Babesia is a malaria-like parasite carried by the same tick that carries Lyme. Because it is a parasite and not a bacterium, the antibiotics typically used for Lyme have no effect on it. It is seldom tested for, so people can finish Lyme treatment, still feel sick, and not understand why.

The CDC classifies Washington DC, Maryland, and Virginia as high-incidence areas for Lyme. Standard two-tier blood testing catches only 22 to 36 percent of early infections, so a negative result does not rule Lyme out when symptoms are present. Free state and county programs identify a tick's species but do not test it for disease, and broader co-infection testing is not routinely ordered.

Hashimoto's is diagnosed by combining findings, not one test: thyroid antibodies (TPO, sometimes thyroglobulin), thyroid function (TSH and free T4), symptoms, and often an ultrasound. A normal TSH does not rule it out, and a low-positive antibody is not always disease. Found early, before the gland is damaged, there is the best chance to protect it and feel better.