A study of the cross-reactivity between viral pathogens and tick-borne diseases reported that, in patients with acute EBV infection, the enzyme-immunoassay (EIA) test for Lyme disease IgM was falsely positive in 53% of cases, while the two-tier test (EIA coupled to western blot) was falsely elevated in 35% of patients. Here, CD40LG is linked to Lyme disease.