Sunday, July 18, 2021

Answer to Case 646

 Answer to the Parasite Case of the Week 646: Gordiid/nematomorph, a.k.a. horsehair or Gordian worm (Nematomorpha: Gordiida). Not a human parasite. 

This is one of my favorite human parasite mimics. It is occasionally submitted to the human clinical parasitology laboratory - often after being found in the toilet or other body of water - and can be easily differentiated from true human parasitic worms by its long slender shape, said to resemble a horse hair. 

In their 2012 publication, "Going Solo: Discovery of the First Parthenogenetic Gordiid (Nematomorpha: Gordiida), Hanelt et al. write: 

The Nematomorpha is the sister phylum to the Nematoda. Although these phyla share many features such as their general body shape, color, cuticle, and body organization, several key differences delineate these phyla. First, all members of the Nematomorpha are parasites as juveniles but free-living as adults. Second, due to their parasitic lifestyle, the nematomorph gut is largely non-functional, and juveniles feed by absorbing materials directly through their cuticle. Freshwater nematomorphs (Nematomorpha: Gordiida), or gordiids, are a unusual group of parasites that mate and oviposit outside of their hosts. Members of this phylum are strongly sexually dimorphic and until now have been described as dioecious. The unique gordiid life cycle involves transition of parasites within terrestrial arthropod hosts to free–living aquatic adults, which is partially achieved by parasite manipulation of hosts to commit ‘suicide’ by jumping into water triggering worms to escape. Freshwater gordiids use various definitive hosts including hemimetabolous insects such as orthopterans (crickets, grasshoppers, and locusts), cockroaches, and mantids, and holometabolous insects such as beetles.

This is the third time we have posted a case of a Gordian worm emerging from its cricket host. Check out the other posts here:

Case of the Week 549 and Answer

Case of the Week 185 and Answer

As noted by Idzi "Always spectacular! Poor cricket…"

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