Photo of a woman (Nanxing Liu, SLU) sitting in the lab by a microscope.
Nanxing Liu doktorerar inom det av Formas finansierade projektet “Markörer för upptäckt av anthelmintikaresitens - från gårdsnivå till gennivå”. Foto: Lisa Chröisty, SLU

More cunning than sheep parasites? For a healthy future and effective medicines – for both sheep and humans

Page reviewed:  15/09/2025

When we or our animals are affected by disease, infection, or parasites, we want to be able to treat it quick and effective. However, as medicines are more frequently used, their effectiveness is in some cases declining. Understanding and counteracting this development is a battle for future health.

Imagine trying to medicate your pet for a life-threatening condition one day and realizing that it has no effect. Or visiting the doctor yourself for an infection in your body only to be told, “We have medicine, but it's ineffective.”

Essentially, this project is about saving sheep. But drug resistance affects far more than just livestock, says Nanxing Liu, continuing: By learning more about resistance, we can also, in the long run, contribute knowledge that may be important for human treatments. This makes it a particularly important project.

Who is outsmarting whom? Humans vs. parasites

For many years, farmers in Sweden and large parts of the world have taken it for granted that sheep should be protected against parasites with deworming medication. Worms can otherwise “eat away” at sheep from the inside. The main culprit, the roundworm Haemonchus contortus, is a parasite that is very common in sheep. By settling in the animal's stomach, it can suck blood from inside, causing anemia, weight loss, and, if left untreated, death.

But over the past fifteen years, more and more Swedish farmers have found that the deworming medication intended to save their sheep from parasites is ineffective. The worms have developed a stronger defense, a resistance we call “resistance.” So what can be done?

Well, you learn to outsmart the parasites.

Photo of a test tube containing sheep feces, photographed from inside a laboratory.
A previous study has shown that up to a quarter of Swedish farms (6 out of 26) have problems with parasites that attack their sheep and are resistant to all the most common types of deworming medication. Lambs and pregnant ewes are most susceptible to the parasite. Photo: Lisa Chröisty, SLU

Not only do the sheep suffer and can die from the parasites, it is also a costly issue for farmers, with significant losses and, for many, a feeling of helplessness. The annual cost of antibiotic-resistant parasitic worms in Europe is estimated at just over SEK 420,000,000, and up to a quarter of sheep farmers (6 out of 26 farms) in Sweden have reported in previous studies that the most commonly used deworming agents are no longer effective in treating their infected sheep.

From farm level to gene level – when the answer lies in the details

That is why Nanxing Liu has now started his doctoral position at SLU, to work in the fight for a better understanding of how worms, the parasite Haemonchus contortus, develop to resist the drugs that are meant to kill them.

This work requires advanced machinery, programming, computer technology, and hours spent in front of a microscope.

The research team is therefore aiming to discover, observe, and understand at the genetic level what changes the worms make in order to resist the medication that should kill them completely. Simply put: How do they survive?

Sheep from many different farms are participating in the project. However, Nanxing Liu is not working with the sheep themselves, but with samples of their feces, where the worms can be found. In the first stage of the project, she has therefore obtained samples from various Swedish farms and is now investigating the differences between gene variations in the worms in the different samples. This can provide important knowledge about how they are constructed at the DNA level and also familiarize Nanxing Liu with the advanced tools she needs to help her.

Starting up has been so exciting! But as soon as the initial joy of being accepted into the project had subsided, I also realized that it's not that simple, but rather a big challenge, says Nanxing Liu.

The main goal for the research team is to find a so-called “gene marker”, simply explained as a special characteristic in the worm's DNA that is linked to resistance. If they succeed in finding the marker, many lives can be saved through early detection in sheep that carry the extra-resistant worms and therefore need special treatment measures to survive.

Jackpot: For animal welfare, the economy, and the future

If the research team succeeds in finding genetic markers linked to resistance, there is a chance of hitting the jackpot: a win in terms of animal welfare, economics, and more sustainable use of medicines. And it is important that farmers are given the tools to only medicate animals where the respective medicine is effective, so that more medicines do not lose their effectiveness. Overuse and drug resistance are future risk scenarios that simply need to be avoided, both for our animals and for us humans.

We want all medicines to work when we need them most. It's worth working for, concludes doctoral student Nanxing Liu.
Photo of a woman (Nanxing Liu, SLU) sitting in the lab by a microscope.
A little time in the lab and a lot of work in front of the computer over the next four years is the plan for Nanxing Liu to achieve the project's ambitious goals—and save large flocks of sheep in the future. Photo: Lisa Chröisty, SLU

Facts:

  • The doctoral position is funded by FORMAS and is expected to run from autumn 2024 to 2028.
  • The doctoral student in the project is Nanxing Liu, together with a research team consisting of:
    • Sofia Mikko, principal supervisor and researcher in molecular genetics at the Swedish University of Agricultural Sciences (SLU).
    • Johan Höglund, principal investigator and supervisor, and professor of veterinary parasitology at SLU.
    • Åsa Ohlsson, supervisor and researcher in molecular genetics at SLU.
    • Paulius Baltrušis at Bio-Rad Laboratories.

 

The project can be easily divided into the following sub-goals and final goals:

  1. The research team collects and examines differences in gene variations in samples from different farms. The aim is to gain knowledge about the worms' gene variations and familiarize themselves with the tools that will be used throughout the project, including Whole Genome Sequencing (WGS) and bioinformatic analysis tools.

  2. Samples will then be examined both before and after deworming treatment.

  3. The ultimate goal is to find the gene marker linked to resistance in the tapeworm Haemonchus contortus.

Illustration of the work process within the project.
Illustration: Nanxing Liu, SLU

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