As of November 14, 2012, no less than 48 states have reported a total of 5,128 cases showing West Nile virus symptoms in people, including 229 deaths.
Of these, 2,601 (51%) were classified as neuroinvasive disease (such as meningitis or encephalitis), suffering paralysis or other lingering neurological damage, and 2,527 (49%) were classified as non-neuroinvasive disease. The 5,128 cases reported thus far in 2012 is the highest number of West Nile virus disease cases reported to CDC through the second week in November since 2003. Thus, the West Nile virus epidemic of 2012 has become the worst on record for the last decade, and in particular for death and brain damage.
Even more serious, however, have been new indications that suggest the virus may be mutating into a more serious and virulent form, as more cases are showing the virus attacking the brain more aggressively than in the past. For instance, the virus has recently been found by some clinicians to damage speech, language and thinking centers of the brain — something that has never been reported before. Elsewhere, brain damage in young, previously healthy patients, not just in older, sicker ones has been seen— another change from past years’ outbreaks.
These disturbing observations have been downplayed by the Centers for Disease Control and Prevention, maintaining that there is no evidence that the virus is causing a different type of brain damage, but rather that more serious cases this year have emerged because there are more cases overall. However, the CDC does not currently collect the kind of data needed to determine whether the virus is causing more-severe brain damage.
Still, there is evidence to suggest the virus has changed: e.g. showing a greater incidence of severe encephalitis – more neuroinvasive, neurovirulent, inflammation of the brain — than in the past.
For instance, a Texas virologist found signs of genetic changes in virus collected from the Houston area. Further, while the virus in the past has typically invaded the brain and spinal cord of people who have weakened immune systems, such as the elderly and transplant or cancer patients, there have been recent cases reported in people much younger and initially healthier. In other cases, patients were found to have lost their ability to talk or write, or became partially paralyzed, suffered stroke, or experienced recurring seizures – not the usual clinical picture most often seen with WNV. The outlook for such patients varies, but most will face years or a lifetime of disability.
With reports still coming in and new cases continuing — infected mosquitoes continue to bite in southern states — 2002′s record of 284 deaths and 2,946 cases of neuro-invasive disease will shortly be left in the dust. The reason 2012 was a record-busting year for West Nile virus is due primarily to weather: abnormally warm overall, and in many parts of the country, the hottest year on record. Increasing temperatures promote virus growth in mosquitoes, making it easier for them to transmit the virus.
And there are more West Nile epidemic outbreaks to come as recent warming patterns of climate change are likely to continue. Most people are still going to be susceptible to being infected in subsequent years. There’s no vaccine, and there’s no treatment. The best advice for avoiding infection involves wearing protective clothing, using insect repellent, avoiding the outdoors at dawn and dusk, and ridding your home of places mosquitoes breed.
A controversial measure to kill adult mosquitoes has been the use of aerial spraying of insecticide. While such spraying is generally considered safe, it’s not totally without risk. And there have been questions about whether it works.
Stay tuned for further data.