STRONGYLOIDES – The Threadworm of dogs
Strongyloidiasis is an uncommon disease caused by an intestinal parasite called
Strongyloides stercoralis, the threadworm of dogs. This parasite has a direct life
cycle (meaning it does not require other intermediate hosts) and can survive outside
the canine host when conditions dictate. Only females are parasitic.
The adults live in the small intestine of dogs, producing eggs that develop into firststage larvae. These larvae hatch within the lower intestinal tract and are passed in
the feces and can contaminate the environment. Infective third-stage larvae develop
in the environment and are ready to infect or re-infect a host by either penetration of
the skin or by being ingested.
Ingested larvae go directly to the small intestine where they burrow in the intestinal
wall and mature there, causing ulceration of the lining of the intestines and
subsequent bloody diarrhea is often seen. Bowel movements may be dark and tarry,
or black in color indicating ulceration and bleeding in the intestines.
Larvae that penetrate the skin migrate to the lungs are coughed up and swallowed,
and take up final residence in the small intestine. Autoinfection can also occur if the
first-stage larvae develop to infective third-stage larvae before passing out of the
host. If this occurs, the larvae penetrate the mucosa of the rectum or perianal skin
and migrate through the body as before.
Infections in older dogs may not show significant symptoms. Clinical signs are more
commonly seen in young dogs and puppies.
Generally, strongyloidiasis occurs in dog kennel situations or breeding situations
where numerous animals are housed together. The parasite can be transmitted to
puppies in utero or through nursing and infected mother. It often begins in warmer
months when there is high rainfall, humidity, and growth of vegetation. Direct
sunlight and dry conditions help to destroy the larvae.
The infection is difficult to clear and dogs may continue to produce new eggs and
larva.
Removing feces promptly from the environment is crucial! Strongyloides larvae are
killed by direct sunlight, cold temperatures, and dry environments. As with other
parasites spread by feces, the yard be kept clean. Good human hygiene measures
are needed including the use of gloves and handwashing. Control and elimination of
Strongyloides from a breeding facility is very difficult because the larvae can be
transmitted to the young in utero and through nursing.
TREATMENT
1) Treatment is usually prolonged in dogs with active hyper-infections because the
drugs do not kill the migrating larvae. Re-treatment and frequent monitoring of stool
samples are usually needed.
3) Panacur (Fenbendazole): 50 mg/kg once daily for 7 days have shown to be helpful
in eliminating infections but periodic re-treatments are often necessary. This
medication is also used to treat the intestinal parasite called Giardia.
4) Monitoring fecal examinations once monthly for at least several months (ideally
for 6 months) AFTER the first negative fecal is recommended to ensure larval output
has ceased.
5) If the affected dog has been defecating outdoors in a wet area, the area should be
avoided until hot dry conditions prevail; otherwise a reinfection can occur.
Special considerations:
Larvae of S. stercoralis can penetrate human skin and result in cutaneous larval
migrans, and inflammation in the skin. It can also cause diarrhea and respiratory
symptoms in people when the larva migrate through the lungs. Therefore, infected
dogs should be isolated until fecal examinations have been negative as noted in the
treatment section.