New Delhi(CNN) The death toll from an outbreak of Nipah virus has risen to 10 in India's southern state of Kerala.
Nine patients that tested positive for the virus have been quarantined and are being treated, Rajeev Sadanandan, additional chief secretary for the state's Department of Health and Family Welfare, told CNN on Tuesday.
The outbreak began in the northern district of Kozhikode and has spread to neighboring Malappuram district, Sadanandan said.
Symptoms of Nipah virus can begin with headache and drowsiness but quickly transform into a coma within a matter of days, according to the US Centers for Disease Control and Prevention.
Other symptoms include acute respiratory syndrome -- where the lungs cannot get enough oxygen to the body -- and fatal encephalitis, an inflammation of the brain.
There is no vaccine, and treatment is limited to supportive care.
Among the dead was a nurse, identified as Lini, who was treating patients at Perambra Taluk Hospital in Kozhikode.
In a tweet, the office of Kerala Chief Minister Pinarayi Vijayan posted his condolences to her family, writing that the nurse's "selfless service will be remembered."
The first cases were reported Saturday in a family from Kozhikode, and then India's Ministry of Health and Family Welfare and the World Health Organization were contacted, Vijayan's office said Monday via Twitter.
Two brothers in their late 20s and their aunt, 50, died from the virus, while their father, 56, remains on life support.
WHO said fruit bats were found in an unused well near the family's house along with some rabbits being bred that had died recently.
Nipah virus is known to infect both humans and animals, with certain species of fruit bat being natural hosts. People can become infected after contact with infected bats, or other animals, and humans.
WHO added it was awaiting findings from experts to determine the source of infection and was in close contact with experts deployed to the affected areas to be "ready for any request for assistance."
A statewide alert has been issued to remain vigilant, and a 24-hour control room to monitor the situation has opened, Vijayan said.
A total of 60 samples have been tested for Nipah virus, which includes people who have already died as well as those who came into contact with patients confirmed to have the virus, Dr. Reena KJ, additional director of public health for Kerala, told CNN.
That number is expected to rise, according to Sadanandan, the Kerala health official, who described it as a "dynamic situation."
Deaths in other districts where people had symptoms of the virus are also being tested.
The state government has made assurances that the "health department is doing everything possible to save the lives of the infected and prevent the advance of virus," the chief minister's office tweeted Monday.
A subsequent tweet urged private hospitals not to "deny treatment for anyone suffering from fever."
India's health ministry has also deployed a response team to Kerala.
JP Nadda, India's minister of health and family welfare, said in a statement Monday that his department was "closely monitoring the situation" and had "dispatched a central team to assist the state government and initiate required steps."
Nipah virus was first identified during a 1998-1999 outbreak in Malaysia, where almost 300 people were infected and more than 100 died, according to the CDC. More than 1 million pigs were euthanized to halt the spread of the illness. The virus was named after the village of Kampung Sungai Nipah, where pig farmers contracted the disease.
There have been subsequent outbreaks in India and Bangladesh, with more than 600 reported human cases between 1998 and 2015, according to WHO. Many parts of Asia as well as Australia, Madagascar and Ghana are at risk of outbreaks.
The virus is on WHO's list of epidemic threats in need of urgent research and development.