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USAID

USAID's NTD Program
USAID's NTD Program

Onchocerciasis

Life Cycle

Step 1: The disease spreads from person to person via the bite of a blackfly.

Step 2: When a blackfly bites a person who has onchocerciasis, microscopic worms (called microfilariae) in the infected person's skin enter and infect the blackfly. The microfilariae develop over two weeks to reach a stage where they are infectious to humans.

Chart illustrating the life cycle of onchocerciasis.  
Source: Giovanni Maki/CDC  

Step 3: An infectious blackfly will typically inject one or two larvae to transmit the disease to another person. Since the worms can only increase their numbers in the human by first mating and then cycling their microfilariae through the blackfly, the intensity of human infection (number of worms in an individual) is related to the number of infectious bites sustained by the individual.
Step 4: The normal incubation period of onchocerciasis ranges from nine to 24 months after the bite of an infected blackfly. Each female worm can reproduce millions of microfilariae during her lifetime. Worms can live for 10 to 15 years.

 

 

 

 

 

Learn more about onchocerciasis: