What is up with West Nile virus this year?

It has been a bad West Nile virus (WNV) season, the worst since the virus arrived on the continent in 1999, and it isn’t over yet. But why? Why Texas, and even more curious, why South Dakota? WNV is a mosquito-born virus, but so is malaria and we don’t have malaria in the US anymore.

To understand the epidemiology of WNV we have to look at nature. It turns out that humans are “dead end” hosts, meaning we aren’t the intended target. That’s because we don’t sustain a significant viremia (meaning there is lots of virus circulating in the blood as happens with malaria for instance). Mosquitoes don’t pick up virus from us to transmit it to others. WNV is a virus adapted for birds and the normal cycle is that an infected mosquito bites a bird. The bird becomes viremic, other mosquitoes bite the bird and perpetuate the cycle. This is how the virus “amplifies” over the summer months.   Most of these mosquitoes specifically feed on birds and don’t bite humans, but there are crossover mosquito species, omnivores if you will, with a taste for bird and human blood. They come into the picture late in the season when the cycle has amplified the virus to infect many birds. Crossover occurs, the omnivores bite birds, pick up the virus then bite humans.  This is why we see most of the cases of WNV in late August and September. Amplification takes time.

Believe it or not WNV mostly causes an inapparent human infection. Only two out of ten get sick, and most of those get a flu-like illness. About one in a hundred get the more serious version, called “neuroinvasive disease.” This is a brain infection that causes weakness, confusion, coma and even death.  Age is a risk factor with 55 years seemingly where the increased risk begins, but anyone with a health condition that impairs the immune system should consider themselves at risk and take precautions when outside during mosquito season.

Mosquito control includes the use of larvacides-chemicals that kill the non-flying stage of mosquito – early in the season and adulticides throughout the season. Adulticides are chemicals that kill the flying adults.  We all remember spraying from when we were kids and chased the fogger down the block on our bicycles (well, some of us remember.)

So what’s a person to do? If you own a home make sure there are no items in your yard that could collect water and serve as a breeding sites for mosquitoes. Ensure that all windows are secure and screens intact. Don’t leave your door open. Peak mosquito biting hours are dusk and dawn but also anytime in between. Permethrin-based repellents can be applied to clothing but not skin.  Long sleeved shirts and pants, if made of thick material can deter bites, but it has been really hot throughout most of the US this summer.  The best put-on-the-skin repellents are DEET and Picaridin and the duration of effectiveness depends on the concentration. DEET can be toxic to small kids, so apply with caution. Oil of lemon eucalyptus is another alternative. CDC’s advice on mosquito repellent use is here: 

http://www.cdc.gov/ncidod/dvbid/westnile/qa/insect_repellent.htm

Back to why is Texas and South Dakota having so much West Nile? The answer is nature. The right combination of rain and sun increases food supply for birds. If there are more birds, there is more food for mosquitoes and then more mosquitoes. Amplification of the virus is increased. The weather and rain also impact on mosquito breeding and hot weather means a higher amount of WNV in mosquitoes. If there are a lot of juvenile birds of the right species, birds that haven’t had been infected with the virus before, then that is the perfect storm. I haven’t been to Texas or South Dakota but I bet there has been an increase in young, naïve birds capable of sustaining the WNV and a bumper crop of all mosquitoes, including the crossover biting ones.

The fallacy of IT security

Forgive me readers for it has been many weeks since I have last written. It is not because infectious diseases have gone away. To the contrary, there is a new new flu virus, H3N2v that has emerged again in pigs and has caused some recent furor though thus far the illness is mild. There have been more iatrogenic outbreaks related to poor infection control and there's even an Ebola outbreak in Uganda with 23 cases and 16 deaths. No info on how the outbreak began though. The reason I have taken a hiatus from the blog is to focus on the new novel and it occupies all of my writing hours.

But when something sticks in my craw I just have to get it down on cyber paper. At work, the latest bureaucratic brainstorm is to require password changes for the application we use to log our time every three months. I want to know if anyone had ever suffered a breach. Really, who would want to crack into this system? Perhaps to steal some sick days? I bet they go for a few hundred apiece on the black and blue market.

Let's see, now I have at least three or four other work related passwords, all of which expire far too frequently, then there's email, twitter, bank accounts... soo many that I've had to write them all down.  In the same location in fact, so that I have them handy in case I forget. Check that multiple locations. But wait, doesn't that defeat the purpose of having expiring passwords?

Yes, it most certainly does. WTF?