We acknowledge the inherent challenges of serological testing for Lyme and related TBDs, especially concerning cross-reactivity [82,83], variable immune response, timing of serum sampling following exposure to tick-borne pathogens [84], and the inherent issues with tests for IgM antibodies [85,86] introduce complexities in accurately interpreting seroprevalence and co-infection data. The gene discussed is CD40LG; the disease is coinfection.