People who get infected while visiting areas with loiasis but do not come from areas where loiasis is found (travelers) are more likely to have symptoms. Most people with loiasis do not have any symptoms. Adult worms may live up to 17 years in the human body and can continue to make new microfilariae for much of this time. If they are not consumed in a blood meal by a deerfly they will die. The microfilariae can live up to one year in the human body. It takes five or more months for microfilariae to be found in the blood after someone is infected with Loa loa.

These microfilariae enter the blood from time to time, usually around midday. Eventually they move into the lungs where they spend most of their time. The microfilaria then move into the lymph vessels of the body (the lymph vessels contain the blood cells that fight infection). Fertilized females can make thousands of microfilariae a day. The adult worms live between layers of connective tissue (e.g., ligaments, tendons) under the skin and between the thin layers of tissue that cover muscles (fascia). Larvae can become adults only inside the human body. It takes about five months for larvae to become adult worms inside the human body. When the deerfly breaks a human’s skin to eat blood, the larvae enter the wound and begin moving through the person’s body.

Then the larvae move to the mouth parts of the fly. After 7–12 days the larvae develop the ability to infect humans. If a deerfly eats infected blood from an infected human, the larvae (non-adult parasites) will infect cells in its abdomen.

The deerflies (genus Chrysops) that pass Loa loa on to humans bite during the day.

Flat worms in my sores