Does PCR Improve Pinworm Detection in Animal Labs?

Plus, why pinworm parasites are so detrimental to research animals and studies

Pinworms are parasitic nematodes common in many animals but very specific to their host species. Species such as Syphacia obvelata are commonly found in mice, including laboratory mice, but would never cross over to a human. In most animals, the pinworm goes through its life cycle within the intestine and sometimes just outside the anus, and leaves the host with few symptoms – so why do we need to worry about them in our labs?

“A pinworm infection will increase immunoglobulin E, so IgE, and that might interfere with studies,” said Ken Henderson, Senior Director of Laboratory Services for Charles River. “And it’s irritating to have pinworms in you. So if you’re doing behavioral studies on mice or rats, and they’ve got pinworms, that is going to influence the way they respond and act.”

Additionally, pinworms can have more serious effects on rodents with suppressed immune systems. Pinworms are easily transmitted and expensive to treat, so an outbreak can lead to costly treatments and stressed animals. 

“Fenbendazole is one of the common drugs used for eliminating pinworms,” said Henderson. “You might have to treat a whole rack of cages with it, but the feed is very expensive, so you don't want to get it in the first place.”

 In the past, common traditional methods for pinworm detection in a rodent colony involved sentinel animals exposed to the soiled bedding of colony animals, in the hope of inducing pinworm transmission.  A method referred to as fecal flotation testing is used to look for eggs in suspended feces, and evaluation of the GI contents under a dissecting scope can be used to directly see worms. Because a female Syphacia spp. lay their eggs in the perianal hairs, a tape test where tape is applied to the animal’s anus can be checked for microscopic detection of pinworm eggs. 

“Pinworms don't necessarily transfer well to soiled bedding sentinels, and when they do transmit, sentinel screening may be performed at the wrong stage of the life cycle when worms or eggs are absent,” Henderson said. “PCR (polymerase chain reaction) used for the detection of pinworms didn’t really occur until around 2010. We published with the University of Miami to look at their facility, where there was Aspiculuris tetraptera.”

The Miami study published in 2011 in the Journal of the American Association for Laboratory Animal Science found that performing PCR testing on mouse fecal matter was more effective than fecal flotation and GI content microscopy for worms, combined, for detecting pinworms. PCR amplifies the DNA of potential pathogens or parasites, making their DNA easier to detect. Since the use of PCR detection for pinworms became more common, a recent prevalence publication reported a dramatic drop in prevalence the prevalence of pinworms, Henderson said.
“So, it’s a really good story about how PCR has impacted prevalence,” he said. “First of all, it let us know where it was. And then because we knew it was there, it could be treated.”

By using more effective detection methods in quarantine, labs were able to prevent potential infestations from spreading to the rest of a facility. Although false positives can occur, the overall trend among laboratory rodents appears to be a decrease in pinworms since the widespread use of PCR.

The main image depicts Aspiculuris tetraptera, a cosmopolitan pinworm species that commonly infects laboratory and wild mice, as well as other rodents.

Photographs provided by Charles River’s Research Animal Diagnostic Laboratory.

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