Brucellosis disease | Causes and complications

Brucellosis disease | Causes and complications

Brucellosis, also known as “undulant fever”, “Mediterranean fever” or “Malta fever” is a zoonosis and the infection is almost invariably transmitted by direct or indirect contact with infected animals or their products. It affects people of all age groups and of both sexes. Although there has been great progress in controlling the disease in many countries, there still remain regions where the infection persists in domestic animals and, consequently, transmission to the human population frequently occurs.

Brucellosis disease | Causes and complications
Members of the genus Brucella are pathogenic bacteria exceedingly well adapted to their hosts.

Brucellosis in humans is a zoonosis of a greatly varied clinical image, caused by small, aerobic, Gram-negative rods of the genus Brucella. After penetration into the body the bacilli proliferate in the lymphatic system, mainly in the lymph nodes, subsequently break through the protective barrier and penetrate into various organs

The genus Brucella was discovered by David Bruce in 1887 and currently consists of ten species (of many serotypes). These are:

1. Brucella melitensis – isolated in 1887 in Malta (hence called Malta fever) by David Bruce from the spleen of a soldier who died from acute brucellosis . The species most pathogenic for humans.
2. Brucella abortus – causing abortions in cattle, for many years the main etiologic factor of brucellosis in animals and humans (Bang’s disease) in Poland.
3. Brucella suis – causing the disease mainly in swine, pathogenic also for humans. In Poland it was also isolated from wild hares.
4. Brucella canis – isolated from dogs, may also be the cause of illness in humans. It was first described by Carmichael in 1966 who isolated the bacillus from the placenta, foetuses and vaginal discharge of bitches that aborted their litters. The disease was earlier diagnosed in the United States in Beagle dogs.
5. Brucella neotomae –

isolated in the United States from rats.
6. Brucella ovis – infects not only sheep, in Poland it was cultured from ram semen.
7. Brucella marina – Brucella ceti – found in sea mammals (whales, seals) in the Atlantic Ocean.

 What animals get brucellosis?

Brucellosis can affect sheep, goats, cattle, pigs, horses, and dogs. Brucellosis can also affect rats and wild animals including deer, bison, elk, moose, camels, water buffalo, and marine mammals.

How can my animal get brucellosis?

In animals, Brucella are usually spread through contact with infected birthing tissues and fluids (e.g., placenta, aborted fetuses, fetal fluids, vaginal discharges). The bacteria can also be found in the milk, blood, urine and semen of infected animals.

Animals can get the bacteria by ingestion (oral), direct contact with mucous membranes (eyes, nose, mouth), or breaks in the skin. Brucella can also be transmitted by contaminated objects (fomites) such as, equipment, clothing, shoes, hay, feed or water. Some animals are carriers; they will have the bacteria but show no signs of illness. These animals can shed the bacteria into the environment for long periods of time, infecting other animals in the herd.

 How does brucellosis affect my animal?

Brucellosis causes reproductive problems (e.g. abortions, stillbirth, and infertility) in most species of animals. Other signs can include arthritis in cows and pigs, mastitis and lameness in goats, and oozing skin lesions in horses (“fistulous withers”).

Can I get brucellosis? Yes. People can become infected by eating or drinking (oral) raw milk or unpasteurized milk products that contain the Brucella bacteria.

Direct contact or aerosol exposure to infected animal fluids are additional ways to be infected. People who work with animals (e.g., livestock producers, veterinarians) may be at higher risk of exposure to Brucella.

The disease in humans

Brucellosis is an acute or sub-acute febrile illness usually marked by an intermittent or remittent fever accompanied by malaise, anorexia and prostration, and which, in the absence of specific treatment, may persist for weeks or months. Typically, few objective signs are apparent but enlargement of the liver, spleen and/or lymph nodes may occur, as many signs referable to almost any other organ system.

The acute phase may progress to a chronic one with relapse, development of persistent localized infection or a non-specific syndrome resembling the “chronic fatigue syndrome”. The disease is always caused by infection with a Brucella strain and diagnosis must be supported by laboratory tests which indicate the presence of the organism or a specific immune response to its antigens.

Disease Complications

Osteoarticular complications

Bone and joint involvement are the most frequent complications of brucellosis, occurring in up to 40% of cases. A variety of syndromes have been reported, including sacroiliitis, spondylitis, peripheral arthritis, osteomyelitis, bursitis, and tenosynovitis. Brucella sacroiliitis is especially common. Patients present with fever and back pain, often radiating down the legs (sciatica).

Children may refuse to walk and bear weight on an extremity. Early in the disease, radiographs and bone scintigrams can appear normal, but, in time, computed tomography (CT) or nuclear magnetic resonance (NMR) scans may show narrowing of the intervertebral disc space.

Gastrointestinal complications

Brucellosis, especially when due to B. melitensis, is often foodborne, and unpasteurized milk or dairy products, such as cheese, are common vehicles of transmission. Foodborne brucellosis resembles typhoid fever, in that systemic symptoms predominate over gastrointestinal complaints. Nevertheless, some patients with the disease experience nausea, vomiting, and abdominal discomfort. Rare cases of ileitis, colitis and spontaneous bacterial peritonitis have been reported.

Hepatobiliary complications

The liver is commonly involved in brucellosis, although liver function tests can be normal or only mildly elevated. The histological changes in the liver are variable, but disease caused by B. abortus may show epithelioid granulomas that are indistinguishable from sarcoidosis lesions. A spectrum of hepatic lesions has been described in cases due to B. melitensis, including scattered small foci of inflammation resembling viral hepatitis.

Respiratory tract complications

Aerosol inhalation is a recognized route of transmission of brucellosis, especially common in abattoirs where infected animals are slaughtered. A variety of pulmonary complications have been reported, including hilar and paratracheal lymphadenopathy, interstitial pneumonitis, bronchopneumonia, lung nodules, pleural effusions, and empyema.

Genitourinary complications

Orchitis and epididymitis are the most frequent genitourinary complications of brucellosis in men. Usually unilateral, Brucella orchitis can mimic testicular cancer or tuberculosis. Although Brucella organisms have been recovered from banked human spermatozoa, there have been a few reports implicating sexual transmission. Renal involvement in brucellosis is rare, but it too can resemble renal tuberculosis. In women, rare cases of pelvic abscesses and salpingitis have been reported.

Pregnancy and breastfeeding

Brucellosis during the course of pregnancy carries the risk of spontaneous abortion or intrauterine transmission to the infant. Abortion is a frequent complication of brucellosis in animals, where placental localization is believed to be associated with erythritol, a growth stimulant for B. abortus. Although erythritol is not present in human placental tissue, Brucella bacteremia can result in abortion, especially during the early trimesters


Cardiovascular complications

Infective endocarditis is the most common cardiovascular manifestation, and it is said to be the most common cause of death from brucellosis. Endocarditis is reported in about 2% of cases, and can involve both native and prosthetic heart valves. The aortic valve is involved more often than the mitral valve.

Aneurysms of the sinus of Valsalva and other vascular structures appear to be most common when infection is caused by B. suis. Mycotic aneurysms, usually involving the middle cerebral artery, can be a neurological complication of infective endocarditis.

Cutaneous complications

A variety of skin lesions have been reported in patients with brucellosis, including rashes, nodules, papules, erythema nodosum, petechiae, and purpura. Cutaneous ulcers, abscesses, and suppurative lymphangitis appear to be more common with B. suis. Occasionally, epistaxis, gingivorrhea, haematuria, and cutaneous purpura occur in association with severe thrombocytopenia, which has been ascribed to hypersplenism, bone marrow haemaphagocytosis, and/or anti-platelet antibodies.

Opthalmic complications

Although uncommon, a variety of ocular lesions have been reported in patients with brucellosis. Uveitis is the most frequent manifestation, and can present as chronic iridocyclitis, nummular keratitis, multifocal choroiditis or optic neuritis.



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