Seals, Stigma and Survival

A very popular activity in the summer is to go to the beach, and possibly go for a swim. In Denmark, and across the Baltic region, beach activities are a frequent aspect of regional tourism promotion. Two popular summer destinations, for example, are Bornholm and Christiansø/Christians Island; islands north of mainland Denmark in the Baltic Sea. But if you’re planning on swimming in the Baltic Sea this summer, it could surprise you to learn that the increasing local seal populations like the grey seals and the harbour seals may have a negative impact on the health and safety of your experience.

Research indicates that “[s]everal parasites that infect marine and coastal animals or contaminate the marine and coastal waters can infect humans and present a significant public health risk”.

During fieldwork for Seals, Stigma and Survival there was an opportunity to speak with Professor Kurt Buchmann, a world leading parasitologist based at the University of Copenhagen.

For decades Professor Buchmann has worked on issues related to parasites in fish species in the Baltic Sea including examining issues of ecosystem factors impacting fish health. This work has led to examinations of seals in the region, their role in the local marine ecosystem and their impact on the parasite profile of the area.

In our discussion a fascinating antidote from his research came up: the issue of seal to human parasite transmission.

In his co-authored 2020 open access paper “Nasal localization of a Pseudoterranova decipiens larva in a Danish patient with suspected allergic rhinitis” in the Journal of Helminthology (co-authors: A. Nordholm, J.A.L. Kurtzhals, A.M. Karami, and P.W. Kania), Professor Buchmann explores the case of a 33 year old man in Denmark who had nasal issues after swimming with seals off the coast of Zealand.

Swimming with seals may not sound like much of a basis for a journal article, but wait. This is a story with a twist. Remember, Professor Buchmann is a parasitologist.

Here’s the situation explored in the article in Professor Buchmann’s own words:

I can tell you that we’ve published…that there was one man that was swimming north of Zealand among seals out there. There were a lot of seals. And then he went to the national hospital here for six months. The doctor tried to treat him for allergic rhinitis. After six months without success, he got drops against rhinitis you know antihistamines and stuff like that. It didn’t work and his nasal cavity was still itching a lot. One morning it was itching so much and out came a worm from the seal.…There were two ways that he could get that worm: by eating raw fish and he said it was a very long time ago that he’d done so [but] there is still a possibility that he could have been eating a piece of raw fish and while he was sleeping it [the parasite] was migrating up into this nose or, and that’s actually one of my suggestions in the paper where I say that we know that the eggs are coming out from the seal feces, they hatch out – there’s a little larvae coming out – and that larvae should be infective to humans. So if he’s swimming around in thousands of eggs, you get water into the nasal cavity when you swim, there is a theoretical a chance that that worm has taken its residence up in his nasal cavity and through the next six months was growing up to the size of four centimeters, itching you know and then coming out. I mean that’s a theory I proposed that in the paper but nobody pays attention to it.

Well we’re paying attention now!

While Professor Buchmann allows that there is the possibility that the parasitic worm that emerged from the man’s nasal cavity may have originated elsewhere, the seal theory has merit.

This begs the question, why aren’t we hearing more about this possibility, at least given a health and safety warning, about the potential impact of seals on swimming areas where they frequent from public authorities before setting off on our beach holidays?

Professor Buchmann posits that: The tourism industry doesn’t “want to talk so much about the seals because the seals look beautiful. They don’t want to talk about the contamination of the waters where you might get infected in if you were there to with too many seals”.

The seal populations in the Baltic Sea are increasing, but the ability of local nations and hunters to hunt or cull them is curtailed by EU regulations. The issue of ecosystem balance is under discussion regionally, and will be discussed more in Seals, Stigma and Survival as the project progresses. But if Professor Buchmann’s theory is right, there is a real possibility of more seal to human parasitic transmission cases and the silence on instances as explored by Professor Buchmann and his co-authors is noticeable.

How many parasitic nose worms need to be sneezed out before the risk of seal parasites to humans swimming along our beaches is discussed publicly remains to be seen. But if you’re interested in learning more, please check out Professor Buchmann’s research (see below).