Parasites such as worms, fleas and ticks can make your dog uncomfortable and even seriously ill. This page describes the most common parasites that can affect dogs. You should consult your veterinarian for the best way to prevent infestation in your dog and your home.

Internal Parasites

Hookworms are common in puppies, though dogs of any age can be infested. Hookworms are acquired by puppies from their mother by nursing and by adult dogs by swallowing the parasite's eggs or having the hookworm burrow into the skin. Infection can be prevented by keeping your dog's environment clean. Your veterinarian can detect hookworms by examining a stool sample under a microscope.

Roundworms are also common in puppies and can infect other dogs and children. They look like white, firm, rounded strips of spaghetti, one to three inches long. Your veterinarian will look for signs of roundworms in the stool sample. Again, keep your dog's environment clean to prevent infestation.

Tapeworms will cause your dog to lose weight and have occasional diarrhea. You'll know if your dog's got them because you'll see segments of the worms around his anus or on his stool. The segments look like grains of rice.

Whipworms are acquired by licking or sniffing contaminated ground. They live in the dog's intestine and are only detectable in a stool sample.

Heartworms enter a dog's bloodstream from the bite of an infected mosquito. The worms mature in the dog's heart, growing to twelve inches in length and effectively clogging the heart -- a very serious condition. Heartworm infection occurs throughout the United States but is particularly common in warm, mosquito-infested areas. Treatment is expensive and can be dangerous. Fortunately, you can keep your dog free from infestation by administering heartworm preventive pills.

External Parasites


Fleas are a very common problem. You will need to be diligent aboutflea control; if you're not, your dog can suffer hair loss, allergic reaction, and worms. You also risk infesting your house and family members as well. You can consult your veterinarian for flea prevention methods. Trifexis is one medication that can safeguard your dog with powerful 3-in-1 parasite protection.  It is a once monthly tablet, and since it is given orally, there is no need to isolate your dog from your kids or other pets.

Fleas are tiny wingless insects that feed on dogs, among other animals. Flea bites make some dogs, that are allergic to flea saliva, so miserable that they bite and scratch themselves raw. Other dogs do not seem to respond to flea bites with the same intensity. If you see evidence of fleas on your dog, it is essential to eradicate them as quickly as possible, before the population grows. Hungry fleas sometimes bite humans too, leaving small, red, itchy bumps most commonly observed on the wrists and ankles.

You may actually see the dark fleas, about the size of sesame seeds, scurrying about on the skin. Their favorite spots include the base of the ears and the rump. Look closely to sparsely haired places like the groin for telltale signs. A more accurate way to diagnose fleas, however, when live ones aren't observed, is to part the fur in several places and look for tiny black specks about the size of poppy seeds. These specks are flea feces, composed of digested blood. If you're not sure whether you're looking at "flea dirt" or just plain dirt, place it on a damp piece of white tissue. After a minute or so, a small red spot or halo will become apparent if it's flea feces, since the blood re-hydrates and diffuses into the tissue.

If your dog has fleas, you should ask your veterinarian for the most effective way to rid them from the dog and its bedding and environment. Effective flea prevention is also available; ask your vet for the best method for your dog.


Ticks can cause a number of serious illnesses, including Rocky Mountain spotted fever and Lyme disease. Check your dog for ticks daily if he spends any time outside, and whenever you see one, take it off immediately. The best way to do this is to numb the tick with rubbing alcohol or petroleum jelly, then pull it off with tweezers. Once removed, kill the tick by putting it in a container of alcohol. Prevent an infestation by treating your dog with a medication, dip, spray or powder as recommended by your veterinarian.

Ticks are categorized in the class of Arachnida, phylum Arthropoda. Even if your Latin is rusty, you might recognize Arachnida as the class of creature that also includes insects such as spiders, scorpions, and mites. While ticks are a hassle, be glad that most of us don't have to worry about keeping scorpions off of our cats.

Arachnida are characterized by four pairs of segmented legs and a body that is divided into two regions.

  • There are over 800 species of ticks worldwide and they all feed on the blood of mammals, birds and reptiles.
  • The two families of tick are called Ixodidae (hard ticks) and Argasidae (soft ticks). The Ixodidae have a hard dorsal scutum (shield). Argasidae have a soft exoskeleton with no scutum.
  • While one would seem to be weaker, both groups unfortunately have the ability to transmit disease.
  • The saliva of the hard tick has an anesthetic effect at the site of the bite.
  • The saliva also helps keep the blood flowing by keeping it from clotting while the tick is feeding.
  • In many hard ticks, the saliva also acts like cement, helping to anchor the tick in place and making it harder for you to remove it.


Mosquitoes are more of a nuisance than a serious threat to dogs. The West Nile virus, an infection carried by mosquitoes, remains fairly low. Regardless of the risk, mosquitoes are a pain. They exist everywhere in the United States, except at elevations above 8,000 feet.

There are approximately 200 different species of mosquitoes in the United States -- all of which live in specific habitats, exhibit unique behaviors, and bite different types of animals. Mosquitoes are insects that have been around for millions of years. During this time, they have been honing their skills so that they are now experts at finding people to bite. A mosquito has a battery of sensors designed to track their prey, including chemical, visual, and heat sensors. Sweat, clothing that contrasts with a background and heat attract mosquitoes. Be aware of these sensors in order to protect yourself and your pet.

Lice and Mites

Lice and mites are microscopic organisms that feed on your dog's skin and cause itching, hair loss, and infection. Lice live in a dog's hair and can be killed by dipping with an insecticide effective against ticks or fleas. Various kinds of mites inhabit different areas of the dog, and the problems they cause are generally known as mange. Ear mites live in the dog's ears. Your dog may have mites if he shakes his head and scratches his ears. Scabies, which affects humans as well as dogs, is caused when mites burrow into the dog's skin and cause intense itching and hair loss. Scabies usually affects the ears, elbows, legs, and face. Demodectic mange causes hair loss around the forehead, eyes, muzzle, and forepaws. It's caused by a mite that lives in hair follicles and causes hair loss, thick, red skin, and infected areas. There is also a mite that causes "walking dandruff" on a dog's head, back, and neck. This mite also causes itchy red spots on humans. All mites should be diagnosed from a skin scraping by a veterinarian.

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