Common Dog Parasites – Hookworms, Heartworms and Fleas

Parasites are common in dogs and most dogs will have some at various times in their lives. They can be external or internal. They include fleas, worms, mites, and ticks. They are easy for your dog to pick up, either from other dogs or from the environment. Left untreated, most parasites can cause serious problems and lead to illness in your dog. Fortunately, most parasites are easy to prevent or treat. Here are some of the most common dog parasites your dog is likely to encounter.

Ear Mites

Ear mites are minute mites that are almost, but not quite, invisible to the human eye. They are found in your dog’s ears. They produce a brownish wax that resembles coffee grounds in the ear. They are contagious and can be passed from one dog to another.

If your dog has ear mites his ears will be inflamed and itchy. Your dog will probably scratch at them which can cause an infection as a secondary condition. Puppies are especially prone to ear mites. They can pass them to each other and they can be passed from a mother dog to her puppies.

Ear mites are easy to treat with a miticide liquid. These products are sold in pet stores or you can consult your veterinarian for advice in choosing one. You should check your dog’s ears often for signs of mites.


Fleas are the most common of all dog parasites. They are most common in warm, humid areas but they can be found virtually anywhere. They are a special problem in summer months. Fleas can be passed from dog to dog, or from other animals to dogs. They also spend much of their time off their host animal in the surrounding environment so a dog who visits an area where fleas are found can easily pick up fleas. Dogs who go to dog parks, vet offices, animal shelters, or other places frequented by lots of dogs can easily pick up fleas.

A dog who has fleas will typically become itchy and he will scratch a lot. You will probably find flea dirt, or flea excrement on your dog. This is a black or red-brown grit on your dog’s skin. It is essentially dried blood from your dog that has been excreted by the fleas. If you go over your dog with a flea comb you will be able to find the fleas. In severe cases or if the dog has a flea allergy, the dog may scratch so much that he removes patches of hair and he becomes bald in places. He may have red, inflamed skin.

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Fortunately, there are now some good products that prevent flea infestations or kill fleas on contact. Topical spot-on flea products such as Frontline and Advantage II are easy to apply on a monthly basis to your dog’s skin and will kill fleas very quickly. They also keep fleas away for a month or more. Other products can be given orally such as CapStar to kill fleas immediately. There are also good flea sprays, powders, and shampoos to get rid of fleas.

When you treat your dog for fleas it is always advisable to treat your home and yard for fleas to get rid of fleas in the environment, too. Use products with an insect growth regulator whenever possible to keep flea eggs from hatching and starting the cycle all over again.


Left untreated, heartworms can be fatal to dogs. Heartworms are spread by mosquitoes. Mosquitoes bite an infected animal and eventually bite your dog. They deposit immature heartworm larvae in your dog’s bloodstream. In a few months these microfilariae migrate to your dog’s heart and lungs where they can grow for years, eventually reaching over a foot in length. There can be dozens of these large worms in your dog’s heart and lungs, choking off blood supply. They will eventually kill your dog. Your dog may not show any symptoms at first but he will slowly show signs such as becoming tired easily, coughing, and shortness of breath.

Again, heartworms are easy to prevent. Most people give a monthly heartworm preventive such as Heartgard or one of the other Ivermectin products. Collies, Shetland Sheepdogs, some other herding breeds, and some sighthounds are sensitive to ivermectin. You should talk to your vet about how to prevent heartworms if you have one of these breeds. If your dog already has heartworms they can be treated and killed, but it is easier and less expensive to prevent them than to treat them.

Other Worms

Dogs are subject to a variety of other common worms, too, including hookworms, roundworms, tapeworms, and whipworms.

Hookworms are nasty little intestinal parasites that live in your dog’s digestive tract. They feed on your dog’s blood. They pass their eggs through the digestive tract and in to the environment where the hookworm larvae hatch. Dogs ingest them in this form or the larvae enter dogs through contact with their skin.

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Hookworms pose a special danger to puppies and elderly dogs because they do cause a loss of blood to the dog. Puppies should be checked for worms when they are young and wormed if necessary. Older dogs should be checked for worms periodically. Some heartworm medications also kill hookworms and roundworms.

Roundworms are the most common worm found in dogs. Nearly all dogs have them at some point, especially when they are puppies. The worms can be passed from the mother dog to the puppies through the milk, for example, or passed from the mother before birth if she has worms. If a dog eats an animal it catches, such as a mouse, and the animal has roundworms, the dog can get the worms.

The worms live in the dog’s intestines. Most dogs don’t show signs of infestation but if your dog has a heavy infestation he will show symptoms such as diarrhea, vomiting, weight loss, and loss of hair. This is especially true of puppies who may also have a pot-bellied appearance. You may see roundworms when your dog coughs or vomits or in the diarrhea. They look like long strands of spaghetti.

Young puppies should be checked for worms and wormed if necessary. Breeding females should be wormed prior to breeding or when they are pregnant using a wormer that is safe for the embryos. Some heartworm medications also kill roundworms and other worms on a monthly basis.

Tapeworms are long, flat, segmented worms that attach themselves to your dog’s intestines. Each of the tapeworm segments has its own reproductive organs. As the tapeworm grows, the end segments break off and are passed through your dog’s intestines with your dog’s feces. You may find the segments attached to your dog’s rear or in his feces looking like grains of rice. When a dog comes in contact with these tapeworm segment, the cycle starts all over again.

Fleas are one of the intermediate hosts for tapeworms which means that if your dog has fleas, chews on his body to get the flea and stop the itching, it can lead to a tapeworm infection in his intestines. Good flea control is one way to avoid tapeworms.

Have your vet check your dog for worms during your visit for vaccinations. Occasional worming may be needed. Many heartworm products will also kill tapeworms and other worms.

Whipworms are one of the most common worms found in dogs. They live in the cecum which is the area where the large and small intestines intersect. Dogs get whipworms by eating and swallowing whipworm eggs found in the soil or eating dog feces that may contain whipworm eggs.

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If your dog just has a few whipworms he probably won’t show any symptoms but more severe infestations can result in bloody diarrhea. Left untreated whipworms can cause severe gastrointestinal issues and even death.

Whipworms can be more difficult to diagnose than the other worms discussed here. It’s best to have your dog wormed when you take him for his regular vaccinations in order to make sure he is not carrying a worm infestation. A simple worming will usually take care of all the worms mentioned here. Many heartworm medications will also kill whipworms and other worms.


Ticks are found in many parts of North America these days. You don’t have to live in the woods. If you simply have brush or a woodpile in your yard, you could have ticks lurking in them.

Ticks attach themselves to a dog with their mouth parts and start consuming your dog’s blood. Some ticks excrete a glue-like substance to help them hang on. In some cases tick bites can result in anemia to your dog. Ticks can also spread disease such as Lyme Disease and Rocky Mountain Spotted Tick Fever.

It’s hard to prevent ticks from getting on your dog but you can use tick prevention products to deter them. Many of the flea control products also have a tick control element such as Frontline Plus and Advantage II. Ticks who come in contact with these ticks will quickly die after biting your dog. Even though they bite your dog, your dog should be safe. It usually takes about 48 hours for a tick to transfer any disease to your dog and they will be dead much faster than that.

If you live in an area where ticks are common, you should treat your yard for ticks to deter them. You can use a product such as diatomaceous earth which will dry out the ticks and kill them. You should also check your dog often for any ticks that could be attached to his body and remove them.

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