Health officials in Papua New Guinea's Morobe province think malaria or typhoid may have been the cause of four deaths at the Buimo jail near Lae over the past month.
At the same time another 31 inmates are afflicted by a mystery illness which the provincial programme advisor on health Dr Likei Theo says dates back two years.
He says the now isolated group is suffering increasing muscular weakness problems which mean they cannot walk unaided.
Dr Theo says they also have vision problems and swelling feet.
But he says the four deaths appear unrelated to the mystery condition but he is still waiting on post mortems.
"they came in with a history of abdominal pain, fever, headache malaise, these sort of symptoms which are typical of common things like malaria or could be typhoid, but again I said I am still waiting for a proper postmortem report or autopsy report to confirm that"
Dr Theo is looking for expertise from national health authorities and groups like the World Health Organisation to isolate the mystery ailment.