I was interested to see that there is a huge outbreak of West Nile virus (WVN) in the US at the moment (various news outlets are reporting e.g., the BBC). According to the CDC, West Nile has been reported from 47 states so far this year, and there have been 1118 cases notified. But worse, 47 people have died. By the way, this is not the ‘fun’ part that I referred to in the title of the post – that’s coming next.
What is WNV? Why is it in the US if it’s named after a river in Africa?
WNV is a flavivirus, which causes fevers and encephalitis in susceptible people, and it has been present in the US since the 1990s. It was first identified following large numbers of bird deaths and people getting sick in 1999 (see the book Mosquito: the story of man’s deadliest foe (by Spielman & D’Antonio) for a nice overview of the first outbreak in the US). It is transmitted to humans by mosquitoes (Culex spp.), and birds are the main reservoir hosts of the virus. Mosquitoes bite infected birds, and suck up the virus in the bird’s blood. Then, when they bite a human (or another bird), some virus particles can be transmitted to the human. Many people who are infected with WNV are asypmtomatic, which means that mosquitoes can bite them, pick up some virus and continue to spread the disease. That’s one mechanism by which outbreaks can grow quickly.
Now, as promised, the fun part. The study of how and why disease outbreaks occur is epidemiology. I never thought I’d find an epidemiologically-related iPad app, but I did. I’ve become a bit addicted to playing Plague Inc. It’s a fabulous little game where you create dangerous pathogens and try to kill the world. There are several elements to consider – the transmission of the pathogen, the symptoms it causes, and the management of mutations to change the way the pathogen behaves. This last part is important because the ‘people’ remaining in the world will try to develop a cure, so evolution of the pathogen is important. Trying to exterminate humanity is surprisingly fun. This is in no way an attempt to trivialise the WNV outbreak – but it gives insight into how viruses can move around and infect people.