Emerging pathogens of the Antarctic

Research into the emerging pathogens of the Antarctic is in its infancy, but some research has had interesting findings concerning the increasing prevalence and virulence of pathogens and increasing susceptibility of the endemic environment. Seven novel strains of Avulavirus, part of the Paramyxoviridae family have been discovered in penguin populations in Antarctica.⁴² Even where territorial claims are unsettled or ‘frozen’, spread of disease by water or aerosol transmission, or even within migration hosts can still occur. Neira et al. reports that Avulavirus was found in Gentoo penguins (Pygoscelis papua) and Adélie penguins (Pygoscelis adeliae) as part of the epidemiological surveillance of avian influenza in 2014-2016, a highly virulent virus affecting poultry stock globally.⁴³ The three new species have been named Antarctic penguin virus A (APVA), Antarctic penguin virus B (APVB), and Antarctic penguin virus C (APVC).⁴⁴ Four additional species were found and reported last year and named avulavirus 17, 18, 19, and 10-like.⁴⁵ Newcastle Disease Virus (NDV), another fatal poultry disease, has also been found in penguins in Antarctica.⁴⁶

Antigenic variation in situ

Clade analysis of Octadecabacter spp. shows genetic differences even between those species in the Arctic and those in the Antarctic. Where

Octadecabacter arcticus resides in the polar North, O. antarcticus resides in the South. The Octadecabacter are bipolar and are phyloge-netically linked.⁴⁷ Their psychrophilic lifestyle indicates that transmission via a “transit over the warm surface waters of the equator is unlikely”⁴⁸ although transmissibility via the colder and deeper water currents could be a possible transport mechanism.⁴⁹

Evolutionary adaptation to polar environments also may have genetic disadvantages for a warming climate. The survival of noto-thenioids, a dominant suborder of Southern ocean fish⁵⁰ historically has depended on its ability to evolve in waters colder and with high oxygen concentration.⁵¹ Part of this response may have been the deletion of a heat-shock response in the Antarctic nototh-enioids, which occurs in temperate notothenioids.⁵² Notothenioids are stenothermal, and have reduced heat shock response which lowers their resilience to change: however they also have duplicate genes⁵³ contributing to improved fitness where up-regulation is specific to the cold pressures of the Antarctic environment.⁵⁴ Icefish have no haemoglobin, losing an oxygen carrier⁵⁵ and this “shift from Hb-mediated oxygen transport and delivery to mechanisms based on diffusion may cause higher vulnerability of icefish to warmer temperatures. This feature would be deleterious, if not lethal, in warmer waters.”⁵⁶ Thus, genetic adaptations can be positive or negative.

Polaromonas spp. are common in high altitude samples collected from air, snow, glacier and ice and have been linked to polar environments, where at least three different high latitude polar locations have been identified as hosting them.⁵⁷ The species contains the gene hipA leaving a question of survival in a dormant state, enabling localised high latitude survival at the Poles (ibid.). The genus rapidly evolve through horizontal gene transfer enabling adaptation to freezing, thawing, drying, and movement.⁵⁸

Virulence factors

Virulence factors are those by which microorganisms become pathogenic or invasiveness to health. Examining avulavirus in Antarctica, of which seven novel species have been found in the last five years,⁵⁹ still has not resulted in understanding its non-pathogenic (non-disease-causing) virulence factors completely. The results are suggestive of penguins being a central reservoir of several species of the avulavirus with some indication of distinct clades in distinct locations, indicating possibly genetic co-evolution with penguin populations, and that the viruses from these reservoirs can infect other avian migratory species.⁶⁰ Conversely, virulence factors have been identified from Antarctic samples of E. Coli relating to pathogenic capacity in the alimentary tract (called enteropathogenic E. coli or EPEC).⁶¹ One virulence factor known as the ‘eae gene isolate’ which is enteropathogenic has been specifically identified. Yet how and when this virulence factors became part of the commensal microbiota of marine mammals is not yet known, but may involve possible geographic movement or association with human waste, as E. Coli is a human commensal, either from other human inhabited places or from human presence in Antarctica.⁶²

Animal susceptibility

Animals can be susceptible in a number of ways. Either their naive status increases the risk of clinical disease manifesting once a pathogen has been infective, or the animal can demonstrate some modification or acclimation, but with immunocompromise, allowing other diseases to manifest, or reduced ability to assimilate food or convert food to energy. The high Antarctic fish species Trematomus bernacchii has demonstrated acclimation to increased water temperatures, but a reduced growth up to 84% of mass and it is hypothesised that this is due to poor food conversion efficiency.⁶³

Animal resilience, a built-in response to a particular pathogen type in the rarefied environment, can alternatively make endemic populations reservoirs. Unknown pathogens that reside in endemic species may affect trade-out, that is, trade in products coming from the polar regions. This is an understudied area. Recently, some evidence suggests that penguin species are the reservoir or maintenance species of Avian avulavirus species.⁶⁴ These viruses are not known quantities, with Wille et al. discovering a possible new species.⁶⁵ Their epidemiology is unknown though the role of the penguin appears key and it has been suggested that avulaviruses may spread into new hosts, affecting agricultural and livestock production and human health.⁶⁶ Newcastle disease virus is an avian avulavirus and has been responsible for outbreak epidemics in poultry across the world.⁶⁷ Different penguin populations have been found infected with the same species of avulavirus and so “potential carrier species, such as the kelp gull (Larus dominicanas), should be investigated. A more complete understanding of the broader geographic and host range of these viruses will enable a more accurate assessment of the potential for spread beyond Antarctica”.⁶⁸