A virus amongst the penguins
Despite its perceived isolation, Antarctica has been invaded by many non-native species, including pathogens. It is not surprising that wildlife in Antarctica could acquire parasites and diseases, but recent evidence of a common poultry virus in emperor penguins has captured scientific interest. Dr Gary Miller and his colleagues have been investigating the origin, spread and nature of the virus in emperor penguins at Auster Rookery.
Diseases and parasites have been detected in Antarctic wildlife populations for as long as scientists have observed and collected samples from them. However, it was not until the 1997 discovery of antibodies to Infectious Bursal Disease Virus (IBDV) in a high percentage of emperor penguin (Aptenodytes forsteri) chicks at Auster Rookery (through research led by Australian Antarctic Division veterinary biologist, Heather Gardner), that disease in Antarctic wildlife was connected with the presence of people in Antarctica.
Dr Gardner and her colleagues suggested that because Auster Rookery is relatively close to Mawson station, the penguins may have been exposed to this common poultry disease through contact with humans or their cargo. In support of this theory, they found no antibodies to IBDV in adult Adélie penguins from Edmonson Point – a more remote colony in the Ross Sea.
However, it is difficult to reconcile that a high percentage of emperor penguin chicks are exposed to IBDV through human contact when you look at their natural history. Emperor penguin colonies live on floating sea ice, and their eggs hatch in the middle of winter, when there is no transport of goods from outside the continent and few personnel are at Mawson station. During the summer months, when most human activity occurs, the penguins are away at sea. In many years the ice from the colony area melts completely, so there is no environment in which the virus can live.
Given these findings and a growing concern for threats to the Antarctic environment, the Australian Antarctic Division hosted a workshop in 1998 to discuss the threats to Antarctic wildlife posed by the possible introduction of diseases. Discussions at the workshop showed that there is a need to understand how diseases persist and the effects they may have on populations. My colleague, Professor Geoff Shellam, and I participated in the workshop and have since been studying the presence of various pathogens in Adélie penguins, South Polar skuas, and now, emperor penguins in Antarctica.
From our recent work we know that adult South Polar skuas in the Davis area are exposed to more diseases than the Adélie penguins there, and at higher rates. We believe that migratory birds, particularly South Polar skuas, may transmit disease to other Antarctic bird species. Because skuas travel outside the Antarctic ecosystem during the austral winter and are well known scavengers and predators, they may pick up diseases outside Antarctica. Their close association with penguins therefore creates an ideal opportunity for transmission of exotic disease to the penguins.
Our more recent testing revealed 96% of emperor penguin chicks near Edmonson Point had antibodies to IBDV. Similar high prevalences of antibodies to IBDV were found in emperor penguin chicks at Auster Rookery (93%) and Amanda Bay (100%). These results contradict the theory arising out of the 1997 research that IBDV is less prevalent in isolated colonies of emperor penguins. As research has also shown that Adélie penguins in the Vestfold Hills have no antibodies to IBDV, but South Polar skuas do (7–17% in different years), there are now more questions than answers.
To address this issue we designed our current project with the primary goal to determine the status and origin of diseases in emperor penguins at Auster Rookery. We have focused on IBDV, but will also test the penguins for a suite of other common poultry diseases, such as avian influenza, Newcastle disease and some common bacteria.The plan is to capture and sample both adults and chicks at four times over winter, to isolate and describe the pathogens. Each penguin will be weighed and various samples taken – two fecal swabs (one for viruses, one for bacteria), one throat swab, and blood from a vein in the flipper – using methods approved by the Antarctic Animal Ethics Committee. Importantly, we will investigate the role that adults play in transmitting IBDV to their chicks.
As this article goes to press, we are most of the way through our sampling effort. The first samples were taken in May during the courtship and egg-laying period, when the birds were in peak condition, having just returned from several months foraging. The second samples were taken from adults in early August, when the chicks were just hatching. These two sets of samples will allow us to determine the disease status of adults before there is a chance to transmit pathogens to their chicks.
The third samples were taken from the chicks in early October, when they were old enough to be left alone at the colony. This is a particularly important sample set because it is the first one of chicks taken before skuas and giant petrels (potential disease vectors) return to the area.
The final samples will be taken from adults and chicks in the early summer. This will coincide with the sampling time from the 1997 study and will occur after skuas and giant petrels have returned to the area.This sampling regime should allow us to determine when IBDV first appears in the colony and how the chicks become exposed to it. The expected high prevalence of IBDV indicates that we should be able to isolate the virus and discover its origin by means of RNA (ribonucleic acid) sequencing. No IBDV has been isolated from any Antarctic species, but it is known that IBDV can infect penguins in captivity. In 2002, researchers isolated an avian Birnavirus from captive African black-footed penguins (Spheniscus demersus) and macaroni penguins (Eudyptes chrysolophus). Those isolates were later identified as IBDV.
If we can isolate IBDV and sequence the RNA, we will be able to completely characterise the virus. The RNA sequence will tell us if it is the same as other known strains of IBDV, or whether the Antarctic variety is different. It is safe to say that this is an important key to the puzzle of how disease gets to Antarctica.
We will have to wait until we return to Australia in March to complete our analyses.
We will test blood serum samples for the presence of antibodies to IBDV and a number of other viruses in the virology lab at the Western Australian Department of Agriculture. We will also culture a fecal swab for a few important bacteria at the University of Western Australia and we will send fecal and throat swabs for RNA sequencing to Dr Daral Jackwood, an expert on IBDV at Ohio State University in the United States. We should have results by June 2009 – about the time the emperor penguins start the breeding cycle again.
Even if our results indicate that the IBDV in emperor penguins has been in Antarctica for some time and, therefore, is not related to human intervention, the study will provide an important, detailed description of the types of pathogens to which the penguins are being exposed. As natural and human-mediated changes to the Antarctic environment continue to occur, it is important to understand the current status and dynamics of disease in Antarctic penguins. Our project, in combination with the earlier study on IBDV, will provide a baseline that can be used to compare any disease-related changes in the future.
GARY MILLER, ROBYN MUNDY and GEOFFREY SHELLAM
University of Western Australia