The San Francisco man who has West Nile hasn't recently traveled outside the Bay Area, which has led public health officials to believe he was infected locally; although, officials say it's unclear which county. The man's case was reported September 21, the first case in San Francisco since 2005. He is now recovering at home.
Since 2007, three dead birds in the city have tested positive for the virus. The most recent case, a dead bird infected with West Nile was found near City College, indicating the virus is in our environment this year.
Dr. Tomas Aragon, health officer for the city and county of San Francisco says it's no reason to panic, that there are many people who do come into contact with the disease who do not actually become sick, "Only one out of five become ill, and they're more likely to experience fever, aches and pains, like a flu-like illness, and not even know that they were infected with West Nile virus. And only one out of 150 will actually develop severe neurologic disease."
That severe neurologic disease is encephalitis. That's the swelling of the brain that can lead to fogginess and confusion. That's what the Bay Area West Nile patient is recovering from. Those at the highest risk -- residents older than 50 or who have weak or compromised immune systems.
The best way to protect yourself around your home is to be sure you have screens on your windows to keep mosquitoes out.
San Francisco is not very mosquito-friendly, but there are certain species that like it here.
"We're not thick with mosquitos. That's why many of us live here. But we do have several species, four species in particular that can transmit West Nile virus in our area," said Shannon Bennett, Ph.D., from the California Academy Of Sciences.
Bennett says the one species most responsible for West Nile in San Francisco feeds on humans, birds and other mammals, and breeds in a variety of places, but most love anywhere with what Bennett calls organic material, like bird poop.
"So if it happens to be breeding near a place where you have a mixture of birds and humans and breeding sites, then you've got the cocktail that means West Nile can occur in greater number," said Bennett.
The city of San Francisco has its own methods of keeping the lid on mosquito breeding. They've hired bike messengers to become mosquito abatement couriers. Donovan Dobbins and 10 others like him spend all day inspecting the city's 26,000 catch-basins for standing water.
"If there is water, we'll treat it with a larvicide packet that's water-soluble. We just drop that straight and then we mark it with dot of paint to keep track of how long, since we've been to every spot," said Dobbins.
The mosquito abatement couriers have managed to get to all 26,000 catch-basins in the past three weeks.