Dr Yong Poovorawan, a virologist with Chulalongkorn University's Faculty of Medicine, said in a Facebook post that the virus has so far infected some 500 people in Europe and the US. Most or 98 per cent of the patients are men in the 20 to 50 age range.
He cited five reasons that made it difficult to control the spread.
Firstly, monkeypox symptoms are not as severe as those of smallpox and there have been no deaths so far. However, he said, because the symptoms are so mild, some patients end up not getting diagnosed.
Secondly, the outbreak of blisters is not large and 30 per cent of blisters are usually in the genital area. When patients have few blisters and their symptoms are not severe, they do not visit the doctor, Yong pointed out.
Thirdly, the virus can spread during intercourse when partners are in intimate contact.
Fourthly, there is no evidence that the virus jumped from animals to humans or that the virus came from Africa. The latest outbreak was spread among humans.
Fifth, if the virus spreads from humans to pets, especially rodents, rabbits and squirrels, they will become carriers as they will have very mild symptoms. Once pets become carriers, the virus will become endemic and become tougher to contain.
The post said monkeypox is already endemic in some African countries and may soon become endemic in Europe as well.