Internal and External Parasites
Coccidia are tiny single-celled parasites that live in the wall of your dog’s intestine. They are found more often in puppies, but they can also infect older dogs and cats.
Dogs become infected by swallowing soil that contains coccidia or other substances in the environment that may contain dog feces. Coccidiosis, the disease caused by coccidia, may not cause any signs in dogs but is usually more serious in puppies. The most common sign of coccidiosis is diarrhea. More severe infections can cause bloody diarrhea. Severe infections, especially in puppies, can kill them.
Parasites are “freeloaders” that live in or on another creature. Fleas are the most common external parasite found on dogs (and cats). Although fleas are more likely to be a problem during warm-weather months, they can also cause problems during cooler seasons due to their ability to continue their life cycle indoors.
How will fleas affect my dog?
You will probably first notice the effects of fleas when your dog repeatedly scratches and chews. On occasion you may actually see tiny brown fleas moving quickly through your dog’s haircoat. Your dog’s constant scratching may lead to visible patches of hair loss and reddened, irritated skin. Fleas may also cause skin allergies and can transmit other parasites, such as tapeworms, to your dog.
How do I check my dog for fleas?
Although your dog may be infested with fleas, they are not always easy to find. One of the best methods for checking your dog for fleas is to look for flea dirt (actually flea feces) in your dog’s haircoat.To check for flea dirt, briskly comb or rub a section of the hair on your dog’s back while your dog is sitting or lying on a white piece of paper. If your dog has fleas, black flecks that look like dirt (as a result, we use the term “flea dirt”) will fall onto the paper. If you transfer these black flecks to a damp piece of paper, in a short time they will appear red or rust-colored (see Figure 1). The red color results because blood sucked from your dog is passed in the flea’s waste matter. If the dirt specks do not turn red, then they are probably “regular” dirt.
Giardia is a single-celled parasite that lives in your dog’s intestine. It infects older dogs but more frequently infects puppies. Dogs become infected when they swallow Giardia that may be present in water or other substances that have been soiled with feces.
How will Giardia affect my dog?
Many dogs infected with Giardia do not get any disease. Giardiasis, the disease caused by Giardia infection, usually results in diarrhea. Having giardiasis for a long time can cause weight loss; poor condition; and even death.
Heartworms are common in dogs throughout the United States (cats can have them, too). They are among the most damaging parasites in dogs but they are almost 100 percent preventable. Heartworms are transmitted by mosquitoes and, once mature, they live in the heart and large blood vessels of the lungs. Adult heartworms can measure over one foot in length.
How will heartworms affect my dog?
The heartworm larvae deposited by the feeding mosquito eventually migrate to the chambers of the heart or into the vessels of the lungs. Once in the heart, the worms can affect blood flow throughout the body. Heartworm infection can affect many different organs of the dog—heart, lungs, kidneys, and liver, for example—so symptoms may be varied. Most commonly though, signs of heart or lung disease are present. A veterinarian may suspect that a dog has been infected if an active animal tires easily or shows shortness of breath or coughing. Early in the disease, dogs are often asymptomatic. Signs are often progressive over weeks to months and untreated, heartworm infection can be fatal.
Similar to tapeworms and roundworms, hookworms are intestinal parasites that live in the digestive system of your dog (or cat). The hookworm attaches to the lining of the intestinal wall and feeds on your dog’s blood. Its eggs are ejected into the digestive tract and pass into the environment through your dog’s feces. Larvae (young hookworms) that hatch from hookworm eggs live in the soil. These larvae can infect your dog simply through contact and penetration of the skin and through the dog eating the larvae when they ingest dirt or during their routine licking (cleaning).
How will hookworms affect my dog?
Hookworms suck blood and therefore cause internal blood loss. They are a serious threat to dogs, especially young puppies that may not survive the blood loss without transfusions. In older animals the blood loss may be more chronic, and the pet may have diarrhea and show weight loss. If you think your dog is infected with hookworms, call your veterinarian to schedule an appointment for evaluation, diagnosis, and safe, effective treatment.
Mange / Demodex
Demodex is a parasitic mite that causes a skin disease often referred to as mange or canine demodicosis. The microscopic Demodex mites live in the hair follicles and oil glands of your dog’s (or cat's) skin or at the skin surface.Many animals have natural mite populations; however, most healthy animals are able to suppress the populations from becoming problematic. Usually, animals that are going to be affected by Demodex show signs of mange early in life. Occasionally, an animal will develop demodectic mange as an adult; however, this usually means that the animal has another medical condition that is compromising the immune system.
How will demodectic mange affect my dog?
Demodex mites create patches of hair loss as a result of mild irritation and itching, usually starting on the muzzle and head and progressing toward the rear. The disease can be limited to a small area of infestation (localized), which most often occurs in young dogs, or more widespread (generalized) infestations. Diagnosis of Demodex mites is made through skin scrapings of the affected areas. Localized infestations can easily be treated, and most are resolved with no treatment. Generalized infestations of Demodex can be more challenging to treat.
Roundworms are the most common of the parasitic worms found inside a dog. Almost all dogs become infected with them at some time in their lives, usually as puppies. Roundworms may be contracted in different ways, making them easy to spread and hard to control. Your dog may be infected with roundworms from the time it is born because often the mother passes the worms to the puppy while it is still in her body. Roundworms can also develop in a puppy after it is born when the puppy eats larvated eggs from the environment or drinks worm larvae (young worms) in the mother's milk. Another way roundworms are passed is when roundworm larvae are present in the tissues of a mouse or another small mammal and the puppy eats the animal.
How will roundworms affect my dog?
Adult roundworms live in the affected dog's intestines. Many dogs do not have signs of infection; however, dogs with major roundworm infections, especially puppies, show diarrhea, vomiting, weight loss, dull hair, and a potbellied appearance. The dog may cough if the roundworms move into the lungs. You may notice the adult roundworms in your dog's feces or vomit. They will appear white or light brown in color and may be several inches long.
Ectoparasites are organisms that live on the outside of an animal. Ticks are fairly common ectoparasites of dogs (and cats). How often you see ticks on your dog and how severe a tick assault will be depends on the region of the country in which you live, the time of year (tick activity varies in warm and cool weather), the habits of your dog, and how and when you use tick control products. Some ticks can infest dogs that spend most of their time indoors, and even dogs that only spend brief periods of time outside can have ticks.
How will ticks affect my dog?
Ticks attach to your dog by inserting their mouthparts into your dog’s skin. Many ticks also produce a sticky, gluelike substance that helps them to remain attached. After attaching to your dog, ticks begin feeding on your dog’s blood. The places where ticks attach can become red and irritated. Although rare, ticks can consume enough of your dog’s blood to cause a deficiency called anemia. Certain female ticks can also cause a rare paralysis in dogs as a result of a toxin they produce while feeding. More important, ticks are capable of causing many diseases in your pet. The disease with which most people are familiar is called Lyme disease.
Lyme disease can cause arthritis and swelling of your dog’s joints, resulting in painful lameness. Rocky Mountain spotted fever can cause fever, lameness, and other signs. There are also other diseases that ticks can transmit to your dog.
The whipworm is one of the four most common intestinal parasites of dogs. Whipworms reside in the cecum, which is inside your dog’s body where the small intestine and large intestine meet. Dogs become infected with whipworms by swallowing infective whipworm eggs in soil or other substances that may contain dog feces.
How will whipworms affect my dog?
Dogs that are infected with a few whipworms may not have any signs of infection. More severe infections can cause bloody diarrhea. If an infected dog is not treated, then severe whipworm infection can cause serious disease and even death.