On the morphology of Haemonchus contortus (Rudolphi) Cobb (Nematoda: Trichostrongylidae) in sheep and cattle.

Abstract

The spicules and paravulval structures were examined in samples of Haemonchus contortus recovered from British sheep and African cattle, and were compared statistically with data published by other workers in Australia and the United States of America. The samples from sheep resembled those found in the northern states of U.S.A., and were different in these characters from the Australian populations of Haemonchus contortus. Although the samples from cattle showed larger spicules and a higher percentage of females with a knob-like vulvar flap than those in sheep, all were significantly different from the Australian Haemonchus placei. It was concluded that although there is a world-wide tendency for populations of Haemonchus contortus in sheep and cattle to evolve into separate strains, intermediate forms exist which form a link between these strains.