The sudden death of 200,000 critically endangered saiga antelopes was caused by unusual environmental conditions, it has emerged.
Professor Eric Morgan, a Professor at the Institute for Global Food Security, Queen’s University Belfast, along with an interdisciplinary, international research team has investigated the sudden death of over 200,000 saiga antelopes (more than 80% of the affected population and more than 60% of the global population of this species) in Kazakhstan in May 2015, which left the world baffled.
In just three weeks, entire herds of tens of thousands of healthy animals died of haemorrhagic septicaemia across an area larger than the UK and Ireland combined. These deaths were caused by Pasteurella multocida bacteria.
But this pathogen most probably was living harmlessly in the saigas’ tonsils up to this point, so what caused this sudden dramatic die-off?
New research by the international research team has shown that many separate (and independently harmless) factors contributed to this extraordinary phenomenon. In particular, climatic factors such as increased humidity and raised air temperatures in the days before the deaths apparently triggered opportunistic bacterial invasion of the blood stream, causing septicaemia (blood poisoning).
By studying previous die-offs in saiga antelope populations, the researchers were able to uncover patterns and show that the probability of sudden die-offs increases when the weather is humid and warm in spring, as was the case in 2015.
The research also shows that these very large mass mortalities, which have been observed in saiga antelopes before (including in 2015 and twice during the 1980s), are unprecedented in other large mammal species and tend to occur during calving.
This species invests a lot in reproduction, so that it can persist in such an extreme continental environment where temperatures plummet to below minus 40 degrees Celsius in winter or rise to above 40 Celsius in summer, with food scarce and wolves prowling.
In fact, it bears the largest calves of any ungulate species relative to the mother’s size; this allows the calves to develop quickly and follow their mothers on their migrations, but also means that females are physiologically stressed during calving.
With this strategy, high levels of mortality are to be expected, but the species’ recent history suggests that die-offs are occurring more frequently, potentially making the species more vulnerable to extinction. This includes, most recently, losses of 60% of the unique, endemic Mongolian saiga sub-species in 2017 from a virus infection spilling over from livestock.
High levels of poaching since the 1990s have also been a major factor in depleting the species, while increasing levels of infrastructure development (from railways, roads and fences) threaten to fragment their habitat and interfere with their migrations. With all these threats, it is possible that another mass die-off from disease could reduce numbers to a level where recovery is no longer possible.
This needs to be countered by an integrated approach to tackling the threats facing the species, which is ongoing under the Convention on Migratory Species’ action plan for the species.
Professor Eric Morgan, Professor at the Institute for Global Food Security, Queen’s University said, “These die-offs were devastating to the saiga antelope, and remind us of the need to support the conservation of large and healthy wildlife populations, able to survive such events. This will require careful planning of human activities, including production of food for growing human populations, to allow for the survival of the ecosystems that ultimately sustain us. These issues are global and urgent, and getting to the bottom of the complex cause of this outbreak showed the value of international teamwork.”
This research was conducted as part of a wide international collaboration, adopting a ‘One Health’ approach – looking at the wildlife, livestock, environmental and human impacts that have driven disease emergence in saiga populations.
The ‘One Health’ approach reflects the values and ethos of The Institute for Global Food Security (IGFS), a Global Research Institute within Queen’s University.
Professor Morgan added, “Research at Queen’s University is tackling the huge global issues of food security and the links between animal disease and the natural environment. This shocking outbreak showed that animals are vulnerable to devastating disease triggered by environmental change, and this could apply also to livestock.
"The research involved a large international team. Although assembled around tragic events, it was encouraging to see that collaboration work so well, and to have Queen’s play an important role in the investigation of a globally important disease event. In future, integrated consideration of environment, conservation and farming should become the standard for disease research.”
Adopting such a holistic approach has enabled the research team to understand the wider significance of die-offs in saiga populations, beyond simply the immediate causes of the 2015 epidemic.