Luckily for dogs, most of these parasites cannot readily invade a dog’s body unless it eats an aquatic animal.
When a dog eats a fish, frog, or crustacean such as a crayfish, the parasites within that animal invade the dog’s intestines, lungs, or tissue under the skin.
One example of a parasitic worm is the Dracunculus insignis, a roundworm that is carried by raccoons and other wild mammals and readily infects domestic dogs.
Dracunculus’ life cycle begins when an adult female living in the skin tissue of a raccoon, dog, or other mammal, senses that its host’s skin is wet. At this point, the Dracunculus pushes through the animal’s skin and releases larvae into the water.
When all of the larvae are released, the female dies inside the mammal’s skin.
Once in the water, the larvae are eaten by a tiny shrimplike animal called a copepod. Your dog can become infected when he or she drinks water containing these larvae-bearing copepods.
The ingested larvae mature and eventually make their way to the tissue beneath your dog’s skin.
The common symptom of Dracunculus infection is an ulcerous wound on the dog’s skin that is created when the female pushes through the skin to release the larvae.
These wounds can become infected, but the infection can be cleared up by means of the surgical removal of the adult female worm.
Another parasite known as the flatworm, which includes flukes and tapeworms, can also infect your dog when it ingests aquatic animals. Some common flukes that can infect North American dogs are:
1. Paragonimus kellicotti – These flukes are passed to dogs when the eat crayfish. Once ingested, Paragonimus make their way from your dog’s stomach to its lung tissue, where the worms lay eggs. The eggs move up the dog’s respiratory passages and are swallowed; eventually they are passed through feces. Having just a few of these flukes flukes will not bother a dog. However, a heavy infestation can cause chronic coughing or gagging and a loss of body weight.
2. Nanophyetus salmincola – This fluke, common to the Pacific Northwest, causes “salmon poisoning” in dogs. Dogs contract this disease from eating salmon that carry Nanophyetus larvae. This type of fluke, which live in the intestines, do not cause any sickness. But a bacterium called Neorickettsia helminthoeca, which lives inside the fluke, causes salmon poisoning. Symptoms of salmon poisoning include high fever, appetite loss, or depression.
3. Alaria is an intestinal fluke that can infect dogs. Alaria create few, if any, clinical signs unless there is a heavy infection. Dogs contract this parasite when they eat any number of aquatic animals, such as frogs, tadpoles, or snakes.
4. Most tapeworms usually infect dogs when they ingest fleas or nonaquatic animals. But in the case of the tapeworm Diphyllobothrium latum, your dog becomes infected by eating a fish that is infected with larval tapeworms.
Diphyllobothrium adults can grow up to 30 feet in length.
Their eggs are released into water through the feces of an infected dog, fox, mink, or even bear.
The eggs are ingested by copepods, which are eaten by small fish. Diphyllobothrium larvae live within the muscles of fish and are passed up the food chain from fish to fish until they are eaten by a mammal, where they mature in the digestive system and lay eggs that are passed through the feces.
Drug therapy is the most common treatment used by veterinarians to control worm and fluke infections. The most popular drug for tapeworms and flukes is Praziquantel, marketed as Droncit by Bayer Corp.
It is possible for a dog to drink pond, lake, or stream water and also swallow the infective stages of two protozoan species: Giardia or Cryptosporidium parvum.
Information on the frequency of these infections in dogs is unclear.
Dogs usually become infected by eating something contaminated by feces from an infected animal.
Dogs may become infected and show no clinical signs or may only have diarrhea.
Drugs such as Flagyl (metronidazole) or Panacur (fenbendazole) can be used to treat Giardia infections.
There are currently no drugs approved for treating Cryptosporidium infections in dogs.