Fecal parasite PCR panel (KeyScreen) in cats and dogs

What it shows

Classic stool tests look for eggs or cysts under the microscope. A fecal PCR panel instead looks for the DNA of parasites in a small amount of stool. The KeyScreen GI Parasite PCR panel lists 20 intestinal parasites:

• worms — hookworms (Ancylostoma, Uncinaria), roundworms (Toxocara, Toxascaris, Baylisascaris), the whipworm Trichuris vulpis and tapeworms (Dipylidium, Echinococcus, Taenia);
• single-celled parasites — Giardia, coccidia (Cystoisospora), Cryptosporidium, Tritrichomonas, Neospora, Toxoplasma;
• extra markers — whether Giardia belongs to the strains (A and B) that can also infect people, and a marker of hookworm resistance to one group of dewormers.

For each parasite found the report also gives an estimated burden — low, medium or high — and shows mixed infections.

Higher than reference — what it may be a sign of

• Detected — the parasite’s DNA is in the sample. DNA can be present when eggs cannot be seen, so PCR can find infections before the worms start laying eggs (the prepatent period) and cases with few eggs.
• Not always the animal’s own infection. A dog that eats faeces sheds the swallowed parasite stages for several days, and a cat or dog that hunts sheds stages of parasites from its prey. In one study, Toxocara cati (the cat roundworm) DNA found in dog samples was considered passage rather than true infection.
• Giardia A/B marker positive — the strain has potential to infect people; the vet takes this into account when discussing the household.
• Resistance marker positive — the hookworm carries a genetic change linked to resistance; the vet decides what this means.
• Found without signs — whether anything is needed is the vet’s decision.

Lower than reference

“Not detected” lowers the likelihood of the listed parasites in this sample, but parasite stages can be shed only from time to time, and one negative stool test is not enough to rule out parasites. The panel covers only the parasites on its list: lungworms and other parasites not on the list need other methods. In the comparison study, some Toxocara results were missed because new genetic variants did not match the test.

Look at together with

• Fecal flotation — in a study of 931 dog and cat samples, the PCR panel found 1.6 times more parasites overall than zinc sulphate flotation: about 3.4 times more Giardia, 2.8 times more whipworms and 1.4 times more hookworms, while for roundworms flotation found slightly more. PCR is advised together with microscopy, not instead of it.
• Giardia antigen, Cryptosporidium and Tritrichomonas — the same parasites by other methods.
• Baermann test — for lungworm larvae, which are not on this panel.

Units and conversion

There are no units and nothing to convert. Each parasite is written as “detected” or “not detected”; for detected ones the burden is given as low, medium or high, and the extra markers as present or absent. In the app the result is stored as text.

Reference range

The reference range is on your lab’s form; the expected result for each parasite is “not detected”. A detected parasite is read together with the stool, age, lifestyle (hunting, eating faeces) and the animal’s signs. The panel needs only about 0.15 g of fresh stool; in the refrigerator the sample can be stored for about 10 days, so it does not have to reach the lab the same day.

Cats and dogs

Sources

1. Antech Diagnostics — KeyScreen GI Parasite PCR
2. Leutenegger CM et al. Comparative study of a broad qPCR panel and centrifugal flotation for detection of gastrointestinal parasites in fecal samples from dogs and cats in the United States. Parasites & Vectors, 2023
3. CAPC (Companion Animal Parasite Council) — Hookworms guidelines
4. Merck Veterinary Manual — Parasitology in Veterinary Practice