Abstract

During the summer of 2004, Alaska experienced its first outbreak of Vibrio parahaemolyticus (Vp) associated gastroenteritis involving 62 people who consumed raw oysters from Prince William Sound.¹ Vp does not thrive in waters with temperatures higher than 15°C, and before this outbreak, Alaskan waters were thought to be too cold to allow Vp to proliferate sufficiently to cause disease. However, surface sea temperatures in 2004 and 2005 were unusually warm and above this threshold for several weeks. Alterations in oyster farming practices, namely lowering oysters below the thermocline prior to harvest, reduced human cases the following year. However, from 25 Jun 05-5 Aug 05, four northern sea otters that stranded in southcentral Alaska cultured positive for Vp. From a group of more than one hundred otters tested for fecal pathogens in a multi-year collaborative project investigating patterns of disease and mortality in northern sea otters, these four otters were the first to test positive for Vp.

The first otter, EL0509, was a ~six month old male pup that live stranded in Homer, Alaska on Kachemak Bay, and died shortly after admission to our rehabilitation facility. Gross necropsy found bruising on the head and tail suggestive of trauma. Vp was only cultured from the nasopharynx. Because histopathology did not reveal changes associated with Vp, this isolate might have originated from items fed during transport. The second otter, EL0510, a live subadult male that stranded in the same area, was admitted with mild neurological signs and died after 10 days in rehabilitation. Gross necropsy revealed hemorrhagic enteritis and cerebellar atrophy. Vp was cultured from feces. The third otter, EL0511, was found fresh dead close to Seward, Alaska on Resurrection Bay. Gross necropsy found injuries consistent with a boat strike. Cultures of blood and intestinal contents grew Vp. The fourth otter, EL0512, was a live ~six month old male that stranded in Cordova, Alaska off Prince William Sound. Initial diagnostic tests were relatively unremarkable, but he developed a rapidly progressive pancytopenia and hypoalbuminemia. After 11 days of rehabilitation he died. Prominent findings at gross necropsy included changes consistent with aspiration pneumonia and gastroenteritis. Vp was cultured from feces obtained at admission and again six days later.

All four otters are presumed to have acquired Vp from shellfish obtained from areas close to the stranding sites. Otter EL0512, was the only animal to come from an area where environmental or shellfish testing had previously documented Vp. Shellfish are also gathered from these areas for human consumption. While commercial producers can lower their shellfish below the thermocline to reduce the presence of Vp prior to distribution, casual or subsistence harvesters are at risk of being exposed to this disease. Finding Vibrio parahaemolyticus in sea otters underscores the importance of these animals as sentinels for diseases which may impact human health. Furthermore, these cases highlight how the changing environment can cause changes in the patterns of disease.

Acknowledgements

The authors would like to thank Otter Works and the other volunteers who help transport and care for these otters. Additionally, the authors appreciate NOAA Grant NA03NMF4390357 for funding portions of this work.

References

1.  McLaughlin JB, DePaola A, Bopp CA, Martinek KA, Napolilli NP, Allison CG, Murray SL, Thompson EC, Bird MM, JP Middaugh. 2005. Outbreak of Vibrio parahaemolyticus gastroenteritis associated with Alaskan oysters. N Engl J Med 353(14):1463-70.