The U.S. is concerned that an outbreak of yellow fever in Brazil can spread across the borders. The National Institute of Allergy and Infectious Diseases published an essay writing that yellow fever can spread through traveling, especially along the Gulf Coast. The Pan American Health Organization said that as of March 2, the virus has killed about 220 people mainly in the states of São Paulo, Minas Gerais, and Espírito Santo. Yellow fever is spread to humans through infected mosquitoes and has a fatality rate of 33%.