With much of India still unvaccinated against COVID-19, a new threat has emerged in the Northern Province of Uttar Pradesh.
A 'mystery' fever has now spread to over 30,000 people in the area and beyond, amid fears of a fresh epidemic. At least 50 people have died, and the new disease seems mainly to attack the young.
Children have suffered joint pains, headaches, dehydration and nausea, alongside severe rashes on their limbs. Although several hundred have been admitted to hospital with the symptoms, none of those affected have tested positive for COVID.
The illness leads to death fast in its severe form. "The patients, especially children, in hospitals are dying very quickly." Said Dr Neeta Kulshrestha, the most senior health official of the Firozabad area, where 32 out of 40 deaths in six districts were amongst children.
Although medics are still uncertain as to what's causing the devastating disease, some believe that dengue, a mosquito-borne, viral infection could be the culprit.
Back in 2017, researchers demonstrated that antibodies generated by a previous bout of dengue could put a sufferer at risk of more severe disease if the virus was contracted again.
Read more: The mystery fever killing children in India
Antibody-dependent enhancement, or ADE, happens when the antibodies have fallen into a certain low range. The scientists studied almost 6,700 children between two and 14, over 12 years, giving blood tests annually and assessing any fever symptoms.
Other scientists however, now suspect that the mystery virus may be due to 'scrub typhus', spread by infected mites, which saw severe outbreaks in India in both 2003 and 2007.
Watch: Scrub Typhus claims 7 lives in Shimla
Symptoms include fever, headache, aches, and a rash. Most cases have been found in rural areas of Southeast Asia, Indonesia, China, Japan, India, and northern Australia.
A team of experts from Lucknow’s King George's Medical University are looking into the outbreak. India Today reports: "Scrub typhus is a re-emerging...infection, earlier reported in India and other South Asian countries. It is a vector-borne disease.
"Its onset is marked by fever and rashes and it affects the central nervous system, cardiovascular system, renal, respiratory, and gastrointestinal systems. People with severe illness may develop organ failure and bleeding, which may lead to death."
During the Second World War, the disease was rife amongst soldiers in the Far East, and became prevalent across India.
There is no vaccine against it, but antibiotics are commonly used. Outbreaks are at their highest during the rainy season, which runs from June to September – so many are hoping that this sudden, devastating explosion of disease will taper off as autumn continues.
Watch: Dengue and other fevers kill at least 50 in India