Many of them complained of joint pains, headaches, dehydration and nausea. In some cases, they reported rashes spreading across legs and arms.
At least 50 people, mostly children, have died of the fever, and several hundred have been admitted to hospital in six districts in the eastern part of the state. None of the dead tested positive for Covid-19.
At a time when India appears to be slowly recovering from a deadly second wave of coronavirus, the deaths in Uttar Pradesh have provoked a rash of panicky headlines about a “mystery fever” sweeping through the countryside of India’s most populous state.
Physicians in a few of the affected districts – Agra, Mathura, Mainpuri, Etah, Kasganj and Firozabad – believe dengue, a mosquito-borne viral infection, could be the main cause of deaths.
They say many of the patients were taken to hospital with a declining platelet – a blood component which helps form clots – count, which characterises a severe form of dengue.
“The patients, especially children, in hospitals are dying very quickly,” says Dr Neeta Kulshrestha, the most senior health official of Firozabad district, where 40 people, including 32 children, have died in the past week.
Transmitted by female mosquitoes, dengue is mainly a tropical disease and has been circulating in India for hundreds of years. It is endemic in more than 100 countries, but some 70% of the cases are reported from Asia. There are four dengue viruses, and children are up to five times more likely to die during a second dengue infection than adults.
The mosquito – Aedes aegypti – breeds in and around houses in containers holding fresh water. “Humans provide breeding places and only humans can take them away,” says Dr Scott Halstead, one of the world’s leading experts on viruses spread by mosquitoes.
Nearly 100 million severe cases of dengue – severe bleeding, impaired organs – are reported worldwide every year. “The combined impact of Covid-19 and dengue epidemics can potentially result in devastating consequences for the populations at risk,” according to the World Health Organization (WHO).
Yet it is still not clear whether an epidemic of dengue is alone responsible for the fever-related deaths in Uttar Pradesh.
A state with more than 200 million people and traditionally poor standards of sanitation, high levels of-malnutrition in children and patchy health care routinely reports such “mystery fever” cases after monsoon rains every other year.
Outbreaks of the mosquito-borne Japanese encephalitis – first identified in Uttar Pradesh in 1978 – have claimed more than 6,500 lives since. The disease mainly spread through Gorakhpur and adjoining districts which border Nepal in the foothills of the Himalayas, all low lying and prone to floods and providing a breeding ground for mosquitoes which transmit the virus.
A vaccination campaign, which began in 2013, has led to a drop in cases, but children continue to die. Seventeen children have died of Japanese encephalitis in Gorakhpur so far this year, and 428 cases have been recorded.
In 2014, reacting to increasing cases of children dying of encephalitis and myocarditis – inflammation of the heart muscle – scientists examined 250 afflicted children in Gorakhpur. They found that 160 of them had antibodies to the bacteria that caused scrub typhus.