by Chick Newman, PhD, DVM
Introduction....Life Cycle....Clinical Signs....Diagnosis....Treatment
Stronglyloides species (Strongyloides stercoralis in dogs [and occasionally in cats], Strongyloides tumefasciens (cats only)) are small nematode worms (dubbed "threadworms") that can reproduce as either a free-living (on decaying organic matter) organism or as parasites of animals and humans. The presence of decaying organic matter and filth, such as may be present in "puppy mills" and other unsavory facilities, increases risk of exposure to the freely-living form of the parasite, and infection. In dogs, Strongyloides stercoralis infestations, mostly a problem in puppies, may be assymptomatic or cause serious illness, including bronchopneumonia and severe, watery diarrhea. In cats, Strongyloides tumefasciens infestation in cats can be assymptomatic or can cause debilitation and chronic diarrhea of the large-bowel type primarily.
These parasites can reproduce in a suitable host or outside the host, if one is not available.. In this respect, Strongyloides are unique parasite variants of animals. The gist of the Strongylodies stercoralis life cycle can be seen here. With the exception of Strongyloides tumefasciens in cats, the adult worms burrows and reproduces in the lining of the small intestine (Strongyloides tumefasciens adults invade the mucosa and submucosa of the large intestine. This can result in the production and proliferation of tiny white nodules in these layers that then manifests as diarrhea and debilitation). The prepatent period...i.e. the time between infection and the appearance of infective eggs and larvae ...is only one week in dogs and cats!!
Animals: As mentioned above, Strongyloides can cause severe, life-threatening diarrhea (easily confused with parvoviral enteritis) and bronchopneumonia in young puppies and kittens. Strongyloides tumefasciens in cats, when symptomatic, causes a primarily large-bowel diarrhea. In addition a very pruritic (i.e. itchy) dermatitis may be noted especially when exposure to filth promotes free-form reproduction and accumulation of large numbers of skin-penetrating infective larvae. Alternatively, infection may be assymptomatic.
Humans: Strongyloides stercoralis causes severe illness and diarrhea in human infants. Once contracted, Strongyloides stercoralis infestation persists for decades! Sometimes, there are no clinical signs, and infective eggs/larvae are not detected by traditonal methods (see below). Alternatively, and without any pattern at all, the victim experiences intense abdominal pain, diarrhea and/or intensely pruritic dermatitis...also known as "creeping eruption". A similar itchy/creepy dermatosis is caused by hookworms larvae. In Stronglyoides infestation, it is postulated that reinfection occurs via perianal ("around the anus") penetration of skin or direct penetration of the bowel by infective larvae. In immune-compromised individuals massive reinfection (aka "hyperinfection") can result in death!
Fecal Flotation: The technique is decribed elsewhere. When looking for Strongyloides eggs and larvae, it is imperative that fecal sample is fresh.
Strongyloides egg and larvae
Baermann Technique: This procedure is designed to separate and concentrate larvae from feces. The principle is based upon the observation that nematode larvae tend to sink in a body of water when there is no surface tension.
- A large fecal sample is broken up, then placed in a tea strainer or cheese cloth
- This sample is placed in luke-warm water in a funnel (with a stopper or spigot on the bottom to prevent water leakage...see below)
- The larvae migrate to the surface of the fecal material to contact the warmth
- Once contacted with the water...in the absence of significant surface tension...the larvae sink to the bottom of the funnel
- Anywhere from one to 24 hours later, the spigot is opened and a drop of water containing (hopefully) concentrated larvae is collected and examined under a microscope for telltale larvae
Baermann apparatus
Fecal Culture: Culturing amplifies the number of larvae initially present and thus increases the probability of finding and identifying causative organisms. Since Strongyloides can reproduce outside the host, this technique requires only storage of the fecal sample in a jar and/or inoculation of nutrient agar culture medium with suspected feces or sample of material collected via Baermann method, above.
- Feces in a Jar: a little bit of water is provided for humidity, then 24-96 hours later, the jar is rinsed with a little water ( the larvae are swimming in condensed water droplets on the sides of the jar), the sample is centrifuged and the sediment is examined under the microscope for larvae
- Nutrient Agar Cultures: Samples collected by Baermann technique (or jar-culture technique, above) are inoculated onto petri dishes with nutrient agar and a small amount of water. After incubation at room temperature for two days the culture will be teeming with Strongyloides larvae
Skin Scapings: When clinical signs lend suspicion to the presence of "creeping of eruption" (intense itching due to migration of larvae through the skin), then deep scraping of skin with a scalpel blade and examination of scrapings under the microscope may reveal the presence of infective Strongyloides larvae.
Diethylcarbamazine 100 mg/kg orally, once
Ivermectin 0.2 mg/kg orally (this can not be given to some breeds...ask your veterinarian)
Mebendazole 20 mg/kg orally, daily for 3-14 days
Fendbendazole 50 mg/kg orally daily for 5 days for Strongyloides tumefasciens in cats
Thiabendazole 125 mg per cat daily for 3 days for Strongyloides tumefasciens in cats
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