Four brothers - two of whom died - and two cousins from Abbotabad, a small city about 30 miles north of Islamabad, were suspected of being infected by the H5N1 virus, said WHO spokesman Gregory Hartl in Geneva. A man and his niece from the same area who had slaughtered chickens were also suspected of having the virus.

Another person in a separate case who slaughtered poultry in nearby Mansehra, 15 miles away, also tested positive for the disease, he said.

Details surrounding the cases remained confusing, with Pakistan's Health Ministry issuing a statement Saturday saying six people had initially tested positive for the virus last month, while the WHO said eight had been reported. Hartl said the discrepancy was likely linked to a technicality since six patients had tested positive using an internationally recommended method while a less reliable test was used on the others.

Specimens were never collected from one of the brothers who died, and many of those who tested positive experienced only mild symptoms and were not hospitalized, Hartl said.

He added a team of WHO experts have been sent to Pakistan to help determine the cause. He said all four brothers were believed to have worked on a farm and poultry outbreaks had earlier been reported in the area. He said WHO has not ruled out limited human-to-human transmission.

"It's possible," Hartl said. "We don't know if brothers two and three were cullers or not, and we do know that brothers two and three cared for brother one."

Further Reading

- You can visit the Avian Flu page by clicking here.