Disease kills penguin chicks
Sunday 10th April, 2005The number of yellow-eyed penguin chicks fledged in Otago this year was the lowest recorded for many years, primarily due to an outbreak of a Corynebacterium infection. The disease was first noticed on the Otago Peninsula in early November and for a short time it appeared that the disease was confined to that location, prompting speculation about point sources of infection and Dunedin's Lawyers Head sewerage outfall being viewed with an increased level of suspicion. However that theory was discounted as cases were soon reported everywhere between Oamaru and Stewart Island. Interestingly the disease was not reported from Codfish Island or the subantarctic islands.
The disease had the largest impact on chicks under two weeks of age and under 500g. Autopsy of the chicks by Associate Professor Maurice Alley of Massey University revealed that many of the chicks had died of starvation because the bacterial infection produced lesions in the chick's mouth and upper respiratory tract and made if difficult for the chicks to swallow. In some cases the infection had spread to the lung or inner ear. Almost 100% chicks in Otago had symptoms of the disease. Mortality varied between sites and ranged from 10-90% with the overall chick mortality estimated at 60%.
Samples taken from dead and live chicks showed the bacteria to be Corynebacterium amycolatum, a species not previously known from penguins. Swabs taken from adults also tested positive for the presence of the bacteria, but the disease was not seen in adult penguins. Swabs were also taken from blue penguins and royal albatross but, although the bacteria were present, Massey is unable to yet say if they are the same strain as seen affecting the yellow-eyes. It seems that the corynebacteria are a large but poorly understood group. Many species of animal have their own (normally relatively benign) species of Corynebacteria, and humans are subject to infection by several species (including C. amycolatum), and one species (C. diphtheriae) is the cause of diptheria, a disease often fatal in young humans. The disease seen in yellow-eyes has similar oral symptoms to diptheria, resulting in it being sometimes referred to as 'avian diptheria', but Massey have named the disease "diptheritic stomatitis" (meaning a diptheria-like condition of the mouth), which is not much of a consolation for those of us who've just learnt to pronounce Corynebacterium.
The bacteria proved sensitive to broad-spectrum antibiotics and courses of up to 10 days were given to chicks at some of the more easily accessible sites. Treatment with antibiotics had varying success. While the supplementary feeding may have improved the chicks' chances, it appears the age of the chick at the onset of the disease was the critical factor. Chicks less than 14 days old and 500 g bodyweight had a low survival rate. Chicks that survived the disease fledged at good weights and showed no ill effects.
Just what caused the disease is a mystery. It is likely that the bacteria are present in the environment all the time and that there is some other factor that triggers the disease. Massey are searching for other disease agents (eg a virus) that may have allowed the bacteria to bloom, but other possible factors include environmental conditions (weather) and food availability. The fact that this is the second time the disease has been seen in Otago (it was first seen two years ago) and that the chick deaths seen at Stewart Island in the last two years may be related, could provide some clues to the disease triggers.
Aside from the impact on the production of chicks, there was also an economic impact for tour operators on the Otago Peninsula and at Oamaru. As nests failed, adult penguins spent less time ashore, providing little for operators to show their clients.
A workshop on the disease outbreak was hosted by the Trust in early April. All those involved in the outbreak, including vets, scientists, penguin monitors, landowners and DoC, were present to share information, discuss lessons learnt and plan for the future.
Attendees at the workshop agreed to:
- set directions and priorities for future research by Massey
- set recommendations for the collection and delivery of better quality samples
- the need for the development of treatment standards (methods, drug, decision trees and training)
- the need for the standardisation of data recording
- the need to maintain hygiene standards when working with wildlife
- the importance of keeping the community informed of developments in their area
- the need for research into the circumstances surrounding the outbreak, e.g. environmental factors