A compound found in a poisonous plant nicknamed the deadly carrot blocks the activity of all COVID-19 variants in isolated cell cultures, according to a new study in the journal Virulence. Known as thapsigargin (TG), the antiviral agent triggers an immune response in host cells that stops viruses from replicating and appears to be effective against all known COVID variants, including the highly infectious Delta variant.

Extracted from a plant called Thapsia garganica, TG has previously been found to inhibit the activity of several influenza viruses as well as the original SARS-CoV-2 strain. However, the emergence of new COVID-19 variants during the course of the pandemic has raised questions as to whether the compound is capable of blocking some of the more virulent forms of the pathogen.

The researchers began by comparing the potency of the Alpha, Beta, and Delta variants. To do so, they infected human cell cultures with each strain, and measured the viral RNA load in these samples 24 hours later.

Initial results indicated that the Delta variant was by far the most prolific, multiplying and spreading at a rate that was four times higher than the Alpha variant and nine times higher than the Beta variant. The researchers also discovered that the Delta strain significantly boosts the multiplication rates of other variants when cells were co-infected with two different SARS-CoV-2 viruses.

Worryingly, all co-infection combinations resulted in what the authors describe as “multiplication synergy”, whereby new virus outputs were greater than the sum of the two variants involved.

The good news, however, is that TG was found to inhibit the replication of each individual variant as well as all co-infection combinations. When applied to cells that had been pre-treated with TG, the ability of all variants to replicate and spread to adjacent cells was diminished by at least 95 percent.

“In [Alpha-Delta] co-infection, the most prolific infection group, combined viral RNA from TG-primed cells fell by 99.6%” in comparison to cells that had been treated with a control substance, the authors write.

“We further showed that TG was effective in inhibiting the replication of the three variants during active infection,” they explain, indicating that the compound is protective when used as a treatment as well as a preventative.

“Our new study has given us better insights into the dominance of the Delta variant,” said study author Professor Kin Chow Chang in a statement. “Even though we have shown that this variant is clearly the most infectious and promotes production of other variants in co-infections, we are pleased to have shown that TG is just as effective against all of them.”

“Together, these results point to the antiviral potential of TG as a post-exposure prophylactic and an active therapeutic agent.”

As promising as these findings may be, however, it's important to note that researchers are yet to develop an actual treatment from the compound, and that self-medicating with deadly carrot is the last thing that anyone should do. For the time being, vaccines remain the most effective form of protection against COVID-19.