Horse mystery

The unusual weather phenomenon, l Nino, may have been to blame for the deadly epidemics among horses in South Africa over the past two centuries. Matthew Baylis and his team at the Institute of Animal Health in Surrey, UK, studied records of horse deaths since the early 19th century. They found that major outbreaks of the disease called African horse sickness occurred during the warm phase of l Nio, which sometimes causes drought in Africa followed by heavy downpours. This weather spreads the disease by bringing together zebras and midges at water holes. Zebras harbour the virus while the midges transfer it to the horses ( Nature , Vol 397, p 574).