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What Is A “Hookworm Antigen” Test?Updated 8 months ago

The antigen is only shed by the adult, so that means the antigen test will discover hookworms for only about a week before the eggs can be detected in the standard way.

Hookworms are among the most common intestinal parasites of dogs and cats and much easier to float and detect during fecal testing compared to some other parasites (like tapeworms). Fecal “O&P” (ova and parasite) by centrifugation and microscopy is the gold-standard way to screen for intestinal hookworm infections.

A proprietary fecal test Fecal Diagnostic Update - IDEXX US promoted by IDEXX Reference Laboratories (and veterinarians that utilize IDEXX) adds a “hookworm antigen” ELISA test to the fecal O&P. This antigen is simply a protein secreted by the adult hookworms (male and female) which can be detected in the pet’s stool if present. The primary purpose of this test type is to detect hookworms during a short (about one week) window of time before they start laying eggs.

So why don’t all veterinarians include hookworm antigen testing? Many vets choose other laboratories for their fecal testing services (hookworm antigen testing is proprietary to IDEXX) because they don’t see the value in this extra test. Why? Because hookworms grow up so FAST! Meaning it only takes about two weeks for ingested hookworm eggs from the environment to become adults in the digestive tract and start shedding their own eggs into the stool (Ref. Georgis’ Parasitology for Veterinarians, 9th Ed., pg. 181). The antigen is only shed by the adult, so that means the antigen test will discover hookworms for only about a week before the eggs can be detected in the standard way. The antigen test will not detect eggs, young worms migrating in the tissues or digestive tract, or hookworm larvae encysted in the muscle or gut walls. 

In perspective, a hookworm infection would only be missed (false negative) by the gold-standard fecal O&P if the hookworm egg ingestion happened just a few days to a week before the stool sample was tested. Since this window of time is so small, many vets don’t add on this extra test.

What about dogs (like greyhounds) with hookworm drug resistance? Hookworms in dogs are often resistant to commonly used deworming medications, and if positive should have a Fecal Egg Count (FEC) performed. Please note though that an FEC cannot be performed off a positive hookworm antigen test unless that dog is also shedding eggs (the FEC is a literal counting of the eggs). Hookworm antigen tests in dogs with a history of hookworm resistance can create interpretation confusion for the vet and pet parent and extra (often unnecessary) fecal testing. Why? Typical hookworm medications “purge” the worms from the intestinal tract at the time they are used (without residual effects – meaning they don’t “stay in the system”). Hookworm reinfections between deworming are common (even expected) and a positive antigen test doesn’t have to mean the deworming meds aren’t working. It may just mean this dog is between deworming and the next purge will clear the worms. Or it may mean the deworming is not working! If this is confusing to you, then you can appreciate why many vets don’t want hookworm antigen testing in these situations!


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