Nodule Worm

Habitat

Oesophagostomum dentatum, the nodule worm, is a common parasite of domestic and feral pigs worldwide. Swine (Sus scrofa) is the only host and harbors the pre-adult and adult stages in the large intestines, especially the caecum. Eggs and early larval stages (L1 to L3) can be found in the environment.

Biology

O. dentatum belongs to a large group of endoparasitic nematodes (roundworms), the Strongylida. It is unsegmented and the adults are up to 14 mm long. The slightly smaller males are characterised by a large copulatory organ at the posterior end, the bursa copulatrix, which is typical for members of the Strongylida. Both sexes have characteristic cuticular inflations at the anterior end and a well-developed oesophagus. They feed on intestinal contents. Eggs appear in the faeces around 3 weeks after ingestion of third stage larvae (L3). They contain blastomeric stages which develop into first-stage larvae that hatch and continue to develop into the infectious stage, the L3, in the environment within the following week. The L3 does not feed and is surrounded by the cuticle of the previous stage, the uvea. Thus protected, it can remain infectious for several months under humid conditions. Once ingested, the larva frees itself from the uvea and invades the intestinal wall of the large intestine. The host's immune reaction leads to the formation of granulomas (hence the name "nodule worm") which harbor the larva until it has undergone ecdysis to L4 and evades the tissue to dwell in the lumen where it finally reaches maturity and copulates. Pigs are known to harbor hundreds and even thousands of individuals for a long time period without clinical signs except reduced food conversion. The parasite spreads within a population (or a farm) by faecal-oral transmission after dissemination of eggs and larvae with faecal material. Although granuloma formation and antibody production indicate specific immune responses a protective effect has not been observed.

Sequencing Plan

A sequencing plan submitted to the NHGRI calls for 6-fold sequence coverage in plasmids, end sequence of a fosmid library at 0.2-fold coverage, and two rounds of directed sequence improvement ("pre-finishing"). To facilitate better gene prediction and to add depth to the analysis of structure-function up to 20,000 ESTs will be generated. To increase the diversity of identified transcripts stage- or tissue-specific cDNA libraries will be constructed. The individual traces will be available from the NCBI Trace Archive, and the sequence assembly will be available upon internal evaluation for quality. Funding for the sequence generation and characterization is being provided by the National Human Genome Research Institute (NHGRI), National Institutes of Health (NIH).

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Contacts

Name	Affiliation
Makedonka Mitreva	The Genome Institute, Washington University School of Medicine
Anja Joachim	University of Veterinary Medicine Vienna

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