Just Ask the Expert: How do you detect Physaloptera species eggs?

Oct 01, 2010

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We are seeing cases of Physaloptera species infection endoscopically but cannot demonstrate the ova in fecal parasite examinations. What technique would you suggest?

Thomas McCoy, DVM
Harvard Avenue Veterinary Clinic
Tulsa, Okla.

Kevin R. Kazacos, DVM, PhD
You've hit on a common difficulty in dealing with stomach worm (Physaloptera species) infections in dogs and cats. These parasites are most commonly associated with chronic intermittent vomiting,1-4 and for several important reasons you may not see eggs in fecal examinations even though the animal is showing clinical signs. The two most important reasons are
1. The worms are within the prepatent period, so they are too young to shed eggs.

2. Physaloptera species eggs are too heavy to be recovered by most routine flotation methods.1-4

In addition, female worms may not produce many eggs; often only a few (one or two) worms are present.1-4

Thus, many dogs and cats with endoscopically positive, clinical Physaloptera species infections will not have eggs in their feces,1-3 or, if they do, the eggs may be few and difficult to recover for a diagnosis. Even a single worm can cause gastritis and intermittent vomiting related to the irritation and inflammation caused by its anterior end being embedded in the stomach mucosa.1,3


Physaloptera species eggs are well-known as some of the heaviest we deal with, having a specific gravity estimated at 1.2376.5 This specific gravity is clearly above that of many flotation solutions routinely used by veterinary hospitals and commercial laboratories, resulting in false negative findings even in patent infections. This presents a diagnostic problem, as does the generally low and variable prevalence of the parasite (1% to 28% of dogs)4 and low infection levels as noted above.

Because of biological variation, a few eggs may float in solutions with slightly lower specific gravity, but flotation solutions needed to recover Physaloptera species eggs (and some others such as taeniid tapeworms) are generally above a specific gravity of 1.24.5-7 Sodium dichromate solution at a specific gravity of 1.36 has been recommended for detecting Physaloptera species eggs,6 and other higher specific gravity solutions would also work well.

My suggestion would be to use Sheather's sugar (sucrose) or sodium nitrate solution at a specific gravity > 1.24 (e.g. 1.25 to 1.27) for routine use in your practice. Or if you use solutions with a specific gravity of 1.20 to 1.22, I would recommend that you keep a bottle of one of the higher specific gravity solutions (sodium dichromate or nitrate solution) on hand for cases in which Physaloptera species infection is suspected.

The specific gravity of solutions is easily checked by using an inexpensive hydrometer.7 Keep in mind that slides using any high specific gravity salt must be examined immediately because of impending crystallization, which can be slowed by ringing the coverslip with clear fingernail polish.