The Life History of Nematodirus helvetianus May, 1920, a Nematode Parasitic in Cattle

Abstract

Nematodirus helvetianus May, 1920, commonly known as the thread-necked strongyle, is a trichostrongylid nematode found in the small intestine of cattle and occasionally also of sheep, goats and camels. Inasmuch as Herlich and Porter (1953) found that this strongyle is potentially pathogenic to calves, it was considered desirable to determine its life history. The only previous work dealing with the life history of N. helvetianus was done by Zviagintsev (1934) who reported that larval development and molting occurred within the egg. Observations made on the effects of specific temperatures on the rate of development will be discussed in conjunction with results of this investigation. Zviagintsev also noted that the infective larvae were very resistant to desiccation, and could live as long as eight months or more at room temperature. He was unable to infect guinea pigs or rabbits, but succeeded in infecting a lamb. He found that larvae fed to calves reached maturity in three to four weeks. Nearly two decades earlier Boulenger (1915) studied the life history of a closely related species, N. filicollis (Rudolphi, 1802) Ransom, 1907, a parasite of the small intestine of sheep. He reported that the embryo developed within the egg and underwent two molts, one complete and the second incomplete. This confirmed earlier observations by Ransom (1911), Railliet and Henry (1912) and Maupas and Seurat (1913). Since the infective larva retained the cuticle of the second molt, Boulenger considered it to be in a state of transition between the second and third stage. He noted that the infective larva shed its sheath in vitro, when exposed to temperatures approximating the body temperatures of mammals. Parasitic larval stages were described by Boulenger on the basis of immature specimens recovered from naturally infected sheep killed for post-mortem examination. He found the first traces of external sex characters in specimens 2.5 mm. long. In the male, this appeared as a distinct swelling just anterior to the tail fork, at about the level of the anal opening. This he considered to be a rudimentary bursa. Specimens measuring 5 mm. long exhibited bursal rays and spicules, and at this stage of development, the characteristic tail fork and caudal process had disappeared. In the young female, the tail fork and caudal process were retained somewhat longer, the process being retained as the terminal spike characteristic of the mature female.