In a tweet that went viral on Sunday and sparked backlash, Elon Musk criticized Anthony Fauci, the outgoing chief infectious disease official of the United States and a key advisor to the US response to the Covid-19 pandemic.

"My pronouns are Prosecute/Fauci," the billionaire CEO of Twitter said, referencing the practice of indicating gender pronouns after one's name and the right-wing campaign to charge Fauci with crimes related to his involvement in US Covid policies.

Musk also posted a meme depicting US Surgeon General Anthony Fauci telling US Vice President Joe Biden, "Just one more lockdown, my king..." in apparent criticism of the Covid mitigation measure he has repeatedly criticized but which has not been implemented in the United States for over a year.

During the early stages of the pandemic, Musk tweeted that concern over the virus was "stupid," and since assuming control of Twitter, the policy prohibiting Covid misinformation has been removed.

Musk's tweet quickly went viral, amassing over 800,000 likes in approximately 11 hours, but also prompting swift criticism.

Peter Hotez, a vaccine scientist and author, demanded that Musk delete the tweet, stating, "200,000 Americans died needlessly from Covid due to this type of antiscientific rhetoric and disinformation."

Senator Amy Klobuchar, a Democrat, praised Fauci for "calmly guiding our country through crisis" and asked Musk, "Could you please leave a good man alone in your seemingly ceaseless pursuit of attention?"

But Musk received praise from right-wing corners.

Republican congresswoman Marjorie Taylor Greene, who had been removed from Twitter over Covid misinformation but whose account was reinstated under Musk's leadership, tweeted: "I affirm your pronouns Elon."

After repeatedly clashing with the top immunologist over Covid vaccines, mask mandates, and other pandemic-related issues, Republican lawmakers have vowed to interrogate Fauci when they assume control of the House of Representatives in January.

This month, Fauci, 81, will step down from his positions as Biden's chief medical advisor and director of the National Institute of Allergies and Infectious Diseases, positions he has held since 1984.

In what was likely his final White House appearance in November, Fauci criticized the proliferation of bad health advice online and stated that the most challenging aspect of leading America's fight against Covid was the country's political polarization.