Health advocates have urged Asean governments to take better care of migrant workers, including those with HIV/Aids, to prevent diseases from spreading.
The warning follows concerns about health conditions for the workers, most of whom do not have access to health services or are reluctant to seek them out.
Many are illegal workers and they encounter problems communicating with health officials, a recent workshop on migrant labourers' reproductive health in Phnom Penh was told.
Sunee Talawat, a Thai activist who monitors workers living with HIV/Aids in Southeast Asia, said many Aids-infected migrant workers stop taking their anti-viral drugs after they run out.
Inconsistent treatment results in increased drug resistance, requiring stronger and more expensive drugs.
Ms Sunee said there should be inter-government help to ensure treatment records of workers in their native country can be referenced.
This would ensure that anti-viral drug treatment can continue when they migrate to another country.
She said the exchange of information among members of Asean is crucial as the grouping moves close to the free mobility of workers in 2015.
It should start with professionals in such areas as medicine, nursing and engineering.
Ms Sunee said better health policies would help contain the spread of cross-border diseases.
Migrant workers who illegally enter another country tend to face more health risks because they do not dare to identify themselves and seek mainstream health treatment when they fall ill for fear of being sent home, said Rachael McGuin, of the Mekong Migration Network.