Epidemiologists have also noticed that a more virulent strain has been making up a disproportionate percentage of this season's early cases.
On The Early Show Thursday, Dr. Alton Barron of New York's Roosevelt Hospital Center noted that 114 cases -- most of them in California -- have already been reported in this new season, compared to almost 4,000 all of last year.
"Since it was first identified in New York City almost a decade ago," Barron told co-anchor Maggie Rodriguez, "there's been a steady westward migration of this West Nile virus."
And, he explained, "Apparently -- this is may be a sign of the times. There has been, as more and more homes are passing into foreclosure and many of those homes have backyard pools, these are being neglected, they're not being maintained. This can become a ripe feeding ground and breeding ground for these mosquito populations."
What might explain the more virulent strain that seems to be making the rounds?
"Viruses are infinitely adaptable. And they (the tougher types) may be pushing out the weaker strains. But what's of great concern to the California officials specifically is that, historically, the more virulent strains have been causing a very small percentage of the cases. But, more recently in this year, of the cases that have been identified, 70 percent are caused by this more virulent, more aggressive strain. And this is the one that actually invades the brain and spinal cord, the central nervous system."
Barron advised that people take precautions to try to prevent mosquito bites, such as wearing long sleeves and pants, avoiding standing water, using insect repellent, and putting screens on windows and doors.
He says people should be sure to see a doctor if symptoms go beyond those normally Associated with viruses: "Clearly, if you just have the viral symptoms, as many of us have, the symptoms of the West Nile virus in approximately 20 percent of cases are just like any other viral illness ... the nausea, vomiting, fever, chills, rashes. Those don't need to be treated.
"But when you become disoriented or you notice your friend or family is becoming disoriented ... having severe muscle weakness, fatigue, even paralysis in the more severe cases, obviously, before these signs come about you need to seek medical care."