Whipworms

Laurie Anne Walden, DVM

Whipworms are intestinal parasites that are relatively common in dogs and can cause serious illness. Some (not all) monthly heartworm preventives prevent whipworm infection.
 
Canine whipworms are small worms about 2 to 3 inches long that live in the cecum, a pouchlike structure attached to the large intestine. The whipworm that infects dogs, Trichuris vulpis, does not infect humans. (Another species of whipworm can infect people.) Whipworms are very rare in cats in North America.
 
According to the Companion Animal Parasite Council (CAPC), almost 50,000 dogs in the United States tested positive for whipworms in 2019. About 2500 of these dogs were in North Carolina, putting North Carolina in the CAPC high-risk category for whipworms.[1]
 
Transmission
Dogs are infected with whipworms when they swallow whipworm eggs in the environment—for example, by licking dirt from their feet.[2] The eggs hatch in the dog’s intestines and grow to adult worms in the cecum. About 2.5 to 3 months after the dog is infected, the adult worms begin producing eggs that pass out of the body in the feces.
 
Whipworm eggs in the environment take about 2 to 3 weeks (or longer) to develop into a stage that can infect dogs. This means that dogs are infected by swallowing contaminated substances, not by eating fresh dog poop. Whipworm eggs in the environment are resistant to temperature changes and sunlight and are able to infect dogs for years.[3]
 
Symptoms
Symptoms of whipworm infection depend partly on the number of worms present and can include the following:

• No symptoms
• Soft stool
• Blood or mucus in the stool
• Bloody diarrhea
• Weight loss
• Dehydration
• Anemia (pale gums)

 
Diagnosis
Whipworm infection can be a little tricky to diagnose. Typical fecal analysis at a veterinary clinic involves looking for worm eggs in a stool sample under a microscope. However, because whipworms don’t produce eggs for the first few months after infection and they don’t produce eggs all of the time, stool analysis with a microscope can miss the infection. Sending a fecal sample to a diagnostic laboratory for a whipworm antigen test can increase the chance of finding the infection.
 
Treatment and Prevention
Antiparasitic drugs to treat whipworm infection are typically given in at least 2 doses spaced a few weeks apart. Monthly heartworm preventives that contain milbemycin (given by mouth) or moxidectin (applied to the skin) will treat and prevent whipworm infection.[3] Other heartworm preventives available at the time of writing (May 2020) are not effective against whipworms.
 
It’s not possible to completely eliminate whipworm eggs that are already in the environment. The CAPC recommends reducing dogs’ risk by removing dog feces from the environment and regularly testing dogs for whipworms.
 
References
1. Parasite prevalence map: 2019, whipworm, dog, United States. Companion Animal Parasite Council. Accessed May 20, 2020. https://capcvet.org/maps/#2019/all/whipworm/dog/united-states/
2. Brooks W. Whipworm infection in dogs and cats. Veterinary Partner. Published May 8, 2004. Updated July 18, 2018. Accessed May 20, 2020. https://veterinarypartner.vin.com/doc/?id=4952061&pid=19239
3. Trichuris vulpis. Companion Animal Parasite Council. Updated October 1, 2016. Accessed May 20, 2020. https://capcvet.org/guidelines/trichuris-vulpis/
 
Image: photomicrograph of Trichuris vulpis egg, 400× magnification. Credit: CDC/Dr Mae Melvin.

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