Dogs are prone to picking up parasites due to their lifestyle—they like to eat whatever they can find, sniff everything, explore everywhere, and of course, roll around in gardens.
Parasites can even affect dogs that are mostly kept indoors through contact with the environment when they go out for a walk, and even from contact with you when you've been outside.
It's important for pet parents to know most common parasites in dogs so they can recognize the symptoms and get their pup the treatment they need.
Dog parasites can broadly be divided into internal and external parasites. Internal parasites are the ones living inside a dog’s body, while external parasites are the ones mostly living on the skin and between the fur of dogs.
Let’s take a look at the most common internal and external parasites in dogs:
Heartworms can cause damage to the lungs, heart, and other organs and can be life-threatening. Mosquitoes inject the heartworm larvae into your dog’s bloodstream when they bite. Adult heartworms live in the heart, lungs, and associated blood vessels in the pet. It takes about 6-7 months for these larvae to mature into adult worms.
Symptoms of heartworm infection include:
Tiring quickly during exercise
Symptoms of heart failure
Heartworm infection is diagnosed with a blood test. The antigen test looks for heartworm proteins released by the adult female heartworms into the bloodstream. The earliest this test can pick up a heartworm infection is about 5 months after the initial mosquito bite. The other blood test that is sometimes used tests for microfilariae in the bloodstream and indicates infection with adult heartworms. The earliest detection for heartworm after the initial mosquito bite with this test is 6 months.
Treatment for heartworm infection often involves multiple trips to the vet, blood tests, x-rays, hospitalization, and a series of injections. It's usually an expensive treatment and can sometimes cause serious complications. For this reason, prevention is much better than cure.
The preventative treatments for heartworm are all prescription medicines, so you will need to get a prescription from your veterinarian. In general puppies, will be tested at around the age of 7 months for the presence of heartworms after which preventative treatment is started. After that, it's ideal to have your dog tested for heartworm once a year.
Roundworms live in your dog’s intestines where they feed on the partially digested food. They are most commonly found in puppies. Puppies can get roundworm infections from the mother before birth (in the uterus) or from the milk. Roundworms are also picked up from the environment if an infected dog has pooped in that area.
Symptoms of roundworms include:
Poor growth or weight loss
A potbelly appearance
A dull haircoat
Signs of abdominal pain
With a large roundworm infestation you will sometimes be able to see the worms in your pup’s stool or vomit.
Roundworms are diagnosed by looking at a stool sample under the microscope. The vet will be able to see the roundworm eggs in the stool.
Roundworms are treated with deworming medications. Speak to your vet about a regular deworming schedule for your dog. It's also recommended to have a stool sample checked two to four times per year, depending on your dog’s lifestyle and risk for roundworm infection.
Tapeworms are long, flat, segmented worms. They can mostly be found in your dog’s small intestine. When mature, the segments break off and are excreted with the stool. They can be seen in the poop with the naked eye and look similar to grains of rice.
Dogs are infected with tapeworm by swallowing fleas when they're grooming or hunting and eating rodents.
Symptoms of tapeworm infection include:
Blockage of the intestine
A dull coat
Scooting or dragging of the hind end
The diagnosis for tapeworm is made when tapeworm segments are seen in the poop or around the anus of the dog.
Treatment for tapeworm includes deworming medication to treat the existing infection and flea and rodent control to prevent reinfections.
Hookworms are small worms that attach to the inside of the intestinal wall using their ‘hook-like’ mouthparts, hence their name. They are only about an 1/8th of an inch long and nearly impossible to see with the naked eye.
Hookworms ingest blood from the small blood vessels of the intestine where they are attached.
Puppies can get infected with hookworm before birth (in the uterus) or through the mother’s milk. Hookworms can also be picked up directly from the environment when your dog sniffs or eats something that has been in contact with an area where another dog has pooped, or it can be picked up through the skin.
Symptoms of hookworm infection include:
Anemia (pale gums)
A dull haircoat
Hookworm is diagnosed by looking for the worm eggs in the stool under the microscope.
Hookworms are treated by using a deworming medicine that is broad-spectrum. Your vet might want to repeat the deworming medicine, so be sure to follow their instructions fully.
Giardia is a microscopic protozoal parasite that commonly infects the intestinal tract of dogs. Giardia parasites can be picked up from contaminated soil, water or food.
Puppies are more likely to develop clinical symptoms of infection. The most common symptom for giardiasis is diarrhea. The diarrhea can be watery or soft and is sometimes mucoid. In milder cases. the dog’s appetite and energy levels will remain unaffected, but in severe cases or in dogs with compromised immune systems, the symptoms can be more severe and can include lethargy and appetite changes.
Giardia infection is diagnosed by looking for the parasite directly or testing for proteins released by the parasite into the stool. Giardia parasites are shed intermittently and can sometimes not be seen directly, but the proteins will be present in the stool if your dog is infected.
Giardiasis can be quite a challenge to treat in some cases, as dogs can easily get reinfected if giardia is present in their environment. Giardia infections can only be treated by veterinarians. They will often use a deworming medication or an antibiotic. These medicines are also often used together.
Coccidia is similar to Giardia in that it is a microscopic protozoal organism that affects the intestinal tract of dogs. Coccidia are found in the stool of other dogs as well as soil that has been contaminated with dog poop.
Puppies are more commonly affected and tend to develop symptoms, including:
Adult dogs can also pick coccidia up from the environment, but tend not to get very ill from it unless their immune systems are not functioning properly.
Coccidia is usually diagnosed by looking for oocysts (immature coccidia) in a stool sample.
Coccidia can only be treated by a veterinarian who will usually prescribe a specific antibiotic. The treatment can sometimes be quite prolonged, but tends to be fairly successful in most cases.
Fleas are small brown insects found on the skin of dogs between the fur. They bite the host in order to feed on blood.
Fleas are picked up directly from other animals or from the environment.
Symptoms of a flea infestation include:
Secondary skin infection
Anemia (reduced red blood cells in the blood), seen in young puppies with severe flea infestations
The diagnosis of a flea infestation is made by seeing the fleas themselves, flea dirt (flea poop visible as black specks when you part the fur), or flea eggs (white specks in the fur). To distinguish flea dirt from normal dirt found on the fur, you can place some of the black specs on some damp paper towel. If the specks turn into reddish-brown blobs, they're made up of old blood and are likely due to fleas.
The treatment for fleas involve a multi-modal approach to try to get rid of the current infestation and prevent re-infestation. There are treatments that will kill the adult fleas currently on the dog. These treatments only last for about 24 hours though, so it will be accompanied by a flea preventative product.
It's also important to treat the environment by regularly vacuuming (empty the vacuum cleaner bag into a plastic bag that can be sealed immediately afterwards), washing of all bedding, and using sprays to treat the environment. Speak to your vet about a regular flea preventative program that will be effective for your dog’s circumstances. Your vet will also base the choice of treatment on the presence of other pets in the household.
Ticks are parasites that are related to spiders and mites, so the adults all have 8 legs. Ticks will feed on the blood of their host by attaching to the skin. There are many different tick species that have different environmental preferences as well as climatic and temperature preferences.
Ticks can carry and transmit diseases like Rocky Mountain Spotted Fever, Ehrlichiosis, Q fever, Lyme disease and Babesiosis (not very common, but seems to be on the increase in certain areas of America). Ticks can also cause anemia if they are present in large numbers on a pet.
Dogs pick ticks up from the environment. The ticks will wait on tall grass and shrubs for a suitable host to come past.
Symptoms of ticks on dogs include:
Licking or chewing
Red or inflamed skin
The diagnosis of a tick infestation is made from the presence of visible ticks or tick bite marks.
Visible ticks should be removed as soon as possible using tweezers to pull them off the skin gently. Grab them as close to the skin as possible. Never remove ticks with your bare hands, as there are some diseases that can be passed to you if you have a small abrasion on your skin. If you're uncomfortable removing ticks from your dog, get them to a vet to help you with this.
Treatment for tick infestations involves the use of topical or oral medicine to kill the ticks present on the pet and prevent re-infestation. It's also a good idea to remove tall grass on your property and prevent your dog from running through tall grass and shrubs.
The most common mites that affect dogs are Sarcoptes mites, Demodex mites, ear mites, walking dandruff, and harvest mites. Mites can be picked up from other pets as well as the environment.
The mites vary a bit in where exactly in the skin they live and can cause different symptoms, but the most common symptoms are:
Redness of the skin
Raised areas of the skin
Secondary bacterial infection is also commonly seen.
Mites are diagnosed by looking at skin scrapings under the microscope and identifying the mites.
Treatment will depend on the type of mite and will need to be prescribed by your vet after diagnosis of the mite itself.
Lice are insects that live on the skin of their host. They chew on the skin or suck blood from their host, depending on the type of lice.
Lice can be picked up directly from another dog or from infected grooming equipment or bedding.
If your dog has lice, you may notice:
A poor hair coat
Anemia in small puppies with heavy lice infestations
Lice are diagnosed by visually looking for the lice themselves or their eggs (nits) visible as small white dots on the hair shafts.
Lice are treated with products used on the dog’s skin, but it's important to also treat the environment by thoroughly washing all bedding and disinfecting grooming equipment. Your veterinarian will prescribe the treatment and recommend how often you should use it to effectively get rid of the lice on your pet.
Ultimately, it's important to know about the many internal and external parasites that can affect your pet and work closely with your vet to find the best preventative treatment for your pup's lifestyle. If you're concerned your pet might have a parasitic infection, chat with one of our Pros at Pawp for some guidance—we can help you decide on the next best step.
Reviewed and fact-checked by
Dr. Mari, DVM at Pawp