Watch Out for the Blood Sucking Female Mosquitoes

For the past several summers we have been worrying about West Nile virus. This virus was first isolated in 1937 from the blood of a patient on the West Nile province of Uganda. Not too far from where I was born. The man had fever. Initially, the outbreaks of the disease were few. But over the years the numbers have increased.

In North America, the virus was first detected in 1999. It was in New York. From there it was exported to Ontario and rest of Canada. Most cases of West Nile virus are mild and self-resolving. But one per cent of cases get infection in the nervous system.

Culex tarsalis is the blood sucking female mosquito that spreads the virus. As the summer comes and the temperature soars, the West Nile virus activity increases. Alberta Health and Wellness undertook a study of West Nile virus prevalence through June 2007. The report is posted on its website.

According to this report, Alberta experienced its first locally acquired clinical cases of West Nile virus (275 confirmed human cases) in the summer of 2003. Since then, clinical (e.g., symptomatic) infections have been detected every year, though the numbers have fluctuated.

From 2004 to 2006, there were very few clinical cases with a combined total of 51. In 2007 there was an increase in the number of infections with 320 cases and the first two deaths associated with the virus in the province. During the 2008 West Nile virus season, only one clinical infection was detected in Alberta and it is thought to be travel-related, says the Alberta Health report.

It is important to remember that for every clinical infection of West Nile virus there are many more undetected infections in humans, since majority of the infections have no symptoms and are never detected.

West Nile virus is carried by birds. Mosquitoes get infected by feeding on the blood of these birds. Infected mosquitoes then transmit the virus to humans when they bite us.

All mosquitoes need water to develop from their immature stages to adulthood. The life cycle takes less than 10 days to complete if the surrounding temperature is favorable. Once the adult mosquito is ready to fly then it looks for something to eat.

Nectar from flowers provides energy to both male and female mosquitoes. While male mosquitoes feed exclusively on nectar, the female mosquito needs blood to produce her eggs. The source of blood can be animals (including people) and birds.

It is important to control the breeding sites around your home by preventing stagnation of water (flower pots, gardening cans, wheelbarrows, puddles, tire swings, bird baths and eavestroughs) even in small quantities. Boats and gardening containers can be stored upside down.

During mosquito season you should limit your outdoor activities. Minimize exposure of your skin by wearing long pants, shirts with long sleeves, socks and shoes when outdoors. Loose clothings will keep mosquitoes away from the skin. Use insect repellents like DEET. Read the directions carefully before using DEET-based repellents especially on children, infants and yourself.

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