Most countries in the world are members of the World Organisation for Animal Health (OIE), which receives formal international reports. However, member countries remain free to decide whether or not to report cases that occur on their territory.
For example, North Korea is a member of the OIE, but has not yet reported any cases despite recent suspicions in several media reports that the disease has entered the country. For its part, China has just announced that it has reduced its hog herd by 22.3% between April 2018 and April 2019, while reporting only 130 cases to the OIE. However, we suspect that the actual number of cases in China is much higher.
So there is a problem with some countries not reporting their true situation and I think there is no easy solution to that.