Three people have died in the first outbreak of the West Nile virus in Serbia, in which 35 contracted the disease, health authorities said.

Those killed by the mosquito-borne disease were between 68 and 81 and suffered from chronic heart problems, Serbia’s public health institute said in a statement.

The outbreak was first reported on Tuesday, when health authorities announced that one person had died and 21 were infected by the virus.

An official with the public health institute called on residents to protect themselves from mosquito bites, notably by avoiding places infested with the insect and by putting mosquito screens on windows. Authorities announced they would spray insecticide in a bid to reduce mosquito numbers.

Earlier last week, Serbia’s Health Minister Slavica Djukic Dejanovic said there was no danger of a West Nile virus epidemic.

West Nile virus can cause symptoms similar to flu, but in extreme cases can result in fever, coma and a lethal swelling of the brain tissue, known as encephalitis. It can also cause meningitis.

First discovered in Uganda in 1937, the virus is carried by birds and spread to humans by mosquitoes. There is no known cure but 80 per cent of those infected do not develop any symptoms at all.

The virus is responsible for more than 60 deaths in the United States so far this year.