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Increased distribution of parasites due to climate change

Example of a trematode-infested mussel (Potamocorbula amurensis) where infestation has caused malformations in the shell. (Image: DOI number 10.1073/pnas.1416747111)

More parasites due to rising sea levels

Climate change leads to steadily rising sea levels. The risk of floods is not the only consequence. An international working group involving FAU researchers has shown that various types of parasites have been spreading rapidly as a result of rising sea levels. Their findings have been published in the renowned American journal Proceedings of the National Academy of Sciences (PNAS)*.

There is growing concern among researchers worldwide who are discussing how parasites are reacting to the current climate change and how they will affect the health of many people in the future. They fear that parasites will spread due to the changed conditions and will become a major threat to mankind.

Getting to the bottom of the problem

An international team of researchers involving FAU’s Chair of Palaeoenvironmental Studies has investigated the fossil record of the past 9600 years. The fossil record comprises all documented occurrences of fossils and is the essential source of information about how life on earth developed. The researchers focused on the Pearl River Delta in south China where traces of parasitic distoma (trematoda: digenea) can be found. Parasites of this group are responsible for many human diseases including bilharzia, a well-known vermicular disease in which the pathogens infect and severely damage the internal organs.

In their study the researchers led by John W. Huntley, University of Missouri, investigated types of parasites which infect mussels, not humans. They investigated the link between sea level fluctuations and the parasite infestation during the Holocene, the most recent post-glacial period of the earth’s geological history. Until now, such investigations had been restricted to much shorter periods of time. The working group has now presented findings which cover almost the entire Holocene, including the sharp rise in sea levels in the post-glacial period, for the very first time. The researchers concluded that the number of trematode-infested mussels had increased strongly during the first 300 years of the Holocene rise in sea levels. Heavily fluctuating salinity in the Delta could be ruled out as a cause.

Will parasites become a serious threat to humans?

‘We were able to prove increased trematode infestation in mussel shells in various depositional environments with different degrees of salinity during periods of rising sea levels – a phenomenon which suggests that the global rise in temperature caused an increase in parasite infestation,’ says Manja Hethke, who worked on the study at FAU’s Chair of Palaeoenvironmental Studies. In light of their findings, the researchers assume that the types of parasites which are dangerous for humans have similar distribution patterns in the corresponding intermediate hosts (mostly freshwater snails). ‘The data we collected is therefore very informative with regard to the spread of parasitic diseases in the future. Based on these findings, an increase in the number of trematodes can be expected as a response to climate change and rising sea levels. This may have a negative impact on wildlife, fishing and human health in general in the affected regions,’ says Hethke.

*Huntley, J.W., Fürsich, F.T., Alberti, M., Hethke, M., Liu, C. in press. A complete Holocene record of trematode-bivalve infection and implications for the response of parasitism to climate change. – PNAS. doi:10.1073/pnas.1416747111

Further information:

Manja Hethke
Phone: +49 9131 8523325
manja.hethke@fau.de

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