Whenever a disease spread quickly and at unexpected rates among non-human animal species, it is called an epizootic. HPAI avian influenza is considered an epizootic, as it is both unusual and causes serious illness.
In contrast, low levels of fairly benign LPAI (low pathogenic) influenza viruses commonly found in wild birds are considered enzootic - or endemic in an animal population.
In addition to avian flu, we've looked as some significant epizootic events in history - but none was probably more dramatic than the great equine epizootic of 1872 (see Morens and Taubenberger: A New Look At The Panzootic Of 1872) which has been theorized to have been linked to concurrent outbreaks of poultry deaths across the country,
Ian York author of the Mystery Rays blog described the impact of this incident back in December of 2009 in a blog called Influenza before 1918, part II: 1872. A brief excerpt:
Without horses, business slammed to a halt; the mail didn't run, groceries didn't reach the cities, crops weren't harvested or transported. After a few weeks, most of the horses recovered and business followed, but the epizootic swept across the country (intensely tracked by the newspapers of the day, warning each city in turn that it was going to be attacked), finally fizzling out the following summer in British Columbia.
Epizootics such as the 1872 event can cause heavy losses, but rarely are entire species threatened.
Over the past two weeks, however, an unidentified disease has claimed the lives of roughly half the world's Saiga Antelopes - an endangered species found primarily in the north-central region of Kazakhstan. While they numbered in the millions a few short years ago, the last estimate put their number at about 200,000.
In the past two weeks, more than 100,000 of those have reportedly died.
The following is an early report from the UNEP/CMS.
Just a little more than a week later and the New Scientist is carrying the following report:
Bonn, 19 May 2015 - About 10,000 saigas have been found dead in Amangeldy district of the Kostanay region in Central Kazakhstan. The Ministry of Agriculture of Kazakhstan reported the first mortality cases on the 12 May, and since then the numbers of dead animals discovered have been increasing. Currently the area affected covers about 16,000 hectares, within the range of the saiga’s Betpak Dala population, the largest in Kazakhstan. The state authorities are investigating the situation in the field, collecting samples for further analysis of the causes and burying the carcasses.
16:42 27 May 2015 by Andy Coghlan
The death toll of iconic saiga antelopes in central Asia has soared to around 120,000, almost half of the world's remaining population, according to unofficial estimates. Today vets and scientists investigating the catastrophe presented their results so far to government officials in Kazakhstan, where the animals are dying.
"The current official figure is 85,000, but we are hearing unofficial estimates in excess of 100,000, approaching 120,000," says Aline Kühl-Stenzel of the UN Convention on Migratory Species.
(Continue . . . )
As the article explains, several possible etiologies are under investigation; hemolytic septicemia, epizootic hemorrhagic disease, and toxemia caused by clostridia bacteria.
In recent years Saiga antelopes have been felled by much smaller, but still significant outbreaks attributed to FMD or hemorrhagic septicemia (pasteurellosis).
None have come close to the size and speed of the current outbreak. We will hopefully learn more once laboratory results are in.