Background: In August, 1997, a woman with no history of travel to malarious regions developed Plasmodium vivax malaria. She lived in a rural area of Italy where indigenous Anophyles labranchiae mosquitoes were present.
Methods and findings: An environmental investigation was done within a 3 km radius of the patient's house. Adult mosquitoes and larvae were collected and examined by PCR with the gene for plasmodium circumsporozoite protein as target. About 200 people living in the area were interviewed to detect possible carriers of P. vivax.
Findings: None of the mosquitoes captured were carrying any malarial organisms. The house-to-house investigation identified a 7-year-old girl who had had a feverish illness a few days after her arrival in Italy from India, and who, 3 months later, still had P. vivax in her blood; she and her mother had antimalarial antibodies.
Interpretation: These investigations suggest that the index case of malaria was caused by local anopheline mosquitoes infected with exogenous P. vivax.