Protozoans of Importance to Pet Owners

Unicellular organisms may not seem so dangerous at first glance, but protozoans can prove to be harmful parasites. Knowing how to avoid these tiny creatures will help to keep your pet safe. Recognizing symptoms of infection will help your pet get effective treatment sooner.

Protozoans are tiny single celled organisms from the kingdom protista. Most protozoans are just harmless free-living organisms. However, there are also several parasitic varieties. Parasitic protozoans can be divided into three subphyla: sarcomastigophora, ciliophora, and apicomplexa.

Sarcomastigophora

Subphylum sarcomastigophora includes the flagellated protozoans and the amoeboid protozoans. In case it has been awhile since your last biology course, flagella are long whiplike structures used for locomotion. Flagellates have at least one flagellum. Amoeboid protozoans move by pseudopodia, or false feet. Knowing a bit about how these parasites function will help you to understand how they'll effect your pets.

Flagellates swim easily in their hosts bodily fluids, including the blood, lymphatic fluid, and even cerebrospinal fluid. These parasites have dormant resistant cyst stages and also motile stages. The flagellates can further be divided into hemoflagellates and mucosoflagellates. The hemoflagellates generally live in the blood stream and the mucosoflagellates live in the mucus lining of the digestive tract, urinary tract, or genital tract.

Hemoflagellates are generally transmitted by bloodsucking insects. In Africa there are several different hemoflagellates, but I'm going to stick to parasites that will possibly be seen in the United States so that I don't end up writing an entire book. One such hemoflagellate is known as Trypanosoma cruzi, or more commonly, Chaga's disease. Chaga's disease is transmitted by the kissing bug (Reduviid bug) and is found circulating in the peripheral blood. This trypanosome does not enter the red blood cells, but rather swims around them. Symptoms include lethargy, pale mucous membranes, fluid build up, fast heart rate, enlarged liver, and an enlarged spleen. Diagnosis is usually determined by a blood smear.

Mucosoflagellates are typically transmitted either through feces from host to host, or by contact with the genital flora. These include the giardia species, which you may be familiar with. Giardia affects dogs, cats, cattle, sheep, and horses, as well as humans. Diarrhea is generally present, but not in all cases. Diagnosis is by either a direct smear of feces or a fecal flotation using a zinc sulfate solution. Since giardia move across the slide quickly and are not always easily seen, sometimes your pet must be treated based on the likelihood that this is probably giardia you're dealing with. Giardia tends to cause the stool to be fatty, not bloody. While your pet will likely experience weight loss, giardia is not generally fatal. Another very important mucosoflagellate that deserves mention is Tritrichomonas foetus. This parasite affects cattle and resides in the genital tract. This trichomonad is responsible for a significant number of cattle abortions. While most people don't keep and breed cattle as pets, this certainly reminds us how tiny parasites can be of great economic importance.

Parasitic ameobas tend to be intestinal parasites, usually of the large intestine. Most amoebas however, are free living and don't typically cause harm to humans or animals. Parasitic amoebas have been reported in dogs, cattle, sheep, goats, horses, and humans. Entamoeba histolytica and Entamoeba coli are the most important parasitic amoebas. These cause extremely painful diarrhea. Dogs usually catch the amoeba through contact with infected humans. Diagnosis is made by performing a standard fecal flotation.

Ciliophora

Subphylum ciliophora consists solely of the ciliates. For a quick refresher, cilia are hairlike projections used for locomotion. Ciliates appear to be covered in tiny hairs. While some ciliates are pathenogenic, some also have beneficial roles in digestion. Like the flagellates, ciliates have both a motile stage and a resistant cyst stage. Basically there are only two ciliates of importance to pet owners: Balantidium coli and Ichthyophthirius multifiliis. Balantium coli affects pigs, cattle, horses, rats, guinea pigs, and humans. Transmission is generally fecal to oral, which means that contaminated feces must be ingested. These protozoans reside in the large intestines and may cause diarrhea, abdominal pain, and blood stained feces. The other common ciliate in pets, Ichthyophthirius multifiliis, is known commonly to fish owners as "Ich". Ich is the most common aquarium fish disease and produces those little white spots seen on sick fish. Ich spreads quickly from one fish to another and is seemingly always present in the environment. It takes over when fish are stressed due to situations such as temperature change, elevates ammonia or nitrate levels, transporting fish, and adding new fish. Infected fish will hide, not eat as much, and rub against objects in the aquarium as if they are scratching themselves. It is best to avoid Ich by not stressing the fish.

Apicomplexa

Subphylum apicomplexa is the most complex and diverse group of protozoans. These protozoans are found mostly in the lining of the intestines and also in the blood. The lifecycles of these parasites are very species specific in most cases, which is good news if you have multiple species because it means that hopefully not all of your pets will acquire these parasites. Coccidians and hemosporidians are probably the most important apicomplexans for pet owners to be aware of.

Coccidians are transmitted mainly by fecal contamination and cause a form of enteritis known as coccidiosis. Their lifecycles are complex, however they prove to be very difficult to get rid of, due to their reinfective cycle. Coccidians include both Eimeria species and Isospora species, which have very similar lifecycles but infect different species. Eimeria affects cattle, sheep, goats, poultry, and rabbits. Dogs and cats are affected by Isospora species. Infection is marked by a great amount of watery diarrhea. Response to treatment is slow, so treatment is best started early to avoid severe dehydration. To avoid contact with infected feces, do not feed your animals directly on the ground and make sure to keep your animals away from the feces of any other animals whenever possible. Once your pet is infected, no further contamination is needed due to the self perpetuating lifecycle of coccidians. Coccidiosis is most common in young animals. Other common coccidia include the extremely tiny Cryptosporidia which infect several species and Toxoplasma gondii, which infects cats. Toxoplasma gondii is not generally harmful to cats, but can be harmful for pregnant women because it causes abortions and birth defects in humans. This is the reason that pregnant women are advised against cleaning the litterbox and gardening in areas where cats may have used the soil as their bathroom area. Less common coccidia include Neospora caninum and Sarcocystis neurona. Neospora caninum affects dogs and cattle. Newborn puppies will exhibit greatly reduced use of their hind limbs in comparison to normal puppies. Adult dogs exhibit neurological signs as well as pneumonia and other problems. The dairy cattle industry is greatly affected by abortions caused by Neospora caninum. Sarcocystis affects dogs, cats, and humans. Infection can occur by ingesting infected flesh or contaminated feces. Generally, no signs are seen and diagnosis is made after death. Sarcocystis neurona is specifically seen in horses and causes lameness, muscle atrophy, constipation, and urinary incontinence. Feed is generally contaminated by opossum feces and then consumed by unlucky horses. Lesions in the spinal cord and the brain occur in the infected horse, which eventually dies.

Hemosporidians are transmitted by bloodsucking arthropods. These include the piroplasms which are transmitted by ixodid ticks and the plasmodia which are transmitted by dipterans. You've probably already heard of at least one type of plasmodia: malaria which is transmitted by mosquitoes. The main piroplasm seen in pets is the Babesia species, which causes hemolytic anemia. Avoid tick infested areas or use a tick repellant product to avoid Babesia. If ticks do attach to your pet, the sooner you get them off, the more likely it is that your pet did not get any diseases from the ticks.

Knowledge of parasites is important in avoiding them. Keep your pets away from contaminated feces, bring them a clean water supply on hikes, and keep biting arthropods away from your pet as much as possible. Tiny unicellular organisms may be capable of bringing down your pet, but if you know where they're found and how they're transmitted, you can avoid them. If your pet is infected, seek treatment immediately so that your pet can be back to normal as soon as possible.