Babesiosis is a vector-borne disease in which the parasite, Babesia, is transmitted through the bite of a tick, or rarely, a blood transfusion. B. microti causes most cases of babesiosis in the U.S.; however, there have been sporadic cases caused by other species. The parasite infects the red blood cells of humans, and many people are asymptomatic or have non-specific flu-like symptoms such as fever, headaches, chills, and sweats. However, It can cause life-threatening hemolytic anemia in people who do not have a spleen, are immunocompromised (AIDS, cancer), are elderly, or have a chronic condition.
The tick-borne vector necessary for transmission is the black-legged or deer tick, Ixodes scapularis, which is found primarily in the Northeast and upper Midwest regions of the U.S. In 2014, the Centers for Disease Control (CDC) received reports of 1,744 cases of babesiosis in the U.S., a decrease of 1% from the total cases in 2013. However, there have been few reports of Babesia in Pennsylvania where it is currently not a reportable disease. Researchers at Main Line Health System in southeastern Pennsylvania reviewed epidemiologic data in response to an increase in the number of cases of babesiosis between 2008 and 2017.
Liu et al. performed a retrospective chart review for a list of positive testing for Babesia from their clinical laboratory. A total of 88 cases were found: 84 patients were from the ER and were hospitalized, and four have little clinical information. They analyzed the four hospitals within their health system and found that the most rural of the hospitals reported the most cases, and the hospital adjacent to Philadelphia had the least. The total number of cases increased from 35 in 2011 to 80 in 2017, but the incidence of babesiosis in this geographical region is probably underestimated since there is no mandatory reporting of the disease.
The average time from initial contact with a healthcare provider to diagnosis was 8.1 days before 2013 and 2.1 days between 2015-2017. The potential for Babesia causing thrombocytopenia was not recognized and was most often attributed to a viral syndrome, which may have affected a timely diagnosis. All 88 cases were diagnosed by a blood smear even though there is polymerase chain reaction (PCR) testing and antibody studies available.
The increased incidence of babesiosis in Pennsylvania has been attributed to a variety of possibilities: climate change with warmer temps and increased rain, increased acorn production, and milder winters.