Answer to Case 509

Answer: Dirofilaria sp.; most likely D. repens based on the presentation, geographic exposure, and morphology of the microfilariae in blood.

Idzi and his group recently published this case in EID; you can read about all of the important diagnostic details such as the length of the adult worm, its cuticle, and the morphology of the microfilariae HERE.

Here a just a few important points from this case:

1. Not all round worms removed from the eye are Loa loa. While loiasis is the ocular roundworm infection that most physicians are familiar with, human dirofilariasis is an emerging infection that should be considered whenever a patient presents with a macroscopic worm moving across the cornea. Unlike L. loa which has a limited geographic distribution (West and Central Africa), Dirofilaria repens is widely distributed throughout parts of Africa, Asia, and Europe, including temperate climates. HERE is a great article outlining the distribution of vector-borne diseases in Africa; it has nice maps showing that loiasis is NOT in Senegal where this patient was presumably exposed.

2. The adult worm of Dirofilaria can be easily differentiated from Loa loa by examining its cuticle. Dirofilaria has longitudinal ridges, which are particularly prominent in this case, while Loa loa does not. To me, the longitudinal ridges look like the bark of a tree (awesome photo Idzi!):

In comparison, Loa loa has irregularly-spaced cuticular bosses or 'bumps' that are located along along the long axis of the worm. Here is a good example of these bosses from Parasite Case of the Week 482:

3. Microfilariae are only rarely seen in human Dirofilaria infections - making this case particularly cool! Unlike Loa loa, the microfilariae of D. repens do not have a sheath, and the nuclei do not go all the way to the tip of the tail. Thus the features of the microfilariae can be used to support the diagnosis in this case. 

Thank you for all of the great comments on this challenging case!

Answer to Case 482

Answer: Loa loa

This great case by Dr. Green shows a gravid female worm with characteristic irregularly-spaced elevations on the cuticle called "bosses". Identification of the bosses allows the adult worm to be differentiated from the similar-appearing adults of many Dirofilaria spp. which have cuticular ridges rather than bosses. William Sears also commented on some of the other characteristic features which aid in identification: a straight buccal canal and muscular esophagus.

Several of you correctly identified the additional test that would be useful for confirming our diagnosis: examination of Giemsa-stained peripheral blood films (collected between 10am and noon) to look for characteristic sheathed microfilariae. This was done, and microfilariae were readily identified:

Note the evidence of a sheath (seen as a negative outline in this case) and nuclei that go to the tip of the tail, consistent with Loa loa microfilariae.

Case of the Week 482

This week's case was donated by Dr. Paul Green. The following worm was removed from the eye of a Nigerian man, and was noted to still be moving after removal:

 Although it was damaged during removal, the key diagnostic features are still visible.

Anterior end:

mid-body with disrupted area:

Closer look at the internal organs:

Posterior end:

Identification? What additional specimen could confirm your diagnosis?