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201407Nov21:14

Could a dog dis­ease wipe out an entire tiger population?

Infor­ma­tion
pub­lished 07 Novem­ber 2014 | mod­i­fied 07 Novem­ber 2014
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Amur tiger at Hamburg ZooAlong with the pres­sures of habi­tat loss, poach­ing and deple­tion of prey species, a new threat to tiger pop­u­la­tions in the wild has sur­faced in the form of dog dis­ease, specif­i­cally, canine dis­tem­per virus (CDV). Accord­ing to a new study from the Wildlife Con­ser­va­tion Soci­ety (WCS) and its part­ners, CDV has the poten­tial to be a sig­nif­i­cant dri­ver in push­ing the ani­mals toward extinction.

CDV has recently been shown to cause fatal neu­ro­log­i­cal dis­ease in the Crit­i­cally Endan­gered Amur tiger (Pan­thera tigris altaica) and has killed at least 1% of the Amur tigers since 2009. A wor­ry­ing symp­tom of canine dis­tem­per in tigers is that the tiger seems to lose its fear for human beings. This increases the chance of human-​tiger con­flicts and leaves the tiger easy prey for poachers.

An exam­ple can be seen in this video, shot on the road between the vil­lage of Vyazemsk and the City of Bikin, Khabarovsk Krai:


Now, the long-​term impacts on tiger pop­u­la­tions has been stud­ied for the first time. The authors eval­u­ated these impacts on the Amur tiger pop­u­la­tion in Russia’s Sikhote-​Alin Bios­phere Zapoved­nik (SABZ), where tiger num­bers declined from 38 indi­vid­u­als to 9 in the years 2007 to 2012. In 2009 and 2010, six adult tigers died or dis­ap­peared from the reserve, and CDV was con­firmed in two dead tigers – lead­ing sci­en­tists to believe that CDV likely played a role in the over­all decline of the pop­u­la­tion. Joint inves­ti­ga­tions of CDV have been an ongo­ing focus of WCS and Russ­ian sci­en­tists at Sikhote-​Alin Zapoved­nik and vet­eri­nar­i­ans at the regional Pri­morye Agri­cul­tural Col­lege since its first appear­ance in tigers in 2003.

The study, pub­lished on 29 Octo­ber in the jour­nal PloS One, led to the the fol­low­ing key find­ing: Mod­el­ling shows that smaller pop­u­la­tions of tigers were found to be more vul­ner­a­ble to extinc­tion by CDV. Pop­u­la­tions con­sist­ing of 25 indi­vid­u­als were 1.65 times more likely to decline in the next 50 years when CDV was present. The results are pro­foundly dis­turb­ing for global wild tigers given that in most sites where wild tigers per­sist they are lim­ited to pop­u­la­tions of less than 25 adult breed­ing individuals.

Com­puter mod­el­ling
The sci­en­tists used com­puter mod­el­ling to sim­u­late the effects of CDV infec­tion on iso­lated tiger pop­u­la­tions of var­i­ous sizes and through a series of trans­mis­sion sce­nar­ios. These included tiger-​to-​tiger trans­mis­sion and trans­mis­sion through pre­da­tion on CDV-​infected domes­tic dogs and/​or infected wild car­ni­vores (such as foxes, rac­coon dogs and bad­gers). High and low-​risk sce­nar­ios for the model were cre­ated based on vari­a­tion in the preva­lence of CDV and the tigers’ con­tact with sources of exposure.

Results showed that CDV infec­tion increased the 50-​year extinc­tion prob­a­bil­ity of tigers in SABZ as much as 55.8 per­cent com­pared to CDV-​free pop­u­la­tions of equiv­a­lent size.

Although we knew that indi­vid­ual tigers had died from CDV in the wild, we wanted to under­stand the risk the virus presents to whole pop­u­la­tions,” said WCS vet­eri­nar­ian Mar­tin Gilbert. “Tigers are elu­sive, how­ever, and study­ing the long-​term impact of risk fac­tors is very chal­leng­ing. Our model, based on tiger ecol­ogy data col­lected over 20 years in SABZ, explored the dif­fer­ent ways that tigers might be exposed to the virus and how these impact the extinc­tion risk to tiger pop­u­la­tions over the long term.”

Dale Miquelle,WCS Rus­sia Pro­gram Direc­tor, said:

Tigers face an array of threats through­out their range, from poach­ing to com­pe­ti­tion with humans for space and for food. Con­se­quently, many tiger pop­u­la­tions have become smaller and more frag­mented, mak­ing them much more sus­cep­ti­ble to dis­eases such as CDV. While we must con­tinue to focus on the pri­mary threats of poach­ing and habi­tat destruc­tion, we now must also be pre­pared to deal with the appear­ance of such dis­eases in the future.

Research pri­or­i­ties
Pri­or­i­ties for future research, accord­ing to the authors, include iden­ti­fy­ing the domes­tic and wild car­ni­vore species that con­tribute to the CDV reser­voir, and those that are the most likely sources of infec­tion for tigers. Tigers are too rare to sus­tain the virus in the long term, so CDV must rely on more abun­dant car­ni­vore species to per­sist in the envi­ron­ment. Under­stand­ing the struc­ture of the CDV reser­voir will be a crit­i­cal first step in iden­ti­fy­ing mea­sures that might pre­vent or con­trol future outbreaks.

In addi­tion, since we now know that small tiger pop­u­la­tions are at greater risk to dis­eases such as CDV than larger pop­u­la­tions, con­ser­va­tion strate­gies focus­ing on con­nect­ed­ness between pop­u­la­tions become all the more important.



(Source: Wildlife Con­ser­va­tion Soci­ety press release, 10.11.2014)


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Goal: 7000 tigers in the wild

Tiger range countries map

Tiger map” (CC BY 2.5) by Sander­son et al., 2006.

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