American Board of Internal Medicine (ABIM) Certification Practice Exam

How is babesiosis primarily transmitted?

1. Through contaminated water sources

2. Via Ixodes ticks

3. By respiratory droplets

4. Through direct person-to-person contact

The correct answer is: Via Ixodes ticks

Babesiosis is primarily transmitted through the bite of infected Ixodes ticks, commonly known as deer ticks or black-legged ticks. These ticks are vectors for the protozoan parasites of the genus Babesia, which are responsible for the infection. When an infected tick bites a host, it can transfer the Babesia parasites into the host's bloodstream, leading to illness. In the context of the other transmission methods presented, contaminated water sources do not play a significant role in the transmission of babesiosis. The parasites are not waterborne and are not transmitted via respiratory droplets, as this mode of transmission is more common for respiratory viruses and bacteria, not for parasitic infections like babesiosis. Direct person-to-person contact is also not a common transmission route; the disease primarily requires an animal reservoir and the presence of the Ixodes tick for transmission to occur. Therefore, the key to understanding babesiosis transmission lies in recognizing the essential role of Ixodes ticks as vectors in this infectious disease process.