Ecology

Haemonchus contortus is an animal endoparasite infecting ruminants worldwide also known as red stomach worm, wire worm or Barber's pole worm, is very common parasite and one the most pathogenic nematodes of ruminants. Adult worms are attached to abomasal mucosa and feed on the blood.

H. contortus is a member of the superfamily Trichostrongyloidea (Strongylida) which contains most of the economically important parasitic nematodes of grazing livestock. These parasites cost the global livestock industry billions of dollars per annum in lost production and drug costs. Resistance to all the major anthelmintic classes is now common worldwide often leading to failure of treatment and control. H.contortus is a close relative of the human hookworm species and belongs to the nearest phylogenetic group of parasites to the free-living model nematode Caenorhabditis elegans. This makes it an important model of parasitic nematode biology that is commonly used for experimental studies. They are dioecious with single females typically producing several thousand eggs per day which pass out of the host in faeces and develop to infective larvae on the pasture.

Eggs develop in moist conditions in the feces and continue to develop into the L1(rhabditiform), and L-2 juvenile stages by feeding on bacteria in the manure. The L-1 stage usually occurs within 4–6 days under the optimal conditions of 24–29 °C. The L-2 rhabditform sheds its cuticle and then develops into the L-3 filiariform infective larvae. The L-3 have a protective cuticle, however under dry hot conditions will not survive long. The L-3 then crawl up the blades of wet grass and wait to be ingested by a grazing animal. Sheep, goats and other ruminants become infected when they graze and eat grasses containing the L3 infecting larvae. The infecting larvae pass through the first three stomachs to reach the abomasum. There the L-3 sheds its cuticle and burrows into the internal layer of the abomasum where they develop into L-4, usually within 48 hours, or pre-adult larvae. The L-4 larvae then molts and develops into the L-5 adult form. The male and female adults mate and live in the abomasum, where they feed upon the blood.

Genome Details

Sex Determination: gonochoristic

Haploid No. chromosomes: 6 (5 autosomes, XO)

Genomics

WormBase first included a reference genome for Haemonchus contortus in August 2009 (WS208). That first assembly, produced by Wellcome Trust Sanger Institute's parasite genomics group, derived from a combination of capillary and 454 sequence reads and assembled into ~60,000 supercontigs, with a total size of ~300 Mb. Gene models were predicted by WormBase using RNAseq data and an early version of the Ensembl RNASeq gene-prediction system (http://www.ensembl.org/info/genome/genebuild/rnaseq_annotation.html)

In Summer 2013, two new H.contortus reference genome sequences (and corresponding annotation) were published. Each utilised more modern sequencing and assembly methods and dramatically improved on the original assembly. The first was an update from the original Sanger Institute genome project (NCBI BioProject PRJEB506). The second was from a new genome project co-ordinated by the University of Melbourne (NCBI BioProject PRJNA205202). Each assembly represents a different key strain (Laing et al 2013; Schwarz et al 2013), and both became available in WormBase in the WS239 release.

External Ressources

• Wikipedia Entry
• The Wellcome Trust Sanger Institute Parasite Genomics group
• The University of Melbourne Faculty of Veterinary Science

References

Laing R, Kikuchi T, Martinelli A, Tsai IJ, Beech RN, Redman E, Holroyd N, Bartley DJ, Beasley H, Britton C, Curran D, Devaney E, Gilabert A, Hunt M, Jackson F, Johnston S, Kryukov I, Li K, Morrison AA, Reid AJ, Sargison N, Saunders G, Wasmuth JD, Wolstenholme A, Berriman M, Gilleard JS, Cotton JA. The genome and transcriptome of Haemonchus contortus, a key model parasite for drug and vaccine discovery. Genome Biol. 2013 Aug 28;14(8):R88.

Schwarz EM, Korhonen PK, Campbell BE, Young ND, Jex AR, Jabbar A, Hall RS, Mondal A, Howe AC, Pell J, Hofmann A, Boag PR, Zhu XQ, Gregory TR, Loukas A, Williams BA, Antoshechkin I, Brown CT, Sternberg PW, Gasser RB. The genome and developmental transcriptome of the strongylid nematode Haemonchus contortus. Genome Biol. 2013 Aug 28;14(8):R89.