Babesia is most effectively detected in blood smears. Whenever possible, specimens should be collected before treatment is initiated. When babesia is suspected, blood smears should be obtained and examined without delay. Since the parasitemia may fluctuate, multiple smears might be needed. These can be taken at 8 to 12 hour intervals for 2 to 3 days.The organism can easily be misdiagnosed as Plasmodium falciparum due to their similarities in morphology. With that in mind it is very important to pay close attention to the morphology of the parasites seen in the smear as well as obtain a complete clinical history of the patient so that Plasmodium falciparum can be excluded in the diagnosis.
Some of the distinguishing morphological characteristics to keep in mind when reading a smear for Babesia is the the lack of pigment; potential to contain vacuoles; the presence of extracellular forms; and protozoa with varying shapes and sizes. Trophozoites within red blood cells that appear in a tetrad formation (maltese cross) are also indicative of Babesia.
The most common of the Babesia spp. to infect humans in the Americas is B. microti (New York, Martha's Vineyard, and Nantucket having a high prevalence) while in Europe the most common is B. divergens.
It is important to be aware of endemic areas as they may occur in various regions. These areas will most assuredly be linked to the presence of the tick vector. In the NorthEastern United States and temperate regions of Europe the primary vector are ticks of the genus Ixodidae.
The prevalence of infections occurs most commonly in the months of May thru September where the levels of tick activity are at their highest.
Disease It Causes And The Clinical Symptoms:
People who contract Babesiosis suffer from malaria-like symptoms and as a result malaria is a common misdiagnosis for the disease, especially Plasmodium falciparum. Symptoms are characterized by irregular fevers, chills, headaches, general lethargy, pain and malaise. Hepatomegaly and/or splenomegaly can present on physical examination as well.
25% of infected Babesia infected adults and half of childhood cases are asymptomatic. The severity of the infection varies from patient to patient with the severity depending on many factors. The greatest factor for predisposing a person to a severe case of Babesiosis is the abscence of a spleen. Severe cases can present with hemolytic anemia, jaundice, shortness of breath, and hemoglobinuria due to the lytic effects of parasitic multiplication. Like Plasmodium falciparum, Babeisa can infect all stages of red blood cells.
Splenectomized indivduals are many times more susceptible to contracting the disease and having a fatal outcome without proper treatment. Often in 5 to 8 days of symptom onset. It is not uncommon for levels of parasitemia to be as high as 85% in splenectomized infected patients. This compares to a 1-10% parasitemia seen in immunocompetent individuals with spleens. Splenectomized patients suffer from severe hemolytic anemia. They can also develop hepatomegaly.
Babesia divergens is a much more pathogenic species. It has a fatality rate of 42% and presents with the most severe symptoms - hemogloinuria, jaundice, persistently high fever, shaking chills, and sweats. Untreated Babesia divergens infections progress into shock-like symptoms with pulmonary edema and renal failure. Babesia divergens infections have a latent period of 1-3 weeks while Babesia microti has a latent period of 1-8 weeks.
Location In The Host:
The parasites are located in the red blood cells of the definitive host and all stages of red blood cell development can be infected. Humans are dead end hosts as the natural definitive host is the white footed mouse.
The primary vector is the tick, genus Ixodidae. In the Americas the tick vector is Ixodes scapularis or the Deer Tick. Reservoirs of the parasite are theorized to be the white-footed mouse (Peromyscus leucopus Rafinesque), microtus voles (Microtus spp.), and the white-tailed deer (Odocoileus virginianus).
Another uncommon source of transmission of the parasite is through blood transfusions.
Test Recommended For Detection/Diagnosis:
A blood smear for examination is the test of choice.Indirect fluorescent antibody (IFA) testing can be used to supplement the blood smear for a higher specificity. Antibody testing in individuals that are asymptomatic are useful in identifying serum prevalence of Babesia.
Babesiosis diagnosis was once carried out with xenodiagnosis in hamsters for B. microti and in gerbils for B.divergens. While xenodiagnosis was successful at identifying the disease, the technique has since then been abandoned for faster and less cost prohibitive diagnostic measures.