Babesiosis is a rare infectious disease caused by single-celled microorganisms (protozoa) belonging to the Babesia family. Babesiosis is an infectious disease caused by intraerythrocytic, tick-borne protozoa of the Babesia species. It is believed that the Babesia protozoa are usually carried and transmitted by ticks (vectors). Babesiosis occurs primarily in animals; however, in rare cases, babesiosis infection may occur in humans. Certain Babesia species are known to cause babesiosis infection in humans (e.g., Babesia microtia), and the deer tick is a known vector. Human babesiosis infection may cause fever, chills, headache, nausea, vomiting, and/or muscle aches (myalgia). Symptoms may be mild in otherwise healthy people; in addition, some infected individuals may exhibit no symptoms (asymptomatic). However, a severe form of babesiosis, which may be life-threatening if untreated, may occur in individuals who have had their spleens removed (splenectomized) or who have an impaired immune system. A different form of babesiosis has been reported in Europe that is associated with a more severe expression of symptoms.
Causes
Babesiosis is caused by single-celled microorganisms (protozoa) from the genus Babesia. These microorganisms are parasites that invade red blood cells (erythrocytes).
Babesiosis is a parasitic infection caused by protozoa of the genus Babesia. Babesia species have been subdivided into four categories, known as clades. Babesia microti is the most prevalent and well-described species and is classified as a Clade 1 organism. Babesiosis is typically acquired by bites from ticks carrying the protozoa. As the parasite infects erythrocytes (red blood cells), the infection can be acquired through blood transfusion and therefore can occur in persons who have not traveled to endemic areas. Transplacental transmission has also been reported.[rx][rx]
There are more than 100 species of Babesia. In most cases, the two species of Babesia that cause disease in humans (pathogenic) are Babesia microtia and Babesia divergens. The species involved vary depending upon specific geographic location.
The major cause of babesiosis in the northeastern United States is infection by B. microti. In California and Washington a new Babesia parasite, called WA-1, is believed to be responsible for the disorder. In Europe, B. divergens and B. bovis are usually responsible for babesiosis.
Babesia protozoa such as B. microti are transmitted to humans through the bite of infected ticks. The ticks serve as “vectors,” the term for any organism that is infected with and later transmits a particular disease agent (e.g., bacterium or virus) to another organism, which may then become infected. The deer tick (Ixodes dammini or scapularis) is the most common vector that transmits babesiosis.
In extremely rare cases, babesiosis may be transmitted following a blood transfusion with blood that is contaminated with the microorganism.
Diagnosis
The diagnosis of babesiosis is made based upon a thorough clinical evaluation, a detailed patient history (e.g., recent tick bite), characteristic findings, and specialized tests such as the examination of blood smear that screens for the parasite inside red blood cells (erythrocytes). The diagnosis may also be confirmed by antibody testing (indirect immunofluorescent assay).
The diagnosis of babesiosis is typically made by identifying the organism on a thin smear of peripheral blood, using Giemsa or Wright staining, and the severity of parasitemia can be assessed. In early infection, it is recommended that multiple thin smears be examined as parasite burden may be low initially. Ring forms are most commonly seen and can have multiple rings per cell. Tetrad formations, also known as Maltese crosses, are occasionally seen. PCR testing is also available at reference laboratories and is more sensitive than peripheral smears. Serology is performed via indirect immunofluorescent antibody testing and can be useful for confirming the diagnosis. A single positive serology cannot distinguish between acute and previous infection, but a four-fold rise in acute and convalescent titers confirms recent infection. Lab abnormalities that may be seen in babesiosis include anemia, elevated LDH, thrombocytopenia, transaminitis, proteinuria, and elevated BUN and creatinine. [rx]
Treatment
In most healthy people, babesiosis usually resolves spontaneously and causes few or no symptoms. People with an impaired immune system may require treatment with drugs such as clindamycin, quinine, and/or other antiparasitic or antibiotic drugs. Clindamycin and quinine are the drugs most commonly used to treat individuals with severe symptoms of babesiosis.
There are two regimens used for the treatment in mild to moderate disease. The first and most commonly used regimen is atovaquone plus azithromycin. The other option is quinine plus clindamycin which has much higher rates of adverse drug reactions compared to atovaquone/azithromycin (72% versus 15% respectively). A 7- to 10-day course of either regimen is recommended. Severe disease, requiring hospitalization or causing organ failure, typically occurs in high-risk populations or in those infected with the B. divergens species. These patients require treatment with clindamycin plus quinine (IV quinidine may also be used, but the patient requires monitoring for QT prolongation).
The duration of treatment is at least 7 to 10 days but is based on clinical and laboratory responses. Some of these patients with immunocompromising conditions will have the persistent or relapsing disease, in which case, a course of at least six weeks is recommended, with treatment continued for at least two weeks after parasites are no longer detected on blood smears. For patients who fail to respond to standard therapy, other regimens have been used including atovaquone plus azithromycin plus clindamycin; atovaquone plus azithromycin plus doxycycline; and atovaquone plus clindamycin plus doxycycline. No particular anti-parasitic combination therapeutic drug regimen has demonstrated superiority. If possible, it is also recommended to reduce underlying immunosuppression. [rx]
Partial or complete red blood cell (RBC) exchange transfusion is indicated in patients presenting with a parasitemia of at least 10% and anemia with hemoglobin of <10 g/dL. Consideration for exchange transfusion should be strongly given in those with infection due to B. divergens pulmonary, renal, or hepatic dysfunction, regardless of parasitemia level.[rx][rx]
Respiratory distress is common in severe diseases and patients must be monitored in the ICU. The respiratory distress is usually due to endotoxin release following medication-induced lysis of the red cells.
Treatment with two different drugs, atovaquone, and azithromycin, has been used in cases where clindamycin and quinine were ineffective. Individuals who have had their spleens removed who have severe cases of babesiosis may be treated with blood transfusions.
Prevention
Individuals who will be exposed to areas with high numbers of tick vectors for the Babesia parasites (e.g., fields, wooded or marsh areas, etc.) should consider taking certain steps to prevent infection. Such steps should include wearing long-sleeved shirts, long pants, and hats; wearing light-colored clothing to make ticks more visible; using appropriate tick repellents, and carefully checking clothing and skin (particularly the scalp and the back of the neck) after being in such locations.
FAQ
What is babesiosis?
Babesiosis is a disease caused by microscopic parasites that infect red blood cells. Many different species (types) of Babesia parasites have been found in animals, only a few of which have been found in people. Babesia microti—which usually infects white-footed mice and other small mammals—is the main species that has been found in people in the United States. Occasional cases caused by other Babesia species have been detected.
How do people get infected with Babesia?
The main way is through the bite of an infected tick.
• Babesia microti is spread by Ixodes scapularis ticks, which are commonly called blacklegged ticks or deer ticks. (Although white-tailed deer are the most important food source for the adult stage of the tick, deer are not infected with B. microti.)
• The parasite typically is spread by the young nymph stage of the tick. Nymphs are mostly found during warm months (spring and summer) in areas with woods, brush, or grass.
• Infected people might not recall a tick bite because I. scapularis nymphs are very small (about the size of a poppy seed).
Other possible ways of becoming infected with Babesia include:
• Receipt of a contaminated blood transfusion (no tests have been licensed yet for donor screening); or
• Transmission from an infected mother to her baby during pregnancy or delivery.
Where do most of the cases of babesiosis occur in the United States?
Most cases occur in the Northeast and upper Midwest, particularly in parts of New England, New York state, New Jersey, Wisconsin, and Minnesota. In the Northeast, babesiosis occurs in both inland and coastal areas, including off-shore islands, such as Nantucket and Martha’s Vineyard (Massachusetts); Block Island (Rhode Island); and Shelter Island, Fire Island, and eastern Long Island (New York state).
What are the symptoms and signs of Babesia infection?
Many people who are infected with Babesia microti feel fine and do not have any symptoms. Some people develop flu-like symptoms, such as fever, chills, sweats, headache, body aches, loss of appetite, nausea, or fatigue. Because Babesia parasites infect red blood cells, babesiosis can cause hemolytic anemia (from the destruction of red blood cells).
Babesiosis can be a severe, life-threatening disease, particularly in people who.
• Do not have a spleen;
• Have a weak immune system for other reasons (such as cancer, lymphoma, or AIDS);
• Have other serious health conditions (such as liver or kidney disease); or
• Are elderly.
How soon after the exposure do symptoms develop?
Symptoms, if any, can start within a week or so. They usually develop within a few weeks or months, sometimes longer.
What should I do if I think I might have babesiosis?
See your health care provider.
How is babesiosis diagnosed in people who have symptoms of the infection?
In symptomatic people, babesiosis usually is diagnosed by examining blood under a microscope and seeing Babesia parasites inside red blood cells. To be sure the diagnosis is correct, your health care provider might have specimens of your blood tested by a specialized reference laboratory (such as at CDC or a health department). In addition, your health care provider might decide to have your blood tested for other possible causes of your symptoms, including other tickborne infections, such as Lyme disease and anaplasmosis.
I have been diagnosed with babesiosis. Do I need to tell CDC?
No. It is not necessary for you to report your case to your health department or CDC.
Reportable conditions are diseases that physicians and/or laboratories must report to their state health department. Babesiosis is reportable in some states but not in others. If babesiosis is reportable in your state, the appropriate authority (a physician, hospital, or laboratory) will submit the necessary information to the health department.
Can babesiosis be treated?
Yes. Effective treatments are available. People who do not have symptoms or signs of babesiosis usually do not need to be treated. The first step is to make sure the diagnosis is correct.
Can babesiosis be prevented?
Yes. People can take steps to prevent babesiosis and other tickborne infections. The use of prevention measures is particularly important for people at increased risk for severe babesiosis (for example, people who do not have a spleen). If possible, areas infested with ticks should be avoided, especially during warm months. If such areas cannot be avoided, use protective measures during outdoor activities. See the Prevention and Control page for tips, such as checking yourself daily for ticks. The tiny I. scapularis ticks that spread B. microti usually must stay attached to a person for more than 36–48 hours to be able to transmit the parasite. Daily tick checks can prevent the transmission of the parasite.
No vaccine is available to protect people against babesiosis.
No vaccine is available to protect people against babesiosis.
References
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