Zoonotic onchocerciasis.

To the Editor: Major human onchocerciasis reported in Africa and Central/ South America is caused by Onchocerca volvulus. This blackfly-mediated parasitosis is also called ‘river blindness’, often resulting in visual disturbance in the endemic area. Ocular involvement by O. lupi, a canine parasite, has recently been the subject of focus. In Japan, infestation of O. volvulus or O. lupi is not seen, but zoonotic onchocerciasis due to O. dewittei japonica, a parasite of wild boar, has infrequently been experienced. We report herein the ninth case of zoonotic onchocerciasis in Japan. The causative agent of our case was identified as O. dewittei japonica by morphometric characteristics and DNA analysis. In Japan, there are six other Onchocerca species known to be potentially infective to human. Onchocerca cervicalis (infecting horses), O. gutturosa and O. lienalis (cattle); O. eberbardi (sika deer: Cervus nippon), O. skrjabini (sika deer and serows: Capricornis crispus), and O. suzukii (serows). We focus here on the histopathologic differential diagnosis of parasitic skin infestation. A 75-year-old woman, living along the Ashida River in Fuchu, the eastern rural part of Hiroshima Prefecture, Japan, noticed a cutaneous nodule on her elbow with rubor and itching without other symptoms in August, 2013. She was engaged in crop work and often bitten by blackfly just before the summer season. Field products were often damaged by wild boar coming down from the forest behind her house. In October, 2013, the patient visited a local hospital to remove the nodule surgically. The deeply situated dermal nodule was hard in consistency and measured 0.8 × 0.4 cm. The gross appearance of her skin lesion was not photographed. The patient’s clinical course was uneventful thereafter. Representative histopathologic features of hematoxylin and eosin-stained sections are illustrated in Figure 1. The cut surfaces of a nematode were surrounded by fibrosing foreign body granulomas. Lymphocytes, plasma cells and eosinophils infiltrated in the fibrous nodule. Microscopically, the nematode body was lined by an eosinophilic cuticle and a thick muscle layer of meromyarian and coelomyarian type separated by two large lateral chords. In the pseudocoelom (body cavity unlined by epi(meso)thelial cells), two empty uteri and small-sized intestine were observed. No microfilariae were seen in the uterine cavity. The diameter of the parasite measured 240–260 μm. The longitudinal cut surfaces demonstrated prominent triangular-shaped, transverse ridges on the cuticle. Inter-ridge spaces ranged from 90 to 240 μm. No inner striae were seen in the middle layer of the cuticle. The parasite was morphologically identified as a female adult of O. dewittei japonica, based on the body size, thick cuticle, prominent outer ridges, relatively long distance between adjacent ridges, and lack of inner striae in the middle layer of the cuticle. DNA, extracted from five slices of unstained 4 μm-thick paraffin sections, was amplified by polymerase chain reaction (PCR) using filarial pairs CO1fF (5′TTGTCTG TTCCTGTTTTGG-3′)-CO1f1R (5′AAAATAATAACATAAAC CTCAGGATG-3′), a fragment of the mitochondrial cytochrome c oxidase subunit 1 gene. The PCR condition was as follows: initial denaturation at 94°C for 2 min, followed by 40 cycles at 98°C for 10 s, 42°C for 30 s and 68°C for 30 s. A single PCR product, 155 bp-long, was observed on the agarose gel electrophoresis. The sequence analysis of the 110 bp fragment inserted between the primers confirmed the complete identity to the sequence of O. dewittei japonica (GenBank/EMBL/DDBJ accession number: AB518689). The design to obtain short PCR products was suitable for analyzing DNA extracted from formalin-fixed, paraffin-embedded sections. Parasitic (helminthic) skin nodules can be divided into two types. One typical example is creeping eruption (cutaneous larva migrans), and another is a non-motile nodule caused by infestation of an adult filarial worm of various genera, such as Dirofilaria, Wuchereria, Brugia and Onchocerca. The lesion of the present case represented the latter. The nodule showed foreign body reactions with tissue eosinophilia against non-motile elongated parasite, and extensive fibrosis was formed. The worm matured to an adult to accompany the uterus, though ova were not formed. Histopathologic identification of the parasite is practically requested to diagnostic pathologists, so that the differential diagnosis of parasitic (helminthic) nodules is thus briefly commented. In case of cutaneous larva migrans, no uterus/ovary or testis is seen in the parasitic body, and foreign body reaction cannot surround the parasitic body because the larva migrates. Foreign body reaction with eosinophilia is often seen around the tunnel-like empty space caused by the migrating parasite. Cutaneous larva migrans is evoked by the larva of either nematode, trematode or cestode. Nematode larvae migrating in the skin include Gnathostoma sp., spiruroid nematode larva (Crassicauda giliakiana) and Ancylostoma braziliense. The size of the larva is much smaller in the latter two than in the former. Trematode-induced larva Pathology International 2015 doi:10.1111/pin.12256 bs_bs_banner