Here we report a case of fatal infection with the highly pathogenic H5N1 Avian Influenza Virus (AIV H5N1) in a white-sided dolphin (Lagenorhynchus acutus). This juvenile male dolphin was found dead stranded on September 5 on a beach near Rimouski (Quebec). The carcass was submitted by the Quebec Marine Mammal Emergency Response Network (RQUMM) to the CWHC – Quebec regional centre for analysis.
The animal was in good body condition, which is suggestive of death from an acute event. Apart from the presence of low intensity parasitic infections, no macroscopic lesion was observed in the animal. Histopathological examination of the tissues revealed the presence of inflammatory and necrotic lesions in the liver, lymph nodes and spleen. Acute inflammatory lesions were also present in the lungs (pneumonia) and brain (very mild encephalitis). Molecular analyzes carried out by the laboratory of the Ministère de l’Agriculture, des Pêcheries et de l’Alimentation du Québec have revealed the presence of an AIV H5N1) in the brain. This result was confirmed by the Canadian Food Inspection Agency laboratory. The results of these examinations indicate that this dolphin died following an acute infection with an AIV H5N1 virus.
Although AIV H5N1 viruses primarily affect birds, several species of mammals are also known to be susceptible. In marine mammals, infections by this virus have been documented mainly in harbour seals, but cases in a few gray seals were also reported. Until recently, no case of fatal infection by an avian influenza virus had been documented in cetaceans (whales and dolphins). To our knowledge, only two cases of AIV H5N1 infection have been reported in cetaceans so far, one case in a bottlenose dolphin in Florida and one case in a harbour porpoise in Sweden. The case presented here, which would therefore be the first case of infection by this virus in a white-sided dolphin, indicates that this species is susceptible to this emerging virus in North America.
The data collected by the RQUMM does not seem to indicate an increase in white-sided dolphin mortality in the St. Lawrence Estuary this summer, despite the presence of an epidemic among harbour seals. This suggests that there has been no transmission of this virus between dolphins and therefore the number of cases should be limited; contact between dolphins and infected birds is probably infrequent.
Although the risk of transmission of this influenza virus to humans and domestic animals seems low, it is recommended not to approach, and especially not to touch, sick or dead marine mammals. Contact between our pets and dead wild animals should also be prevented.
Stéphane Lair – CWHC Quebec / CQSAS, Faculté de médecine vétérinaire, Université de Montréal