West Nile virus spreading quickly in the U.S.

West Nile virus is spreading at an increasing rate and at a faster pace than it has been in years, according to health officials.

Marc Fischer, a specialist in mosquito-borne diseases with the Centers for Disease Control and Prevention said that states are reporting more cases than usual, according to USA Today.

"There's been a lot of mosquito activity in most states" this year, Fischer says, USA Today reports.

Texas is suffering the worst of it, with 16 people dying from the virus in Texas this summer alone. There have been a total of 381 cases of the illness in the state this year.

"We're on track to have the worst year ever," Christine Mann, a spokeswoman for the Department of State Health Services in Austin, said, USA Today reports.

There have been 693 cases of the disease nationwide, resulting in 28 deaths, according to the CDC, which is up from 390 cases and eight deaths in the previous week.

The mosquito population built up early in the summer after a wild winter and spring rains. Heat and a lack of rainfall this summer created stagnant water pools, which are mosquito breeding grounds, Michael Merchant of the Texas AgriLife Extension Service in Dallas, said, USA Today reports.

Cases of West Nile have been reported in 32 states, the CDC said. Louisiana reported six deaths in 68 cases, Oklahoma saw one death in 55 cases, Mississippi reported one death in 59 cases, Arizona had one death and seven cases. California, meanwhile saw 23 cases with one death and South Dakota had one death in 37 cases.

Approximately 70-80 percent of people infected with West Nile Virus never know they have it, while 20-30 percent develop West Nile fever, which has symptoms of headaches, fever, joint pain, vomiting or diarrhea, and rash.

Less than one percent of those infected with the virus develop West Nile neuroinvasive disease, which causes inflammation in the brain, spinal cord or the tissue surrounding the brain. This will result in the death of approximately 10 percent of those infected, Fischer said. People over 50 and those who have compromised immune systems are more likely to develop this form, USA Today reports.