Strongyloides In Dogs: Signs, Symptoms & Treatment Of Parasitic Nematodes

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Imagine handfuls of half-inch-long, worm-like creatures, resembling slender threads of white cotton, eerily penetrating the skin in something called transdermal transmission — no, it's not science fiction — they're threadworms, also known as pinworms and technically referred to as Strongyloides stercoralis. And they infect dogs, cats, and their people. Once the females of these parasitic nematodes get inside a dog's body via the skin or by ingestion, they migrate through the bloodstream and tissues of the throat, windpipe, and lungs to the small intestine where they thrive by diverting nutrients and feeding off of blood, tissues, and cells to facilitate their growth.

Hatching from eggs laid in the digestive tract, threadworms' offspring (larvae) escape the dog's body buried within the feces. These larvae then invade another canine host by burrowing through the skin — especially in high-density kennels, rescues, or other unsanitary environments where feces build up — and the cycle starts once again. Ideal conditions for strongyloides are hot, humid, subtropical climates and the infection is most prevalent along the Gulf Coast and the southeastern United States.

Thankfully, in many cases, these creepy strongyloides parasites usually cause only mild symptoms in your dog, such as slight diarrhea. On the other hand, they can play major havoc with your dog's health in more severe cases. Keep in mind that some dogs may not show observable symptoms of illness or any distress at all so the infection goes undetected, thereby growing in intensity.

Threadworm, illustration
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Is the strongyloides parasite zoonotic and can my dog pass the threadworms on to me?

Although threadworms can infect dogs, cats, and humans, experts believe different species of threadworms infect different hosts. But one thing is clear — threadworms in dogs are zoonotic and are therefore contagious to humans, and vice versa.

Are some dogs more vulnerable to threadworms and what are the clinical signs of infection?

A threadworm infection is dangerous for breeding females since the parasite may infect the mammary organs late in a bitch's pregnancy or while she's lactating. A nursing mother may, in turn, transmit the threadworms to her puppies through her milk in transmammary transmission. And puppies, with their immature immune systems, are at risk of severe illness and often a heavy infestation of threadworms is fatal for them.

For many dogs, a threadworm infection is relatively mild and may present as only slight diarrhea. On the other hand, for some dogs, symptoms are more pronounced and may even be severe. If you see any of these clinical signs of illness in your dog, it's wise to seek veterinary care at once.

  • Loss of appetite.
  • Weight loss.
  • Lack of energy or lethargy.
  • Dehydration
  • Weakness
  • Coughing or difficulty breathing which is caused by threadworms migrating through the lungs.
  • Diarrhea
  • Tummy ache.
  • Pneumonia
  • Skin rash or inflammation at the threadworm entry site.

Because so many symptoms of illness in dogs are the same, similar, or perhaps only vaguely noticeable, when your intuition tells you something is wrong — it usually is — a visit to your veterinarian at the first onset of unwellness or uncharacteristic behavior gives you peace of mind. And, of course, your vet will hopefully be able to make your canine pal feel better, especially if his tummy is queasy and his intestines are filled with threadworms.

Gastrointestinal nematodes
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Diagnosis of strongyloides or threadworms in dogs.

Ruling out other illnesses is one of your veterinarian's primary jobs as she evaluates evidence gleaned from a full physical examination and a review of your dog's medical history. She will also pay close attention to the observations you've made at the first onset of signs of illness in your dog. It's a good idea to record your dog's symptoms, the time they occur, and their duration on your smartphone or in writing so your vet has as much information as possible to make a diagnosis.

Once she suspects threadworms are the culprit, a definitive diagnosis of strongyloides infection is made by visually identifying the parasite's larvae in a fresh stool sample when viewed under a microscope. Numerous fecal examinations may be required since the larvae are shed irregularly, and old stool may contain the larvae of other similar internal parasites such as hookworm.

Sad Faced Dog with Big Brown Eyes
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Treatment and recovery from strongyloides infection in dogs.

The orally administered drugs thiabendazole, ivermectin, and fenbendazole are the current treatment protocol for threadworms. Sometimes strongyloides larvae will migrate to other areas of the body outside the intestine where they encyst themselves, which means they become enveloped in a cyst. Medication cannot remove the encysted larvae. Therefore further intestinal irritation may develop requiring another round of treatment.

How can I prevent my dog from getting a threadworm infection?

Controlling or preventing your dog from a threadworm infection requires following a few simple steps:

  • Strongyloides parasites need heat and humidity to survive. Keep your dog cool and dry. So if you live in a hot, humid environment, air conditioning or at least fans will help keep your pooch comfortable and lessen the risk for infection.
  • Keep lawns fece-free. Regular poop-scooping goes a long way in preventing threadworm infection.
  • Keep litter boxes fece-free.
  • Always keep in mind that threadworms can be spread to humans. Protect yourself by wearing rubber gloves when picking up or otherwise handling your dog's feces. Babies and young toddlers are most at risk for a severe infection.
  • Routinely test breeding females for threadworm infestation. The puppies of infected mothers should be treated periodically throughout nursing if the infection is a slight one. Otherwise, severe infestation in puppies is often fatal.