Affects: Dogs
Brucellosis is a zoonosis (zoonotic disease) spread primarily via ingestion of unpasteurized milk from infected animals. It is also known as undulant fever, Malta fever, and Mediterranean fever.
The bacteria causing this disease, Brucella, are small, Gram-negative, nonmotile, nonspore-forming, rod-shaped (coccobacilli) bacteria. They function as facultative intracellular parasites, causing chronic disease, which usually persists for life. Four species infect humans: B. abortus, B. canis, B. melitensis, and B. suis. B. abortus is less virulent than B. melitensis and is primarily a disease of cattle. B. canis affects dogs. B. melitensis is the most virulent and invasive species; it usually infects goats and occasionally sheep. B. suis is of intermediate virulence and chiefly infects pigs. Symptoms include profuse sweating and joint and muscle pain. Brucellosis has been recognized in animals and humans since the early 20th century.
Signs And Symptoms: The symptoms are like those associated with many other febrile diseases, but with emphasis on muscular pain and night sweats. The duration of the disease can vary from a few weeks to many months or even years.
In the first stage of the disease, bacteremia occurs and leads to the classic triad of undulant fevers, sweating (often with a characteristic foul, moldy smell sometimes likened to wet hay), and migratory arthralgia and myalgia (joint and muscle pain). Blood tests characteristically reveal a low number of white blood cells and red blood cells, show some elevation of liver enzymes such as aspartate aminotransferase and alanine aminotransferase, and demonstrate positive Bengal rose and Huddleston reactions. Gastrointestinal symptoms occur in 70% of cases and include nausea, vomiting, decreased appetite, unintentional weight loss, abdominal pain, constipation, diarrhea, an enlarged liver, liver inflammation, liver abscess, and an enlarged spleen.
This complex is, at least in Portugal, Israel, Palestine, Syria, Iran, and Jordan, known as Malta fever. During episodes of Malta fever, melitococcemia (presence of brucellae in the blood) can usually be demonstrated using blood culture in tryptose medium or Albini medium. If untreated, the disease can give rise to focalizations or become chronic. The focalizations of brucellosis usually occur in bones and joints, and osteomyelitis or spondylodiscitis of the lumbar spine, accompanied by sacroiliitis, is very characteristic of this disease. Orchitis is also common in men.
The consequences of Brucella infection are highly variable and may include arthritis, spondylitis, thrombocytopenia, meningitis, uveitis, optic neuritis, endocarditis, and various neurological disorders collectively known as neurobrucellosis.
Cause: Brucellosis in humans is usually associated with consumption of unpasteurized milk and soft cheeses made from the milk of infected animals—often goats—infected with B. melitensis, and with occupational exposure of laboratory workers, veterinarians, and slaughterhouse workers. These infected animals may be healthy and asymptomatic. Some vaccines used in livestock, most notably B. abortus strain 19, also cause disease in humans if accidentally injected. Brucellosis induces inconstant fevers, miscarriage, sweating, weakness, anemia, headaches, depression, and muscular and bodily pain. The other strains, B. suis and B. canis, cause infection in pigs and dogs, respectively.
Overall findings support that brucellosis poses an occupational risk to goat farmers with specific areas of concern including weak awareness of disease transmission to humans and lack of knowledge on specific safe farm practices such as quarantine practices.
Transmission Through Hunting And Game Meat Consumption: Hunters and individuals who consume wild game face an elevated risk of brucellosis exposure due to direct contact with infected animals and inadequate meat preparation. Transmission can occur during field-dressing or handling of infected carcasses, as Brucella bacteria can enter the body through skin abrasions, mucous membranes, or inhalation of aerosolized pathogens. Additionally, the consumption of undercooked or improperly handled wild game meat remains a significant risk factor, particularly in regions where game animals constitute a primary food source. Implementing protective measures, such as the use of personal protective equipment (PPE) during handling and ensuring thorough cooking of game meat, is essential to mitigating the risk of brucellosis transmission within hunting communities.
Diagnosis: The diagnosis of brucellosis relies on:
Demonstration of the agent: blood cultures in tryptose broth, bone marrow cultures. The growth of brucellae is extremely slow (they can take up to two months to grow), and the culture poses a risk to laboratory personnel due to the high infectivity of brucellae.
Demonstration of antibodies against the agent, either with the classic Huddleson, Wright, and/or Bengal Rose reactions, either with ELISA or the 2-mercaptoethanol assay for IgM antibodies associated with chronic disease
Treatment: Antibiotics such as tetracyclines, rifampicin, and the aminoglycosides streptomycin and gentamicin are effective against Brucella bacteria. However, the use of more than one antibiotic is needed for several weeks, because the bacteria incubate within cells.
The gold standard treatment for adults is daily intramuscular injections of streptomycin [dose — ask your vet] for 14 days and oral doxycycline [dose — ask your vet] twice daily for 45 days (concurrently). Gentamicin [dose — ask your vet] by intramuscular injection once daily for 7 days is an acceptable substitute when streptomycin is not available or contraindicated. Another widely used regimen is doxycycline plus rifampicin twice daily for at least 6 weeks. This regimen has the advantage of oral administration. A triple therapy of doxycycline, with rifampicin and co-trimoxazole, has been used successfully to treat neurobrucellosis. Doxycycline plus streptomycin regimen (for 2 to 3 weeks) is more effective than doxycycline plus rifampicin regimen (for 6 weeks).
Doxycycline can cross the blood–brain barrier, but requires the addition of two other drugs to prevent relapse. Ciprofloxacin and co-trimoxazole therapy are associated with an unacceptably high rate of relapse. In brucellic endocarditis, surgery is required for an optimal outcome. Even with optimal antibrucellic therapy, relapses still occur in 5 to 10% of patients with Malta fever.
Prevention: Prevention of human brucellosis depends largely on controlling infection in animals and reducing exposure to contaminated animal products and animal tissues. Common public health measures include pasteurization of milk, avoidance of raw dairy products, use of protective clothing when handling potentially infected animals or animal tissues, and biosafety precautions in laboratories.
In areas where brucellosis is endemic in livestock, prevention strategies may include animal vaccination, testing, surveillance, movement control, and culling of infected herds where feasible. People at increased occupational risk, including veterinarians, farmers, slaughterhouse workers, hunters, and laboratory personnel, are advised to use personal protective equipment and avoid unprotected contact with placentas, fetuses, blood, and other potentially infectious materials. There is no widely available human vaccine for brucellosis, so prevention in humans relies primarily on food safety, occupational precautions, and control of the disease in animal populations.
Prognosis: The mortality of the disease in 1909, as recorded in the British Army and Navy stationed in Malta, was 2%. The most frequent cause of death was endocarditis. Recent advances in antibiotics and surgery have been successful in preventing death due to endocarditis. Prevention of human brucellosis can be achieved by eradication of the disease in animals by vaccination and other veterinary control methods, such as testing herds/flocks and slaughtering animals when infection is present. Currently, no effective vaccine is available for humans. Boiling milk before consumption, or before using it to produce other dairy products, is protective against transmission via ingestion. Changing the traditional food habits of eating raw meat, liver, or bone marrow is necessary, but difficult to implement. Patients who have had brucellosis should probably be excluded indefinitely from donating blood or organs. Exposure of diagnostic laboratory personnel to Brucella organisms remains a problem in both endemic settings and when brucellosis is unknowingly imported by a patient. After appropriate risk assessment, staff with significant exposure should be offered postexposure prophylaxis and followed up serologically for 6 months.