What disease is carried by deer ticks?

Deer ticks, also known as black-legged ticks, are primarily known for transmitting Lyme disease to humans and animals. Lyme disease is caused by the bacterium Borrelia burgdorferi, which is often transmitted through the bite of an infected deer tick. Symptoms of Lyme disease can include fever, headache, fatigue, and a characteristic skin rash known as erythema migrans.

While other diseases like Rocky Mountain spotted fever are associated with different types of ticks, they are not primarily transmitted by deer ticks, which have a specific association with Lyme disease. Similarly, West Nile virus is spread by mosquitoes, and tick-borne encephalitis is transmitted by specific species of ticks, different from deer ticks. Therefore, Lyme disease is uniquely linked to the deer tick, making it the correct answer in the context of this question.