Four farm workers in Madera County have fallen ill to malaria this week, and county officials are warning residents to avoid bites from disease-carrying mosquitoes. County Health Director Dr. C. Dean McClure said that three of the workers were briefly hospitalized for treatment. McClure called the disease a major public health threat and said it can spread easily in the harvest season when many farm workers sleep outdoors or near streams and riverbeds. He said three of the cases were reported among farm workers living at a ranch west of Chowchilla near the Chowchilla River. The Health Department and the mosquito abatement district are trying to rid the area of mosquito breeding sites, McClure said. Regional physicians are being alerted to watch for signs of malaria, such as headaches, sweating, high fever, jaundice, chills and other symptoms.