Brucellosis is a zoonotic infection transmitted from animals to humans by ingestion of infected food products, direct contact with an infected animal, or inhalation of aerosols. This last method of transmission is remarkably efficient given the relatively low concentration of organisms (as few as 10-100 bacteria) needed to establish infection in humans and has brought renewed attention to this old disease. First officially diagnosed as an infection in British soldiers, brucellosis now is touted as a potential biological warfare agent. However, its relatively long and variable incubation period (1-8 wk), as well as the fact that many infections are asymptomatic, has made it a less desirable agent for weaponization.
The disease is transmitted primarily through contaminated or untreated milk (and its derivates) or through direct contact with infected animals, which may include dogs, pigs, camels and ruminants, primarily sheep, goats, cattle, bison. This also includes contact with their carcasses. Leftovers from parturition are also extremely rich in highly virulent brucellae. Infection may also occur by injesting contaminated grass, roughage, feed, or water Once the susceptable animal injests the organism, the bacteria progress to the regional lymph nodes where it resides during the incubation period. The incubation period, which is the time between exposure to the organism and the ability to detect the disease, may range from two weeks to two months and longer.
Brucellosis is very difficult to treat successfully. A combination of minocycline and streptomycin is thought to be most effective but is expensive. Tetracycline can be substituted for the minocylcine to reduce costs but also lowers the effectiveness of treatment. All infected animals should be neutered or spayed to prevent sexually related transmission. All infected animals should be considered to be lifelong carriers of the disease, even if treated.
Approximately 100 - 200 cases occur in the U.S. each year. People working in jobs requiring frequent contact with animals or meat -- such as slaughterhouse workers, farmers, and veterinarians -- are at high risk.
The acute brucellosis incubation period is 1-3 weeks. The onset is insidious, with malaise, headache, weakness, generalized myalgia and night sweats. The fever pattern is classically undulant, although continuous and intermittent patterns are also seen. Lymphadenopathy, hepatosplenomegaly and spinal tenderness may be present; arthritis, osteomyelitis, orchitis, epididymitis, meningoencephalitis and endocarditis have all been described.
Humans are generally infected in one of three ways: eating or drinking something that is contaminated with Brucella, breathing in the organism (inhalation), or having the bacteria enter the body through skin wounds. The most common way to be infected is by eating or drinking contaminated milk products. When sheep, goats, cows, or camels are infected, their milk is contaminated with the bacteria. If the milk is not pasteurized, these bacteria can be transmitted to persons who drink the milk or eat cheeses made it. Inhalation of Brucella organisms is not a common route of infection, but it can be a significant hazard for people in certain occupations, such as those working in laboratories where the organism is cultured. Inhalation is often responsible for a significant percentage of cases in abattoir employees.
Brucellosis is characterized by a fever which may be continuous, intermittent or irregular. Some other possible symptoms include headache, weakness, sweating, chills, arthralgia (pain in the joints), depression, weight loss and generalized aching. This disease may last for days, months, or as long as a year if untreated.
