A sign has recently appeared at a local park that warns visitors that whipworm contamination has been determined to be a problem there. In spite of the fact that the sign is present in only one place, it really could be applicable to any location where lots of dogs congregate, so it is worth knowing something about whipworms in general if you take your dog out in public at all.
We do not diagnose whipworms commonly in this area. The infective eggs are pretty tough and can live in the soil for years, even withstanding freezing weather, but like the little vampires they are, they don’t like direct sunlight and dryness, of which we seem to have an ample supply in these parts. As a result, they tend to be a much more common problem in warm, humid parts of the country like the southeast.
A dog gets whipworms when it ingests the eggs that have been deposited in the soil in the feces of a previously infected dog. The eggs have to go through a one month development period after being deposited in the soil before they are ready to infect another animal, so contact with fresh stool doesn’t run the same risk of infection. Once a mature whipworm egg is ingested, say as a result of licking dirt with eggs mixed in off of feet, it takes about three months for the immature whipworm to develop into a mature worm that burrows aggressively into the lining of the large intestine and sustains itself on the blood of the host. That burrowing can cause quite a bit of irritation which sometimes manifests as intermittent, possibly bloody diarrhea if the number of worms is large enough. The signs are more often minimal to non-existent when only a few worms are present. Weight loss and anemia are technically possible too, but it would require an extraordinarily large infestation to cause those types of problems, and it would be very unusual to see those sorts of cases in this area.
Diagnosing whipworms can be tricky. We look for the microscopic eggs in stool samples, but those shifty worms tend to release eggs intermittently, and in lower numbers that many other types of intestinal parasites, so it is possible to look at a stool sample from an infected animal and not see the eggs. Sometimes multiple samples need to be evaluated.
Treating whipworms can sometimes be tricky too. Most over the counter dewormers contain pyrantel pamoate, which is very effective against common roundworms, but will have absolutely no effect on whipworms. Your veterinarian, however, has effective products for killing whipworms. In order to completely clear the infestation a dog usually needs to be treated several times about 3 weeks apart because the medication kills adult worms but leaves the developing juveniles behind. After the first dose we wait for the leftover youngsters to mature to adults and then zap them with another dose when they become susceptible.
Reinfection from a contaminated environment can be significant problem. Picking up stool daily helps remove recently shed eggs before they can reinfect a dog, but for the eggs already in the environment there is nothing to do besides wait them out. Pouring bleach all over the ground just ruins your yard, puts poison into the environment, and causes infective whipworm eggs to giggle amongst themselves at the ineffectiveness of your efforts.
People get whipworms too, especially hot and humid parts of the world. The whipworms that affect people, however, are a different species than the type that gets into dogs, so there is no significant risk that dog whipworms will cross the species line and affect people too, although the same cannot necessarily be said of other types of intestinal parasites, so just to be safe it would be best not to eat dog poop or dirt that could be contaminated.