Answer to October 2019 Photo Quiz

Answer: Onchocerciasis. The elements corresponded to a visualization of adult worms (see Fig. 1A in the photo quiz). Each worm was surrounded by a dense cuticle with a discrete annealing, which was most patent on longitudinal sections. Under the cuticle, the muscle was thin and had 6 to 10 protruding cells per quadrant, with a pseudostratified appearance (Fig. 1B, arrowhead, in the photo quiz). Each worm had two uteri per section (a “paired uterus”), which did not completely fill its body cavity (Fig. 1B, black arrows, in the photo quiz). The gut was also observed (Fig. 1B, white arrow, in the photo quiz). Within each uterus, numerous microfilariae at variable stages of life were observed (Fig. 1C in the photo quiz). All in all, these findings were consistent with detection of Onchocerca volvulus worms.

Onchocerciasis, commonly known as river blindness, is a parasite-borne disease caused by the filarial worm Onchocerca volvulus and transmitted by blackflies of the genus Simulium (1). This infection is endemic in Africa and has been subjected to many control and elimination programs since 1974, with marked reductions of transmission and prevalence (2; http://www.who.int/mediacentre/factsheets/fs374/en/). In our case, the patient came from the Congo, which is one of the countries in which onchocerciasis is endemic (http://www.who.int/mediacentre/factsheets/fs374/en/).

O. volvulus larvae transmitted during a blackfly bite become adults in around 3 months to 1 year in dermis, with formation of a nodule around the worms. Thousands of microfilariae can be released daily by an adult female and migrate into the skin, eyes, or other organs, leading to intense inflammation, severe itching, and diverse skin lesions. In cases of eye lesions, the inflammation can result in visual impairment and permanent blindness (1).

Diagnosis can be performed by identification of microfilariae emerging from skin in skin snips, which is the “gold standard” test (3). However, this test’s reported sensitivity is only 45% to 73%. As a result, in many cases the diagnosis is not parasitologically proven (4). While sensitivity may be increased by parasite DNA detection, this method is poorly adapted to countries of endemicity. Microscopic observation of adults by histological examination of a nodule, the less conventional method of slit lamp examination of the anterior part of the eye, diethylcarbamazine patch testing, and serology are other diagnostic methods (3, 4). Serological results should be interpreted with caution, because given the many cross-reactions, the specificity of serology is poor. Hypereosinophilia is also frequently reported but presents low specificity (4). In the present case, diagnosis was performed by microscopic histological examination of the excised nodule. Positivity for filaria was also found by serology using immunoprecipitation and immunoelectrophoresis techniques. Blood eosinophil count was not performed. The patient received a 6-mg single dose of ivermectin, which was repeated after 10 days. On the control examination, she was asymptomatic, and no other nodule was found.

Ivermectin is the usual treatment, at times combined with doxycycline or diethylcarbamazine (4). Ivermectin is effective only on microfilariae, not on adult worms. Used in a mass administration program, this treatment must be repeated, because adult worms can live for up to 15 years inside the human body (1; http://www.who.int/apoc/onchocerciasis/control/en/).

We reported a case of onchocerciasis in a child presenting only one nodule. The presence of a nodule or skin lesion in a traveler or migrant is likely to indicate this disease. In such a case, blood eosinophil count, skin snip and histological observation, and serology must be performed. Moreover, images will guide anatomopathologists in their diagnoses.

See https://doi.org/10.1128/JCM.01265-18 in this issue for photo quiz case presentation.