The Zoonotic Parasite Dirofilaria repens Emerged in the Baltic Countries Estonia, Latvia, and Lithuania in 2008-2012 and Became Established and Endemic in a Decade

The zoonotic parasite Dirofilaria repens has spread toward north in Europe, and cases of autochthonous dirofilariosis caused by D. repens have emerged in the Baltic countries Estonia, Latvia, and Lithuania. We conducted a review on the emergence of dirofilariosis in humans and domestic dogs in these three countries in northeastern Europe. Based on the available literature and reports, the first finding in the Baltic countries was made in Latvia in 2008, followed by the first in Lithuania in 2010, and the first in Estonia in 2012. In all three countries, further findings were reported soon after the first reports. By the end of 2019, autochthonous human D. repens infections had been described from Latvia and Lithuania, and autochthonous canine D. repens infections had been described from all three Baltic countries. While no epidemiological studies estimating prevalence or incidence of the human infections have been published from the three countries, a substantial proportion of investigated dogs have tested positive for microfilariae in studies performed in Latvia and Lithuania. Dirofilariosis is an emerging zoonosis in northern Europe, and the summarized data confirm that D. repens has become established and endemic in the Baltic countries. The available data do not provide a good overview of the situation, and further epidemiological studies are needed. Awareness about the recently emerged zoonotic parasite should be increased among medical doctors, veterinarians, and the general public. Managing this zoonotic infection is a public health challenge that needs to be addressed using a One Health approach. Investigating the spread of D. repens in the Baltic countries could be useful for better preparedness for the anticipated further spread to the Nordic countries.