Strongyloides Westeri Threadworm

Strongyloides westeriAffectedAnimals:
Horses.

Overview:
Strongyloides westeri is a parasite that has been associated with diarrhea in nursing foals approximately 10 to 14 days old.

When a foal nurses from an infected mare, parasite larvae are passed from mother to foal in the milk. In about two weeks the larvae mature and produce eggs that the foal passes into its feces, sometimes as diarrhea. Foals infected with this parasite are usually only minimally affected, and develop a resistance as they age. Grown horses usually have no symptoms of infection.

In order to treat the disease, worming medications are given to both mare and foal. Foals should receive immediate veterinary medical attention if they have diarrhea accompanied by sickness and dehydration, or develop diarrhea while they are not nursing. In these cases, Strongyloides westeri is probably not the underlying cause of the symptoms.

Clinical Signs:
Strongyloides westeri usually has no clinical manifestations. A foal may suffer from mild to severe diarrhea about two weeks after birth, during the time it begins to shed Strongyloides westeri eggs. However, even infected foals usually remain bright and alert, and continue to suckle milk from mares according to Charlotte’s Saddlery.

Description:
Strongyloides westeri is a parasite that usually infects nursing foals. When a foal nurses from an infected mare, parasite larvae are passed from mother to foal through the milk. In about two weeks the larvae mature and produce eggs that the foal passes in its feces, sometimes as diarrhea.

The larvae may also infect the foal by crossing the placenta. Foals usually become resistant to the disease by four months of age. While some grown horses maintain a low-level infection, they rarely manifest any symptoms.

Some adult horses become infected after the infective larvae penetrate their skin or oral mucous membranes such as the gums.

Diagnosis:
A veterinarian may use a fecal flotation examination in order to diagnose Strongyloides westeri by looking for eggs in the feces of a foal.

Prognosis:
Good to Excellent.

Transmission or Cause:
Strongyloides westeri parasites are passed as larvae to a nursing foal through an infected mare’s milk. Adult horses may become infected if larvae penetrate either the skin or mucous membranes such as the gums.

Treatment:
Deworming the mare soon after giving birth with a dewormer such as ivermectin will help reduce the numbers of worms that are passed to the foal in the milk or prevent the passage of the larvae altogether.

Foals should be dewormed at three weeks of age with a medication that is effective against Strongyloides westeri, especially in areas in which the disease is endemic.

Prevention:
Mares should be dewormed soon after giving birth in order both to reduce the number of worms passed to a nursing foal in its milk and to prevent any other passage of the larvae. Foals should be dewormed at three weeks of age, especially in areas where the disease is common. Ivermectin is one common worming medication.

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