Ocular pentastomiasis in the Democratic Republic of the Congo

Abstract

Ocular pentastomiasis is a rare infection caused by the larval stage of pentastomids, an unusual group of crustacean-related parasites. Zoonotic pentastomids have a distinct geographical distribution and utilize reptiles or canids as final hosts. Recently, an increasing number of human abdominal infections have been reported in Africa, where pentastomiasis is an emerging, though severely neglected, tropical disease. Here we describe four ocular infections caused by pentastomids from the Democratic Republic of the Congo. Two cases underwent surgery and an Armillifer grandis infection was detected by morphological and molecular approaches. Thus far, 15 other cases of ocular pentastomiasis have been reported worldwide. Twelve cases were caused by Armillifer sp., recorded almost exclusively in Africa, where such infections occur as a consequence of hunting and consuming snakes, their final hosts. Seven further cases were caused by Linguatula serrata, a cosmopolitan pentastomid whose final hosts are usually canids. Intraocular infections caused permanent visual damage in 69% and a total loss of vision in 31% of reported cases. In contrast, ocular adnexal cases had a benign clinical course. Further research is required to estimate the burden, therapeutic options and pathogenesis of this neglected disease.

Figure 1. Annulated foreign body in the anterior chamber of the left eye from Case 1.

A, lateral view. The eye shows marked conjunctival injections and the foreign body fills the whole pupil blocking the eyesight completely. B, frontal view. The high number of annulations of the parasite is clearly visible.

Figure 2. Extracted pentastomid nymph from Case 1, morphologically and molecularly identified as Armillifer grandis.

The nymph is still surrounded by its shed translucent cuticle (exuvia), a characteristic feature of pentastomid larvae as they moult in the intermediate hosts' tissues. A. grandis is the smallest of the zoonotic African Armillifer species with the most body annulations (9–15 mm body length and >25 annulations; A. armillatus, the nearest geographical neighbour for comparison: 12–23 mm length and 18–22 annulations (2). A. grandis is the least often encountered zoonotic Armillifer species worldwide. Scale bar = 3 mm.

Figure 3. Local villagers often find pentastomids in snakes sliced for consumption.

Adult Armillifer armillatus (confirmed by 18S rRNA gene PCR) in the lung of a young Ball Python (Python regius) before consumption in Sankuru district, Democratic Republic of the Congo. Sometimes local people do not clean and cook the snake properly just spit out the parasites while eating, so the eggs may accidentally be swallowed. The ova may also contaminate snake meat during butchering. Unless properly cooked, an egg may hatch in the intestine of an accidental human intermediate host. While most larvae migrate to visceral organs, a few will make their way to the eye .