Antarctic Wildlife Diseases

Infectious disease is one of the main causes of mortality in wild animals worldwide.  Moreover, pathogens and parasites can cause sub-lethal effects to hosts, such as the reduction in reproductive output by physiological changes, which can in turn contribute to population decline. Infections can also interact with toxins (such as persistent organic pollutants) (1) increasing the host vulnerability to secondary infections from other pathogens and parasites, or reduce the ability of animals to accommodate to extreme environmental changes. Emerging infectious disease also presents a significant threat to populations, particularly when a species is unable to mount an effective immune response to novel pathogens with which it did not co-evolve.

A broad variety of pathogens and infectious diseases has been reported in seabirds in Antarctica and the Sub-Antarctic, either through direct evidence of infection or through serological evidence (Table 1).

Table 1: Pathogens, and potential pathogenic microorganisms recorded in seabirds from the Antarctic (above 60ºS)(A) or Sub-Antarctic (below 60ºS)(S). References in square brackets.

Knowledge of infectious diseases in marine mammals is less extensive than for seabirds and is restricted to pinnipeds (8), with no information on cetaceans in the Southern Ocean. Salmonella has been described in numerous Antarctic pinniped species (9, 10), Cryptosporidium was detected in a single elephant seal faecal sample (11), and Sealpox Virus has been reported in a Weddell seal (3).

The presence of antibodies against several pathogens has been demonstrated in pinnipeds in Antarctica and the Sub-Antarctic (Table 2).

Table 2:  Pathogens and potential pathogenic microorganisms recorded in marine mammals from the Antarctic (above 60ºS) (A) or Sub-Antarctic (below 60ºS) (S). References in square brackets.

Mass mortality events are apparently unusual in Antarctica, which suggests that: a) disease outbreaks and health problems have posed a very low risk to Antarctic wildlife, and/or b) the effects of infectious diseases have been underestimated due to the scarcity of studies and lack of a systematic long-term surveillance for mortality events. To date, only eight recorded mortality events probably caused by diseases have been reported, mainly involving seabirds (Table 3).

Table 3: Mass mortality events recorded in Antarctica region in seabirds and marine mammals.

However, in some cases it is difficult to attribute mortality directly to disease, as in the majority of circumstances, limited or no diagnostic investigations have been undertaken.

The introduction of pathogens to Antarctic wildlife may arise from two main sources: a) migratory species that disperse over great distances between the Antarctic and other areas (20, 21) (for example, albatrosses, polar skuas, giant petrels, Arctic terns, elephant seals, Antarctic fur seals); or b) through human activity (scientific and associated logistic activities and tourism). Multiple pathways for the introduction of non-endemic species, including direct transport and inadequate management of waste and sewage from ships, research stations and field camps, have the potential to introduce micro-organisms (22). Introduction of novel pathogens through human activities must be one of the principal concerns for long-term conservation of the Antarctic ecosystem. Human presence has increased in the last decades with recent data (2013-2014) from IAATO and COMNAP showing that 37,405 tourists visited Antarctica and at least 4462 researchers plus logistics staff worked in the region in one year. Given the higher density of activities in the Antarctic Peninsula and Ross Sea regions, these areas could have the higher risk of novel pathogens introduction if the pathways are similar to those for the introduction of invasive plant propagules (23). Special attention also needs to be paid to the risk of anthropogenic spread of potential pathogens between locations within Antarctica.

Monitoring the health of Antarctic wildlife is a necessary part of good environmental stewardship. Parties have previously recognised the importance of wildlife disease research and the importance of establishing co-ordinated international programmes of research and monitoring, as yet without success. Current knowledge on Antarctic wildlife diseases is limited to only a few research groups studying organisms in their areas of expertise, without any overall framework.  This results in a bias towards disease-related information from small geographical regions or on a limited number of species, for example penguins in the South Shetland Islands, with little known or observed data for much of the continent. To address knowledge gaps in Antarctic wildlife health and disease status a working group for health monitoring of Antarctic species has been created within the SCAR Expert Group of Birds and Marine Mammals (EGBAMM).

While there are existing tools to assess disease risks for wildlife, for Antarctic wildlife the fragmented and limited nature of available disease information makes their use impossible. Effective health monitoring encompassing long-term studies on a broader number of species and populations at selected sites, including ecological information on Antarctic wildlife, their pathogens and parasites, and resident microbiome, are all required to understand potential risks. The establishment of tissue banks would allow material to be reanalysed in future with new methods whilst the application of genomic techniques could substantially change our understanding of the pathogen/host interactions.