The first phlebovirus found to cause illness in humans in the Western Hemisphere was discovered due to two severely sick farmers, U.S. researchers say. Two men from Missouri independently went to a medical facility with fever, fatigue, diarrhea, a decrease of platelets in blood and a decrease in the number of white blood cells in the blood, which places individuals at increased risk of infection. Both farmers had been bitten by ticks five to seven days before the onset of illness. Ehrlichia chaffeensis are pathogens naturally transmitted between animals and humans. The researchers said the lone star tick was suspected as the causal agent. Electron microscopy revealed viruses consistent with members of the Bunyaviridae -- a family of negative-stranded RNA viruses. Next-generation sequencing and analysis identified the viruses as novel members of the phlebovirus family -- which is novel in the Americas -- as the cause of the illness, the researchers said. The findings were published in The New England Journal of Medicine.