Histomonas wenrichi n. sp. (Mastigophora: Mastigamoebidae), a Nonpathogenic Parasite of Gallinaceous Birds

SYNOPSIS. A nonpathogenic histomonad, morphologically identical to that found in pheasants by Wenrich in 1943, is described as Histomonas wenrichi n. sp. Its dimensions are about 1.5 × those of H. meleagridis. It has 4 flagella instead of the 1 or 2 that characterize the latter species. It does not multiply in the host tissues nor produce visible responses to its presence there, and it does not exist as the clear “tissue form” that is common in active H. meleagridis infections. Histomonas wenrichi n. sp. can be transmitted to turkeys, chickens, and pheasants by either rectal inoculation or by feeding embryonated eggs of Heterakis gallinarum grown in birds harboring the nonpathogenic histomonad in the ceca. Usually fewer than half the female heterakids so grown produce eggs capable of transmitting this histomonad, and a total of 200 to several thousand eggs from worms recovered from Histomonas‐infected birds may be required to produce one Histomonas infection. Histomonas wenrichi n. sp. has been propagated in more than 2000 chickens and turkeys over an 8‐year period, during which time it has been transmitted by 18 generations of Heterakis. It has frequently been grown in birds in which H. meleagridis was also present, and upon reisolation it maintained all of its original characteristics. It has not yet been cultivated in vitro.