Epidemics in seals what have we learned?

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1 Epidemics in seals what have we learned? Jonas Teilmann Department of Bioscience Aarhus University, Roskilde, Denmark

2 Epidemics in European harbour seals by PDV started on Anholt Mortality rates in ,000 harbour seals died Anholt ,000 harbour seals died Härkönen et al. 2006

3 2007 An unknown pathogen kills a few hundred harbour seals starting on Anholt! Influenza causing lower mortality than in 2014?

4 Bird influenza (H10N7) killed a few thousand harbour seals in Northern Europe in 2014 starting on ANHOLT! Dead harbour seals reported in Denmark About 26% of the Danish Wadden Sea population was found dead in 2014 Lasse Fast Jensen 2015

5 What happened in 1988 and 2002? 1. In 1987/1988 harp seals moved south from Norway and invaded the North Sea because of capelin depletion in the Barents Sea 2. In 1989 it was documented (Dietz et al. 1989) that a previously unknown Morbilli virus (PDV) closely related to Canine Distember Virus was endemic to the Arctic seals (fx harp seals) 3. It is therefore likely that harp seals were spreading the disease to harbour seals on Anholt in spring 1988, although no harp seal were observed here. 4. In 2002 the same disease (PDV) started on Anholt again. 5. This time no harp seals or other arctic species was observed in the region. Could there be other virus carriers than arctic seals? 6. What is so special about Anholt? 7. Harbour seals and grey seals live close together on the sandy beaches of Anholt. Grey seals are known to travel far distances and may have been a healthy carrier of the virus to Anholt in 2002 as grey seals show no symptoms, but do carry the disease. 8. What have we learned?

6 Is the virus present all over the world? Prevalence of antibodies against PDV/CDV in different seal species PDV Year No. tested % positive Europe Harbour seals Grey seals % 0% % 96% Western Atlantic Harbour seals % Grey seals % North Atlantic Harp seals % Hooded seals % Ringed seals % Bearded seals % Walrus % North Pacific Spotted seals % Ribbon seals % Stellar sea lion % Härkönen et al CDV Lake seals Baikal seals % Capian seals % Antarctica Crabeater seals % Weddel seals % Leopard seals %

7 1. Are the surviving harbour seals immune? - Age structure of 1350 females that died during the two epidemics in 1988 and Fem 1988 Fem 2002 Fem AS Age 1. Lifetime immunity 2. No immunity for seals born between epidemics Härkönen et al. 2007

8 2. Could the virus circulate in the harbour seal populations between epidemics? Probably not as there is there are no signs of the virus between outbreaks Also, it has been estimated that it requires about individuals to have a live mobili virus circulating in an area (each individual can only have the virus for about 2-3- weeks and then develop lifetime immunity or die)

9 3. Could low genetic diversity be a contributing factors? Probably not as relatively high genetic diversity and limited gene flow between sub-populations was found in Danish/Swedish harbour seals. Olsen et al Molecular Ecology

10 Contaminants as a contribution factor? PFOS (ng/g ww.) PFOA (ng/g Example of pollutant that is widely used in industry Toxic chemical that binds to blood proteins Wadden Sea Limfjord North Kattegat South Kattegat Central Kattegat The Sound PFHxS (ng/g ww.) West Baltic Wadden Sea Limfjord North Kattegat Central Kattegat Probably not as measured contaminant levels are highly variable between areas while the mortality rate was about the same South Katte T Dietz et PFOSA al (ng

11 Why only harbour seals? No obvious weakness in the harbour seal populations that can explain high mortality from virus infections Lack of robustness (genetic selection) towards proper immunesystem response to infections may be explained by harbour seals being very very local and until recently not exposed to very many virusses?

12 Influenza is not new to seals Curtesy of Wendy Puryear

13 Influenza spreading Curtesy of Wendy Puryear

14 Most likely spreading in seals

15 Aerial surveys of seals on land in August What does it look like in Kattegat (Anholt) and the Limfjord? Kattegat (DK) Brand Bird new influenza data epidemics from last weeks survey!? PDV epidemics Photographic aerial surveys to monitor population trends in harbour seals Limfjord Bird influenza epidemics? PDV epidemics

16 What can we expect in the future? 1. We know a lot about the PDV morbillivirus in harbour seals. Next year (2016) it is 14 years ago the last epidemic hit northern Europe. Will we experience a new epidemic after 14 year again? - or has the genetic selection made them immunologically tolerant like in the North American harbour seals? 2. As the Influenza A can survive over winter in various reservoirs we may see the disease turn up again, however, more likely birds (or humans?) will spread a mutated new influenza with regular intervals and varying mortality. 3. Both type of virus epidemics do not seem to diminish the populations over time.