India, May 20 -- The World Health Organisation (WHO) director-general openly worried on Tuesday over the "scale and speed" of an outbreak of a rare Ebola variant in eastern Congo, where authorities reported a sharp increase in suspected deaths - to at least 131 - and over 500 suspected cases.

The virus spread undetected for weeks after the first known death as authorities tested for a more common strain and came up negative, health experts and aid workers said. This Bundibugyo virus, a rare variant, has no approved medicines or vaccines.

Congo's health minister, Samuel Roger Kamba, said investigations were underway to determine whether the deaths and 513 suspected cases were "actually linked to the disease." WHO director-general Tedros ...