The latest Paper of the Month for Parasitology is “Cystic echinococcosis in Iceland: a brief history and genetic analysis of a 46-year-old Echinococcus isolate collected prior to the eradication of this zoonotic disease” and is freely available.

Humans have been parasitised with various zoonotic helminths throughout their evolutionary history. One important shift in human history that contributed to the increase in parasite load was the beginning of farming, when life gradually started to be dominated by the production and consumption of domesticated plants and animals (known also as the Neolithic Revolution). This new way of living that combined foraging and farming, increased exposure to parasites due to more frequent contacts between humans and animals. In the past, dogs in combination with livestock such as sheep and cattle created favourable conditions for propagation of parasites that require more than one host for their life-cycle. One such example is the tapeworm Echinococcus granulosus sensu stricto that uses predominantly ruminants as intermediate and dogs as definitive host. Humans can also act as intermediate hosts and the sad story is that only intermediate hosts suffer, due to growing parasite cysts in various internal organs. The disease is called cystic echinococcosis (CE) and it has been a severe health problem worldwide, including in Europe.

The study started with an e-mail from Prof. Karl Skirnisson (University of Iceland). He had listened to my presentation on Echinococcus genetic variability, phylogeography and identification at the 9th Conference of the Scandinavian-Baltic Society for Parasitology held in Vilnius, 2021. Karl was interested to know the genetic identity for Echinococcus cysts collected in 1977 from a sheep who was the second to last animal found to be infected in Iceland. We quickly reached an agreement to collaborate and after a while a package arrived, containing cyst material and DNA samples purified by Thorunn Soley Björnsdottir. CE (‘sullaveiki’ in Icelandic) is considered the most severe parasitic disease that ever affected the human population in Iceland. ‘Sullaveiki’ was endemic already in the 12th-13th centuries, mentioned in Icelandic sagas written in this period.

Archaeological excavations have revealed numerous cases, including skeletons with large cysts of up to 20 cm in diameter. Before the start of an eradication campaign in the 1860s, people in Iceland suffered immensely due to CE, with nearly every fifth adult dying of CE or its complications. Eradication of CE from Iceland by 1979 was a huge success story that still serves as one of the great examples of parasite eradication. However, there was no genetic information on Echinococcus parasites from Iceland. Since different species and genotypes vary in their infectivity, it is important to perform genetic analysis, which is the only way to know the identity. With this study we revealed this identity for one of the last Echinococcus isolates in Iceland, obtained from a sheep 46 years ago. We sequenced a large portion of the mitochondrial genome and identified the isolate as Echinococcus granulosus sensu stricto genotype G1. Since G1 is known to be the most dangerous genotype to humans, it can at least partly explain why such a large proportion of human population in Iceland were infected and died in the past. Genotype G1 dominates and causes severe problems in Europe also today. Our study demonstrates that analysis of old parasite samples can reveal important information on human-parasite relations of the past.

The paper Cystic echinococcosis in Iceland: a brief history and genetic analysis of a 46-year-old Echinococcus isolate collected prior to the eradication of this zoonotic disease by Urmas Saarma, Karl Skirnisson, Thorunn Soley Björnsdottir, Teivi Laurimäe and Liina Kinkar, published in Parasitology, is freely available.