The worst outbreak of West Nile virus in US history has killed two more people - bringing the death toll to seven so far.

The latest victims were women from Louisiana, where the other five deaths occurred.

Mosquito-spraying efforts have been increased

About 110 others have been infected - most than half of them in the past week - in five states and Washington DC.

Spraying has been intensified to prevent the spread of the mosquito-borne virus, and officials plan to hand out insect repellent.

West Nile virus was first identified in the United States in 1999, when 60 people were infected, and seven died in the initial outbreak.

The disease can produce flu-like symptoms; complications can include swelling of the brain which may lead to paralysis, brain damage, or death.

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

Spreading

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

An outbreak in New York in 2000 killed seven people

Louisiana Governor Mike Foster has declared a state-wide emergency.

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

Other states currently affected include Mississippi, Alabama, Texas, Illinois, and Washington DC.

Since its first appearance, the disease has been detected in 35 US states.

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

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