The reproductive potential of Heterakis gallinarum in various species of galliform birds: implications for survival of H. gallinarum and Histomonas meleagridis to recent times

The reproductive potential of Heterakis gallinarum was substantially higher in the ring-necked pheasant than in any of the eight other species of galliform birds used on the 67 tests here reported. Pheasants on four tests yielded an average 19·4 times as many eggs that embryonated as were used to infect the birds, while for those on tests with a highly virulent strain of Histomonas meleagridis present the return was 21·1 eggs per egg used. Corresponding returns for chickens were 5·2 and 2·4; for guinea fowl, 9·7 and 1·3; and for turkeys, 1·9 and 0·17. Birds of the other five species gave even poorer returns. Previous studies had indicated that 10–30 times as many heterakid eggs must embryonate as survive to be ingested, under natural conditions. Inasmuch as the traditional host of Heterakis gallinarum must also have been that of the virulent strains of Histomonas meleagridis that have become man's contemporaries, we regard the ring-necked pheasant, or some very close relative, as being the most likely host of these parasites in the late Cenozoic and Recent Eras.