The disease
A bacterial zoonosis
Brucellosis (sometimes also called Malta fever) is a bacterial zoonosis caused by bacteria of the genus Brucella. Three species are predominant:
Brucella melitensis, the most pathogenic, invasive, and widespread species worldwide,
Brucella abortus,
Brucella suis.
Other less common species exist, with varying pathogenicity for humans (B. canis, B. ovis, B. marimum, B. inopinata, etc.)
In sharp decline in France since the 1960s, approximately 80% of infections diagnosed today in our country occur in people who became infected while traveling in an enzootic country through the consumption of infected dairy products or through direct contact with an infected animal.
While severe forms (brain abscess, endocarditis) are rare, brucellosis can progress in humans to a chronic form with complications, particularly in cases of joint infection (arthritis).
Key statistics on brucellosis
An animal disease transmissible to humans
Brucellosis is present in many countries and affects most mammalian species, particularly ruminants—both domestic and wild—as well as suids (pigs and wild boars) and lagomorphs (hares).
In France, the disease has been virtually eradicated in ruminants. France has been officially free of bovine brucellosis since 2005 and has not experienced any outbreaks of brucellosis in small ruminants since 2003. Nevertheless, the disease is present in wild boars and hares, with bacterial strains that are very rarely pathogenic to humans (B. suis biovar 2).
Human brucellosis is endemic and enzootic in the Mediterranean Basin, the Middle East, Asia, Africa, and Latin America.
Humans can become infected in several ways:
through direct contact (entry of the pathogen through the skin or mucous membranes, facilitated by wounds or abrasions) with sick animals, animal carcasses, abortion products, placentas, animal vaginal secretions, manure, or through accidental contact with biological materials in laboratories;
by ingesting contaminated food (unpasteurized milk and dairy products from infected animals, more rarely raw vegetables contaminated by manure, or, exceptionally, undercooked meat and offal);
through inhalation (of bedding dust or contaminated aerosols in laboratories or slaughterhouses).
Human-to-human transmission is limited to healthcare workers exposed to biological samples.
Health and safety guidelines to follow to prevent the disease
Professionals working in direct contact with infected animals (livestock farmers, veterinarians, slaughterhouse staff, personnel in veterinary or medical testing laboratories, etc.) are the individuals most at risk of brucellosis. In practice, this situation no longer occurs in France due to the absence of animal brucellosis outbreaks among ruminants (cattle, sheep, goats).
Prevention of occupational exposure relies on biosecurity and workplace hygiene measures.
For consumers, raw milk dairy products produced in France come from herds that are subject to mandatory brucellosis surveillance. The residual risk lies in the consumption of dairy products in countries where animal brucellosis is not controlled, or products brought back from these countries after a trip.
Symptoms
The incubation period for brucellosis varies, ranging from one week to several months.
Clinical forms:
Primary infection may be asymptomatic, and the disease may not manifest until several months or years later.
In symptomatic cases, clinical signs vary widely but typically progress through three phases:
An acute primary invasion phase: nonspecific febrile syndrome associated with muscle pain and a feeling of malaise;
A secondary phase in which isolated or multiple foci of infection develop: osteoarticular (spondylodiscitis, knee arthritis, etc.), genitourinary (orchitis, epididymitis), hepatic (liver abscess), neurological (meningitis, meningoencephalitis, cerebral abscesses…), cardiac (endocarditis…);
Possibly, particularly in cases of inadequate or poorly followed treatment, a chronic phase with two distinct manifestations
either general symptoms (asthenia, pain, fatigue),
Or more localized symptoms (chronic progression of infectious foci).
The diagnosis of brucellosis is based on the isolation of the bacterium (blood cultures, cerebrospinal fluid culture, biopsy, etc.).
Serological tests are also available but are nonspecific and have low positive predictive value in a context of low human prevalence, such as in France.
These mainly include:
The Wright seragglutination test
The Rose Bengal test
In addition, certain pathogens can cause cross-reactions in serological tests, including:
Yersinia enterocolitica (especially O9 and O3),
Francisella tularensis
And, to a lesser extent, Salmonella group D and Coxiella (Young EJ. Brucella species. In: Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases, 5th edition. Churchill Livingstone ed., Philadelphia 2000:2386-93).
This is why a positive serology result in an epidemiologically non-suggestive context (particularly in the absence of travel) must lead to verification of the positive result, for example through the CNR.
Contact with the laboratory is required before sending any specimen.
Treatment
Once the diagnosis is confirmed, treatment for human brucellosis involves administering specific antibiotics for several weeks, and, if necessary, surgical management of the sites of infection.
The case-fatality rate is less than 2% even in the absence of treatment.
