Playing hide and Zika with mosquitoes

The pesky mosquito: everyone’s bête noire.

Entering my room in a tiny hotel in the French town of Moret-sur-Loing (where the Impressionist painter Alfred Sisley spent ten years of his life), I was met by a dense cloud of mosquitoes. The window had been left open. I seized the nearest weapon at hand: a can of mosquito spray the size of a fire extinguisher.

Mosquitoes leave lumps and welts in inaccessible places; at three in the morning they emit a high pitched wail like a miniature buzz saw; and when they don’t see you coming, they leave a nasty mess on the wallpaper.

Worse still, more than one million people die every year from mosquito-borne infections and disease – making the mosquito the most deadly living organism in the world. Mosquitoes have been around a very long time. The oldest known mosquito with an anatomy similar to modern species was found in 79-million-year-old Canadian amber from the Cretaceous Period. A sister species with more primitive features has been found in Burmese amber dating back 95 million years.

Apparently, there are more than 460 sub-species of the Anopheles mosquito (known as the “malaria mosquitoes”). Some 20% of the genus are capable of spreading the virus to humans. The female Anopheles mosquito transmits malaria after biting an infected human and then passing on the deadly parasite to the next unsuspecting person.

The World Health Organization (WHO) estimates that despite the number of malaria cases dropping by 47% over the past 15 years, one child still dies from the disease every minute. While anti-malarial drugs are available, there is currently no vaccine.

The Aedes mosquito is the most invasive. It is the carrier of a number of viral infections, such as dengue fever, yellow fever and the Zika virus. Once only found in water-filled habitats, Aedes has adapted to rural, suburban and urban human environments. The WHO reports that in recent decades it has spread from Asia to Africa, the Americas and Europe, surprisingly through international trade in used tyres in which eggs are laid when they contain rainwater.

Known as the common house mosquito, the Culex mosquito typically feeds on birds instead of humans, seeking their blood at dawn and dusk. There are close to 1,000 sub-species of this type of mosquito, but it is not considered as much of a threat to humans as the Anopheles and Aedes mosquitoes. However, Culex can spread an array of other diseases that can be harmful to people, such as the West Nile virus, lymphatic filariasis, and Japanese encephalitis.

While the Aedes mosquito was originally thought to be solely responsible for the spread of the Zika virus, scientists are now studying if the Culex mosquito could also be to blame for the current emergency.

MosquitoesAs a river pilot, the American writer Mark Twain must have been plagued by mosquitoes. In Life on the Mississippi (1883), a passenger on a riverboat describes the mosquitoes of Arkansas as having been “persistently represented as being formidable and lawless; whereas ‘the truth is, they are feeble, insignificant in size, diffident to a fault, sensitive’ – and so on.”

But it is the mosquitoes of Lake Providence, Louisiana, described as “colossi”, that provoke terror:

“He said that two of them could whip a dog, and that four of them could hold a man down; and except help come, they would kill him – ‘butcher him’, as he expressed it… ‘The life policy in its simplest form is unknown in Lake Providence – they take out a mosquito policy besides.’ He told many remarkable things about those lawless insects. Among others, he had seen them try to vote. Noticing that this statement seemed to be a good deal of a strain on us, he modified it a little: said he might have been mistaken, as to that particular, but knew he had seen them around the polls ‘canvassing’.”

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