Three people have died in the first ever outbreak of the West Nile virus in Serbia, in which 35 contracted the disease, health authorities said Saturday.
"The infected people are aged over 50 with some chronic disease, meaning at a higher risk of getting a more severe form of the virus," Serbia's public health institute said in a statement on its web site.
Those killed by the mosquito-borne disease were aged between 68 and 81 and suffered from chronic heart problems, it said.
The outbreak was first reported on Tuesday, when health authorities announced that one person had died and 21 were infected by the virus.
Jelena Obrenovic, 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 have announced they will spray insecticide over the weekend in a bid to reduce mosquito numbers.
Earlier this 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 percent 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.
Explore further: One dead in Serbian West Nile virus outbreak