Our pets can be hosts for a wide range of parasites. Some of these parasites are harmless to humans, but others can cause serious illness if we become infected. Many of these infectious parasites are transmitted via the feces of our pet dogs (or cats), making it important to understand how these parasites live, breed, and especially, the best ways to prevent our pet’s environment from becoming infective and causing a health-risk to us. One such parasite is the dog whipworm which can cause severe intestinal problems.
Whipworms are a group of several species of parasitic, nematode worms. The species of whipworm that infects dogs, occasionally cats and rarely, humans, is known as the dog whipworm (Trichuris vulpis).
As the name suggests, in the adult form, this parasitic worm has a whip-like shape. It has a small, narrow head at the front, which is the part of the worm that eats and digests material. The tail part, which is much larger and thicker (the ‘handle of a whip’), is the reproductive part of the worm. Their length ranges from 30 to 50 mm, making it one of the smaller parasitic worms.
Eggs from the whipworm are oval in shape with obvious plugs (caps) on the top and bottom. The eggs have a thick outer shell and range in size from 72 to 90 μm in length and 32 to 40 μm in width.
Adult whipworms live in the large intestines of dogs. They lay many eggs into the large intestine which are released to the external environment via the feces. These eggs form embryos after about 2 to 4 weeks in the soil; they are then infective if ingested by a new host. The embryo continues to develop within the egg to become an infective larva. After the new host has eaten the infective eggs, these move to the gastro-intestinal (GI) system of the new host.
Once in the GI system, the eggs hatch, usually in the small intestine. They penetrate the mucous membrane layer and then develop for a further 2 to 10 days before moving to the large intestine.
Once in the large intestine, the larvae continue to develop and grow while burrowing into the surface of the tissue lining the colon and caecum. Although the worms invade intestinal cells in many places, they only develop to become mature adults in the colon or caecum.
Once they become an adult, their tail end greatly enlarges. The worms then push through the walls of the large intestine such that the head remains embedded in the large intestine walls, but the tail dangles into the lumen (space) of the colon. Adult whipworms live inside the cecum, colon and rectum before they lay eggs to be released in feces about 10 weeks after infection. The eggs are laid intermittently.
Once the eggs are in the external environment, they are highly resistant to extremes of sunlight and temperature and may remain infective for many years.
DISTRIBUTION AND EPIDEMIOLOGY
Vulpis infects canines throughout the world. Older dogs normally have a higher level of infection than younger dogs. The eggs of T. vulpis are prevalent in shady, moist soil areas that have been contaminated by canine feces. In the United States, it has been reported that 14.3% of shelter dogs are infected with this parasite.
Low burdens of dog whipworms often produce no symptoms in the host dog – owners may be completely unaware that their dog even has the parasite. In these cases, the whipworms may remain undiagnosed or the eggs might be discovered during a routine fecal flotation examination. However, in large numbers, canine whipworms can produce severe disease symptoms including –
Your dog’s behaviour
- Frequent defecation: the dog tries to pass feces very often but usually passing little or no faeces
- Straining to defecate: the dog looks like it is having to push hard to defecate
- Abdominal pain: the animal may be sensitive to touching the abdomen or stand very tense and still
- Restlessness: the dog may pace a lot and refuse to settle
- Slimy feces: jelly-like, often containing mucus
- Watery diarrhea: often containing mucus
- Feces are blood stained or blood tinged: the blood is usually red and fresh
- Vomiting: a rare symptom, but can happen in dogs with severe large bowel inflammation
- Flatulence: frequently expelling gas
Appearance of your dog
- Anemia (low numbers of blood cells): this can be seen as very pale gums
- Bloating: swelling of the abdomen
- Rectal prolapse: dogs that are frequently straining can prolapse the lining of the rectum through the anus
On rare occasions, a potentially life-threatening imbalance of the potassium and sodium salts in the body, termed “Pseudo-Addisons disease” can develop.
DETECTION AND DIAGNOSIS
Dog whipworm infection is usually diagnosed using a test called fecal flotation. Because whipworm females shed their eggs into the environment intermittently, repeated fecal floats may be needed for a completely positive or negative diagnosis.
Sometimes, whipworm infection will be diagnosed while the vet is performing a colonoscopy on the canine patient for another disease. A colonoscopy is the insertion of a small video camera into the GI tract – the worms can be seen dangling from the walls of the large intestinal tract.
In circumstances where many dog whipworm eggs have contaminated the pet’s environment, the owner will need to repeat-worm their dog (or cat) every 2 to 3 months to control the adult whipworm numbers. Unfortunately, eggs have been known to survive for 7 years, so treatment might be a long-term prospect. Clearly, prevention is better than treatment.
It is very important to pick up and dispose of all dog feces immediately after the dog has passed them. When feces are given the chance to break-down on soil or lawns, they release the whipworm eggs into the environment. Other ways of preventing the development of an infective environment include –
- Housing dogs on sand, gravel or concrete: these are easier to disinfect than soil or lawn
- Bleaching and steam-cleaning environments: these methods can help kill the resilient eggs
- Regularly replacing the soil or lawn, e.g. every 3 to 6 months
- Worming dogs regularly
- Worming all dogs (animals) on the premises on the same day
- Weighing before worming so the correct dose of wormer is given
- Rotating worming medications to avoid whipworm drug resistance
- Changing wormers if the one you are using does not seem to be working
INFECTION OF HUMANS
Although dog whipworm is generally considered to be of relatively low importance to human health, it IS infective to people. Both dog whipworms (Trichuris vulpis) and pig whipworms (Trichuris suis) have been discovered in the GI tracts of humans. These infections produce severe signs of intestinal disease and diarrhoea. For dog whipworm, the route of transmission to humans is via the feces of the dog (or cat). This means it is extremely important to keep you and your dog’s environment free of feces and for you to maintain high levels of hygiene. This will prevent your pet’s environment from becoming infective and lower the risk of you or your family becoming infected.