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Protozoan Infections

Parasites are organisms that live on or in another organism, getting their nourishment from their hosts, the animals being parasitized. The pathogenic effect of a parasitic infection may be subtle or life-threatening. Pathogenic effects fall into several categories: (1) destruction of the host's cells, tissues, and organs; (2) diversion of nutritive substances; (3) toxin production; and (4) serving as vectors for other disease agents. Protozoans are single-cell animals that constitute a large group of many types of organisms. Each type has its own life cycle, ranging from one to many stages. Pathogenic protozoans are endoparasites as adults.

Coccidia is a collective term for organisms that infect the intestines and cause a watery diarrhea in newborn puppies. The parasites are commonly found in normal feces, but they multiply when puppies are stressed, have other internal parasites, such as roundworms, or live in unsanitary conditions. Diarrhea in puppies may progress from watery to bloody. Puppies often stop eating and become dehydrated. Treatment includes hydration, improving hygiene, eliminating other parasites, and antiprotozoan drugs. Antibiotics, especially sulfonamide drugs (trimethoprim-sulfa), are sometimes used to eliminate any bacterial infection that follow the underlying protozoan invasion. Coccidia parasites are passed in the feces. To prevent the parasites from spreading, it is important to isolate sick animals from healthy ones. Good hygiene should be maintained, and young puppies subjected to minimum stress.

Giardiasis is a chronic protozoal infection caused by Giardia lamblia. Dogs contract giardiasis by drinking water contaminated with cystic forms of the parasite (oocysts). In most cases, there are no obvious signs of disease, but some affected dogs pass bulky, smelly stools. These unpleasant bowel movements may occur intermittently, or may become chronic, continuing for weeks or months. Oocysts are only shed intermittently by the Giardia parasites. They are seen when stool samples are examined under a microscope. Infected dogs sometimes do not produce any detectable oocysts, so blood tests are more accurate. Giardiasis is relatively simple to treat with either metronidazole (Flagyl) or fenbendazole (Panacur). Metronidazole should not be given to pregnant female dogs. Drinking water that may be contaminated by wildlife is the cause of both human and dog infection.

Leishmaniasis, also called kala-azar, is a serious protozoan infection in humans and the most common parasitic disease of dogs in southern Europe. Leishmaniasis affects up to 40 percent of dogs throughout Greece, extending halfway up the Adriatic coast of former Yugoslavia and Italy. The disease does not occur in Australia. In North America it was first reported in 2000 among pack hounds in some areas of the southeastern United States.

Leishmania protozoa

Leishmania sp. protozoa
Courtesy of CDC

The Leishmania parasite is acquired as a result of sandfly bites and affects macrophages white blood cells. A sandfly picks up white blood cells infected with parasites when feeding on an infected dog and transmits the parasites to another animal when it takes another meal. There are two forms of the disease. In the usually nonfatal cutaneous form, the affected dog develops crusty, dandruffy areas that may become discolored or ulcerated. In the almost fatal visceral form, there is anemia, sometimes diarrhea, and damage to the liver and spleen. Leishmaniasis is diagnosed by finding organisms in smears taken from lymph nodes or skin scrapings. Anti-Leishmania drugs are licensed in some countries, although even with treatment, the outlook is poor for any dog with the visceral form of the disease. Sandflies bite at night. Dogs should be kept indoors from dusk until dawn in locations where sandflies are known to exist.

Rhipicephalus sanguineus, brown dog tick

Rhipicephalus sanguineus

The brown dog tick is known to transmit diseases to animals including canine babesiosis, bovine anaplasmosis, East Coast fever and Texas cattle fever.

Courtesy of CDC

Babesiosis is infection with Babesia parasites which are transmitted by ticks. The disease is unusual in North America, although it is found in some dogs in the southeastern United States, ranging up to Massachussetts. Affected dogs develop a severe anemia, become listless, andy pass dark-colored urine. Babesia may be detected via blood samples and a antibody tests. As with leishmaniasis, anti-Babesia drugs are licensed in some countries. Dogs in regions of Europe, Asia, Africa, and Australia where this parasite lives should be routinely treated with tick prevention measures such as the use of fipronil (Frontline) spray or the wearing of an amitraz (Preventic) collar.

Trypanosoma brucei

Trypanosoma brucei Courtesy of CDC

Trypanosoma brucei causes a severe disease in all domestic animals, including horse, cattle, sheep, dogs, and cats. The protozoan parasite Trypanosoma cruzi is common in Central and South America but rare in North America. It is transmitted by blood-sucking insects called "kissing bugs." While feeding, the bug defecates, passing the protozoa in its feces. The infected dog or person scratches the bite, and the protozoa enter the bloodstream, where they invade white blood cells. As with all parasites, puppies are more susceptible than adults. Signs of American trypanosomiasis (also known as Chagas' disease) may include enlarged lymph nodes, fever, and loss of coordination. The heart and muscles may be affected. Blood tests are used during acute stages of the disease, as well tests to detect antibodies. There is no effective treatment for this disease. Transmission of the disease can be reduced by the use of insecticides that will eliminate the bloodsucking bugs from homes.

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