Hexamitiasis, caused by the protozoan Spironucleus meleagridis, is an acute, infectious, catarrhal enteritis of turkeys, pheasants, quail, chukar partridges, and peafowl. Natural infection has not been observed in chickens. Pigeons are susceptible to S columbae. Hexamitiasis is rare in North America. The highest mortality occurs in birds 1–9 weeks old.
The causative protozoan parasite in turkeys, S meleagridis (formerly Hexamita meleagridis) is spindle-shaped, averages 8 × 3 mcm; and has four anterior, two anterolateral, and two posterior flagella. It has not yet been cultured in experimental media, although it has been grown in the allantoic cavity of developing chicken and turkey embryos. It is transmitted directly by ingestion of contaminated feces and water. Encysted hexamitids are resistant to environmental conditions outside the bird and, therefore, may be more important in the transmission of the disease. Up to ⅓ of the recovering birds become carriers and shed parasites in their droppings.
Signs of hexamitiasis are nonspecific and include:
Birds may die in coma or convulsions. Bulbous dilatations of the small intestine (especially duodenum and upper jejunum) filled with watery contents are characteristic. The crypts of Lieberkühn contain myriad S meleagridis, which attach to the epithelial cells by their posterior flagella.
Diagnosis of hexamitiasis depends on finding the flagellates by microscopic examination of scrapings of the duodenal and jejunal mucosa. Spironucleus spp move with a rapid, darting motion (in contrast to the jerky motion of trichomonads). To avoid contamination of instruments with other cecal protozoa, the duodenum should be opened first. Spironucleus spp may be demonstrated in poults that have been dead for several hours if the scrapings are placed in a drop of warm (104°F [40°C]), isotonic saline solution on the slide. Presence of a few Spironucleus in birds >10 weeks old may be unimportant in terms of the disease but still act as a reservoir of infection.
Because many birds remain carriers of Spironucleus, breeder turkeys and young poults should be raised on separate premises if possible, preferably with separate attendants. Wire platforms should be used under feeders and waterers. Pheasants and quail may also be carriers and should not be raised in the same location as poults. Indirect transmission can occur if affected fecal material is transferred to another location by contaminated equipment or clothing.
The infected form of Spironucleus is a cyst. Therefore, if a flock is positive for this parasite, removal of the litter and disinfection with heat (45°C for 30 minutes) or standard cleaning products of the farm and all equipment is necessary before placement of the next flock.
There is no effective treatment or vaccine for hexamitiasis, although oxytetracycline (0.011% in the feed for 2 weeks) or chlortetracycline (0.022%–0.044% in the feed for 2 weeks) may be of some benefit to control secondary infections.