It's ironic that mammals, the most complex organisms in nature, can fall prey to the simplest of organisms – protozoa. Protozoa, as we all remember from junior high biology, are one-celled organisms – the most basic forms of life. But while most single cell organisms are free-living and innocuous, a sinister few can invade our pets, causing a range of problems including serious diarrhea, which can lead to weight loss, debilitation and even death.
Many of these organisms are difficult to detect with conventional laboratory analyses. The most challenging aspect of dealing with these parasites is actually confirming their presence in a patient. Often, veterinarians arrive at a presumptive diagnosis without laboratory confirmation, prescribe proper medications, and wait for a positive response to confirm the diagnosis. This approach is called "diagnostic therapeutics," and is often used for medical conditions that are uncommon and difficult to diagnose by conventional means.
Even though they are some of the simplest forms of life, intestinal protozoa can cause serious damage to the intestinal tract of house pets – usually in puppies and kittens. To avoid these infections, all pet shops, breeders, boarding kennels and catteries should minimize the crowding of animals, constantly monitor their fecal eliminations and strive to maintain a sanitary environment.
The following is a brief explanation of the more common intestinal protozoan parasites that threaten companion animals. Just as with the other intestinal parasites, such as intestinal worms, pet owners should be familiar with these organisms, the threats they pose and how to effectively deal with them. If you suspect that your pet is infected, see your veterinarian immediately.
Coccidia are intestinal protozoa that invade and infect the lining cells of the small intestine. There are many species of coccidia and almost all domestic animals can become infected. Of the numerous types that infect dogs and cats, Isospora is the most common. Coccidia spread when an animal eats infected fecal material or an infected host, such as a small rodent. Many researchers maintain that virtually all dogs and cats have been infected with the organism at one time or another during their life.
Most coccidial infections are harmless, cause minimal symptoms and are eliminated by normal body defense mechanisms. More serious coccidial infections cause severe watery or bloody diarrhea and are often seen in high-density confinement situations such as kennels, catteries and pet shops. Treatment of the entire population of animals with specific sulfa drugs, along with a general cleaning of the premises, is usually necessary to eradicate the problem.
Cryptosporidia are a different type of coccidial organism that infects house pets, and, currently, there is no cure. However, most healthy adult dogs and cats can effectively control the infection without showing symptoms. But if their immune systems are compromised from feline leukemia, immunodeficiency virus or other debilitating diseases, they are likely to develop the typical intestinal signs of coccidiosis on a continual basis. More importantly, the infection is transmissible from pets to humans suffering from immunosuppressive conditions, such as HIV or those receiving chemotherapy. Unfortunately, there is no effective medical treatment for humans either.
Giardia are pear-shaped, one-celled organisms that infect the small intestine of dogs and cats. Similar to other protozoan infections, most clinical cases of giardia in young animals cause explosive, watery diarrhea, dehydration, weight loss and an unkempt appearance. Adult animals are capable of harboring the infection without showing clinical signs.
Giardia is commonly found in wild animals, especially beavers, and it is believed that they probably serve as the primary reservoir for the infection. Most domestic animals contract giardia from drinking contaminated pond or stream water. Treatment for clinical giardiasis is generally effective using drugs such as metronidazole. But this can be a serious gastrointestinal illness and most diagnosed cases need long-term therapy so it is not to be taken lightly.
Keeping your home sanitized and preventing fecal contamination of food and water supplies is essential for reducing re-infection.
Giardia infections have been diagnosed in humans showing similar intestinal symptoms. As yet, although there is suspicion by researchers, animal to human transmission has not been confirmed.
Although not seen with the frequency of coccidia organisms and giardia, a number of other protozoa can also infect the intestinal tract of house pets. Organisms called trichomonads, a species of amoeba, are occasionally encountered in confined populations of animals. They cause the typical watery, sometimes bloody, diarrhea, sometimes leading to dehydration and weight loss. Younger animals, again, are at the highest risk, and frequently the presence and virulence of the infection stems back to crowding and unsanitary environmental conditions. But keeping sanitation levels up can effectively get rid of these organisms as well.