The invention relates to compositions and methods for the detection of various infectious organisms, including heartworm (Dirofilaria immitis), Ehrlichia Canis, Anaplasma phagocytophilum, and Borrelia burgdorferi. More particularly, this invention relates to antibodies that bind to a heartworm antigen, the E. Canis gp36 polypeptide, the A. phagocytophilum p44 polypeptide, the B. burgdorferi OspA, OspC, OspF, p39, p41 and VlsE polypeptides, and uses thereof.