Wednesday, 16 February 2011

Echinococcus multilocularis in Sweden

“Deadly Parasite Found in Sweden:” the internet headline caught my eye, and I had a strong suspicion right away. Scanning the article, I picked out the word fox, and I knew I was right. Apparently Echinococcus multilocularis has made its way to Sweden. I discuss this parasite in my book because of the way it has spread in North America from the north to the Midwest, and probably to the East Coast, primarily due to human activities.

[caption id="attachment_244" align="alignleft" width="300" caption="Foxes carry Echinococcus multilocularis, I, Malene: Creative Commons 3.0"][/caption]

The internet article, published by The Local (, Feb 14) doesn’t speculate about how the parasite got there; it just reports that it’s never been found in Sweden before, despite regular monitoring of foxes.  People will come up with lots of theories about the spread of this parasite, but the fact is, the prevalence of E. multilocularis has been increasing in Europe in both humans and foxes for decades. At the same time, it appears to be steadily spreading to new places. It’s appearance in Sweden was probably inevitable.

Researchers point out that the number of red foxes in Europe has increased dramatically in recent years due to environmental changes and human activities, and foxes are much more common in urban areas than in the past. These factors, as well as an increased awareness of the parasite, likely account for the higher numbers of human cases diagnosed. A study published in the June 2009 Issue of PLoS Neglected Tropical Diseases suggests that the original focus was in Switzerland or nearby, and that this focus has seeded expansion to new areas in Europe (Knapp, Jenny et al. “Genetic Diversity of the Cestode Echinococcus multilocularis in Red Foxes at a Continental Scale in Europe”)

Infected rodents could potentially be spreading it as well as foxes, and one wonders about this possibility with respect to Sweden, since an overland route for migrating foxes around the Baltic Sea and the Gulf of Bothnia would take a very long time. But, realistically, any number of animals could bring it in, and there is also the possibility that it has been present for decades at a low level, and is only being discovered now because people are actively looking for it. Interestingly, I found a report that said the population of red foxes in Sweden declined by more than 70% in the 1970s and 80s due to sarcoptic mange, so the fox population there may be on the rise due to recovery from that as well (“Red Fox: Vulpes vulpes.” D.W. MacDonald and J.C. Reynolds,

The spread of E. multilocularis to humans is certainly bad news: Roberts and Janovy say it chillingly and well: “this parasite… grows and infiltrates processes into the surrounding host tissues like a cancer.” (Foundations of Parasitology, 6 ed. McGraw Hill, 2000)