Scientists from the University of Pittsburgh, USA, and the Aggeu Magalhães Institute in Recife, Brazil, have found an explanation for an intriguing phenomenon: people of African descent tend to experience milder cases of dengue fever than those of European descent, who are more likely to have the severe form. The scientists injected the dengue virus into skin samples donated by individuals who self-identified as of European or African descent and had undergone weight-loss surgery, then observed the immune responses. The reaction was much greater in the samples from people of European descent: inflammatory cells became infected and spread the virus around the body rather than containing it. In samples from individuals with higher proportions of genetically confirmed African ancestry, the inflammatory response and viral replication were both lower, indicating an adaptation by previous populations exposed to lethal mosquito-borne viruses. When inflammatory molecules called cytokines were added, the protective effect disappeared (PNAS, June 30).
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