Police have stepped up patrols outside a cardiologist's home after he was suspended from his job and targeted by vigilantes who exposed him on social media for not social distancing at an anti-lockdown rally in Wisconsin.

Dr. David Murdock, a cardiologist at Aspirus medical group, has been banned from seeing patients for the 'foreseeable future' after photos of him flouting social distancing rules and not wearing a mask at a protest last month went viral on Facebook.

The doctor of 33 years was exposed when Kevin Rusch spotted a photo of him in the crowds at the rally and shamed him for breaking the state's stay-at-home order and putting his patients at risk of exposure to the virus.   

Murdock, 68, admitted he attended the event but insisted he was social distancing.  

Authorities have now had to step up protection for the Wausau-based medic after someone left a bag of feces on the front steps of his home - part of a growing spate of social distancing vigilantism emerging across the US as the pandemic continues to divide the American people.