Welcome back!

Phylogeny represents the evolutionary relationships among a taxonomic group of organisms. Inserted below are two phylogenies: one phylogenetic tree displays numerous species within the genus Enterobius and the other phylogeny presents three genera within the family Oxyurata.

Both phylogenies organized the parasites based on the respected host for each species within each group.

The above image displays a phylogenetic tree of species in the genus Enterobius with their corresponding host to the right. Enterobius vermicularis is closely relative to Enterobius buckleyi. 

The above image shows a phylogenetic tree of organisms in the family Oxyurate. However, Enterobius vermicularis is closest to Enterobius anthropoiteci. 

There are numerous species within the genus Enterobius, all parasites, grouped accordingly by their specific host. 

The first phylogenetic tree suggests that E. vermicularis closest relative are E. buckleyi. However, the second phylogenetic tree proposed that E. anthropiteci are the closest relative to E. vermicularis.

As you already know, E. vermicularis can only infect one host, homo sapiens. Specifically, humans in the temperate regions such as Japan and South Korea as demonstrates in the first phylogeny.

It is interesting that the second phylogenetic tree list chimpanzees as an additional host for E. vermicularis even though they have their pinworm species, E. anthropiteci. This can be explained by a study conducted in Japan. In a zoo in Japan, scientists collected feces of captive chimpanzees to test for parasites, and the human pinworm was found in the collected feces, resulting in placing E. anthropiteci closest to E. vermicularis.

Enterobius gregorii, also used human as its host, are not listed in both phylogenies above but supposedly a sister species of E. vermicularis shown in the phylogenetic tree below. This is because this species’ existence is controversial due to insufficient evidence and some believe that E. gregorii is a younger stage of E. vermicularis. Otherwise, evidence indicates that E. gregorii is identical to E. vermicularis with one minor difference; a slightly smaller spicule in E. gregorii.

The image above shows that Enterobius gregorii is the closest relative to Enterobius vermicularis which are not shown in the other phylogenetic trees.

Citations: 

http://www.ps-survival.com/PS/Diseases/Common/Pinworm_Parasite-2016.pdf

https://www.researchgate.net/figure/Phylogenetic-relationship-among-primate-pinworms-inferred-from-18S-rDNA-gene-sequences_fig2_329358452

https://www.researchgate.net/figure/Phylogeny-of-the-oxyurids-of-Old-World-primates-Redrawn-from-Brooks-and-Glen-1982_fig4_226249412

https://www.researchgate.net/figure/Oxyurid-phylogeny-used-in-the-study-The-genera-are-Lemuricola-L-Madoxuris-M_fig1_14150003

https://carta.anthropogeny.org/moca/topics/enterobius-vermicularis-infection