Virus emergency declared in Texas

The mayor of Dallas has declared a state of emergency in the ninth largest US city as it struggles to contain an outbreak of mosquito-borne West Nile virus that has claimed the lives of 17 people so far this year.

Mayor Mike Rawlings has declared a state of emergency and announced the first aerial spraying in the city and its suburbs since 1966 in response to the growing number of victims of the virus, which spreads to humans via mosquito bites and is reaching epidemic proportions in north Texas.

According to Texas department of state health services figures, 465 West Nile cases have been confirmed in Texas this year, including 17 related deaths - on track for the most cases since the disease first reached the state a decade ago.

Ten deaths and more than 200 cases have been reported in Dallas County, which with a population of around 2.4 million is the ninth most populous county in the US. Houston, the largest city in Texas, has recorded seven cases and one fatality.

The Center for Disease Control and Prevention (CDC) said that as of August 14, 43 states have reported West Nile infection in people, birds or mosquitoes this year, with over 80% of cases from six states: Texas, Mississippi, Louisiana, Oklahoma, South Dakota and California.

The 693 human cases reported to CDC through the second week in August is the highest number for that time of year since the virus was first detected in the US in 1999. At least 26 people have died.

"The city of Dallas is experiencing a widespread outbreak of mosquito-borne West Nile Virus that has caused and appears likely to continue to cause widespread and severe illness and loss of life," Michael Rawlings said on Wednesday.

Officials say spraying is the most effective way to fight the mosquitoes that carry the disease despite safety concerns about exposing people to chemical pesticides.

There have been cases of infection reported in people, birds or mosquitoes in 42 US states, with 80 per cent of the cases in Texas, Mississippi and Oklahoma.

The number of infections usually peaks around mid-August, the CDC said.

Health officials said the reasons for the increased activity were not clear. Factors such as weather, numbers of mosquitoes and human behaviour contribute to when and where outbreaks happen.

The virus was first discovered in 1937 in Uganda. It is carried by birds and spread to humans by mosquitoes.

In extreme cases, symptoms can include high fever, loss of vision and paralysis. Milder manifestations can include headaches and skin rashes.