NEW REPORT IS THE FIRST PUBLISHED STUDY TO CONFIRM DISTEMPER AS A KILLER OF AMUR TIGERS
NEW YORK (August 14, 2013) – The first-ever published study to genetically characterize canine distemper virus (CDV) in tigers confirms that CDV acts as both a direct and indirect cause of death in the endangered big cats in the Russian Far East (RFE). The study was conducted by health experts from the Wildlife Conservation Society’s Bronx Zoo (WCS), the Primorskaya State Agricultural Academy, Sikhote-Alin Reserve in Russia,Ussurisk Department of Health Services and Terney County Veterinary Services in Russia, and the Albert Einstein College (AEC) of Medicine of Yeshiva University.
Over the course of the investigation, scientists from WCS and the Russian veterinary institutions performed a series of tests on tissues from five adult tigers that died or were euthanized in 2001, 2004, and 2010after exhibiting abnormal neurologic signs. Microscopic examination using routine and special immunologic staining of brain tissue (available from two of the tigers) were highly suggestive of CDV infection. PCR, a highly sensitive and specific test, was used to genetically confirm that CDV was the cause of disease and death in these two tigers and had infected a third. It was also noted that during the study, three tiger cubs died as a result of abandonment by their CDV-infected mother.
The study, Canine Distemper Virus: An emerging disease in wild endangered Amur tigers, appears online in the current edition of mBIO (http://bit.ly/mbiotip0813b).
The scientists began to become concerned about CDV as an emerging threat in wild Amur tigers in response to abnormal tiger behavior that was initially observed in 2001. This included incidences of the normally reclusive Amur tigers—which number less than 500 in the wild—uncharacteristically walking into villages and onto roadways, and showing a complete lack of fear of humans and absence of response to external stimuli.
It remains unclear how tigers may have contracted CDV and whether it originated in another wild animal species or in domestic dogs— both of which can act as reservoirs for the infection. Distemper, a disease of global importance, is the second most common cause of infectious disease death in domestic dogs and a significant threat in endangered and non-endangered wildlife. In the mid-1990s, distemper infection killed nearly a third of the lions in the Serengeti ecosystem. It has also caused significant mortality events in Baikal seals, contributed to the near extinction of the Santa Catalina Island fox, and remains a constant threat to the survival of the endangered black-footed ferret in the United States.
Recent reports suggest fewer than 3,500 tigers (all subspecies) remain in the wild worldwide. Of those, approximately 1,000 are breeding females. Poaching, loss of prey and habitat fragmentation all ontribute to tiger decline. CDV, an infectious disease, now must also be added to that list as a potential threat. “We now know that in 2010 alone CDV was the direct or indirect cause of death in approximately one percent of the Amur tiger population. However, these are only the cases we know about and we suspect more undetected deaths have occurred,” said Denise McAloose, WCS’s Head Pathologist.
“At this point, we do not know if canine distemper is a rarity in the system, or common enough to affect population dynamics of the Amur tiger,” said Dale Miquelle, WCS Director of Russia Programs. “But the dramatic decline of tigers in Sikhote-Alin Reserve coincided with diagnosis of the disease in at least one animal there, a reproductive female whose three cubs died after being abandoned by their sick mother, so disease cannot be ruled out as a factor that can depress tiger numbers.
“This is an important discovery,” said Irina Korotkova of the Primorskaya Agricultural Academy. “Confirmation of this disease in wild tigers will change the way we understand this disease and change the way we think about the influences of diseases on tigers.
Since no incidences of Amur tigers exhibiting abnormal behavior before 2001 had ever been observed, the scientists suspect that tiger CDV is an emerging disease and a new threat to tiger survival. The authors also note that the location of positive cases over an expansive geographic area suggests CDV is widely distributed across tiger range.
Identifying the reservoir species and CDV strains that are transmissible to/among wildlife species is essential for guiding conservation efforts. Dr. Tracie Seimon, lead author of the study and Molecular Scientist from the WCS Zoological Health Program said, "Now that we have the genetic fingerprint of the virus in tigers, we can search for a genetic match in other species that carry and spread the virus, for example domestic dogs or foxes, to determine source of infection for tigers.
WCS is currently working with staff from the Primorskaya Agriculture Academy and other partners to establish a wildlife lab in Ussuriisk to facilitate local diagnostic testing, although it will take several years until the lab is adequately funded and fully functional.
“Tigers exist across Asia mostly in small, isolated populations, and because of their small size, each of these populations is highly susceptible to a potential disease outbreak,” said Dale Miquelle. “To date, conservationists have not focused on the threat of disease, so we really know very little about how it may have affected tiger populations in the past. But the results of this research are a ‘wake-up’ call. In addition to the major threats of poaching and habitat loss, we must be attentive to the potential impact that disease may have on tiger populations.”