk yield by at least 10%. The placenta might also be retained, and the animal can suffer from purulent vaginal discharge. In males, the infection can cause acute orchitis and epididymitis, and in turn infertility. Arthritis can also occur. Brucellosis can be confirmed with the help of post mortem lesions in the reproductive tract, udders, and supramammary lymph nodes. While these are not pathognomonic for brucellosis, they can help farmers determine if their herds are infected.

 

 

 

Transmission:

In animals

  1. melitensis is transmitted by the stable fly. It can also infect other animals through contact with the placenta, fetus, fetal fluids, and vaginal discharge of infected animals.

In humans

  1. melitensis can be transmitted to humans through ingestion of contaminated dairy products.

Treatment:

In humans, brucellosis is usually treated with a prolonged course of antibiotics, combining two or more drugs for part or all of the treatment course. Monotherapy is reported to have a high relapse rate. Different antibiotics may be recommended, depending on the patient’s age, pregnancy status and syndrome. The Rev-1 vaccine strain is resistant to streptomycin. Relapses can be seen (most often within 3-6 months) if brucellosis treatment is inadequate. Surgical intervention may occasionally be required for localized foci.

Prevention:

Human exposure can be reduced by controlling brucellosis in livestock. The Rev-1 vaccine strain is also pathogenic for humans; it must be handled with caution to avoid accidental injection or contamination of mucous membranes or abraded skin. Pasteurization is recommended to destroy B. melitensis in milk products. The fermentation time necessary to ensure safety in ripened, fermented cheeses made from unpasteurized milk in unknown, but it has been estimated to be approximately 3 months. The World Health Organization (WHO) recommends storing soft cheeses > 6 months if they were made from unpasteurized milk. Meat, blood and internal organs from animals should be handled carefully and cooked thoroughly. While the amount of B. melitensis in skeletal muscle (meat) is generally thought to be lower than in visceral organs such as the liver, kidney and spleen, one recent study found comparable concentrations in muscles and viscera from experimentally infected goats. Good hygiene, together with personal protective equipment (gloves, face/ eye protection, protective clothing and respirators, as appropriate) can decrease human exposure when handling infected animals. Wounds should be covered. Particular care should be taken when animals are giving birth or aborting, or when large numbers of animals are shedding organisms in a concentrated area, and during activities that may aerosolize organisms (e.g., pressure washing, sawing into infected tissues). Detailed precautionary measures for specific locales such as contaminated farms, abattoirs and laboratories have been published by sources such as the World Health Organization. Precautions should be used when butchering potentially infected carcasses of wildlife, as well as when handling domesticated animals and their tissues. Prophylactic antibiotics and/or monitoring may be offered to laboratory workers who have been exposed to B. melitensis. Antibiotic prophylaxis may also be needed in some vaccine accidents, including needlestick injuries or conjunctival splashing. A few countries have employed brucellosis vaccines for humans; however, commercial vaccines that meet international standards for safety and efficacy are currently unavailable.

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