Reports of humans affected were also investigated by the Department of Health last week.
The Department of Agriculture and Food ruled out serious viruses, like vesicular stomatitis.
A private veterinarian reported the mouth papules, or small solid lumps in the mouths of horses, on three properties.
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READ NOWFacebook reports of horses with black tongues were likely due to staining from treatment or feed and not related to the condition.
Last week, the Department of Agriculture and Food reminded horse owners to contact their local veterinarian if they notice unusual signs in their horses.
There are no restrictions on horse movement in WA or on events.
The department’s standard horse biosecurity recommendations are that only healthy horses should attend events and they should not share feed, water, or tack and equipment with other horses.
A Department of Health spokesman said at this stage it was unclear whether there was a relationship between the lesions reported in horses and people, and testing had not as yet revealed a cause for the lesions in either horses or people.
Further testing will be conducted if indicated.
‘The department advises that people handling affected horses should take general precautions such as wearing disposable gloves and a face mask, and wash their hands well after contact,’ he said.
If they are concerned about their health they should consult their GP.
For more information about horse biosecurity, visit agric.wa.gov.au and search ‘horse alert’.