The lowly mosquito was once thought to be mostly an annoyance in the U.S., but in recent years has become a feared agent in the spread of disease. In its latest update, the U.S. Centers for Disease Control and Prevention (CDC) says mosquitoes have contributed to a record U.S. outbreak of West Nile Virus.

As of August 21, 38 states reported infections with the most cases in Texas. Before 1999, the disease was unheard of in the U.S. As of this week, the CDC said more than 1,100 people had been infected and 41 people had died.

21 deaths

The Texas Department of State Health Services last week reported 552 state-confirmed cases of the disease, including 21 related deaths. The state has carried out aerial spraying in some areas that have been particularly hard hit but urged all residents to protect themselves by using insect repellent and draining standing water, which can be a breeding ground for mosquitoes.

Serious illness from West Nile Virus is still fairly rare. Many people who are infected show no signs at all. If you do exhibit symptoms they are likely to include vomiting, fever and headache. They can last anywhere from a few days to a few weeks.

Mosquitoes can be disease transmitters because, when they bite an infected person they draw some of the victim's infected blood. When the mosquito bites the next person, it can transmit the infection.

Virus from Asia

In addition to West Nile Virus mosquitoes can also carry a disease-causing virus from Asia. In laboratory experiments, researchers at SRI International demonstrated that mosquitoes from Virginia and Georgia can transmit a virus called Chikungunya (CHIKV), which has infected more than 2 million people in Asia, Africa, and parts of Europe since 2005. The U.S. has never witnessed an outbreak of CHIKV, although a number of infected people have been identified with a CHIKV infection acquired from travel to Asia.

Although CHIKV infection is rarely fatal, patients may suffer persistent complications, such as debilitating arthritis that can last from months to years. Currently, there is no drug to treat CHIKV and no vaccine is available.

"The findings underscore the importance of control measures, such as eliminating mosquito breeding sites, to prevent mosquito-borne viral infections for which there are no cures," said Rajeev Vaidyanathan, Ph.D., associate director of Vector Biology and Zoonotic Diseases in the Biosciences Division of SRI and lead study author.

For the experiment, researchers used the Asian tiger mosquito from the southeastern U.S. The tiger mosquito is common in Texas and the Midwest and along the East Coast as far north as New Jersey.

How to control mosquito populations

To control mosquito populations in your yard or neighborhood you must control standing water, which is the breeding ground for the mosquitoes. Don't allow garbage pails or buckets to collect rain water.

Keep gutters clean and free of debris that can cause clogs. That will reduce standing water in the gutters themselves and also prevent the overflow from spilling onto the ground next to the house and collecting.

Keep Swimming pools clean and chlorinated, even when not in use. Unattended swimming pools can quickly become mosquito breeding grounds.

Ornamental ponds should be aerated to keep water moving. Mosquitoes prefer still water for laying eggs.

Researchers at SRI say that, unfortunately, the huge number of foreclosures has contributed to the mosquito problem. Neglected property often ends up providing plenty of places for mosquitoes to breed.

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