Dog Parasites

Signs, Treatments, and Prevention

by Dr. Audrey Harvey, BVSc (Hons)

Dog parasites are not uncommon, and can cause serious illness for our canine companions. Although microscopic in size, parasites can be very debilitating, and in extreme cases cause death.

External Dog Parasites

External parasites live on the outside of your dog, and even if you can't see them, their effects are usually obvious. These are the common external dog parasites that we commonly see.

1. Fleas

dog fleaFleas are little jumping insects that need a blood meal to survive and reproduce. Some dogs are allergic to flea saliva, and will have a severe reaction to the bite. They often scratch so much that their skin becomes red, and their hair falls out. Even if a dog is not sensitive to flea bites, these little pests can still cause problems. A large flea population can cause blood loss anemia, and they also are responsible for infecting your dog with the flea tapeworm.

You can control fleas on your dog with monthly Comfortis tablets, or by applying a topical spot treatment such as Frontline or Revolution. However, this kills only a small part of your flea population because the bulk of them are in the environment in the form of eggs, larvae and pupae. This means you need to use a product that will break the life cycle, and stop these immature fleas developing into adults. Sentinel tablets given to your dog once a month will do this, as will a fogger or a yard spray containing the insect growth regulator methoprene. (The dog flea scientific name is Ctenocephalides canis.)

2. Ticks

dog tickTicks also drink blood, but their main claim to fame is that they spread potentially fatal diseases such as Lyme Disease and Rocky Mountain Spotted Fever. One species of tick will cause paralysis in dogs, and it too can kill. Ticks can be controlled by the use of a tick collar; popular brands include Preventic and Scalibor. Frontline Plus and Advantix are both topical spot on treatments that kill ticks for up to two weeks. No matter which preventative product you choose to use, make sure you run your hands over your dog regularly to check for ticks, and remove any that you do find. Some common dog ticks are Amblyomma americanum (Lone star tick), Dermacenter variabilis (American dog tick), and Ixodes scapularis (Deer tick).

3. Ear Mites

dog ear miteEar mites are tiny little parasites can't be seen by the naked eye, but you will definitely see what they do to your dog. They cause severe itching in their ear, and your dog will dig and scratch at their ear all the time. The inflammation inside the ear caused by the mites often develops a painful secondary infection, and the trauma your dog causes to its ear can result in an aural hematoma – a blood blister that forms between the skin and cartilage of the ear flap.

If your dog has painful itchy ears, it is best if you have them examined by your veterinarian. Not all ear problems are caused by mites, and using an over the counter medication isn't a good idea in case it delays treatment. Also, ear drops that only kill mites don't contain antibiotics or anti-inflammatory drugs, both of which are necessary to treat any secondary infection. If your dog has a confirmed case of ear mites, Cerumite, Mitaclear or Otomite Plus drops will clear them out quickly. (The scientific name of the dog ear mite is Otodectes cynotis.)

4. Skin Mites

dog demodexSome mites prefer living on your dog's skin. A mite infestation is often referred to as mange. The two main culprits are Demodex and Sarcoptes. Demodex mites live in the hair follicles of all dogs, and usually don't cause any problems. The drama starts if your dog's immune system is suppressed for any reason. The mites multiply, and cause skin scaling, hair loss, itching, and secondary infection. Most cases of demodex infestation in young dogs cause small patches of hair loss, and they recover quickly. However some dogs develop a generalized form, where their whole body is affected. Diagnosis involves scraping some tissue from the surface of the skin with a scalpel blade, and examining the tissue under the microscope. The mites are easily seen. Demodex infection can be treated with Mitaban dips, or Promeris spot on treatment applied every 2-4 weeks. (The scientific name of dog demodex is Demodex canis and Demodex injai.)

5. Sarcoptes

dog sarcoptes mangeSarcoptes mites live on a dog's skin and are extremely contagious; they will easily spread between dogs. These mites cause severe itching, particularly on the elbows, the tummy and the edges of the ear flaps. Sarcoptic mange is difficult to diagnose, because the mites aren't often found on skin scrapings. Many vets will suggest a trial of treatment to see if there is any response. Mitaban dips or Revolution applied every two weeks will clear your dog's skin of these irritating little creatures.(The scientific name of dog mange is Sarcoptes scabiei.)

Internal Dog Parasites

Heartworm and intestinal worms are the main internal dog parasites that we dogs have to contend with.

1. Heartworms

Heartworms are worms that are spread by mosquitoes, so are only a problem in areas where their preferred species of mosquito is found. The larvae enter a dog's bloodstream while the mosquito is having a blood meal. The worms make themselves comfortable in their host's pulmonary artery, which carries blood from the right side of the heart to the lungs. This can result in inflammation and blood clots in the artery. The heart has to work much harder to pump blood through the damaged blood vessel. If a dog has enough worms, they will extend right into the heart itself. Heartworm disease results in right sided heart failure, characterized by coughing, lethargy and even sudden death.

While heartworm disease can be treated, your dog may still suffer its effects for a long time. Also, treatment is not cheap, and it is very hard on your dog. It is much better to prevent infection with heartworm in the first place. Monthly tablets such as Heartgard or Interceptor will prevent your dog getting heartworm disease. Alternatively, a topical spot on product such as Advantage Multi not only controls heartworm, but also intestinal worms and fleas. This is very convenient for the busy dog owner. A third option is an injection, Proheart 6, which will prevent heartworm infection for 6 months. (The scientific name of dog heartworm is Dirofilaria immitis.)

2. Intestinal Worms

dog hookwormThere are four types of worms that live in the intestines of our dogs, and they vary in their significance. Hookworm are tiny blood suckers, and cause anemia and black sticky diarrhea. They have been known to kill dogs if enough blood is lost. Roundworms are larger, and can be easily seen in an infected dog's feces. In large enough numbers, they will cause a blockage of a dog's intestine. See: symptoms of worms in dogs. Both of these worms can infect people, with roundworms being the most serious. Their larvae can migrate through the human brain and eye, causing severe damage. (The scientific name of dog hookworms are Ancylostoma and Uncinaria.)


dog whipwormWhipworms are less common, and live in the large intestine. Infection in your dog results in weight loss and bloody diarrhea. Their eggs live for a long time in the environment, and can be a constant source of reinfection. The last type of worm that infect dogs are tapeworms. The most common tapeworm is spread by fleas. When the worm segments are passed out in your dog's feces, the result is an itchy bottom and embarrassing scooting. (The scientific names of dog whipworms are Trichuris vulpis and Trichuris campanula.)

Deworming Dogs

drontal plus for dogsRegular worming is essential to keep your dog in good health. You can give them a tablet such as Drontal Plus to kill all intestinal worms. Alternatively, a combination product may be more convenient for you. Advantage Multi will control heartworms, intestinal worms, and fleas, with one simple application.

Dog parasites, both internal and external, can adversely affect health, but so can the treatment used to kill them if it is used incorrectly. Make sure you follow the directions on the packet carefully, and don't use any more than is prescribed, or use it more frequently than recommended.

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