Parasites are organisms that spend most of their lives on or inside of other living things, and can be found living on or inside almost all animals. As such, Parasites form unique relationships with their host species, which may or may not contribute to discomfort or disease. Parasites always gain some advantage from their relationship with their hosts. When both the parasite and the host benefit from their association, the relationship is called "symbiotic." Unfortunately, companion dogs usually do not gain any benefit from parasites.
Whether a host is harmed or simply annoyed by a parasite depends upon a number of things. These include environmental, immunological, physiological and ecological factors. In addition, the associations between parasites and their companion animal hosts are constantly evolving. This process is influenced by the introduction of new drugs, modern vaccination protocols, improved sanitation techniques, better managed breeding programs and stricter environmental controls, among other things.
How Parasites Affect Dogs and Why We Worry About Them
Some dogs are well-adapted to the parasites that affect them and develop few, if any, adverse symptoms from their association. However, many dogs cannot tolerate the consequences of parasites and become irritated and very ill. Sometimes, parasitic infestations can be fatal.
Parasites have the potential to affect our canine companions in a number of different ways:
Some parasites are annoying, worrisome or frightening to their hosts but do not harm them directly. This "worry and scare" situation is exemplified by the equine bot fly, which causes horses to suffer extreme distress but does not really cause any long-term damage.
Some parasites cause physical irritation to their host, including pain or intense itchiness ("pruritis"). This can lead to self-mutilation from licking, chewing, biting, rubbing or scratching in an attempt to relieve the discomfort.
Some parasites injure their hosts by feeding on their blood or other bodily fluids. This can cause symptoms and diseases ranging from mild annoyance to severe blood loss anemia, which can be fatal. Anemia is an abnormal reduction in the number of circulating red blood cells. Red blood cells are necessary to deliver oxygen and other key nutrients throughout the body and to remove waste products from all tissues.
Some parasites secrete toxic substances into their hosts, which can cause illness up to and including death.
Some parasites create physical or mechanical barriers that block important biological passageways in their hosts. For example, they can partially or completely obstruct key blood vessels, airways or body cavities, with mild to potentially catastrophic consequences.
Some parasites cause mechanical damage to the host's internal or external bodily tissues, especially in and around the particular areas where the parasites reside. This can lead to traumatic sores and other lesions. It can also increase the risk of infection in affected areas.
Some parasites disrupt the metabolism of their hosts. "Metabolism" is defined as the sum of all physical and chemical processes by which internal substances are built up and sustained, and by which large molecules are broken down into smaller molecules, to make the energy that is essential to life. Basically, these parasites disrupt the digestion and disposition of nutrients that are absorbed from the host's gastrointestinal tract into the bloodstream. This can happen when the parasites compete with their hosts for essential nutrients, leading to weight loss, weakness and illness in the host animals.
Some parasites are transferred from animals to people. This is called a "zoonotic" infection or disease. The results of zoonotic infections can be minimal. Unfortunately, they also can be deadly.
Some parasites do not harm their hosts directly, but instead act as carriers and transporters of other infectious organisms. Diseases caused by these other transported infectious organisms are considered to be "parasitic" in nature, because they only develop as a result of the parasite intermediary. For example, mosquitoes and ticks may be only minimally annoying to an animal. However, certain types of mosquitoes and ticks carry and can transmit organisms that are responsible for very severe illnesses, such as malaria and Lyme disease, among others.
Some parasites are not particularly bothersome to their host, but greatly disturb the dog's owner. These typically include parasites that are visible to the naked eye, such as those that end up in a dog's feces and those that can be seen crawling around on its skin, fur or bedding.
Types of Parasites that Affect Domestic Dogs
Canine parasites can be classified into those that live on the outside of a dog's body (external parasites) and those that spend all or most of their time inside of their host (internal parasites).
The most common types of external parasites that affect companion dogs are:
Fleas: Tiny, wingless, blood-sucking insects that are an annoyance to people and their pets
Flies: Bothersome external parasites that cause irritation and disease in our pets
Lice: Tiny, species-specific external parasites that live on the skin and hair coat of dogs
Mites (Sarcoptic Mange; Demodectic Mange; Walking Dandruff; Ear Mites)
Ticks: Arthropods, closely related to mites, scorpions and spiders
The most common types internal parasites that affect companion dogs are:
Roundworms: Large, unsegmented internal parasites
Whipworms: Common, bothersome intestinal parasites of domestic dogs
Hookworms: Parasites of the gastrointestinal tract of dogs
Threadworms: Tiny internal parasite that lives inside of a dog's small intestine
Heartworms: Particular internal parasites, Dirofilaria immitis
Tapeworms: Parasites that live in the small intestines of their mammalian hosts
Tracheal Worms: Parasites that infect the respiratory tracts of dogs, causing a localized reaction
Coccidia: Internal parasites that most often live in the cells that line the gastrointestinal tract
Giardia: Tiny, one-celled protozoal parasites found in the gastrointestinal tract of most domestic
Salmon Flukes: Parasitic worms carried by certain types of fish
There are a number of things that owners of companion dogs can do to manage their pets' health and well-being, and at the same time enhance the chance of determining whether they are infected by external or internal parasites. For example, a good grooming regimen is helpful on a number of levels. Not only does regular grooming keep a dog's skin and coat healthy and clean, but it also gives the owner (or groomer) an opportunity to look for signs of external parasites. Evidence of parasites living on the outside of a dog's body might include the actual "bugs," if they are large enough to be seen without a microscope. It also might include other signs of the parasites, such as traces of their feces (so-called "flea dirt"), skin sores, areas of hair loss or dry, flaky, patchy areas of skin.
Owners can also check the consistency and contents of their dogs' feces. Some parasites – especially those that live in the stomach or intestines - are expelled in the feces, either when they die or in larval form. For example, segments of tapeworms are often found in fecal matter. Some of these look like grains of rice. They also commonly become stuck to the hair around an infected dog's anus.
Attentive owners usually are the first ones to notice signs of internal parasite infestation in their dogs. This can be something specific, such as loss of appetite or diarrhea, but more commonly the dog will just be "off." This is sometimes called being "ADR," which stands for "ain't doing right." If a dog acts lethargic or generally different than normal for more than a few days, a trip to the veterinarian is probably a good idea. Early detection and treatment of parasites are very important to a dog's overall health, and often to the well-being of other animals living in the dog's environment, as well.