Abstract: A method for screening for Lyme borreliosis and other infectious diseases early in the course of the disease are disclosed. It has been found that there is a dramatic difference in surface binding of cultured infectious agents to naturally occurring polymorphonuclear leukocytes (PMNs) (e.g., neutrophils) between infected and noninfected animals, which may be present early in the course of the disease, before measurable antibody response. This binding response can be rapidly and accurately distinguished and quantitated using various detection techniques. The method involves visualizing the surface binding of the cultured infectious agent to naturally-occurring PMN to detect the infection.