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Solving the suspicious saiga silencing

Solving the suspicious saiga silencing
17 Jan
2018
Warm and humid conditions are found to be the trigger for a mysterious die-off of saiga antelopes

The Central Asian steppe, in which saiga antelopes inhabit, is renowned for being an extreme part of the world in which to live, with temperature swinging wildly from below -40°C in winter to above 40°C in summer. Add in the risks posed by hungry wolves, insecure food supplies, disease, and – of course – the ever-present threat of humans (through poaching and sprawling development), and the saiga’s continued survival, even with a growing population, is admirable. Nevertheless, their ranking of ‘critically endangered’ on the IUCN Red List is a constant reminder of the precariousness of their existence.

Yet even this harsh lifestyle had scientists unprepared for the scale of the 2015 sudden die-off of saiga antelopes, a so-called ‘Mass Mortality Event’ (MME). In only a few weeks, just as the animals were calving, over 200,000 saiga in Kazakhstan simultaneously succumbed to a lethal infection. More than 60 per cent of the global population was wiped out in a matter of days.

The culprit: the bacteria Pasteurella multocida. With an over 80 per cent mortality rate among even healthy infected individuals, the pathogen tore through entire herds, causing haemorrhagic septicaemia (blood poisoning) and imminent death.

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However, researchers reviewing the tragic incident pondered why the bacteria had taken hold and caused the MME, when it had previously been living harmlessly in the saiga’s tonsils with no signs of outbreak. What had caused the bacteria to suddenly invade the bloodstream, ruthlessly killing off entire herds?

‘The recent die-offs among saiga populations are unprecedented in large terrestrial mammals,’ reflects Richard Kock, professor in emerging diseases and lead researcher at the Royal Veterinary College. ‘The 2015 Mass Mortality Event provided the first opportunity for in-depth study, and a multidisciplinary approach has enabled great advances to be made.’

Working alongside a team of experts from a wide range of international institutions, Kock et al. identified a particular combination of climatic factors which they believe aligned to create ideal conditions for Pasteurella multocida to unleash in this way. In particular, increased humidity and raised air temperatures indicated that such phenomenons are most likely to occur when the weather is humid and warm, as happened prior to the 2015 MME.

These results suggest that previous saiga antelope MMEs, such as during the 1980s, may have been triggered by similar conditions. The perilous existence of the saiga means these MMEs are continually making the species more vulnerable to extinction (the current population is a shadow of the estimated 1,250,000 during the 1970s).

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‘The use of data from vets, biologists, botanists, ecologists and laboratory scientists is helping improve our understanding of the risk factors leading to MMEs – which was beneficial when another MME occurred, this time in Mongolia in 2017,’ explains Kock. ‘Improved knowledge of disease in saiga, in the context of climate change, livestock interactions and landscape changes, is vital to planning conservation measures for the species’ long-term survival.’

‘MMEs are a major threat for the saiga antelope and can wipe out many years of conservation work and saiga population growth in just a few days,’ adds Steffen Zuther, project manager for Kazakhstan at the Frankfurt Zoological Society and Association for the Conservation of Biodiversity of Kazakhstan. ‘Therefore, understanding these MMEs, what triggers them and what can be done to combat them is extremely important to develop effective saiga conservation strategies. The triggering of such MMEs in saiga through weather conditions shows that not much can be done to prevent them occurring, and therefore how important it is to maintain saiga populations of sufficient size for the species to survive such catastrophes.’

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