Family Heligmosomidae
The related families Heligmosomidae and Heligmonellidae have complex cuticular ridges, collectively known as the synlophe, which attach the nematode to villae as they coil about these structures in the intestine (Durette-Desset, 1971).
In the Heligmosomidae the axis of orientation of the ridges is subfrontal and in the Heligmonellidae the axis is generally oblique (Durette-Desset, 1983). The female in the heligmosomids has a terminal caudal spine lacking in females of the heligmonellids and there are differences in details of the bursal rays. Durette-Desset (1971), in her classic thesis, used the structure of the synlophe to relate genera of these nematodes to the evolution and dispersal of their hosts during the course of evolution.
Bansemir and Sukhdeo (1996) suggested from experimental results that Heligmosomoides polygyrus in the intestine of mice tended to select regions in the intestine with the longest villi.
Heligmosomids are common parasites of soricoid insectivores and oriental, holarctic and neotropical rodents. The family contains the genus Heligmosomoides, with the well-studied species H. polygyrus of mice.
Heligmosomoides
H. polygyrus polygyrus (Dujardin, 1845)
H. p. polygyrus (syn. Nematospiroides dubius Baylis according to Durette-Desset, 1971) is a parasite of the duodenum (Panter, 1969) of wild house mice (Mus musculus), white-footed mice (Peromyscus maniculatus) and field mice (Apodemus sylvaticus) (Elton et al., 1931; Spurlock, 1943; Ehrenford, 1954). It is readily maintained in mice in the laboratory and has been the subject of various studies.
Spurlock (1943) showed that various inbred strains of mice could easily be infected orally. According to Ehrenford (1954) eggs were 70-84 X 37-53 mm in size and were passed in faeces in the 8- to 16-cell stage. At 23-28°C hatching took place in 26 h and first-stage larvae were 300-600 mm in length. Ehrenford (1954) noted a moult at 48 h after hatching and assumed this was the final moult leading to the sheathed infective larva. He claimed 4-6 days were required for the development of the infective larvae, which were 480-563 mm in length. Larvae migrated to the edge of the culture dishes and assumed a 'vertical stance using the tail as a foot.' They also remained motionless for long periods unless stimulated by mechanical vibration, air currents or heat.
Infection was by oral ingestion and larvae were unable to penetrate the skin. In the gut of mice, larvae exsheathed and were found 24 h postinfection in the small intestine. From 24 to 48 h postinfection, larvae penetrated the intestinal mucosa and came to lie close to the longitudinal muscle layer of the gut wall; they could be seen grossly from the outside of the intestine. The third moult occurred 2 days postinfection and the final moult (the fourth, but regarded by Ehrenford as the third) 6-8 days postinfection, after which worms returned to the intestinal lumen and matured. Eggs appeared in faeces 9 days postinfection and were produced for up to 8 months. Bansemir and Sukhdeo (1994) suggested that H. polygyrus feed on host tissue and not on host ingestion or blood.
Fahmy (1956) collected worms from A. sylvaticus and M. musculus in Scotland. Eggs kept at 22°C hatched in 23-24 h. Eggs kept at 26°C hatched after 19.5-20 h. First-stage larvae were 343-365 mm in length. The tail was conical but sharply pointed. Larvae examined 24 h after hatching were 418-440 mm in length. Sheathed third-stage larvae, present in 48-56 h, were 443-461 mm long (presumably excluding the sheath). Eggs were found 12 days postinfection in faeces of mice given larvae orally.
Bryant (1973) restudied H. p. polygyrus and reported for the first time the two moults in the free-living stages. At 20°C eggs hatched in 36-37 h. The first moult occurred in 28-29 h and the third 17-20 h after the first moult. In mice, the third moult occurred in the intestine in 70-96 h and the fourth in 144-166 h postinfection. The first eggs were detected in the faeces of mice in 10 days.
Dobson (1962) showed that the mouse (M. musculus) is a more suitable host for H. p. polygyrus than the rat. Development was slower in the rat than in the mouse and worms lived further down the intestine of the rat.
Bawden (1969) noted that more larvae of H. p. polygyrus established themselves in mice on inadequate diets than on ample diets but the 'low plan' diet reduced the ability of the adult worms to survive.
Lewis and Bryant (1976) reported on the distribution of H. p. polygyrus in the intestine of mice and Behnke and Parish (1979) studied the arrest of larvae in immune mice. Hernandez and Sukhdea (1995) stressed the significance of self- and allogrooming in the transmission of H. polygyrus. Kavaliers and Colwell (1995) suggested that female mice can discriminate between the odours ofparasitized and non-parasitized male mice.
Sukhdeo and Mettrick (1983) transplanted adult worms into different regions of the intestine of mice. Worms consistently migrated anteriorly to the duodenum. Liu (1965) reported that, in mice, larvae were in the gastrointestinal mucosa as early as 4 h after oral inoculation. They moved into the deepest portion of the gastric mucosa of the fundic region. Larvae left the gastric mucosa within 36 h postinfection and entered the intestine. Larvae encapsulated in the muscularis externa on day 3. Worms vacated their capsules by day 8 and emerged into the lumen of the intestine.
Brown et al. (1994a) studied the epizootiology of H. polygrus in a wild population of A. sylvaticus in England. The parasite had an overdispersed distribution, with higher prevalences in males and heavier mice. Brown et al. (1994b) concluded that eggs per gram of faeces fluctuated according to a 24 h cycle and that the origin of this cycle lay in the pattern of egg release by worms. Prevalence in intensity peaked in spring and declined in autumn. Infected mice moved further and faster than uninfected mice but the reasons for this are still unclear.
N'Zobadila et al. (1996a,b) contrasted the morphogenesis of H. p. polygyrus in Apodemus flavicollis and M. musculus with Heligmosomum mixtum of Clethrionomys glareolus and Heligmosomoides laevis of Microtus arvalis. The results revealed the close affinities of Heligmosomoides and Heligmosomum.
H. kurilensis kobayashii (Nadtochii, 1966)
Asakawa (1987) studied the development of this species, collected from Apodemus speciosus from Japan, in mice and jirds (Meriones unguiliculatus). Larvae hatched after incubation for 24 h at 20°C. The first moult occurred between 24-48 h after hatching and infective larvae appeared in 5 days. In mice infected orally the fourth-stage larvae appeared in the mucosa of the small intestine and in about 10 days the adult worms appeared. In jirds, adults elicited capsules under the serosa of the upper small intestine and died.
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