Globalization, land use, and the invasion of the West Nile Virus (Kilpatrick, 2011)
Review article in Science, 21 October
WNV endemic in Africa, childhood disease (>80% of people over 15 having antibodies), considered nearly asymptotic & once even studied as an anti-cancer therapy.
WNV was first observed in the Americas in 1999, in New York City. In four years it was on the west coast, and after 10 years it had reached deep into South America. It had also (by 2002) changed 3 nucleotides/1 amino acid to increase transmission efficiency in C. pipiens and C. tarsalis mosquitos. In the US, 1.8 million people have been infected, 360,000 illnesses (20%), 12852 encephalitis (0.7%), and 1308 deaths (0.0007%). Big cost in blood donor screening. Given a US population of 250 million, these numbers do not seem alarming.
The disease is much worse in birds. Regional-scale population declines >50% have been reported in corvids, chickadees, titmice, wrens, and thrushes.
Robins (the bird, a species of thrush) are a preferred food source for mosquitos. The dominant WNV vectors are the mosquito species C. pipiens, C. restuans, and C. tarsalis. Some 30-80% of their feedings are on robins, though robins make up only 1-20% of the studied avian communities.
Robins do exceptionally well in human altered landscapes. Populations have doubled over the last 25 years (or is this because we stopped using DDT?? What were robin populations 100 years ago?)
WNV has chosen the “kill them fast” reproductive strategy. Sick animals are more vulnerable to mosquito bites, and increased virema increases the odds that a bite will infect the mosquito. In the (non-anthropod) host, death does not reduce transmission probabilities, as time to recovery and time to death are both 4-6 days.
Mosquitos hitchike on airplanes.