Although nearly all dogs are infested with parasites at one time or
another, most develop an immunity that keeps the parasite population in check.
This immunity can break down, however, under conditions of stress or ill
health. When that happens, the worms increase in number and eventually produce signs
of intestinal infection, including diarrhea, weight loss, anemia, and blood in the
Dogs develop the highest level of immunity to worms that have a larval phase
that migrates in tissue. These are the ascarids, hookworms, and threadworms.
Whipworms and tapeworms do not have a
migratory phase and thus produce little immunity.
House soiling, or inappropriate urination or defecation, is a common problem in dogs. While in many cases house soiling is due to a behavioral problem, sometimes medical issues are to blame. It may be difficult or even impossible for a pet parent to distinguish between behaviorally caused house soiling and medically caused house soiling. For this reason, the first step in solving a house-soiling problem is to take your dog to a veterinarian for a thorough check-up and urinalysis.
Immunosuppressive drugs such as cortisone have been shown to
activate large numbers of encysted hookworm larvae. Stressful events such as pregnancy, surgery, severe
illness, trauma, and emotional upsets (such as shipping or going to a new home)
can also activate dormant larvae.
Although some deworming medications are
effective against more than one species of worm, no single medication is
effective against them all. A specific diagnosis is necessary to choose the
safest and most effective drug. This requires an examination of the dog’s stool
and determining whether the parasite is in the egg, larval, or adult stage. It
is not advisable to deworm a dog suffering from an unexplained illness that is
assumed to be caused by “worms.”
All anthelmintics (medications that act to expel or destroy parasitic worms)
are poisons-meant to poison the worm but not the dog. Dogs debilitated by heartworms or some other
infestation may be too weak to resist the toxicity of the dewormer. Be sure to
check with your veterinarian before using any dewormer. It is also important to
give the medication exactly as prescribed.
Most young puppies are infested with ascarids. Other worm parasites may also
be present, but they’re not as common. It is advisable to have your
veterinarian check your puppy’s stool before deworming for ascarids, because if
other worms are present, a broad-spectrum deworming agent may be
Puppies should be dewormed at 2 weeks of age (before ascarid eggs are passed
in the stool) and again at 4, 6, and 8 weeks of age. Then, it’s prudent to put
them on a monthly heartworm preventive for life that also protects the dog
against other parsites, or at least continue monthly deworming for six months.
This schedule kills all ascarids, whether acquired in utero, through infected
mother’s milk, or by ingesting the eggs. Pyrantel pamoate (Nemex or Strongid)
is an excellent choice for ascarids and can be safely given to 2-week-old
puppies. It is available as a liquid suspension or tablet.
Worm medications can be harmful to puppies that are ill from a respiratory
infection, chilled, crowded in unsanitary surroundings or abruptly weaned from
their mothers. Stressful conditions such as these should be corrected before
administering the dewormer. Do not deworm a puppy who has diarrhea unless your
veterinarian has determined that the diarrhea is caused by the parasite.