In the worst cases, migrants have no contact with physicians. And even if doctors and remedies were available, the victims are often reluctant to seek treatment because that would involve some kind of record - and the risk of being tracked down and deported. The government generally tolerates the thousands of migrants who sneak into northern Thailand daily in search of better-paying jobs. After all, they provide cheap labor for many industries. But political pressure to protect jobs for locals and diplomatic considerations regularly induce crackdowns on this underground community.
Language barriers can compromise diagnosis and treatment.
For instance, a group of Myanmar migrants who got malaria drugs in one town were later found to suffer HIV - after a translator became available. Often, patients fail to complete the course of drugs, either because they don't understand the instructions or have no experience taking medicines. This builds immunity in parasites, and as different strains come into contact when infected people travel, stronger varieties emerge. The Thai government recognizes the gravity of the situation. Besides, the authorities are realizing that borders can't be completely sealed to migrants - and certainly not to microbes.