There is always the chance that your beloved dog may develop some kind of rare or unusual internal parasite that may be difficult to diagnosis because the vet doesn't think to check for the parasite or the owner doesn't tell the vet that the dog has been in a different area or around strange dogs. This is more commonly the case when dogs go on vacation with their owners to different states, countries or locations. It can also happen when dogs from other areas are abandoned or left in different locations, which then introduces new parasites to the local canine population.
Hunting dogs and dogs that are outdoors and in contact with wild animals such as rabbits, foxes, coyotes, raccoons, wild birds and even larger mammals often develop different types of intestinal and internal parasites that are not typically found in domestic dog populations. Typically these parasites will have a relatively short lifecycle as the dog is not an ideal host, but some can cause significant and even life threatening conditions.
Having a general idea of some of the less common internal parasites and how your dog may be exposed is important, both in being aware as an owner as well as in helping your vet with the information that can speed up the diagnosis and identification of the problem.
Infestations with the single celled parasite Babesia canis result in symptoms such as vomiting, jaundice, anemia, fever and kidney infections. These conditions can be chronic or they can come and go over time. Babesia canis is found in ticks, which transmit the parasite to dogs when they bite. The parasite actually lives in red blood cells, eventually bursting the cell and moving to a new one, infecting more and more cells. This is why anemia and jaundice are so problematic, as with the concurrent kidney dysfunction and eventual failure if not treated.
Babesia canis, while not common, is also not rare in some parts of the southwestern areas of the United States. The condition is confirmed through blood tests, then the vet will begin a treatment using a variety of medications designed to kill the parasite. In extreme cases the dog will need blood transfusions to eliminate all parasites from the circulatory system, however in these cases the change of re-occurrence is fairly high.
Although not common, there is a parasite known scientifically as Thelazia californiensis, and less formally as eyeworm, that can infect the eye of the dog as well as several other mammals. They are most commonly found in dogs on the Pacific coast, but can also be transferred to humans, so knowing the symptoms is important. Eyeworms do not cause serious damage on their own, but they are an irritant that can result in the dog injuring their eye through rubbing and scratching. Eyeworms are very tiny and take residence in the tear ducts and behind the third eyelid in the dog's eye. The female worm lays eggs that are washed out of the eye in the tears, then are ingested by face flies and moved to a new host animal. When the fly feeds around another animal's eye the larvae migrate into the eye and repeat the cycle.
Dogs that have eyeworms will have excessive tearing, irritation of the eyelids leading to conjunctivitis, and some sensitivity to light. The worms are very small and are usually not seen by the naked eye, although they are easily seen under a microscope or magnifying glass. Antibacterial treatments will not remove the eyeworms, however the eye can be anesthetized with a topical gel and then the worms removed, or Ivermectin in very small dosages can be applied to the eye to kill the worms. Only a vet should attempt these treatments as there is a risk of injury to the eye if done incorrectly.
Trichinella spiralis is the specific organism that causes Trichinosis in dogs, cats, other mammals and even in humans. Since it is most serious in people, dog owners need to be aware of the risks of feeding their dog raw or undercooked pork. Basically the Trichinella spiralis lives its entire life in the intestines but the larva crawl through the muscle tissue and form cysts in the muscle. When the dog, or person for that matter, eats the meat they also consume the cyst, which if it has not been properly cooked and killed, will start to develop and grow within the host.
Generally dogs will have few if any symptoms of an infestation of Trichinella spiralis. Humans, on the other hand, will have severe vomiting, diarrhea and inflammation of the blood vessels due to the movement of the larvae through the body. When the parasites encyst in the muscle there is extreme pain, lack of strength and range of movement and bleeding in the eyes and the cuticles of the nails. In extreme cases swelling in the brain and heart can lead to fatality.
Vets, if they discover trichinosis in a dog, can treat the condition with Mebendazole, which is also used in treating roundworms. All cases of trichinosis in dogs or other animals must be reported to the CDC (Centers for Disease Control). There are less than 100 cases of human trichinosis diagnosed per year so it is certainly not as common as it was before proper food handling, especially with pork, became routine.
Toxoplasmosis is more common in cats, but it can occasionally be found in dogs, and will definitely be a serious condition if humans contact Toxoplasma gondii. Pregnant women in particular have to be careful to avoid contact with cat feces, undercooked meat and unpasturized infected goat's milk. Dogs can also have the same methods of getting the disease.
Dogs that are infected with Toxoplasma gondii will have a variety of symptoms, depending on where the infection is located within the body. Symptoms can include anemia, pneumonia, eye infections, low-grade fevers, seizures and neurological problems, digestive issues or even paralysis. The symptoms can be either chronic or they may come and go, sometime varying in how they impact the dog.
About 60% of all dogs that are healthy before developing Toxoplasmosis will recover with antibiotic treatments. Dogs that have other illnesses or have immune problems as well as senior and very young puppies are most at risk. Preventing your dog from eating cat feces or digging through the litter box, minimizing any contact with raw or undercooked pork and other meats or raw goat meat or milk can help to eliminate the chances of developing this condition.