onchocerca

•  Onchocerciasis is a parasitic disease caused by the roundworm Onchocerca volvulus.
• Transmission: It’s transmitted to humans through the repeated bites of infected blackflies of the Simulium genus. These flies thrive near fast-flowing rivers and streams, giving the disease its common name.
• Location: Primarily found in tropical regions, particularly sub-Saharan Africa, parts of Latin America, and Yemen.

Symptoms

Onchocerciasis includes a range of symptoms, the most severe being blindness:

• Skin problems:

  • Intense itching
  • Skin rashes
  • Bumps or nodules under the skin (these contain adult worms)
  • Thickening and discoloration of the skin

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Onchocerciasis nodules

• Eye problems:

  • Inflammation of the eye (conjunctivitis, keratitis)

  • Damage to internal eye structures (optic nerve, retina)

  • Vision impairment

  • Blindness

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    Onchocerciasis eye damage

How does the infection work?

2. Infected blackfly bite: An infected blackfly bites a human, introducing larvae of the O. volvulus worm into the skin.
3. Larvae mature: The larvae mature into adult worms, forming nodules under the skin.
4. Reproduction: Adult female worms produce millions of microscopic larvae called microfilariae.
5. Microfilariae migrate: Microfilariae migrate throughout the skin, causing itching and rashes, and can also enter the eyes.
6. Blackfly bites again: A blackfly bites an infected person and ingests microfilariae.
7. Cycle continues: Inside the blackfly, the microfilariae develop further and become infective, continuing the cycle of transmission.

Treatment:

• Ivermectin: This medication is highly effective in killing the microfilariae, preventing skin and eye damage. It’s typically given annually in affected areas.
• Doxycycline: This antibiotic can kill a bacteria called Wolbachia that lives in symbiosis with the adult worms, helping to gradually eliminate them.
• Nodulectomy: Surgical removal of nodules containing adult worms may be considered in some cases.

Prevention:

• Vector control: Efforts to reduce blackfly populations through insecticides.
• Mass drug administration (MDA): Regular distribution of ivermectin in endemic areas helps interrupt transmission.
• Personal protection: Using insect repellent and wearing protective clothing can reduce the risk of bites.