The first sign that something was wrong in the small southern Pakistani town of Ratto Dero appeared in February.

Axar.az reports citing BBC.

A handful of worried parents had taken their children to the doctor, complaining that their little ones could not shake off a fever.

Within weeks, more children came forward suffering from a similar illness.

Bemused, Dr Imran Aarbani sent the children's blood away for testing. What came back confirmed his worst fears. The children were infected with HIV - and no-one knows why.

"By 24 April, 15 children had tested positive, though none of their parents were found to be carrying the virus," the hospital doctor told the BBC.

It was only the tip of the iceberg.

In the past month, more than 607 people - 75% of them children - have been diagnosed with the virus after rumours of an outbreak sent families rushing to a special camp set up at the town's government hospital by the health department of Sindh province.

Perhaps more surprising, however, is the fact that this is not the first outbreak to hit the region in recent years.

Rumours of a possible outbreak in Sindh province's Larkana, of which Ratto Dero is a sub-division, prompted thousands of people to get tested back in 2016.

On that occasion, 1,521 people were found to be HIV positive, according to figures available with Sindh Aids Control Programme (SACP).

The vast majority of those infected were men and, at the time, the cause was linked to the area's sex workers, who were mainly transgender and 32 of whom were found to be carrying the Aids virus.

The discovery of the outbreak led to a crackdown on Larkana's travellers' inns, where sex workers had been able to ply their trade relatively freely, despite a ban on prostitution in Pakistan.