Medical Parasitology

Diagnostic Parasitology

Diagnosis of parasitic infections in small animals is challenging, interesting, and fun, and involves the recognition of parasite stages based on size, morphology, color, and movement. Size and morphology are the major diagnostic parameters, and a calibrated microscope is the essential tool in the diagnostic laboratory. The fecal flotation technique is used routinely for the diagnosis of most parasites that reside within the gastrointestinal tract. The specific gravity and type of solution used often will influence the results obtained. Other techniques for diagnosis of specific gastrointestinal parasites include the direct smear and the merthiolate-iodine-formalin preservative method for diagnosis of Giardia sp, the Baermann technique for diagnosis of lungworm and other live larvae, the direct sedimentation technique for diagnosis of trematode eggs, the ether-formalin-sedimentation technique for diagnosis of trematode eggs and concentrating protozoan cysts from feces with high fat content, and the McMaster technique, a dilution modification of the fecal flotation technique. Techniques for evaluation of parasites in blood include the Knott's test, hematocrit method, and direct blood smear for diagnosis of microfilariae and thick and thin stained blood smears for diagnosis of Babesia sp, Haemobartonella sp, Cytauxzoon felis, Hepatozoon canis, and Trypanosoma cruzi. Tissue impression smears are used commonly for the diagnosis of Leishmania sp in dogs and biopsy specimens or aspirates are used for the diagnosis of Pneumocystis carinii. Diagnosis of acute toxoplasmosis can be accomplished with peritoneal and thoracic fluids, and organisms occasionally are detected in blood or spinal fluid. Serological tests for many parasitic diseases have been developed and often are used as supportive diagnostic tests in diagnostic parasitology.