Babesiosis is a disease caused by a parasite that infects red blood cells. It is spread by the bite of an infected deer tick and occurs in coastal areas in the northeastern United States. Symptoms usually begin to appear from 1 to 8 weeks after being bitten by an infected tick. Most of those who are bitten show very mild signs or no signs at all. If symptoms are present, they include fever, chills, headache, achy joins and muscles, fatigue, nausea, vomiting, abdominal pain, and dark urine. These symptoms can last several months. People without a healthy spleen, elderly people, and people with weakened immune systems are more likely to develop potentially life-threatening symptoms. Babesiosis can be treated with medication.