Parasites in Your Pets. Can Fido and Fluffy Make You Sick?


Pets bring us a lot of joy and companionship, but they can also bring some unwelcome guests – parasites. According to research, up to 54% of dogs and 45% of cats in the United States are infected with intestinal parasites. While parasites like roundworms, hookworms, and giardia can live in your pets without causing noticeable problems, they can be transmitted to humans and lead to serious health issues, especially in children and the elderly. Understanding how pets get parasites, the symptoms, and prevention methods is key to keeping your furry friends and family safe.

What are Parasites?

Parasites are organisms that live on or in a host organism and get their food from or at the expense of the host. There are many different types of parasites that can infect dogs and cats.

Some of the most common parasites found in pets include:

  • Roundworms – These are long, thin worms that live in a pet’s intestines. They are particularly common in puppies and kittens. Roundworm eggs are shed in the feces and can contaminate soil. Pets can become infected by eating contaminated soil or prey animals that have roundworms. [1]
  • Hookworms – Hookworms attach themselves to the intestinal wall of the host and feed on blood. Hookworm eggs are passed in the feces and hatch in the soil. Pets can become infected through contact with contaminated soil. [2]
  • Tapeworms – Tapeworms live in the small intestine and absorb nutrients from partially digested food. Tapeworm segments containing eggs break off and pass out in the feces. Pets get tapeworms by ingesting fleas or infected prey animals. [1]
  • Heartworms – Heartworms live in the heart and blood vessels of infected pets. They are transmitted by mosquitoes. Heartworm infection can be serious and even fatal if left untreated. [2]

How Pets Get Parasites

There are a few main ways pets such as dogs and cats can become infected with parasites:

Ingesting eggs or larvae: One of the most common ways pets get parasites is by ingesting microscopic eggs or larvae shed in the feces of an infected animal. These eggs and larvae may contaminate soil, food or water sources.

Transmission from mother: Some parasites like roundworms can be passed from a mother dog or cat to her offspring before birth or through the milk when nursing. This allows the infection to be transmitted between generations. [1]

Eating prey animals: Dogs and cats that hunt and eat raw prey like rodents and birds can ingest parasites that infect those animals. This includes parasites like tapeworms. [2]

Common Parasites in Dogs

Dogs are susceptible to a variety of internal and external parasites. Some of the most common parasites that infect dogs include roundworms, tapeworms, hookworms, and heartworms (Source).

Roundworms are one of the most prevalent intestinal parasites found in dogs. The roundworm species Toxocara canis and Toxascaris leonina are most common in dogs. Puppies usually get infected with roundworms from their mother at birth. Roundworm eggs are passed in the feces of an infected dog where they can contaminate soil or water. Other dogs then ingest the eggs by eating contaminated dirt or licking their paws after walking through an infected area (Source).

Tapeworms like Dipylidium caninum and Taenia species are also very common in dogs. These segmented worms attach themselves to a dog’s intestinal wall. Tapeworm eggs are ingested by fleas during grooming or by dogs if they swallow an infected flea. Tapeworm segments containing eggs break off and pass through the dog’s feces where they can reinfect dogs or fleas (Source).

Hookworms such as Ancylostoma caninum infect dogs when larvae penetrate the skin and travel to the intestines. Hookworm eggs hatch in the environment and can infect other dogs through contaminated soil. Hookworms are especially dangerous in puppies where they can cause anemia, weight loss, and death (Source).

Heartworms like Dirofilaria immitis are spread by mosquitoes and prevent the heart from functioning properly. Dogs get infected with heartworms when bitten by a mosquito carrying the larvae. The larvae then migrate to the heart and grow into worms over several months. Heartworm infection can lead to heart failure, lung disease, and damage to other organs (Source).

Common Parasites in Cats

There are several parasites that commonly infect cats. The most prevalent include roundworms, tapeworms, hookworms, and toxoplasmosis.


Roundworms are extremely common in cats, with over 45% of cats estimated to be infected according to one study [1]. Roundworms are long, spaghetti-like worms that live in a cat’s intestines. Kittens are often infected from their mother’s milk, while adult cats pick up roundworms by ingesting infective eggs from soil or feces. Roundworms can cause a pot belly appearance, vomiting, diarrhea, and impaired growth and development.


Tapeworms are another common intestinal parasite, infecting about 14-34% of cats [2]. Cats get tapeworms by ingesting infected fleas or small animals. The worms absorb nutrients, leading to weight loss and poor growth. Tapeworm segments may also be visible in a cat’s feces or around their anus.


Hookworms infect 10-15% of cats [3]. Cats get hookworms from contaminated soil, feces, or milk from their mother. Hookworms attach to the intestinal wall and suck blood, causing anemia, diarrhea, and weight loss. Kittens are especially vulnerable to hookworms.


Toxoplasmosis is a protozoal parasite that infects about 30-40% of cats [1]. Cats get toxoplasmosis by eating infected rodents, birds or raw meat. Most cats show no symptoms, but it can cause fever, pneumonia, and central nervous system issues. Toxoplasmosis can also infect humans, especially pregnant women, so proper handling of cat feces is important.

Symptoms of Parasites

Parasites can cause a variety of concerning symptoms in pets. Some of the most common symptoms to watch out for include:

Diarrhea – Intestinal parasites like roundworms, hookworms, whipworms, and giardia can all cause diarrhea in pets. The diarrhea may be intermittent or persistent depending on the type of parasite and level of infestation. Severe infestations can lead to bloody diarrhea. Source

Vomiting – Parasites irritating the stomach and intestines often leads to vomiting in pets. Vomiting may occur occasionally or frequently. In severe cases, pets may vomit up actual live worms. Source

Weight loss – Parasites deprive pets of nutrition, which can lead to gradual but progressive weight loss. Pets may have increased appetite but still lose weight. Source

Dull coat – Parasites can cause coat and skin issues like dry flakes, hair loss, and a dull, brittle coat. This is due to the parasites irritating the skin and depriving the pet of proper nutrients. Source

Diagnosing Parasites

A veterinarian can diagnose parasites in dogs and cats through various tests and procedures. The main methods used are:

Fecal Exam

Performing a fecal exam (fecal flotation test) on a fresh stool sample is the most common and effective way of detecting intestinal parasites like giardia, roundworms, hookworms, whipworms and tapeworms. The stool sample is mixed with a special solution that causes parasite eggs or cysts to rise to the top where they can be examined under a microscope.

Blood Tests

Certain parasites like heartworm can be detected via a blood test. The blood is checked for the presence of microfilariae, immature heartworms. Blood tests can also sometimes reveal antibodies produced by the body in response to a parasitic infection.


X-rays and ultrasound imaging allow a veterinarian to visually identify larger parasites like heartworms in the heart and lungs. They may also show abnormalities or inflammation caused by parasitic infections.

Treating Parasites

Once parasites have been identified through a fecal exam, a vet will prescribe deworming medication targeting the specific parasite. Common dewormers used include fenbendazole, milbemycin, moxidectin, and pyrantel pamoate. Depending on the parasite, medication may be given orally or by injection. The medication kills the parasites so they are expelled from the body in the feces.

It’s important to complete the full course of deworming medication, usually 2-4 weeks, to ensure all life stages of the parasite are eliminated. Puppies and kittens may require more frequent and prolonged treatment. After treatment, the vet will recommend repeat fecal exams to confirm the parasites have been fully cleared from the body before discontinuing medication.

In addition to deworming medication, environmental clean up is important to remove parasite eggs from the home and yard and prevent reinfection. This includes thoroughly cleaning areas pets frequent and disposing of feces promptly. Preventative measures like routine deworming and flea/tick control are key for protecting pets from acquiring parasites again.


The most effective way to prevent parasites in dogs and cats is through consistent preventative care. There are several key prevention methods pet owners should follow:

Deworming: Deworming medication given on a regular schedule can kill intestinal parasites before they can multiply and spread. Puppies and kittens should be dewormed starting at 2 weeks old, then every 2 weeks until 12 weeks old. Adult dogs and cats should be dewormed at least 2-4 times per year based on risk and vet recommendation. Products like pyrantel pamoate, fenbendazole, and milbemycin oxime are commonly used. Source

Flea/Tick Control: Fleas and ticks can transmit parasites and bacteria that make pets sick. Using monthly spot-on or oral flea/tick preventatives keeps these pests under control. Products with active ingredients like fipronil, selamectin, sarolaner, or fluralaner can repel and kill fleas and ticks. Source

Clean Environment: Keeping the home and yard clean reduces exposure to parasites. This includes regularly vacuuming and washing bedding, promptly picking up pet waste in the yard, and keeping pets out of areas with standing water or dense vegetation. Good hygiene and sanitation removes parasites so they cannot spread. Source


Parasites can infect both dogs and cats, leading to health issues if left untreated. Some of the most common parasites found in pets include roundworms, tapeworms, hookworms, giardia and coccidia. Pets can pick up parasites through contact with infected feces, eating rodents or bugs, or transmission from mother to offspring. Symptoms of parasites include diarrhea, vomiting, weight loss, dull coat, and abdominal swelling or discomfort. If you suspect your pet has parasites, bring a fresh fecal sample to the vet for testing. Treatment usually involves deworming medications to kill parasites and stop reinfection.

Prevention is key to protecting your furry friends from parasites. Keep your home and yard clean, wash your hands after handling pets, practice good hygiene habits, treat pets monthly with preventives, and get regular fecal exams. Stopping parasites before they spread is much easier than dealing with an infection afterward. With some simple precautions and care, you can keep your pets happy and parasite-free.

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