Monograph

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definition: 

Brucellosis is a contagious animal disease of bacterial origin (genus Brucella) that mainly affects ruminant animals but also humans, pigs or dogs. 

The disease causes loss of animal productions and has an important economical impact. It is one of the most important serious diseases of Livestock and it must be notified to OIE.

Situation in America: 

Enzootic disease in many parts of the world including the Caribean.

Susceptible species: 

The disease mainly affects ruminant animals (cattle, bison, buffaloes, goats, sheep). Swines, humans and dogs can also be affected. Isolates of Brucella have recently also been discovered in marine mammals.

Farmers, ranchers, veterinarians, and packing plant workers are infected more frequently because they come into direct contact with infected animals.

Etiological agent: 

The disease is caused by a Gram negative, intracellular bacteria of the genus Brucella. Each Brucella species is associated with certain hosts.Six species occurs in animals : B. brucella, B. melitensis, B. ovis, B. suis, B. canis and B. neotomae.

B. abortus usually causes Brucellosis in cattle, buffalo and bison 

  B. suis mainly affects swine and reindeer but also cattle and bison

B. melitensis is the most important species found in sheep and goats. B. ovis can cause infections in sheep and rams.

B. canis affects dogs and B. neotomae affects rodents.

 


 

Methods of transmission
Source: 

Direct contact with infected animals or with an environment that has been contaminated with discharges from infected animals. Placenta, foetus, foetal fluids, vaginal discharges are sources of transmission.

Uterine discharges present after an infected animal has aborted or calved are all highly contaminated with infectious Brucella organisms.

In years past, prior to pasteurization, raw milk was considered the prime source of brucellosis in humans.

Transmission: 

Vertical:
Not common but the transmission from the mother to the foetus or the newborn is possible (colostrum).

Veneral transmission varies with the species. It is the primary route of transmission for B. ovis and B. suis.

Horizontal :
-    Direct : contact with infected animal or with discharges from infected animals
-    Indirect : raw milk or inhalation of aerosols from an infected environment

Method of contamination: 

Entry into the body occurs by ingestion and by direct contact through the mucous membranes or broken skin. The disease may also be spread when wild animals or animals from an affected herd mingle with brucellosis-free herds. Sexual transmission is also possible.

Today, most humans contract the disease by coming in direct contact with aborted fetuses, afterbirth, and uterine discharges of diseased animals or with infected carcasses at slaughter. He can be infected by ingesting raw milk.

There is no danger from eating cooked meat products because the disease-causing bacteria are not normally found in muscle tissue and they are killed by normal cooking temperatures.

Rarely, if ever, does a human contract the disease from another human.

Symptoms: 


•    Animals

Abortion (10 to 15% of cases) occurs during the second half of pregnancy in ruminants, usually between the fifth and seventh month of gestation. However, in pigs, abortion occurs at any stage of gestation.

Infected cows usually abort once (75 to 90% of cases), but a percentage will abort during additional pregnancies, and calves born from later pregnancies may be weak and unhealthy.

So, the most obvious signs are reproductive troubles. Abortions, stillbirths, infertility, orchitis, retained afterbirths with resulting uterine infections, articular and peri-articular hygromas, especially in the tropics, characterize the disease. Milk production may be reduced in cattle caused by abortions and delayed conceptions.

Even though their calves may appear healthy, infected cows continue to harbor and discharge infectious organisms and should be regarded as dangerous sources of the disease.

•    Humans

The incubation period lasts from 5 days to 3 months. Most infections become apparent within 2 weeks.

Brucellosis is a multisystemic disease.  It typically starts with acute febrile illness that can last 2 to 4 weeks. Most people recover but some people may develop other forms of the disease.
Three possible forms:
- Undulant form (Malta fever) intermittent fever with other persistent symptoms that wax and wane at regular intervalls
- Subacute or localized form: affecting any organ (testes, heart, lungs, joints ...)
- Chronic form: no fever, characterized by high fatigue, musculoskeletal pain, neurological signs (5% of cases)

In pregnancy, brucellosis can cause acute abortion or premature labor.

Undulant fever does not often kill its victims, but the disease is too serious to be dealt with lightly.

Lesions
Macroscopic lesions: 

Granulomatous lesions in the lymphoid tissue, the genitals, udder and the synovial membranes.


Necrosis can affect the target organs of infection:
-    necrotic placentitis
-    orchitis, epididymitis, prostatitis necrotic


Acute mastitis

Aborted fetuses are some anomalies:
-    splenomegaly, hepatomegaly
-    hemothorax, hemoperitoneum


Cotyledonary necrosis or edema: they become thick and gray

Diagnostics
Clinical diagnosis: 

No specific symptoms : abortions, sterility and postnatal mortality for animals and undulant fever for humans

Differential diagnosis: 

Other causes of abortion in late pregnancy or Epididymo-orchitis.

Laboratory diagnosis: 

Samples:
• Several cotyledons, possibly necrotic or hyperemia, taken soon after birth or abortion.
• Fetus or organs of stillbirths after approval by the reference laboratory.
• Collection of blood serum into the fridge
• Organs lesions, collected in a sterile manner from suspicious animals (testis, epididymis, spleen or regional lymph nodes)
• Milk

Direct identification :
Stamp staining by the Ziehl-Neelson method allows identification of samples by microscopy. False positives by cross-reaction with Brucella ovis, Chlamydophila psittaci and Coxiella burnetii may occur.

Culture in selective media resulted in the identification of genus and species and possibly the characterization of biovar.


Brucella test:
subcutaneous injection at the lower eyelid

Serological diagnosis: 

- The buffered Brucella antigen test (BAT or rose bengal test)

- Complement Fixation Test.

Preferably used the buffered antigen test in infected areas and the association buffered antigen test and complement fixation in the free areas (because of the percentage of false positives).


- ELISA: recommanded test by the oiE for trade purposes

 

 

Treatment: 

•    animals
No treatment. Repeated attempts to develop a cure for brucellosis in animals have failed. Occasionally, animals may recover after a period of time. More commonly, however, only the signs disappear and the animals remain infected. Such animals are dangerous sources of infection for other animals with which they associate.

•    humans
it is important to implement early treatment to prevent chronic infection.
Using tetracycline and rifampicin often associated with streptomycin chloramphenicol and sulfonamides (WHO recommends rifampicin 600mg / d and doxycycline 200 mg / d). The treatments are suitable if the patient is a pregnant woman or a young child. The treatment lasts about 6 weeks for brucellosis phase tank. Phase focused, treatment lasts from 2 to 4 months because the majority of bacteria are located in the cells and is then more difficult of access to drugs.

Prophylaxis: 

Sanitary prophylaxis

Animals

Compliance with hygiene and quarantine. detection and elimination of positive animals

Humans

Pasteurization of dairy products

Good hygiene and protective clothing to avoid contamination of the skin

Vaccines: 

Live attenuated vaccine strain of B. melitensis Rev-1. It can cause abortions and interfere with serological tests.

Two B. abortus attenuated vaccines can be used in endemic areas, the strain 19 and the strain RB51. The second one induces less abortions than the first one but it is less effective when challenged with heavy dose of the bacteria.

The B. suis strain 2 vaccine has not yet received agreement for commercialization.


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