Is There a Blood Test for Parasites?

From time to time, dogs acquire parasites from their environment. While low parasite levels may not cause serious symptoms or illness, routine parasite tests can help keep your furry friend healthy and parasite-free. Additionally, as some of your dog’s parasites may infect your family, routine testing is wise. While some parasite tests focus on clues found in your dog’s feces, blood tests are the only way to diagnose some parasites.

Vomiting, intestinal disturbance, coughing, lethargy, skin irritations and poor coat condition can all signal that your dog may have parasites. Additionally, some dogs -- particularly young puppies -- develop a “pot-bellied” appearance when afflicted with worms. Some parasites provide visual clues to their presence. Tapeworm segments are often visible to the naked eye, looking like grains of rice on your pet’s feces. Roundworms are occasionally visible in stool or vomit. However, veterinarians must perform laboratory tests to identify most parasites. The two most common types of tests are fecal and blood tests.

Many parasites inhabit the gastrointestinal system, so it makes sense for veterinarians to examine your dog’s feces for signs of their presence. In a fecal exam, either doctors prepare a slide made from direct contact with the stool, or they use a technique called fecal flotation. When performing this technique, veterinarians place your dog’s stool in a liquid that causes the parasite eggs to float. When testing blood, veterinarians either examine samples microscopically for the presence of parasitic organisms, or search for antibodies produced by the body to combat the infection.

Five major types of worms infect dogs, but some are not detectable in fecal exams. By contrast, blood tests are effective for most types, and are the only method for detecting some. For example, whipworms do not always show up in fecal exams, but blood tests will reveal their presence.As they live in your dog’s heart rather than gastrointestinal system, veterinarians must use blood tests for determining if heartworms are present. Blood tests also detect the presence of roundworms or tapeworms.

Mycoplasma parasites are bacteria that infect the red blood cells of dogs. Transmitted primarily by flea or tick bites, infection is often asymptomatic, though it may cause anemia. Dogs who have had their spleen removed, and therefore lack the body’s primary filter for damaged red blood cells, are more susceptible to the infection. If your veterinarian suspects a mycoplasma infection, he likely will smear some of your pup’s blood onto a slide, stain it to provide contrast and visually inspect the slide through a microscope to verify the presence of the bacteria.

Protozoans are microscopic, single-celled organisms that often parasitize dogs. Babesiosis, diagnosed via blood tests, is a disease caused by protozoan parasites of the genus babesia. This disease can vary in severity from mild and short-lived to fatal. Veterinarians document the presence of other protozoal parasites, such as Trypanosoma brucei, which spreads via the bite of some flies, by microscopic examination of the blood.