An outbreak of African swine fever, a severe haemorrhagic disease of pigs, has spread to a fourth province, the department of agriculture, forestry and fisheries said on Monday.

The department said the latest outbreak of the disease was reported in the Heilbron area of the central Free State, after the disease was detected in the North West, Mpumalanga and Gauteng in April.

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The affected areas have been placed under quarantine and investigations are being carried out to trace the origin of the outbreaks and identify other farms that may be affected, the agriculture  department said in a statement.

The disease is incurable in pigs but harmless to humans. It has spread to China since 2018, causing major losses to the world’s largest hog herd.