Morphological criteria of Haemonchus contortus (Rudolphi) (Nematoda: trichostrongylidae)

In his review of the genus Haemonchus Almeida (1935) recognised seven valid species and two doubtful ones. A tenth species, H. lawreneei Sanground 1933 he considered as more appropriately to be placed outside the genus. Accepting Almeida’s work in toto Travassos (1937) does not deal with the genus Haemonchus in his review of the Trichostorongylidae. The Russian workers Skrjabin, Shikhobalova and Shults (1954), in a later account of the genus, accept the two species inquirendae and include H.lawrencei in the genus in addition to the seven regarded as valid by Almeida. To these 10 they further add the three species described subsequently to Almeida’s work, namely H. okapiae van der Berghe 1937, H.tartarious Evranova 1940 and H.santomei Guterres 1949. These 13 species, however, are not universally accepted; for example, Madsen & Whitlock (1958) consider that H.lunatus Travassos 1914, which is known from one specimen only, could represent an aberration of H.contortus. Out of the possible 13 species, 7 have been recorded from domesticated cattle and sheep, and 6 are known only from other ruminants. Two of the seven have been found in both cattle and sheep (H.con tortus Rudolphi 1803 and H.similis Travassos 1914), two (H.lunatus and H. santomei) have been found in cattle only, and the remaining three (H. bedfordi Le Rue 1929, H.longistipes Raillet & Henry 1909 and H.tartaricus Evranova 1940) are described from sheep only. Nevertheless, of all the named species only one, namely, H.contortus .has been implicated to any significant degree in the helminthiasis of domestic ruminants. Several workers have drawn attention to morphological differences between samples of this species taken from sheep and cattle hosts (Veglia (1915), Travassos (1921), Monnig (1928), Le Roux (1929), Almeida (1935)). A systematic morphological study by Roberts et al (1954) led then to the conclusion that there were two distinct species in Queensland, Australia, one in sheep for which the name H,contortus was retained, and the other in cattle to which they gave the name H.placei (Place 1893). These morphological findings were confirmed by Bremner (1955), on cyto-genetical grounds, who found that the X-chromosomes in H.place! were twice the size of those in H.contortus. In the U.S.A., Drudge, Leland & Wyant (1957), working with, steep, found female worms of a type intermediate between the Australian species, and Madsen & Whitlock (1958) found males occupying a similar position. In the same year Herlich, Porter and Knight, found two separate strains in sheep and cattle, which were comparable with those found in Australia, but not exactly the same. Their sheep strain resembled that found by the other American workers only differing greatly in the spicule length of the male. The aim of the present study is to examine Haemonchus contortus, on the basis of the morphological criteria which have been used by the previous workers, as it occurs in Britain and in particular, at the Moredun Institute, Edinburgh. There a culture of English sheep-derived worms has been kept experimentally in sheep since 1957, when it was started with infective larvae, supplied by the Cooper Technical Bureau, Berkhamsted, Herts. The experimental conditions are such that only worms descended from these larvae can occur in the sheep, so that one is, in effect, examining one large population, and not a mixture of several, as might occur in material from other sources. The data obtained will be presented in separate sections, concerning the egg, the infective larva and the adult worm.