Neuroinvasive disease means the patient developed encephalitis, meningitis, or acute paralysis, which is mainly due to an infection of the virus of the spinal cord.
The CDC added that the numbers of reported cases of West Nile virus infections so far this year are the highest since 1999, when it was first detected in the USA. Texas accounts for 45% of all cases. Michigan, Louisiana, Oklahoma, Mississippi, South Dakota and Texas account for 70%. The only states with no human infections so far are Alaska and Hawaii.
Dr. Lyle Petersen, director of the U.S. Centers for Disease Control and Prevention's Division of Vector-Borne Infectious Diseases, said it is not possible to accurately predict what the total numbers will be for the whole of 2012. However based on reports that have come in so far, the CDC believes it will exceed the 2002-2003 record years when over 3,000 infections were reported and over 260 people died each year.
US public health authorities base their estimates on reports of neuroinvasive disease, because cases of West Nile fever (non-neuroinvasive disease) are commonly underreported. Petersen believes the 2012 epidemic is peaking now in the southern states and will soon do so in the northern ones. Dr. David Lakey, commissioner of the Texas Department of State Health Services, believes it will be a while yet before numbers in Texas peak.
Petersen does not believe that Hurricane Isaac will affect the spread of West Nile virus. After Hurricane Katrina, infection rates only went up slightly.
Dr. Lakey informed that Texas had 783 confirmed cases of West Nile Virus on August 29th, 2012, an increase of 197 in just one week. 31 patients have died (10 over the last week). 416 were cases of neuroinvasive disease, an increase of 93 in one week. He says he expects these numbers to continue to rise.
Dr. Lakey believes this will be Texas' worst year with West Nile virus.
Dr. Lakey said, regarding Texas:
"Assuming normally disease progression, it looks like it's going to be our worst year with West Nile. We have 416 cases of West Nile neuroinvasive cases. 2003, we had 439. Looking at the progression, this will be on our worst year. In 2003, we had 40 deaths. Again, we're at 31 so far this year. So we're closely evaluated the disease incidents from all counties in the state of the Texas, but focusing on certain counties that have been hardest hit."
West Nile virus comes from the Flaviviridae family. The virus infects humans and animals after they are bitten by some types of infected mosquitoes. The virus belongs to the same family as the ones that cause dengue fever and Japanese encephalitis.
West Nile virus mainly infects birds, but can also infect reptiles and humans. Most people who are infected have no symptoms and are probably unaware of their infection status, even if some experience headaches or a rash, they soon go away.
Approximately 1 in every 5 cases of West Nile virus infection does cause illness, and a small proportion of these people develop complications, which may sometimes be life-threatening. Those most at risk are seniors and people with weakened immune systems.
Geographically, West Nile virus has moved northwards. It used to exist only in temperate and tropical areas. The first WNV (West Nile virus) human infection in New York occurred in 1999. Today, the whole of the USA (except for Hawaii and Alaska) and many parts of Canada are affected.
Written by Christian Nordqvist