20 February 2023

Contraception is the future of rat control

Plant chemistry

University of Copenhagen researchers have gotten yeast cells to brew triptolide, a substance typically extracted from a rare Chinese plant. Their research makes it possible to control rats with the substance on a large scale – both humanely and sustainably.

Photo: Getty images

The father of Indiana Jones is famously terrified of them. And as spreaders of the Black Death and many other a horrid disease throughout history, they have terrorized more people than any human reign of terror. Nevertheless, their populations continue to boom, from Copenhagen to Singapore.

Rats thrive wherever there are humans. Together with us, they have colonized every continent except Antarctica. Destruction and disease comes in their wake. Yet our fight against them has proven both ineffective – partly due to resistance – and

dangerous to ecosystems.

Using research from the Department of Plant and Environmental Sciences and spinout company TriptoBIO, an American company called SenesTech is now ready to spread an effective and environmentally friendly alternative on a much larger scale. And, because the product impedes the ability of rats to reproduce instead of killing them, it is humane.

"I joke a bit about this being a 'woke' product. It is sustainable, ethical to animals and even strong on gender equality, as male rats are also targeted by this contraception. They become infertile for about a month after consuming it, which causes rat populations to drop dramatically," says Johan Andersen-Ranberg of the Department of Plant and Environmental Sciences, one of TriptoBIO’s founders.

A rare Chinese plant

Rats are lured to a sweet and sticky liquid from a feeder developed by the American company. Among the sweet rat treat’s active ingredients is triptolide, a substance that makes the liquid a kind of contraceptive stew for male and female rats alike.

The substance is derived from Tripterygium wilfordii, also known as Thunder god vine, a rare Chinese vine plant that is harvested in the mountains by local gatherers. According to Andersen-Ranberg, in addition to being difficult to find and unstable in delivery, the plant also produces very little of the active substance.  So little, that its value by weight is fifteen times more than gold.

Now, the UCPH researchers have found the enzymes and genes in the plant responsible for the substance, decoded the relevant DNA, and encoded it in the genetic material of a yeast. By doing so, they have been able to ferment and produce the substance in a much faster, more stable and, not least, cheaper way.


This plant-based rat contraception slows rat fertility for a limited time rather than killing them. As such, it is not an environmentally harmful poison, but a rat contraceptive that can be used as a permanent solution.

"Due to its toxicity, rat poison used today can only be put out for limited periods of time. A rat population grows rapidly once the poison is removed, which means that more poison must be set out into the environment. This solution can be permanent and keep rat populations at stable low levels, without causing any unintended damage to the environment," says Johan Andersen-Ranberg.

Current methods are extremely toxic

Extremely potent poisons are now used for rat control. But rats are cunning critters. If a poison encountered by a rat is not strong enough to kill it, the rodent will quickly find out how to avoid human traps. Furthermore, in Denmark among other places, many rats have developed resistance to milder poison variants.

The powerful poisons damage ecosystems and degrade very slowly, often taking a year before their effect is halved. During this time, birds and any scavengers that eat the rats can also receive lethal doses and carry the poison with them into the wild.

The authorities are aware of these "extremely toxic" current remedies, as the Danish Environmental Protection Agency refers to them, but allow them for a lack of alternatives and because the danger posed by rats is considered to be greater.

While nearly seven hundred years have passed since the Black Death here in Europe, as carriers of disease, rats are still

considered a threat to public health. Elsewhere in the world, the problem is much greater. They are also responsible for significant economic damage. Their burrowing can damage sewer lines and even cause a home’s foundation to shift, making them a source of expensive to repair damages.

First Manhattan, then the world.

The yeast developed by the researchers can be scaled to produce enough triptolide that even a problem as global and pervasive as rat control can realistically be solved with TriptoBIO as a supplier of this valuable substance.

"With our research and the yeast, we’ve now developed, we can ensure supply and get the price of triptolide down to a level where it is realistic for this environmentally friendly and ethical alternative to existing rat control to be widely used. We are starting in the US, but are optimistic about getting the rest of the world on board," says Johan Andersen-Ranberg, who continues:

"Initially, we will probably only make a few kilos of the substance. But when rat control using our substance grows as large as demand leaves us to believe that it will, we will be producing it by the ton. And we'll be ready. On top of that, there are plenty of other perspectives for this substance. A number of other projects are also under development in which triptolide is a necessary ingredient. Fortunately, we can easily scale up," says the researcher.

About TriptoBIO

TriptoBIO is a start-up and plant biosynthesis business spinout at the University of Copenhagen’s Department of Plant and Environmental Sciences.

The company recently signed a patent contract with the University of Copenhagen regarding the development and sale of triptolide from genetically modified yeast cells.

The company's first customer is the American company SenesTech, which combats rats using a contraceptive based on, among other things, triptolide.

TriptoBIO has received investments from The Danish Growth Fund and the Bioinnovation Institute.

 Originally contained a passage saying that film hero, Indiana Jones is afraid of rats. That is false, it is of course his father who fears and hates them.


Johan Andersen-Ranberg
Assistant professor
Department of Plant and Environmental Sciences
University of Copenhagen
+45 35 33 77 88

Kristian Bjørn-Hansen
The Faculty of Science
University of Copenhagen
+45 93 51 60 02


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