Here in Ohio, spring is in full swing. Trees are budding fervently, reptiles can be spotted basking in the midday sun, and the forest floors are beginning to grow a healthy layer of undergrowth to cover last autumn's leaf litter. Hiking is presently a joy, as the mosquitoes have not yet made their presence felt, and the days of high humidity and sweltering temperatures are still a few months away. I've been spending an abundance of time outside and, although it is only early May, have already noticed an unusual pervasiveness of a certain arachnid: Dermacentor variabilis -- the wood tick. In the last week I've found them in my car, on my dog, and even in the house. I'm not particularly worried, as D. variabilis isn't regarded as a particularly competent vector for serious human disease (especially in Ohio), but the sightings do make me wonder if this will be a bad summer for another species of tick, Ixodes scapularis--the deer (or black-legged) tick.
Ixodes scapularis is of serious concern to humans for a variety of reasons. First of all, it is much smaller than the wood tick, and is far more likely to feed unnoticed by the host. The black-legged tick is also a more efficient vector of human pathogens, including Lyme disease. While nearly everyone has heard of Lyme disease, and its notoriety has been enhanced by media and pop culture, the opposite is true of Babesia microti and babesiosis. Apart from parasitologists, Babesia is virtually unknown. Although mammalian infection with this parasite is ubiquitous, human infection is less common, and many cases are asymptomatic.
B. microti is a piroplasm, a protozoal parasite, that bears some similarity to malaria, causing hemolytic disease which results in generalized "flu-like" symptoms that are often difficult to accurately diagnose. These include headaches, body aches or pains, diarrhea, fatigue, lethargy, chills, and fever. In severe cases of infection where parasitic load is high, more serious symptoms/complications like jaundice, hemolytic anemia, respiratory failure, renal failure, and congestive heart failure can occur. The risks of Babesiosis are greatly increased for patients who have had the spleen removed or are otherwise immunocompromised.
Life cycle of Babesia microti.
1. Despommier, Gwadz, Hotez, Knirsch. Parasitic Diseases (5th Ed.), Apple Trees Productions, LLC. New York: New York (2005).
2. Centers for Disease Control, Parasites - Babesia. http://www.cdc.gov/parasites/babesiosis/