Mosquitoes are the known vectors for a myriad of diseases. When a mosquito bites, she also injects saliva and anti-coagulants into the blood of its prey which may also contain disease-causing viruses or other parasites, such as malaria, yellow fever, dengue fever, West Nile virus and chikunganya.
Adult females are blood-sucking parasites, not so the males that feed only on nectar and other plant juices and do not bite. Females feed on plant juices too, but need blood to be able to produce eggs. Thus, female mosquitoes feed on the blood of a host of preys, like cattle, sheep, goats, pigs, poultry, dogs, cats and humans.
 collected blood-engorged mosquitoes at poultry farms during an outbreak of highly pathogenic Influenza A(H5N1) in Central Thailand. These mosquitoes tested positive for Influenza A(H5N1) virus.
Therefore, if infected mosquitoes bite humans, these might in turn become infected with the potentially lethal Influenza A(H5N1) virus. These findings suggest a previously unknown route of infection.
And did I already mention that global warming will greatly expand the areas that are inhabited by mosquitoes?
 Barbazan et al: Detection of H5N1 avian influenza virus from mosquitoes collected in an infected poultry farm in Thailand in Vector-Borne and Zoonotic Diseases - 2005
 Kurane: The Effect of Global Warming on Infectious Diseases in Osong Public Heath and Research Perspective - 2010