Since parasitic diseases have the potential to affect most organ systems, no one set of clinical signs or syndromes characterizes parasitic disease diagnostics.

Diagnosis of parasitic disease has always been part of ADDL’s standard services to its clients. These services have always been provided through the Clinical Parasitology Service in the Department of Comparative Pathobiology of the Purdue University School Veterinary Medicine. Since this service was considered a subcontracted test, information on parasitology testing was difficult to find on the ADDL website and was not specifically listed in the ADDL fee schedule. The updated ADDL website will provide information on availability and cost of testing for parasitic diseases.

A variety of diagnostic techniques are available for parasitic diseases, depending upon what type of parasite and the species of host involved. Diagnosis of enteric parasites is still routinely done the old-fashioned way: direct smear and fecal flotation for detection of most nematode and cestode eggs. Alternatively, zinc sulfate or Streather’s sugar flotation, combined with centrifugation, is utilized for its enhanced ability to detect nematode eggs and protozoal cysts (including Giardia sp.) and oocysts. Acid fast staining for Cryptosporidium, which enhances detection, is also available. The ProtoFix procedure is another staining technique that aids in the identification of flagellates such as Tritrichomonas and other protozoa such as amoeba. Quantitative flotation provides a count of parasite eggs per gram of feces. Such information can be used to determine whether a pasture is contaminated, the presence of shedding animals, and for monitoring parasite control programs.

The sedimentation technique is used for detection of parasite eggs that do not float well. This is the desired method of diagnosis for trematode infections as well as demonstration of heavy nematode eggs that do not float in routine flotation solutions.

Some nematode infections result in shedding larvae in the feces. These include Strongyloides stercoralis in dogs, cyathostomes in horses and lungworms of cats, cattle, small ruminants and donkeys. The preferred method of diagnoses for such parasites is the Baermann technique. Since lungworm infections in horses are not patent, diagnosis requires direct examination of tracheal wash fluid that contains numerous eosinophils and may reveal the presence of larvae.

Since equine strongyle eggs and trichostrongyle eggs, especially those affecting small ruminants and camelids, are almost indistinguishable, identification to the genus or species level requires use of fecal culture. The eggs are hatched and the third stage larvae can then be examined and identified. Identification to this level can be valuable in establishing a control strategy. Morphologic identification of gross specimens of both endoparasites and ectoparasites is also available.

Detection of heartworm disease in dogs and cats differs because of the low parasite load that characterizes feline heartworm disease. In the past, blood samples from dogs were routinely examined for microfilariae using the Modified Knott’s technique, but this should be considered as a complementary test used in conjunction with more sensitive methods. Because of the possibility of amicrofilaremic infections (occult infections) in dogs and the low parasite load common in cats, immunodiagnostic tests based on the ELISA method are the current primary mode of testing. In dogs, the serologic test detects antigen to female Dirofilaria worms. Since cats may be infected by a single worm and male only infections are common, an antibody detection test is the primary test, often followed by an antigen test.

Identification of protozoal and metazoan parasites in tissue sections is provided by histopathology. Protozoa in tissue that are difficult to distinguish, such as Cryptosporidium, Neospora, Toxoplasma or Sarcocystis can be positively identified by immunohistochemical staining.

PCR technology is available at ADDL for Encephalitozoon, Neospora caninum, and Toxoplasma gondii. This procedure also identifies the organisms in tissue. Visit the Molecular Diagnostics section on our web page for information on the preferred specimen.

The tests listed below are currently available through ADDL. If there are additional diagnostic tests for parasitic diseases which our clients would like ADDL to offer, please contact us at 765-494-7440 or email us at addl@purdue.edu and efforts will be made to establish those tests if possible.