Onchocerciasis (River blindness)

Notes
  • It is spread by blackflies, Simulium sp, which breed in swiftly flowing streams.
  • Statistics: the 4th leading cause of preventable blindness; about 270,000 peole have been made completely blind by the disease; another 500,000 are visually affected; Kenya is classified as low risk country for the disease; countries with the highest prevalence of the disease include: Democratic Republic of Congo, South Sudan and the Central African Republic, extending in the South into Angola, in the East into Uganda and in the West into South Chad, Cameroon and Nigeria.
  • volvulus requires the bacteria Wolbachia for survival and embryogenesis hence justifying the use of doxycycline as adjuvant in the treatment regime for the infestation.
  1. Transmission
  • Life cycle of Onchocerca volvulus:

_An infected blackfly, Simulium sp, (that breeds in swiftly flowing streams) bites a healthy person.

_Infective larvae are inoculated into the skin

_Larvae in the skin develop into adult worms (after 1-1.5yrs).

_Adult worms (19 - 50cm long) may lounge in subcutaneous nodules for upto 15yrs

_Female worms produce microfilariae

_Microfilariae may migrate through the skin ;and invade the eyes and cause blindness.

Symptoms
  • Sometimes asymptomatic
  • Ocassionally pruritis
  • Skin nodules (onchocercoma)
  • Lymphadenopathy
  • Lymphatic obstruction
  • Premature wrinkling
  • Localized oedema
  • Secondary excoriations
  • Hyperkeratosis
  • Punctuate keratitis
  • Uveitis
  • Optic neuritis
  • Chorioretinitis
  • Optic atrophy
  • Sclerosing keratitis
  • Blindness (complete or incomplete)
Diagnosis
  • Physical examination
  • Microscopic examination of a skin sample (microfilariae in skin snips)
  • Slit-lamp examination of the cornea and anterior chamber of the eye (microfilariae may be visible)
  • Molecular diagnostics (DNA PCR)
Management

_Tabs Ivermectin150mcg/kg Stat.

_Cap Doxycycline 100mg OD or BD x 6/52

(The dose of Ivermectin may be repeated every 3 to 12 months, depending on the recurrence of symptoms and/or microfilariae. Ivermectin does not kill adult worms).

_Diethycarbamazine can be used but it is not recommended as it can kill so many microfilariea and cause a Mazzotti reaction (severe hypersensitivity) that can damage skin, eyes and cardiovascular system.

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