San Diego County has confirmed its fourth human case of West Nile virus this year, prompting health officials to urge residents to take precautions against mosquito bites as peak transmission season approaches.”Four cases doesn’t sound like very much,” said Ian McHardy, Ph.D., senior director of microbiology and infectious disease at Scripps Health. “But when you look at the number of people that need to be infected in order for you to actually get a symptomatic case, it actually starts to sound a whole lot more relevant.”Most people infected with West Nile virus never develop symptoms, but in rare cases, he said the virus can spread to the brain or nervous system and become life-threatening.“About 80% of cases are asymptomatic, 20% generate a mild to moderate flu-like illness, and less than 1% will go on to develop meningoencephalitis, or some kind of neuroinvasive disease,” McHardy said.He said the virus follows a seasonal pattern.”Cases start to pick up around the summer, and they start to maximize right around August and September, with some cases continuing to get reported into October and even November,” McHardy said. “The vast majority of the season for West Nile is ahead of us.”So even though it’s a relatively low amount, McHardy said it’s possible that these 4 cases could represent a significant start to the season, with much more to see ahead.The virus is spread by infected Culex mosquitoes, which he said are most active during the evening, overnight and early morning hours.Older adults and people with weakened immune systems face the greatest risk of severe illness.He recommends using insect repellent if you are outside during dusk and dawn, and removing standing water around your home where mosquitoes can breed.”We’ve had a hot summer so far,” he said. “People leaving their pools uncovered and neglected, plant saucers, clogged gutters, buckets, toys, old tires, wheelbarrows … there are lots of different ways mosquitoes can breed.”He said that residents can request free mosquito-eating fish from the county for ponds, fountains and unused swimming pools to help control mosquito populations.McHardy said that prevention remains the best defense.”Unfortunately, we don’t have any extremely effective antivirals at this time,” he said.People who develop severe symptoms should seek medical care immediately.”If the patient has high fever, stiff neck, disorientation, confusion, muscle weakness, paralysis, vision loss, all of these would be indications of a severe infection, perhaps neuroinvasive, and we’d want to make sure that patient gets to a hospital so they can get the care they need,” McHardy said.“It’s much safer to just put on mosquito repellent, long sleeves, long pants, and prevent the actual infection, rather than going down the path of having perhaps lifelong consequences with West Nile,” he said.
