Nematospiroides dubius

Heligmosomoides polygyrus
Female H. polygyrus from the digestive tract of a woodmouse
Scientific classification
Kingdom:	Animalia
Phylum:	Nematoda
Class:	Chromadorea
Order:	Rhabditida
Family:	Trychostrongylidae
Genus:	Heligmosomoides
Species:	H. polygyrus
Binomial name
Heligmosomoides polygyrus

Heligmosomoides polygyrus, previously named Nematospiroides dubius, is a naturally occurring intestinal roundworm of rodents. It belongs to the family Trychostrongylidae, and male and female worms are morphologically distinguishable. The parasite has a direct life cycle with its larval form being the infective stage. H. polygyrus has the ability to establish chronic infections in rodents and alter host immune responses. This nematode is widely used as a gastrointestinal parasitic model in immunological, pharmacological and toxicological studies.

This parasite has a direct life cycle with no intermediate hosts. The life cycle takes about 13–15 days to complete. Infected mice will pass faeces containing eggs and egg sizes vary between 70–84 micrometres (µm) in length and 37–53 µm in width. Eggs are shed from the host at the 8–16 cell stage and will hatch in the environment, roughly 24 hours after passing through the host. L1 larvae will emerge from the egg and measure between 300–600 µm in length. Three lip-like structures can be seen around a rudimentary mouth. L1 larvae moult to L2 larvae after 2–3 days, entering bacterial-feeding larval stages present in the environment. The L1 stage cuticle will loosen from either end of the larvae but will remain loosely associated with the L2 larvae, becoming an outer sheath up until infection. After 3 days, the L2 partially moults into ensheathed L3, the infective non-feeding stage. Infective larval stages measure between 480–563 µm long.

Mice ingest the L3 stage of the parasite and after 18 hours, exsheathed L3 appears in the intestinal lumen. The L1 sheath is shed following ingestion at which point the larvae shorten slightly and measure between 376–540 µm in length. After 24 hours post ingestion, larvae will invade the mucosal layer of the intestine. After approximately 4 days post ingestion, L3 moult into L4 in the submucosa of the intestine. Approximately 6 days post ingestion they will encyst in the muscle layer of the intestine and starts maturing in to adult parasites. By day 14 post ingestion, adult male and female worms will come into contact in the lumen of the intestine, mate and produce eggs that are passed in the faeces continuing the life cycle. Adult males are tightly coiled and usually measure 8–10mm in length (5). The females are also tightly coiled but larger, measuring between 18–21mm in length. Adults are characterized by a dark red pigmentation, whereas the free-living larval forms are mostly translucent.

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Wikipedia