Such cases, when a disease has spread 50 km away from previously identified cases, had not been seen in Latvia prior to the disease being found in Baldone, said Balodis.
It's difficult to predict when the disease will spread further as ASF is distributed by wild boar or by humans eschewing hunting hygiene, he said.
"However the case in Baldone looks more like a 'human factor' case," Balodis told Latvian Radio.
He said that while the disease is not far from Rīga, in order to sound alert there would have to be infected wild boar frolicking in Rīga. "If there aren't any, there won't be any real threat to the city," said the chief of the food-hygiene service.
Balodis said that if the disease is detected in the capital, it could cause problems with the transit of animal products through Rīga port.
There have been 580 cases of ASF detected in wild boar in 2016. However no domestic pigs have been affected this year. If an infected pig is found in a farm all pigs in the particular farm have to be culled, causing losses to farmers.
It first arrived in Latvia in June 2014, believed to have been carried across the border from Belarus by wild boar. A series of quarantine zones and culls in the months since have failed to stop its advance across Latvia and into Estonia.