Babesiosis (Babesia Infection)
Babesiosis (Babesia Infection)
Babesiosis (bab-EE-see-OH-sis), also known as Babesia infection, was first reported in humans in 1957 and first appeared in the United States in 1969. Since then, there have been at least 300 cases reported in the United States. As symptoms are either mild or do not arise in people with strong immune systems, some people are unaware they are infected. The majority of reported cases occur in people with weakened immune systems.
Infection occurs when humans are bitten by ticks infected with parasites of the genus Babesia. When symptoms arise from infection, they usually include fever, chills, muscle aches, and fatigue. In severe cases, liver and kidney damage can occur.
Babesiosis can be treated using a combination of antibiotics and anti-parasitic medications, and can be prevented by avoiding tick bites. This is done by covering up bare skin and wearing insect repellent.
Babesiosis was first recognized in humans in 1957 after a Croatian cattle farmer contracted the disease. Prior to that case, babesiosis was thought to affect only animals. The biologist Victor Babes (1854–1926) first discovered the Babesia parasite in infected cattle. In 1893, Theobald Smith (1859–1934) and Frederick L. Kilbourne (1858– 1936) determined that the parasite was transmitted via a tick vector, resulting in the disease babesiosis.
Babesiosis was first recorded in the United States in 1969 after an outbreak in Nantucket, Massachusetts. Since then, there have been further outbreaks throughout the U.S., mainly in the Northeast. Babesiosis outbreaks have also occurred in parts of Europe.
Babesiosis is caused by several species of parasites belonging to the genus Babesia. Although there are a number of species that cause the disease, the most common species that infect humans are Babesia microti and B. divergens. The parasite is transmitted from an infected animal to humans by ticks. The ticks feed off infected animals and ingest the parasite. When a tick bites a human, it transmits the parasite. The parasite then attacks the host's red blood cells, which results in infection. The parasite remains in the bloodstream and can be transmitted to other humans by blood transfusions.
Symptoms of babesiosis include fever, chills, sweating, muscle aches, fatigue, an enlarged spleen, and hemolytic anemia. These symptoms may appear one to eight weeks after infection, and in some cases, an individual may not show symptoms for months or even years.
Babesiosis occurs worldwide, although it is predominantly reported in the United States. The prevalence of this disease is unknown in malaria-endemic countries, since the Babesia parasite may be misidentified as Plasmodium, the parasite that causes malaria.
In the United States, the coastal areas of the Northeast, such as New York and Massachusetts, are the areas where babesiosis usually occurs. The parasite B. microti has been identified as the primary causal agent in these areas, although other species have been reported to cause infections in Washington, California, and Missouri. In Europe, the parasite B. divergens has been found to cause infection.
The majority of babesiosis cases involve people with weak immune systems, such as the elderly, very young children, people with immunodeficiencies, and people whose spleens have been removed. Severe complications such as low blood pressure, liver problems, anemia, and kidney failure may occur with this disease. Most people exhibit mild symptoms or show no symptoms at all. Symptoms often go unnoticed so that people are unaware they are infected.
Treatment of babesiosis usually requires removal of the parasites with anti-parasite medications in conjunction with antibiotic therapy. Two treatments are available. The first uses the drugs clindamycin and quinine, but these drugs sometimes are not well tolerated by patients. Another treatment uses the drugs atovaquone and azithromycin. Both treatments have been found to be equally effective. In some cases, no treatment is necessary for the infection to resolve.
No vaccine is available to protect humans from babesiosis. Avoiding contact with ticks is the most important way to keep from getting the disease. A variety of measures to avoid tick exposure can be used, including wearing protective clothing (such as longsleeved shirts and long pants) and using insect repellents to discourage or kill ticks. If a tick has attached to a person's body, quick removal of the tick may prevent infection. Therefore, a thorough body check for ticks and the quick removal of any ticks discovered is a wise prevention strategy after any outdoor activity in a tickinfested area.
WORDS TO KNOW
EMERGING INFECTIOUS DISEASE: New infectious diseases such as SARS and West Nile virus, as well as previously known diseases such as malaria, tuberculosis, and bacterial pneumonias that are appearing in forms that are resistant to drug treatments, are termed emerging infectious diseases.
ENDEMIC: Present in a particular area or among a particular group of people.
VECTOR: Any agent, living or otherwise, that carries and transmits parasites and diseases. Also, an organism or chemical used to transport a gene into a new host cell.
Most known cases of babesiosis occur in the United States. However, it is likely that cases in malaria-endemic countries are not being identified due to similarities between the parasites causing each infection. Therefore, the distribution of this disease, and thus its impacts worldwide, may be understated.
In the United States, babesiosis is most common in the northeastern coastal states, including Massachusetts, Connecticut, Rhode Island, and New York. The disease is considered endemic in parts of these states. Babesiosis has also been reported in New Jersey, California, Georgia, Washington, and Minnesota. The increasing number of cases and increasing area of incidence indicates that babesiosis is an emerging disease.
The most common explanation for the increasing occurrence of babesiosis is an increase in the number of hosts for the parasite. The Babesia parasites reproduce in mice and other rodents, with the parasites being introduced into the mice while the tick feeds. While deer are not sites for parasite reproduction, they are a host for adult ticks. As a result, they have an indirect influence on the Babesia life cycle, since they ensure tick survival. Increased deer populations result in increased populations of ticks. This causes a higher likelihood that the parasite will be transmitted and a higher likelihood of human infection. In recent years, the size of deer populations in the United States has increased significantly, and this is thought to partially account for the increased incidence of babesiosis.
Mandell, G.L., J.E. Bennett, and R. Dolin. Principles and Practice of Infectious Diseases. Vol. 2. Philadelphia, PA: Elsevier, 2005.
New York Department of Health. “Babesiosis.” June 2004. <http://www.health.state.ny.us/diseases/communicable/babesiosis/fact_sheet.htm> (accessed February 1, 2007).
Stanford University. “History [of Babesiosis].” May 24, 2006. <http://www.stanford.edu/class/humbio103/ParaSites2006/Babesiosis/history.html> (accessed February 1, 2007).