Flagellates posses one or more long, slender flagella used for locomotion. They multiply by binary fission and some species posses cyst stages. The flagellates will be discussed in two groups; 1) intestinal and urogenital parasites, and 2) haemoflagellates.
The genus Trichomonas consists of many species two of which infect man (a third Pentatrichomonas hominis has five free flagella). All trichomonads posses three to five anterior flagella, an undulating membrane, and a recurrent flagellum attached to the edge of the undulating membrane. All flagella originate from an anterior basal body. An axostyle extends the length of the trichomonad and extends posteriorly. A cyst stage is not known for this genus.
Trichomonas foetus- Agent of bovine trichomoniasis .
This trichomonad is a parasite of the reproductive tract of bovines. Similar species are reported from other mammals. The parasite is transmitted by coitus. In the females, the infection may cause low grade inflammation, sterility and poor conception rate. In males, the clinical picture varies from no apparent signs to inflammation of the prepuce. Like all trichomonads, the organism multiplies by simple binary fission and does not posses a cyst stage. Diagnosis is based on microscopic evaluation of the trophozoite stage. Samples of vaginal mucus or exudate or saline washings from the vagina and preputal cavity are best for microscopic examination. Washings should be left to settle for an hour or two or centrifuged for examination of the sediment. In cases of abortion, allantoic and amniotic fluids as well as fetal tissues and membranes should be examined. Serologic tests (agglutination)are now available. Treatment is difficult and usually not attempted. Slaughter or breeding rest (females) are the usual methods employed in dealing with bovine trichomoniasis.
Trichomonas vaginalis- Agent of human trichomoniasis.
This trichomonad is a parasite of the reproductive tract of humans. This is one of the most common sexually transmitted diseases of man and often occurs with other more severe concurrent infections. Chronic reproductive and urinary problems can occur in females. Transmission is by sexual contact with this species occurring only in humans. Prevelance is reported to be between 10 and 25% among women, depending on the degree of hygiene practiced. About 15 % of infected women show clinical signs.
Disease is produced when normal cell destruction in the infected vagina is unable to provide glycogen for normal populations of bacillus. These bacteria metabolize glycogen to lactic acid thus keeping the normal pH acid. With this change in pH, opportunist bacteria and trichomonads can survive.
Treatments with metronidazole is successful although contraindicated in pregnant patients. Restoration of normal vaginal pH is necessary.
Other trichomonads known to infect humans include Trichomonas tenex from the tarter and gums of the mouth and Pentatrichomonas hominis from the human colon..
Trichomonas suis
A parasite of hogs found in the nasal passage, stomach, colon and large intestine.
Trichomonas gallinae- Agent of avian trichomoniasis.
A parasite of the upper digestive tract of many gallinacious birds and doves (above). Some strains may also produce liver and lung lesions. The parasite is transferred to young from the mother during feeding. Transmission between birds may also occur from contaminated feed and water. Most deaths occur vary acutely and young appear in good condition. The presence of this organism in doves is a common source for infections in both free-ranging and trained falcons and hawks.
Trichomonas gallinarum
A parasite of ceca and liver of gallinacious birds.
Trichomonas spp
Intestinal parasites of many animals including dogs, cats and rodents.
Trichomonas equi
Intestinal parasite of horses. A potential problem in young animals..
Hexamina meleagridis
A parasite of small intestine of gallinacious birds.
Pentatrichomonas (Trichomonas) hominis of humans dogs, and cats.
Infections and clinical signs in both humans and canines resemble those seen in Giardia spp infections. In canines, this may be an opportunistic pathogen.
Giardia lamblia- Agent of intestinal giardiasis.
The number of true species of Giardia is not truly known and it appears that the host range is extremely broad. The trophozoites attach to the mucus epithelial cells of the small intestine. Cysts are usually formed prior to being passed with the feces.
Giardia infections can be inapparent or cause severe enteritis and diarrhea in humans, dogs, cats, caged birds, and probably a variety of other domestic and wild animals. The cyst stage (upper left) is usually recovered from formed stools while the trophozoite (upper right) is most common in cases of diarrhea. Differences in virulence, host genetics and immune status all may contribute to the outcome of infection. Pathogenic factors include inhibition of some host intestinal enzymes active in lipid and carbohydrate digestion. This can result from both mechanical damage to the microvillar glycocalyx and substances released by the parasite. Rapid sloughing of intestinal epithelial cells leads to failure of new epithelial cells arising in the crypts, which would differentiate into columnar cells with microvilli. Blunting of intestinal villi and microvilli results in decreased absorptive surface area. Malabsorption of nutrients, including fat, disaccharides, some vitamins, and iron can occur. Diagnosis is by recovering and microscopically identification of either stage in feces. Serologic tests (ELISA) are available but used only in human medicine. A non-clinical carrier state appears to be common. Treatment in dogs is with quinacrine, although side effects are common. Metyronidazole (drug of choice in humans) is also effective in dogs and cats but is more expensive but lacks side effects. Treatment in caged birds is with dimetridazole.
Giardia is the most common intestinal parasite of people in North America. Infants and children in day care facilities appear to be the group most at risk. Giardia is not host specific and infections can be zoonotic, although most human cases are the result of hand-to-mouth infections from other humans and/or drinking cyst-infected water. Many human cases result from infection via contaminated water, often contaminated by wild species such as beaver.
Chilomastix spp
This is another intestinal protozoan parasite known to infect many animals including man and birds. The life cycle and clinical disease are similar to that of Giardia sp. Both a trophozoite (right) and cyst stage (left) occur.
Histomonas meleagridis- Agent of "black-head".
The agent of "black-head" in poultry. The trophozoites and resulting lesions are confined to the ceca and liver. The infected caecum is enlarged and the mucosa becomes necrotic consisting of leather-like cheesy material. The parasites lie singly or in small groups in the spaces between cells. From the mucosa, they can spread to the submucosa and muscle layers and eventually be carried to the liver via the portal blood. The liver has circular areas of necrotic tissue usually resulting in impaired function (below). Early liver lesions are small in size, spherical and cream-colored while older lesions are large with depressed dark centers and a pale periphery. Clinical signs include drowsiness, weakness, and sulfur-colored droppings. Transmission can be by ingestion of trophozoites or ingestion of Heterakis gallinae (nematode) egg containing the trophozoite. In the latter case The flagellated form of the H. meleagridis is ingested by the co-habitating H. gallinarum nematode. The Histomonas passes through the gut wall of the female worm and penetrates into the ovary. It multiplies in the ovary and invades the oocysts. When embryonated Heterakis eggs are ingested by the susceptible host, the Histomonas escapes into the lumen of the caecum.
Young birds usually have an acute form of the disease while older birds may appear sick for several days prior to becoming emaciated. Heaviest losses occur at 3 to 12 weeks of age. Many other species of birds including quail and pea fowl are also susceptible to infection. Treatment is with nitroimidazole. Separation of species and ages is vital in preventing this disease.
Haemoflagellates:
These parasites live in the blood, lymph, and tissue spaces and are typically transmitted from one host to another by blood-feeding arthropods The most important genera are Trypanosoma and Leishmania.
Infection in mammalian hosts occurs either through the bite of the infected arthropod (salivarian) or through contamination of the host's mucus membranes or abraded skin by the arthropod's infected feces (stercorarian).