Peripheral blood smear

A 23-year-old man has developed a high fever with shaking chills 2 weeks after returning from a trip to West Africa. On examination his temperature is 38°C. His peripheral blood smear is seen here. Which of the following events most likely led to his illness?

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  1. Ingestion of primaquine
  2. Drinking water with Escherichia coli
  3. Spread of non-Hodgkin lymphoma
    4) Bite from a mosquito
  4. Lead poisoning