A fluffy grey dog smiles at the camera.

Dangers are everywhere, and some are beyond what the eye can see. 

Parasites are some of the most dangerous threats to a healthy dog’s well-being, and they can worsen the condition of a debilitated animal. There are many different kinds of parasites, and each requires specific treatments to rid the animal of the infection.

A parasitic infection can be difficult to recognize for pet owners until the animal starts showing symptoms, as the parasites themselves are often too small for the naked eye. Some pups with parasitic infections will show no symptoms at all, which is why most veterinarians strongly advise a yearly fecal exam to screen for any infection. 

Parasites can even kill your dog, so it is crucial to learn the basic signs of infection and be vigilant about abnormal behaviors. Below, we have listed some of the most important information to know regarding these unwanted intruders.

Common Internal Parasites Found in Dogs

Below, we have listed some of the most common types of parasites to watch out for.


Most other parasitic worms live in the intestines, while heartworms can grow up to 14 inches long and live in an affected dog’s heart and pulmonary arteries. Dogs can be easily susceptible to heartworms because they travel through mosquitos. In 2016, The American Heartworm Society (AHS) reported a 21.7%  increase in heartworm infections in dogs.

Treatment for heartworm infection is expensive and even grueling for a dog to endure, frequently resulting in significant complications. Unfortunately, if left untreated, the infection can lead to symptoms of heart disease and may ultimately lead to heart failure and death. 

Thankfully, heartworm prevention pills are generally inexpensive and easy to find. Consult with your pet’s veterinarian before starting a year-round prevention treatment.  


These worms live in the intestines, rapidly sucking your pet’s blood, and they can cause severe anemia. 

Generally considered to be the most threatening of the intestinal parasites if left unchecked, hookworms are not visible to the naked eye and get the name because of the way they hook onto the intestine to suck blood. They can be especially dangerous because extreme cases of anemia may require a blood transfusion and hospitalization. This type of intestinal parasite is also common in puppies and kittens but can still affect adults. 

To diagnose hookworms, a vet will conduct a microscopic examination of the pet’s stool, provide anthelmintic medication (drugs that rid the body of parasitic infection) such as albendazole and mebendazole, and repeat the exam after two weeks. 

Hookworms are uncommon in humans but can be transmissible and will usually appear in the form of skin lesions. Transmission usually occurs through the feet when a person comes into contact with feces-contaminated soil.  


These worms are, as described, round and also resemble spaghetti pasta with their pale white color and 2-4 inch length. 

Transmission occurs when a pet comes into contact with infected feces, which is contaminating the yard. A vet can diagnose roundworms after an examination of a pet’s feces. This type of worm can affect both dogs and cats but is most common in young puppies. 

To treat roundworms, a vet can provide anthelmintic medication in two-week intervals as needed. 

A pet may show no symptoms at all, but diarrhea and vomiting are most common. In large numbers, this type of parasite can cause an intestinal blockage and can even be coughed up or passed through the stool. Preventative heartworm care is known to also protect against roundworm infection. 

While transmission to humans is rare, a child exposed to contaminated dirt, sand, or grass may develop visceral larval migrans (roundworm infection in the skin and/or eyes). This is generally considered a mild condition when promptly treated with anthelmintic medication but could result in loss of vision if ignored. 


Whipworms only affect dogs and cannot be transferred to humans. These parasites are very small and generally can’t be seen by the naked eye. They migrate to the lower part of the intestine — the colon — and can cause symptoms like bloody diarrhea, vomiting, and weight loss. 

The colon is responsible for extracting water, nutrients, and electrolytes from food and then absorbing them back into the body, so serious cases of whipworms can prevent the ability of this essential function, leading to hospitalization due to malnutrition and dehydration. 

To diagnose this type of parasite, a vet will need to examine multiple fecal samples because whipworm eggs will pass in irregular intervals, making them easy to miss in a single examination. The treatment is an oral medication that may be prescribed for anywhere from 2 to 6 weeks. 


This type of intestinal worm is transferred to dogs in a more unique way than some of the other parasites. Instead of traveling through contaminated fecal matter, tapeworms actually come from the fleas around dogs. When a dog bites at and chews on the fleas, irritating their skin, the developing tapeworm that lives inside the flea can latch on to the pup. 

These tapeworms will attach to the intestine and grow in proglottids (segments) that break off as the worm grows and passes in the infected animal’s stool. 

To diagnose tapeworms, a vet won’t need to perform a fecal exam, as the parasite can usually be diagnosed with observation. A vet can see these dried-up proglottids around an infected animal’s anus, which are often small, like grains of rice, and dry up to a pale yellow color. Treatment may be oral medication or an injection, but note that tapeworm treatment does not prevent future infection and will only have an effect on the current parasitic infection. 


This is one of the most common intestinal parasites found in dogs but is not a worm like some of the others. This infectious, single-celled parasite can infect a healthy dog if they eat the infective stage of the parasite. In mild cases, there may be no symptoms, but severely affected animals may have bloody stool, dehydration, and abnormal distress. 

Treatment for a Coccidia infection will vary depending on how severe it is affecting the pup’s quality of life. An asymptomatic case may go untreated because the animal can rid the body of the infection on their own. For dogs that are showing signs of dehydration and have abnormal stool, an at-home oral medication may be offered. Hospitalization may be necessary in cases where the infection has caused severe dehydration or malnutrition. 

Transmission to humans is rare but possible, so prevention includes thoroughly cleaning the dog’s living area. 


Giardiasis is another common parasitic infection but is not a worm. This single-celled parasite lives in a dog’s intestines, but can also infect other animals and humans. Found in contaminated food, water, and soil, giardia parasites attach to the intestine and can cause diarrhea with mucus, weight loss, and lethargy. 

Most commonly, animals that have just come from a kennel-living situation will contract this parasite. Diagnosis is made by analyzing a fresh stool sample, but an overwhelming amount of positive patients will test negative in the examination. Because of this, treatment may be offered without a diagnosis.  

Common External Parasites 

In addition to the nasty internal invaders described above, a dog can pick up quite a few different types of hitchhikers.


Dogs are man’s best friend, and fleas are dog’s worst enemies. Fleas are extremely common, with an average of 1 in 7 dogs carrying the parasite

Fleas are most notorious for causing scratching and skin irritation, but a flea infestation can be more than just an uncomfortable itch for your dog. These external parasites can cause secondary skin infections and, as previously stated, carry tapeworms that can latch onto a dog’s intestines. Fleas will feast on your dog’s blood, so an extreme infestation can cause anemia or even death in young pups. 

Flea collars, pills, and topical applications have all been proven to work against fleas, but prevention is the best way to stop a serious infection. Different dog breeds and stages of life will require unique preventative care, so talk to your vet about a monthly flea treatment for your dog’s needs. 


Dermacentor variables, more commonly recognized as the American dog tick, are common external parasites that your dog can pick up while out in densely vegetated land. These parasites live in areas with tall grass, large bushes, and trees and then attach themselves to your dog while they play outside. 

It isn’t always easy to spot a young tick as it latches itself onto your pup because they find hidden areas to rest on: behind the ears, in dense patches of fur, or around the groin. Many of the most common flea treatments also attack tick infestations, but it is important to consult with a vet about the best course of action. 


A dog can come into contact with various types of harmful mites: ear mites, Sarcoptes mites, and Demodex mites are the most common. 

Ear mites are easier to see than other types of infectious mites because they are not burrowing parasites, so they may be visible on the surface of the ear. 

Demodex mites burrow into a dog’s hair follicles, while sarcoptes mites burrow into the skin. Both of these mites can leave painful lesions and irritating scabs. 

Mites multiply quickly, so an infestation may worsen exponentially if ignored. 


Just like in humans, lice can attach to a dog’s fur. While most common in puppies, dogs of any age can contract lice. This type of parasite is less common than the others, and most pets fortunately respond rapidly to treatment. Also, most lice are particular about the species they infest, so transmission to humans is fairly unlikely. 

Will a Parasitic Infection Go Away on Its Own?

In most cases, a parasitic infection will only worsen if left untreated and will not go away on its own. 

Your dog is like a buffet for both internal and external parasites, providing all of the nutrients they could possibly need in their blood. Even though these infectious creatures are microscopically small, they can significantly harm even the healthiest of dogs. Untreated, a parasitic infection may lead to death.  

A consistent bathing schedule is a proactive way of preventing a parasite infestation. Many internal parasites are transmitted by an external parasite, so simply committing to a weekly bathing schedule can reduce the risk of many different infections. 

Greenlin Staff Is Trained To Identify Active Infections

Greenlin Pet Resorts offers luxurious dog bathing services that will make your pup look squeaky clean when returned to you. While we ask that you not bring in a dog who is known to have an active infection, we can help spot the signs of undetected infections on your pet’s skin and fur.

Our trained dog bathers will know what to look for when assessing the condition of your pup’s coat and can safely remove external critters like fleas and ticks. Our spa day service can be added to any package, so after a long day of canine fun, your dog can enjoy a pampering treatment. 

To find out more about our dog bathing services, reach out to one of our six Pennsylvania locations today  or book your pet’s stay online! 

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