Five people in the US state of Louisiana have died after contracting the deadly West Nile virus, authorities have confirmed.

Mosquito-spraying efforts have been increased

Two more cases have been reported in Illinois and in the capital region, Washington DC, bringing the total of those suffering from the disease to more than 100.

It is the now the worst ever outbreak in the US following the first discovery of the disease in the country in 1999, when 60 people were infected, seven of whom died.

The southern states of Mississippi, Alabama and Texas have also reported cases of the disease.

State-wide emergency

Health officials in Louisiana have increased mosquito-spraying efforts and have told people to stay away from pools of still water, which are breeding grounds for mosquitoes.

The virus originates in birds, but is passed on to mosquitoes which feed on animals and humans.

An outbreak in New York in 2000 killed seven people

While healthy people may suffer only flu symptoms, the disease can prove fatal for the elderly or those with weak immune systems.

Most of the victims die from West Nile encephalitis, a swelling of the brain that can be caused by the virus.

Louisiana Governor Mike Foster has already declared a state-wide emergency after 26 new cases were confirmed in one day.

A special team from the Centre for Disease Control and Prevention (CDC) in Atlanta, Georgia, has also been sent to the state to deal with the outbreak.

34 states affected

Following news of the capital region's first case, officials in Washington said on Wednesday that mosquitoes captured and tested had shown up positive for the virus.

This brings the total of states in which the disease has been detected to 34, CDC officials said.

There are fears the virus, which has never been detected further west than Houston, Texas, may spread across the entire country.

"It will eventually get to all the western states over time, we believe," said the CDC's Dr Roy Campbell.

West Nile virus is believed to have been brought to the US by travellers returning from Africa.