Co-Infections & Related Illnesses

Ticks are capable of harboring multiple pathogens. When an infected tick feeds, it may transmit more than one organism at once. Co-infections can make symptoms more severe, prolong illness, and complicate treatment if not identified and addressed.

Anaplasmosis

Caused by Anaplasma phagocytophilum, anaplasmosis is transmitted by the same black-legged tick that carries Lyme disease, making co-infection common. Symptoms include high fever, headache, muscle aches, and low white blood cell count, typically beginning within 1–2 weeks of a bite. Doxycycline treats both Lyme and anaplasmosis — one reason it is the preferred first-line antibiotic.

Babesiosis

Babesiosis is caused by microscopic parasites (Babesia microti and related species) that infect red blood cells, similar to malaria. Symptoms range from mild (flu-like illness) to life-threatening hemolytic anemia, particularly in older adults or immunocompromised patients. Critically, babesiosis does not respond to doxycycline — it requires antiparasitic medications: atovaquone plus azithromycin (mild to moderate) or quinine plus clindamycin (severe cases).

Ehrlichiosis

Caused by Ehrlichia chaffeensis, transmitted primarily by the lone star tick. Symptoms — fever, headache, fatigue, muscle aches — typically develop 1–2 weeks after a bite. Treatable with doxycycline.

Powassan Virus

A rare but serious viral infection transmitted by black-legged ticks. Unlike bacterial co-infections, there is no specific antiviral treatment — care is supportive. Powassan can cause severe brain inflammation (encephalitis) with a case fatality rate of approximately 10–15%. The fact that it can be transmitted in as little as 15 minutes of tick attachment makes prevention especially important.