Anti-parasitic activity of seaweed extracts and effects of dietary seaweed supplementation on nematode infections

PhD student: Charlotte Smith Bonde

The project

Infections with parasitic worms are common in livestock causing substantial economic losses and posing health risks to infected animals. Parasitic worms of pigs include species such as the large roundworm (Ascaris suum) and nodular worm (Oesophagostomum spp.). The nodular worm is a smaller worm up to 1.5 cm long, located in the large intestine of pigs. The large roundworm is located in the small intestine of the pigs and females can grow up to 40 cm long. This parasite can also infect humans.

Parasitic worms are usually treated with synthetic drugs, but resistance against these drugs is increasing worldwide. Increasing resistance against different drug classes has been reported for the nodular worm in pigs in Europe, but not for the large roundworm. However, resistance has been found in similar parasite species in other hosts, such as turkeys, horses and humans.

It is therefore important to find alternative approaches to treat these infections to slow down the development of further drug resistance. Some plants contain compounds able to kill parasitic worms. An Asian seaweed (Digenea simplex) has been used in traditional Chinese herbal medicine as treatment against infections with the large roundworm of humans. Seaweeds are a large plant group divided into three different types (green, red and brown) based on colour and chemical composition. They tend to be rich in minerals and bioactive compounds, and consumption of seaweed has been associated with various health benefits in humans.

The purpose

 The purpose of this project was to investigate the possibility of using seaweeds as a dietary feed additive against parasites in pigs. Here we wanted to investigate if extracts from local Nordic seaweeds were able to kill parasites in a laboratory setting and isolate the active compounds in the seaweeds. Furthermore, we also wanted to test how inclusion of seaweed in the diet to pigs affected the parasitic worm burdens, bacterial composition in the intestines, and immune function in parasitic worm infected pigs. Lastly, we wanted to test how diet inclusion of a fermented seaweed-rapeseed product would affect infections with parasitic worm under natural conditions at an outdoor farm.

The results

This project found that brown seaweeds species such as L. digitata, S. latissima and Fucus spp. are a source of potential anti-parasitic compounds, with organic extracts from these species showing high anti-parasitic activity against larvae of Ascaris suum in a laboratory setting. Three omega-3 fatty acids (α-linolenic acid, steradonic acid, eicosapentanoic acid) were isolated from active fractions. However, the activity of the extracts from seaweeds depends on the species, geographical location, and harvest time. We also found that organic extracts of a commercial fermented rapeseed-seaweed feed supplement also showed anti-parasitic properties in the laboratory setting, and replacement of rapeseed with mustard meal in the supplement mix significantly decreased the activity.

A 5% diet inclusion of seaweed to infected pigs initially showed a reduction in parasite egg excretion of Oesophagostomum spp., but this could not be reproduced at a larger scale when the inclusion was increased to 8%. The inclusion did increase the diversity of the gut microbiota and modulated it in a positive way. Furthermore, it modulated the immune genes in the small and large intestine differently during infection with intestinal worms. A long-term feeding trial with the fermented rapeseed-seaweed product also modulated the gut microbiota of pigs at an out-door farm at a 2% diet inclusion. Furthermore, it tended to reduce parasite egg excretion and infection levels of Ascaris suum in naturally infected pigs. However, we also found a negative impact on weight gain and large variations in effect depending of the supplement batch.

The future

 Further research should include examination of the mode of action of the fatty acids found in the laboratory setting. This should include research on how these bioactive compounds can be transported to the location of the parasites without being absorbed or altered in the process. Further research should also be conducted on the mode of action of the anti-parasitic activity of the fermented rapeseed-seaweed blend and how to minimize the batch differences seen on farm when using as a dietary supplement.