Tick bites are the main mode of transmission of Babesia, just as with Lyme disease transmission but the ticks in question may be different. Lyme disease ticks include the western black-legged tick, Ixodes pacificus, whereas Babesia-transmitting ticks include cattle ticks such as Rhicephalus (Boophilus) microplus and R. (B.) decoloratus as well as Ixodes scapularis. Unlike Ixodes ticks cattle ticks only take a meal from a single host animal during each feeding cycle. Lyme disease ticks may have several hosts during each stage of the tick lifecycle. As an Ixodes tick may be infected with both Babesia and Borrelia it is possible that a single tick bite could cause both infections in a human patient. Host reservoirs for Babesia also mirror those of Lyme disease, such as white-footed mice, and deer which can help clinicians determine the relative risk of Babesiosis and Lyme disease given the presence of such animal host reservoirs in an area.
IFA used for Babesiosis diagnosis has a much higher rate of specificity than blood smears with 88-96% of infection detected successfully in patients. Some people remain asymptomatic and IFA helps in detecting the presence of Babesia in such individuals. As with Lyme disease morphology, the morphology of Babesia is interesting as the protozoa become cyclical in the red blood cells, forming into a trophozoite ring before turning into merozoites with a tetrad structure. This structure is specific to Babesia, making a blood smear easier to assess when comparing Babesia to the non-Maltese cross form malaria parasite. The rapid spread of Babesia in the blood is due to the protozoa’s ability to burst the host erythrocytes and release vermicules through the circulation.
Tests for Babesia
Unfortunately, tests for Babesia only currently detect B. microti and WA-1, with other strains proving difficult to detect using serological and nuclear analysis. Further problematizing Babesiosis diagnosis, it is thought that blood smears are only helpful in detecting the early stages of infection (in the first two weeks) or for milder infections. Treatment for Babesiosis is often given despite negative serological tests or the absence of results. PCR tests for Babesia can more effectively identify B. microti than blood smears but is not able to detect other strains of Babesia.
FISHing for Babesia
A fluorescent in-situ hybridization assay (FISH) is an advanced form of blood smear test that is significantly more sensitive to Babesia than a standard blood smear. Instead of using ink-based stains, the FISH assay makes use of a fluorescent-linked RNA probe and UV light which makes it easier to identify Babesia protozoa. B. microti is the only strain that is currently able to be detected using this method, however, which somewhat limits its use, particularly in Europe.
Stages of Infection
Fortunately, unlike Lyme disease, Babesiosis infection status can be determined in large part by titers with persistent positive titers on Western Blot testing indicative of persistent infection. Antibodies to Lyme disease may remain high even after infection has been eradicated, or may appear low when infection is actually causing severe symptoms; just one of the reasons Lyme disease diagnosis can be so confounding.
In humans, Babesiosis may simply resolve of its own accord with mild, or no, Babesiosis symptoms and no need for treatment. In those who are immunocompromised the infection can become acute and life-threatening very rapidly and will require treatment with oral and intravenous medications. Standard treatment for Babesiosis was, up until recently, oral or intravenous Clindamycin and oral quinine but in the past decade this has switched to a regime of oral Atovaquone and oral azithromycin. These drugs have been found to result in fewer adverse reactions and undesirable side-effects during Babesiosis treatment. Treatment may depend on the strain of Babesia as B. microti tends to be more responsive to medications or may resolve without medication, unlike B. divergens. There are some severe cases of B. microti infection, however. Where a patient’s condition is extremely dangerous they may have a blood exchange transfusion in an effort to lower the concentration of parasites and make subsequent treatment more effective. Of course, application of effective and timely treatment relies on accurate Babesia diagnosis, which can be missed in cases of Lyme disease co-infection.