Many imported dwarfs are infected with Iridovirus before they leave Singapore.
Currently most of the Trichogaster lalius are arriving in pet shops with a virus (Dwarf Gourami Iridovirus (DGIV)) in them. This causes lethargic behaviour, darken of colour, tumours and death within a year. This virus is also believed to infect other fish like Swordtails and Mollys, possibly some Cichlids. There is no treatment for this virus.