The West Nile virus spreading throughout the U.S. is expected to be the deadliest on record as the number of fatalities increased 36 percent in the past week to 118 people, U.S. health officials said.
There have been 2,636 infections reported, 53 percent of which were the most severe form of the disease, according to the Centers for Disease Control and Prevention. Every state other than Alaska and Hawaii has reported cases of the virus with 40 percent occurring in Texas, the agency said.
The outbreak may have peaked in late August, though unseasonably warm weather in some parts of the U.S. may continue driving new infections, said Lyle Petersen, director of the CDC’s division of vector-borne infectious disease. The record year for West Nile may be a result of warmer-than-usual weather as well as environmental factors, like the bird populations and rainfall patterns, he said. All of the major outbreaks in the U.S. have occurred when the weather was hotter than usual.
“This year’s outbreak is the most serious to date,” Peterson said. “The longer the weather stays warm, the more transmission that is going to occur. It is certainly possible that in some areas of the country the outbreak may not have peaked yet.”
West Nile virus, first detected in the U.S. in 1999, is passed to people by diseased mosquitoes. Four of five people infected with the virus show no symptoms. Most cases are mild with less than 1 percent of people infected developing a severe illness with symptoms such as a high fever, disorientation and convulsions, according to the Atlanta-based agency.
The 118 deaths reported so far this year are expected to exceed the previous high mark of 284 in 2002, given the number of severe cases already reported, Petersen said. Researchers believe there is no evidence that the virus is more deadly this year and that the increase in deaths is due to the increase in total infections.
Of the infections, 1,405 were of the most deadly form of the disease in which it has spread to a person’s nervous system, the CDC said. Only about 2 to 3 percent of people who come down with a fever from the virus are reported to the government, the CDC said last week.
The outbreak is concentrated in Texas, South Dakota, Mississippi, Oklahoma, Louisiana and Michigan, the agency said.