Doctors are struggling to identify the sudden outbreak of “a mysterious viral infection” that has so far killed 256 people in India.

The mystery disease strikes mainly children and the elderly, with symptoms that include vomiting, headaches and high fever before killing its victims. Children are most vulnerable due to poor nutrition causing an inferior immune response to infections.

“The disease started from Ahrauli Sheikh village in Amraudha block and within a month’s time spread to 48 villages, housing 3,000 families. It was also learnt that the infants who fell victims to the disease were suffering from acute malnutrition. ‘The infants were suffering from malnutrition and that made some of them vulnerable to the killer virus,’ said [a] district nodal officer…” (“Mystery fever: Death toll continues to rise,” The Times of India).

Doctors and microbiologists are performing detailed tests on blood samples at the National Institute for Communicable Diseases in New Delhi, but remain puzzled by the virus, speculating whether it could be a mutant form of dengue fever or malaria.

In its news article “7 kids die of mystery fever in Moradabad,” The Times of India also reported, “According to information gathered by State Infectious Disease Cell, the complication started with sore throat followed by fever. In some patients, fever resulted in swelling of tonsils while in some, it caused encephalitis (inflammation of brain due to virus) or meningitis (inflammation of the membranes that cover brain).”

Unhygienic living conditions have been blamed for the outbreak in Lucknow, a north Indian city with a population of more than 5 million inhabitants, where another 340 cases of the mystery disease have been reported.

Fever-related deaths from malaria, dengue, H1N1 (swine flu) and measles are common in parts of India, where many live in filthy neighborhoods and do not have access to clean running water, sanitation or adequate healthcare. The water supply in these areas consists of dirty, polluted rivers or tap water unfit for drinking and cooking.

With basic healthcare unavailable for most citizens, an easily treatable disease can become life-threatening, causing many preventable deaths. In most cases, by the time patients receive specialized treatment from Delhi hospitals, it is too late.