Brucella melitensis is a bacterium belonging to the Brucella genus. It is a zoonotic pathogen, transmitting from animals to humans. It is the most common Brucella species causing human infections, responsible for an estimated 70% of all cases globally. While eradicated in some nations, it continues to cause economic losses and health burdens in many developing regions.
The Disease It Causes
In humans, Brucella melitensis causes brucellosis, also known as undulant fever, Malta fever, or Mediterranean fever. It is a systemic infection, affecting various organs including the liver, spleen, joints, kidneys, and heart. A hallmark is an undulating fever, where body temperature rises and falls in waves. The disease can manifest in acute, subacute, or chronic forms, with symptoms potentially lasting for years or recurring after periods of remission.
In livestock, particularly sheep and goats, which are the primary hosts for Brucella melitensis, the infection often leads to reproductive issues. These include abortions, stillbirths, and infertility, resulting in significant economic losses for farmers.
How It Spreads
Brucella melitensis primarily spreads from infected animals to humans through several routes. A common way people get infected is by consuming unpasteurized dairy products, such as raw milk and cheeses.
Direct contact with infected animal tissues or fluids also poses a risk, including exposure to blood, placentas, aborted fetuses, or vaginal discharges, particularly during birthing or slaughter. Professions with close animal contact, such as farmers, veterinarians, and slaughterhouse workers, are at higher risk of this type of transmission. Inhalation of aerosols containing the bacteria in contaminated environments, like barns or laboratories, is another recognized route of transmission.
Recognizing the Symptoms
Brucellosis symptoms can be non-specific and resemble other illnesses, making diagnosis challenging. After exposure, symptoms typically appear within two to four weeks, but the incubation period can range from five days to six months.
Acute symptoms often include fever, which can be high-grade and accompanied by chills, excessive sweating, malaise, and headache. Patients commonly experience muscle and joint pain, particularly in the hips, knees, or lower back, along with fatigue, weakness, and appetite loss.
If left untreated, the disease can become chronic, leading to recurrent fever, persistent joint pain, and more severe complications. These chronic manifestations can include arthritis, spondylitis (inflammation of the spine), and neurological complications such as meningitis, encephalitis, or peripheral neuropathy. Depression and other neuropsychiatric symptoms are also reported.
Diagnosis and Treatment Approaches
Diagnosing brucellosis often begins with a thorough medical history, including questions about potential animal exposure or consumption of unpasteurized dairy products. Laboratory tests are then used to confirm the presence of the infection.
Blood tests are primary, including serology to detect antibodies against Brucella and blood cultures to isolate the bacteria itself. Automated blood culture systems can detect acute cases within five to seven days, though longer incubation or additional techniques like lysis-centrifugation may be needed. Other diagnostic methods, such as bone marrow cultures, cerebrospinal fluid cultures, or imaging tests like X-rays, CT scans, or MRIs, may be employed to identify complications or affected organs.
Treatment typically involves a prolonged course of antibiotics to ensure eradication and prevent relapse. The standard regimen often combines two antibiotics, such as doxycycline and rifampicin, administered for at least six weeks. Another effective combination is doxycycline with streptomycin or gentamicin for two to three weeks, followed by doxycycline alone. Completing the full course of treatment is important to reduce relapse risk.
Preventing Infection
Preventing Brucella melitensis infection largely centers on minimizing exposure to infected animals and contaminated products. A primary preventive measure is to avoid consuming unpasteurized dairy products, including raw milk and soft cheeses made from it. Pasteurization effectively kills the Brucella bacteria, making dairy products safe for consumption.
For individuals who work with animals or animal products, practicing good hygiene is important. This includes wearing protective gloves and other personal protective equipment when handling animal tissues, blood, or birth fluids, and thoroughly washing hands afterward.
Vaccination of livestock, particularly sheep and goats, helps control the disease in animal populations, reducing the risk of human infection. While effective vaccines exist for animals, there is no routine human vaccine currently available. Occupational safety measures for at-risk professions, such as veterinarians, farmers, and slaughterhouse workers, are also implemented to reduce exposure.