The Hidden Epidemic
The most recent outbreak of PDV, prior to the present epidemic, was in April 1988 when approx. 18,000 Harbour Seals around Europe died. However, the death of a large number of Crabeater seals in Antarctica in 1955 among others, suggest that PDV may be responsible for mass deaths among seals for centuries, according to Dr. Seamus Kennedy of Northern Ireland's Veterinary Sciences Division. PDV was first discovered in the N. Atlantic in 1988.
PDV (Phocine Distemper Virus) is a morbillivirus, of the same family as measles, and related to canine distemper. It attacks the seals' brain causing disorientation and convulsions, and the lungs causing pneumonia. Later it attacks the seals' immune system leaving them susceptible to secondary infections - typically pneumonia, gastric ulcerations, enteritis and skin and mouth infections. Symptoms include respiratory problems, vomiting, diarrhoea, disorientation, and oral and nasal discharge.
During the 1988 epidemic, approx. half the European Harbour Seal (Phoca vitulina) population perished. The first cases were reported from the Danish island of Anholt in the Kattegat Strait between Sweden and Denmark. It spread from Denmark to the Netherlands and then to the UK. It first appeared in early summer when harbour seals hauled out into dense colonies to breed.
|South West England||50|
|North East England||60|
|South East England||24|
Fig. 1 Estimated seal deaths in the U.K. 1988. (Courtesy RSPCA)
Ireland appeared unaffected in 1988, but in retrospect this appears to be more a case of undetected in the absence of monitoring and recording. Anecdotal evidence to the Irish Seal Sanctuary (I.S.S.) from that period is of unusual clusters of seal carcasses buried (on instructions of Local Authorities and the National Parks and Wildlife Service, as posing a risk to dogs).
Researchers do not know what triggered the latest outbreak or why it took 14 years for the virus to reappear, but confirmed that the virus had spread quickly from Denmark up the Swedish west coast.
With news of the 2002 outbreak in Kattegat, the I.S.S. went on immediate alert and notified all relevant authorities, N.G.O's and monitors. The I.S.S. asked the Minister and Dъchas to establish a hotline and co-ordinating committee and put our resources at the Minister's disposal. Prof. Brian Sheehan of the Veterinary Faculty at U.C.D. did likewise for post mortems.
We requested that a scaled down version of proceedures applying to F.M.D., Salmon Anaemia Virus or Equine Flu be implemented.
Regrettably, this was dismissed (by Dъchas) as alarmist and the collective scientific wisdom was that PDV had not hit Ireland in 1988, would not in 2002 and such steps were unneccesary. The I.S.S. did not accept this line on historic evidence and rejected the scientific opinion proferred that it would not affect the Republic of Ireland, having hit in 1988 England, Wales, Scotland, Cornwall and the North of Ireland (see Fig. 1). The I.S.S. also rejected the view that PDV would necessarily follow the same path as the single known precedent, by nature of the virus, it's transmission and harbour seal behaviour and distribution.
At this point (June 2002), the I.S.S. was receiving anecdotal evidence of deaths and queries for information from Local Authorities, D.V.O's, Coastguard, Gardaн, private vets, Dъchas rangers, N.G,O's and the public. The I.S.S. provided information as best it could and commenced recording. Dъchas, at this juncture agreed to circulate it's Rangers and to bring in "fresh Harbour Seal carcasses in suspect circumstances" for post mortem.
The trend emerging from public reports, resulted in the first PDV case confirmed in Ireland from a cluster on the Aran Islands, post mortemed by Jane Gilleran of N.U.I., Galway and Dr. Seamus Kennedy on October 8th 2002. Unusually, for our East coast, our volunteers and public found harbour seal carcasses (see. Fig. 2) during this period (Sept. - Nov. 2002).
Fig.2 Dead Harbour Seal, Lough Shinney, Co. Dublin, Sept 22nd 2002.
During this period, only one carcass was suitable for post mortem. Of a further 6 post mortems, no further case of PDV was confirmed.
Our figures show unusual clusters and unexplained group deaths and Jane Gilleran's post mortem confirms the presence of PDV in the Republic of Ireland, which somehow made the jump from Northern Europe and the East coast of England and Scotland to the West of Ireland. Reports of group deaths in Cork and buried by the Local Authority, and the scarcity of Harbour Seals in Donegal Bay, reported by fishermen, reinforce the case for monitoring our wildlife populations.
The I.S.S. kept detailed records during the months of July through December 2002. This data is shown in the following diagrams. While it should be stressed that not all seal deaths are due to PDV, it should be noted that an abnormally high number occured on the West coast (Galway and Mayo) and the majority of these were of Harbour seals.
The epidemic tailed off in Europe in late October and England in Nov. 2002. There was a notable reduction of reported seal deaths in Ireland in Nov 2002 also. Only three dead seals were reported in the month of December. Although there were fewer casulties in Ireland, this is probably due to the fact that it struck here after the pupping season.
The I.S.S. has now requested resources be made available to census Irish Seal Populations, establish baseline data and monitor future population trends. Our work with volunteers and the public has ensured that this is no longer a hidden epidemic.
Much more needs to be done to establish the extent of PDV in Ireland, both the historically and into the future. Based on scientific evidence, we believe it will strike with increased severity and at smaller time intervals partiality in areas with poor water and environmental quality. Baseline health studies will yield much more information on wildlife populations and will also serve as economic and efficient environmental monitors.Brendan Price, Terry Flanagan Irish Seal Sanctuary.
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