Onchocerciasis

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Epidemiology

Onchocerciasis is a chronic tropical parasitic disease, caused by the nematode Onchocerca volvulus, most widely known for causing “river blindness” and severe dermatological problems.[1] It is found in 28 African countries with the highest prevalences in sub-Saharan West African nations like Ghana, Nigeria, Liberia and Mali.[2] Around 17 million people are affected worldwide.[3]In Africa, where the the burden of onchocerciasis is greatest, years of treatment and eradication programmes have led to a dramatic decrease of transmission.[4][5]

Etiology and pathogenesis

The vector of Onchocerca volvulus is the Simulium or black fly which lives close to fast moving, oxygen rich water. After infection it takes 12 to 18 months before the first clinical signs present. The female larvae develop to adulthood and form fibrous capsules, the so called onchocercomata.[6] During adulthood, the female worm sheds hundreds of thousands of microfilaria which migrate through the skin of the human host and cause severe itch, and, after repeated infections, in some regions blindness. Like in other filarial infections symbiosis with the Wolbachia bacteria is essential for multiplication and development of the parasite. A biopsy or skin snip test may show microfilaria.

Clinical findings

The most common skin problem in the first stage is troublesome itching with some erythematous hyper pigmented papules and patchy lichenification. In the chronic stage there can be pruritic generalized lichenification and depigmentation (“Leopard skin”) later on. Sub dermal nodules (“onchocercomata,”) are mostly seen over bony prominences like the hips but can be present anywhere. The loss of elasticity may cause so-calles hanging groins and lymph edema.[7][8]

Differential diagnosis

  • Food allergy
  • Other parasitic infestations
  • Leprosy
  • Syphilis

Management

  • The standard treatment is ivermectin orally every 6 to 12 months). For the dosages see cutaneous larva migrans. Single-dose ivermectin effectively kills microfilariae but has little effect on adult worms; therefore, it controls but does not cure the disease.[9]
  • A patient staying in an endemic area needs treatment every 3 to 12 months, not only to kill new microfilaria but also for the treatment of reinfection.[10]
  • Together with the ivermectin treatment a 6-week course of doxycycline (100–200 mg per day) given to eliminate the Wolbachia bacteria. Because of the deposition of tetracyclines in growing bone and teeth it should not be given to children under 12 years or to pregnant or breast-feeding women. [2]

Photos

Literature

  1. Mackenzie CD, Homeida MM, Hopkins AD et al. Elimination of onchocerciasis from Africa: possible? Trends Parasitol 2012; 28: 16-22.
  2. 2.0 2.1 Udall DN. Recent updates on onchocerciasis: diagnosis and treatment. Clin Infect Dis 2007; 44: 53-60.
  3. Murdoch ME. Onchodermatitis. Curr Opin Infect Dis 2010; 23: 124-31.
  4. Dadzie Y, Neira M, Hopkins D. Final report of the Conference on the eradicability of Onchocerciasis. Filaria J 2003; 2: 2.
  5. Hodgkin C, Molyneux DH, Abiose A et al. The future of onchocerciasis control in Africa. PLoS Negl Trop Dis 2007; 1: e74
  6. Okulicz JF, Stibich AS, Elston DM et al. Cutaneous onchocercoma. Int J Dermatol 2004; 43: 170-2.
  7. Murdoch ME, Asuzu MC, Hagan M et al. Onchocerciasis: the clinical and epidemiological burden of skin disease in Africa. Ann Trop Med Parasitol 2002; 96: 283-96.
  8. Okello DO, Ovuga EB, Ogwal-Okeng JW. Dermatological problems of onchocerciasis in Nebbi District, Uganda. East Afr Med J 1995; 72: 295-8.
  9. Duke BO. Evidence for macrofilaricidal activity of ivermectin against female Onchocerca volvulus: further analysis of a clinical trial in the Republic of Cameroon indicating two distinct killing mechanisms. Parasitology 2005; 130: 447-53.
  10. Omura S. Ivermectin: 25 years and still going strong. Int J Antimicrob Agents 2008; 31: 91-8.
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