Yellow and dengue fever, tropical illnesses rarely found in California, may become a seasonal threat after two types of mosquitoes known for carrying the illnesses were seen around the state, reports SF Gate.  Experts are trying to kill off the mosquitoes before the threat becomes a reality.

Specialists in mosquito control are going door-to-door in several Bay Area counties to hunt for signs of Aedes aegypti, also called the yellow fever mosquito, which was found in San Mateo County in August. The same mosquito type was seen in at least two other California counties over the summer.  Over the past three years, there have also been reports of the Aedes albopictus, also known as the Asian tiger mosquito, in Los Angeles County.  Public health officials are concerned that they could spread to other parts of the state.

Earlier this year, the Daily Democrat reported that experts in the west Sacramento area in California were evaluating a potential threat of West Nile Virus.  Many dead birds were found and 18 tested positive for West Nile Virus.  Additionally, 58 mosquito tests have also been positive for the disease.  Though more intense in Sacramento County, West Nile Virus was also presenting in other areas.  Yolo County had six dead birds and 19 mosquito samples that were infected.  There was one human case that has been confirmed by the California Department of Public Health.  To respond to the threat, officials were considering aerial spraying to kill mosquitoes and prevent the further spread of the virus.

The New York Department of Health explains that West Nile Virus is a mosquito-borne illness that can be spread to humans.  Reducing the risk of being bit by a mosquito reduces the risk for contracting the disease.  Twenty percent of individuals that are infected by the virus develop West Nile fever, which shows mild symptoms similar to a fever or common infection.  A less likely development is West Nile encephalitis, which is more severe, including symptoms such as tremors, high fever, paralysis, and coma.  According to the Centers for Disease Control and Prevention, other illnesses transmitted by mosquitoes include dengue fever, malaria, yellow fever, and several diseases that cause encephalitis.

It is unclear why the mosquitoes that carry dengue and yellow fevers are starting to spread into California.  Some scientists say that climate change is a possible explanation.  However, controlling the mosquito population is a reliable method for decreasing the risk of infections carried by mosquitoes.