Final answer:
The diagnostic test to detect adult Dirofilaria spp. is C. ELISA, which is the most reliable method for finding antigens produced by the adult worms.
Step-by-step explanation:
The correct option is C:
When diagnosing infections caused by Dirofilaria spp., which is the causative agent of heartworm disease in animals, there are several tests that can be utilized. These tests aim to either detect the presence of the microfilariae (the larval stage of the worm) or the presence of antigens released by adult worms. The diagnostic options A, Knott's filter test, and B, Direct blood smear, are mainly for the detection of microfilariae, whereas D, Buffy coat exam, is less commonly used due to its lower sensitivity and specificity compared to antigen tests. The most reliable method among the listed options for detecting adult Dirofilaria spp. is C, ELISA, which stands for enzyme-linked immunosorbent assay.
An ELISA test is designed to detect specific antigens or antibodies in a blood sample. For heartworm disease, antigen-detection ELISA kits are used to detect antigens produced by adult female heartworms. This test is typically very sensitive and specific, making it the preferred method for diagnosing infections with adult Dirofilaria. Unlike direct microscopic examination of a blood sample, the ELISA can detect infections in an earlier stage, even when microfilariae are not present, and is thus a valuable tool in both human and veterinary medicine.