Hantavirus outbreak in Germany

Hantavirus is a group of viruses spread mainly by rodents and can produce specific diseases in people.  The virus is shed in urine, feces and saliva, and people can be infected by aerosol or direct contact with these excreta, or less frequently, by a bite from an infected host, usually rodents.

Two viral groups can be identified: Hantaviruses in the Americas, known as “New World” Hantaviruses, and those present mostly in Europe and Asia, known as “Old world” Hantaviruses. The first group of viruses may cause Hantavirus Pulmonary Syndrome (HPS), infecting a specific “new world” rodent host species, identified in the subfamily of Sigmodontinae.

The “Old world” Hantaviruses may cause a hemorrhagic fever with renal syndrome (HFRS). The European Hantaviruses show a higher genetic variation, and the most significant viruses are: Puumala Hantavirus (PUUV) transmitted by bank voles (Myodes glareolus), Dobrava hantavirus (DOBV) transmitted by Apodemus agrarius and Hantaan hantavirus (HTN) transmitted by Apodemus flavicollis. Puumala Hantavirus is a specific rodent-host-species and is widely distributed in Europe.

Recently, the number of cases of Hantavirus in Germany has dramatically increased. Today experts consider the city of Stuggart the epicenter of the disease; the regional council announced that so far 211 cases have already been reported in 2019. Hantavirus infection was registered in 2017 in the state of southwest Germany, and a total of 441 human cases were reported.

The outbreaks are probably related to an increase in the bank vole populations; the hantavirus most likely involved in these cases is Puumala virus, which is endemic in southwestern and western Germany causing a hemorrhagic fever with renal syndrome (HFRS).

Dr Jan Clement MD, President of the International Hantavirus Society, Hantavirus Reference Centre Laboratory of Clinical and Epidemiological Virology & Rega Institute for Medical Research, University of Leuven, Belgium, indicated that “It is unusual that a German city like Stuttgart should have become the "epicentre" of a HFRS disease, since urban HFRS outbreaks worldwide are caused in fact by a wild rat-transmitted (Rattus Norvegicus) Seoul hantavirus (SEOV), not by PUUV.  Moreover, Dr Clement underlines the need to take a landscape ecological view of hantaviruses, their rodents hosts, the ecological factors that affect those host populations, and human behaviors that determine exposure to the virus.

“Besides, a "bumper year" however means a markedly increase in the local bank vole  (Myodes glareolus) population (which can reach up to 10-20 times the norm) (1), it can be the consequence of a massive amount of available "mast" (beechnuts and acorns) the autumn before (2018), which by itself is again a consequence of a hot summer the year before (2017), a climate-dependent but recurrent phenomenon described as the "mast connection" (2,3). A profusion of mast was noted during autumn 2018 around several German cities, including Berlin ”(4).

“The illness caused by PUUV is the so-called hemorrhagic fever with renal syndrome (HFRS), with extremely variable fatality rates, depending not only from the infecting hantavirus species, but also for a big part from the immune response itself of the infected patient. Hence, the terminology used such as "a potentially deadly disease" has to be translated preferentially as "bearing a fatality rate” between 0.1% and 15%", with lowest fatality rate for PUUV-induced HFRS (1), prevalent in most of Europe and European Russia.”

“Finally, another statement like "More voles equals more infections" might seem evident at first sight, but appeared not always so, with increased knowledge of the complex mechanisms (including increased human exposure), explaining European PUUV-HFRS outbreaks. A more exact statement would be "More PUUV-infected voles equals more human PUUV infections." PUUV prevalence in bank vole populations depend on several changing factors, resulting sometimes in denser vole populations, but with lower PUUV prevalence. Hence, the recent Belgian study titled: "Why hantavirus prevalence does not always increase with host density: modelling the role of host spatial behaviour and maternal antibodies", which it will be discussed at the International Conference on Hantaviruses next 1-4 September 2019 in Leuven, Belgium (5).

References

1. Clement J. Acute kidney injury and hantavirus disease. In: Oxford Textbook of Clinical Nephrology (OTCN), 4th edition. Eds: Turner N,Lameire N, Goldsmith D, Winearls C, Himmelfarb J, Remuzzi G, et al.. Published online: June 2018
https://oxfordmedicine.com/view/10.1093/med/9780199592548.001.0001/med-9780199592548-chapter-24

2. Clement J, Vercauteren J, Verstraeten WW, et al. Relating increasing hantavirus incidences to the changing climate: the mast connection. Int J Health Geogr. 2009; 8:1

https://ij-healthgeographics.biomedcentral.com/articles/10.1186/1476-072X-8-1

3. Clement J, Maes P, van Ypersele de Strihou C, et al. Beechnuts and outbreaks of nephropathia epidemica (NE): of mast, mice and men. Nephrol Dial Transplant. 2010; 25(6): 1740-6.
https://urlsand.esvalabs.com/?u=https%3A%2F%2Facademic.oup.com%2Fndt%2Farticle%2F25%2F6%2F1740%2F1894425&e=653065ec&h=5073a30c&f=n&p=y

 or https://academic.oup.com/ndt/article/25/6/1740/1894425 

4. Leirs H. Evolutionary Ecology, University of Antwerp, Belgium. Personal communication

5. Leirs H, et al; abstract no. 152 at the XI Int. Conf. on Hantavirus, September 1-4, 2019, Leuven, Belgium. https://www.hantavirus2019.org/