Four prisoners who died earlier this year at the Buimo prison in Lae in Papua New Guinea's Morobe province, were suffering from a virus infection of the heart.
In his autopsy report, pathologist Dr Philip Golpak, says that morbid and congested conditions at the prison probably contributed to the contraction and spreading of the virus.
At the time the prisoners died there were over 700 inmates crowded into the facilities built for 400.
Dr Golpak says all four died from viral myocarditis, a medical term that simply means viral infection of the heart muscle.
At the same time as the deaths, the prison had 30 inmates with a mysterious muscle wasting condition.
The prisoners eventually recovered after an improvement in their diet.