Rampant loss of universal metazoan genes revealed by a chromosome-level genome assembly of the parasitic Nematomorpha.

Parasites may manipulate host behavior to increase the odds of transmission or to reach the proper environment to complete their life cycle.1,2 Members of the phylum Nematomorpha (known as horsehair worms, hairworms, or Gordian worms) are large endoparasites that affect the behavior of their arthropod hosts. In terrestrial hosts, they cause erratic movements toward bodies of water,3,4,5,6 where the adult worm emerges from the host to find mates for reproduction. We present a chromosome-level genome assembly for the freshwater Acutogordius australiensis and a draft assembly for one of the few known marine species, Nectonema munidae. The assemblies span 201 Mbp and 213 Mbp in length (N50: 38 Mbp and 716 Kbp), respectively, and reveal four chromosomes in Acutogordius, which are largely rearranged compared to the inferred ancestral condition in animals. Both nematomorph genomes have a relatively low number of genes (11,114 and 8,717, respectively) and lack a high proportion (∼30%) of universal single-copy metazoan orthologs (BUSCO genes7). We demonstrate that missing genes are not an artifact of the assembly process, with the majority of missing orthologs being shared by the two independent assemblies. Missing BUSCOs are enriched for Gene Ontology (GO) terms associated with the organization of cilia and cell projections in other animals. We show that most cilium-related genes conserved across eukaryotes have been lost in Nematomorpha, providing a molecular basis for the suspected absence of ciliary structures in these animals.

NEW DEFINITIVE HOST RECORD FOR CHORDODES MORGANI (NEMATOMORPHA) IN NEBRASKA WITH NOTES ON ECOLOGY.

The life cycle and ecology of the horsehair worm Chordodes morgani (Nematomorpha) in Nebraska remain unknown. To identify its definitive host, we installed a series of pitfall traps along 3 first-order streams at 4 sites: Elk Creek, Upper Elk Creek, Maple Creek, and West Oak Creek, all located northwest of Lincoln, Nebraska. In addition, we opportunistically hand-collected insects at these sites, including wood cockroaches (Parcoblatta virginica), and maintained them in the lab until they passed adult worms. Two of these field-collected wood cockroaches each yielded 1 adult worm, which was identified as C. morgani by microscopy, showing that P. virginica serves as a definitive host. Experimental infections of captive-reared Parcoblatta americana supported this result. The wood cockroach was found at all 3 creeks, but C. morgani was not found at West Oak Creek, suggesting that the definitive host does not limit the distribution of C. morgani. Physical properties of the streams were measured to examine how these properties influenced the distribution of the worm. Flow rate and pH differed between the 3 sites where C. morgani was found and the West Oak Creek site, suggesting an important role for these abiotic factors in the distribution of this horsehair worm species.

A Horsehair Worm, Gordius sp. (Nematomorpha: Gordiida), Passed in a Canine Feces.

Nematomorpha, horsehair or Gordian worms, include about 300 freshwater species in 22 genera (Gordiida) and 5 marine species in 1 marine genus (Nectonema). They are parasitic in arthropods during their juvenile stage. In the present study, the used gordian worm was found in the feces of a dog (5-month old, male) in July 2014. Following the worm analysis using light and scanning electron microscopes, the morphological classification was re-evaluated with molecular analysis. The worm was determined to be a male worm having a bi-lobed tail and had male gonads in cross sections. It was identified as Gordius sp. (Nematomorpha: Gordiidae) based on the characteristic morphologies of cross sections and areole on the cuticle. DNA analysis on 18S rRNA partial sequence arrangements was also carried out, and the gordiid worm was assumed to be close to the genus Gordius based on a phylogenic tree analysis.

A Horsehair Worm, Gordius sp. (Nematomorpha: Gordiida), Passed in a Canine Feces

Nematomorpha, horsehair or Gordian worms, include about 300 freshwater species in 22 genera (Gordiida) and 5 marine species in 1 marine genus (Nectonema). They are parasitic in arthropods during their juvenile stage. In the present study, the used gordian worm was found in the feces of a dog (5-month old, male) in July 2014. Following the worm analysis using light and scanning electron microscopes, the morphological classification was re-evaluated with molecular analysis. The worm was determined to be a male worm having a bi-lobed tail and had male gonads in cross sections. It was identified as Gordius sp. (Nematomorpha: Gordiidae) based on the characteristic morphologies of cross sections and areole on the cuticle. DNA analysis on 18S rRNA partial sequence arrangements was also carried out, and the gordiid worm was assumed to be close to the genus Gordius based on a phylogenic tree analysis.

Two human cases infected by the horsehair worm, Parachordodes sp. (Nematomorpha: Chordodidae), in Japan.

The present study was performed to describe 2 human cases infected by the horsehair worm, Parachordodes sp., in Japan. Two gordiid worms were collected in the vomit and excreta of an 80-year-old woman in November 2009 in Kyoto city, and in the mouth of 1-year-old boy in December 2009 in Nara city, Japan, respectively. Both worms were males having bifurcated posterior ends and male gonads in cross sectional specimens. They were identified as Parachordodes sp. (Nematomorpha: Chordodidae) based on the characteristic morphologies of cross sections and areoles in the cuticle. DNA analysis on 18S rRNA partial sequence arrangements was also carried out and both worms were assumed to be close to the genus Paragordionus based on tree analysis, and far from Gordius sp. which has already been reported in humans in Japan. DNA sequencing of the Parachordodes worm does not appear on the database; therefore, more information on the gene sequences of the genus Parachordodes from humans, animals, or intermediates is required.

Two Human Cases Infected by the Horsehair Worm, Parachordodes sp. (Nematomorpha: Chordodidae), in Japan

The present study was performed to describe 2 human cases infected by the horsehair worm, Parachordodes sp., in Japan. Two gordiid worms were collected in the vomit and excreta of an 80-year-old woman in November 2009 in Kyoto city, and in the mouth of 1-year-old boy in December 2009 in Nara city, Japan, respectively. Both worms were males having bifurcated posterior ends and male gonads in cross sectional specimens. They were identified as Parachordodes sp. (Nematomorpha: Chordodidae) based on the characteristic morphologies of cross sections and areoles in the cuticle. DNA analysis on 18S rRNA partial sequence arrangements was also carried out and both worms were assumed to be close to the genus Paragordionus based on tree analysis, and far from Gordius sp. which has already been reported in humans in Japan. DNA sequencing of the Parachordodes worm does not appear on the database; therefore, more information on the gene sequences of the genus Parachordodes from humans, animals, or intermediates is required.