Onchocerciasis (River Blindness)

Paraffin sections of an adult worm were prepared, placed on glass slides, and viewed at x100 magnification (Figure 2). Histopathology was typical of subcutaneous nodules, with outer walls of dense fibrous tissue extending between the worms. Skin biopsy specimens extending just into the dermis were obtained from the left buttock, embedded into paraffin, and stained with H&E (Figure 3). Eosinophils were present around degenerating microfilariae. Progressive fibrosis of the dermis was present, and the epidermis showed acanthosis and hyperkeratosis.
The patient was admitted to the hospital, treated intravenously with one dose of ivermectin 10,000 mg (150 mg/kg), and monitored overnight. To prevent a hypersensitivity reaction secondary to massive microfilarial death, he was treated orally with both 25 mg of diphenhydramine every 6 hours and 25 mg of hydroxyzine, as needed, for itching. The patient tolerated the treatment well and was told he should be treated with ivermectin biannually for the next several years. He was discharged the following day. back to top

Comment O volvulus is 1 of 8 filarial nematodes that can infect humans and is endemic to west and central Africa, Central and South America, and the Arabian Peninsula (Figure 4). It is estimated that 17.7 million people are infected with O volvulus. More than 99% of these infections occur in sub-Saharan Africa. Nearly 1 million people today can attribute their blindness or severe visual impairment to onchocerciasis.2,3 In areas near fast-moving water where the incidence of river blindness is high, villages cease to be economically viable and are deserted for less productive land, further away from the Simulium breeding sites.4

The parasite is spread among humans by the bite of an infected female Simulium blackfly, which breeds in fast-moving rivers. Once inside the human host, O volvulus larvae mature into adult worms (macrofilariae) and become encased in a soft tissue fibrotic nodule (onchocercoma). Inside the nodule, adult pairs mate and release 1300 to 1900 microfilariae per day for up to 9 to 11 years.5 These tiny offspring (250–300 mm long) migrate through the dermis and commonly invade the anterior chamber and uvea of the eye, as was observed in our patient.

Subcutaneous microfilariae live 6 to 24 months, then die and cause a cutaneous host inflammatory response, which is responsible for the majority of clinical symptoms.6 The initial dermatologic presentation includes intense pruritus, subcutaneous nodules, and localized discrete papules or plaques with erythema and induration. Chronic skin changes include areas of hyperpigmentation and hypopigmentation (“leopard skin”) and lichenification. The cutaneous inflammatory response to the microfilariae leads to breakdown of dermal collagen and elastic tissue. The skin becomes progressively atrophic and wrinkled, leading to gross disfigurement and skin laxity (eg, “hanging groin”).7

The common name for onchocerciasis, river blindness, is well deserved because of its potential for causing blindness in nearly one half of men and one third of women in some untreated, endemic areas.3 It is the fourth leading cause of blindness worldwide.8 Ocular pathology in onchocerciasis is caused by an intense eosinophilic and granulomatous response to dead and dying microfilariae. Frequently, this inflammatory process causes uveitis, which leads to glaucoma. Punctate keratitis is often present and, if left untreated, leads to sclerosing keratitis. Posterior segment lesions such as chorioretinitis and optic atrophy also have been observed.9 Our patient’s history of numerous episodes of conjunctivitis was related to irritation by microfilariae that were migrating to the cornea and the anterior chamber of the eye.3,6

Although our patient’s condition was discovered by slitlamp examination, cutaneous biopsies known as skin snips are the most common diagnostic tool because they are simple and provide definitive diagnosis. A razor blade is used to slice down to the dermal papillae to obtain a bloodless skin sample of 2 to 4 areas from the iliac crest or below.10,11 After placing the specimens in warm saline for 10 to 60 minutes, motile microfilariae are visualized on a wet mount, using low-power microscopy. Fixed and stained specimens, blood examination, excised nodules, and DNA amplification with polymerase chain reaction also can be used if diagnosis is still questionable.2,12

Histologically, onchocercal microfilariae are characterized by a cephalic free space, followed by anterior nuclei that are side by side, a caudal space free of nuclei, and a tail tapered to a fine point (Figure 3). These features readily differentiate O volvulus from Dipetalonema streptocerca, which are the only other microfilariae that live in dermal collagen throughout the body.13