INTRODUCTION
Peste des petits ruminants (PPR) is an acute, serious, contact
infectious disease caused by peste des petits ruminants virus (PPRV)
belonging to the genus of morbilliviruses(Li et al., 2018). PPR
is characterized by sudden depression, high fever, anorexia, nasal and
ocular discharge, mouth erosive lesions, pneumonia and severe
diarrhea(Alemu et al., 2019, Alfred et al., 2018). PPRV is mainly
transmitted through direct or
indirect contact, and the incubation
period is typically 2-7 days(Kumar et al., 2014). The morbidity rate can
reach 100% with a high case fatality with the acute form of
disease(Parida et al., 2016). Both
the domestic and wild ruminants are susceptible to PPRV, while the
goats and sheep are the most susceptible hosts. The pig was recorded to
be infected(Nawathe and Taylor, 1979){Shabbir, 2020 #5;Nawathe, 1979
#16}. At present, the prevention and control measures for PPRV are
mainly based on herd immunity by live attenuated vaccine in endemic
area(Enchery et al., 2019). In PPR free area, slaughtering of infected
animals, environmental sanitation sustainability, prohibition of animal
transportation and quarantine are measures adopted
generally(Couacy-Hymann et al., 1995). Although many measures have been
taken in prevention, PPR is still widely distributed worldwide(Banyard
et al., 2010). Above 63% of the domestic small ruminants in the world
remains under the threat of PPR, and the risk to wildlife is
unknown(Baazizi et al., 2017). The
livestock industry has been greatly ruined or decreased by PPR in the
affected countries and regions, and even jeopardized the food security
system, causing economic recession(Baron et al., 2017). PPR has
attracted the attention of international organizations and relevant
national authorities, which is listed as a transboundary animal disease
need to be controlled and eradicated by FAO and OIE(OIE and FAO, 2015a).
PPR was first discovered in the early
1940s in Cote d’I voire and then expanded cross over nearly the whole
world(OIE and FAO, 2015b). Now around 70 countries have either reported
infection to the OIE or are suspected of being infected(Shaila et al.,
1996). Of these, more than 60% are in Africa and the others are in Asia
and the Middle East. There are another 50 countries are considered to be
at risk for PPR(Liu et al., 2018). In China PPR first outbreak in the
Ngari region of Tibet in 2007 with a 5751 death of sheep and goats
accounting for 16% motility rate(Wang et al., 2009). This epidemic was
effectively controlled by ways combing slaughter, mass immunity and
restriction of animal transportation. However, PPR re-emerged in
Xinjiang, China in December 2013 and rapidly spread to much of China in
the first half of 2014 through the large live-sheep trading network(Bao
et al., 2014). 23 provinces,
autonomous regions and municipalities (P/A/M) of PR China (PR China is
administratively divided into 34 P/A/M) have been involved into this
pandemic and caused a heavy loss of sheep and goat industry of China(Bao
et al., 2017).
There are four known lineages of PPRV (I-IV). The lineage I and II are
distributed in the West Africa; the lineage III are popular in East
Africa, the Arabian Peninsula and southern India; the lineage IV is
popular in the Arabian Peninsula, the Middle East, South Asia and
Africa(Kwiatek and Olivier, 2011). Phylogenetic analysis revealed that
the Chinese 2013–2014 strains and Tibet strains isolated previously in
2007, both belonged to lineage IV but in different sub-branches.
Nevertheless, compared with the Tibet strains, the Chinese 2013–2014
strains shared high degree of genetic homology with those from Pakistan
and Tajikistan(Xia et al., 2016). As
early as 1991, an outbreak of PPR was reported in Pakistan bordering
Xinjiang(Anees et al., 2013). Similarly, outbreaks of PPR were reported
in Tajikistan bordering Xinjiang in March 2004, and phylogenetic
analysis indicated that the isolates belonged to lineage IV as
well(Kwiatek et al., 2007). So we consequently speculated that the
Chinese PPR epidemic was spread more possibly from bordering countries
into China.
The part of the western border of China (N29°54 ’- 44°32’) borders 7
countries, 6 of which are PPR endemic countries (India, Pakistan,
Afghanistan, Tajikistan, Kazakhstan
and Russia). Though the epidemiological situation in Kyrgyzstan, another
neighbor, is not clear, serum positive reports of PPR are existed. In
the border areas of China-northern India, China-Pakistan,
China-Afghanistan, China-Tajikistan, China-Kyrgyzstan and
China-Kazakhstan, crisscrossed huge high mountains and low valleys is
the dominant landform. Since ancient times to now, the nomadic nations
constitute the main part of local population. Therefore, transboundary
grazing is the local typical style of production and life and domestic
ruminant exchanges and migration frequently(Padhi and Ma,
2014). Due to the existence of large
area of no man’s land and harsh environment, border control between
countries is always difficult to be fully realized, and transboundary
grazing is still widespread until 1990s here. Moreover, in this region
many wildlife protected areas host a large number of wild ruminants
(Ovis ammon , Capra ibex , Gazella subgutturosa ,Procapra picticaudata , Pantholops hodgsonii ,Pseudois nayaur ), which provide a big sum of carriers of PPRV for
transboundary spreading(Li et al., 2017). Wild ruminants, goats and
sheep all are capable to cross the barbed wire mesh on the boundary in
the need of foraging, migration and other activities. Also due to the
imperfect establishment of the barbed wire mesh in some areas the
transboundary spread of PPR has become natural(Liu et al., 2020).
Combined with the above possibilities, all susceptible animals in this
area contact frequently by common utilization of water sources, food and
habitat, so the virus is particularly easy to spread from one side to
another(Rahman et al., 2019).
In 2013, after the PPR epidemic which caused huge economic losses to
China’s sheep industry, in December 2015, the Ministry of Agriculture of
China officially issued the National Plan for the Eradication of Peste
des Petits Ruminants (2016-2020). It planned that by 2020, except
constructing a 30 km width immune isolation belt in the border counties
and plantations along the border line, the whole nation is going to
achieve the goal of a national wide ”free zone without immunization”.
Considering the impossibility of immunization of wild ruminants, the
construction of the free zone should be based on cutting off all
possible routes of transmission and eliminating imported cases firstly.
In ecology, resistance coefficient is used to express the willingness of
a species to pass through a specific landscape unit or the suitability
index of the landscape unit for a species(Zeller et al., 2012). In the
process of passing through a specific environment, if the energy and
time consumption of individuals is small and the mortality rate is low,
it means that the environmental resistance is low(Hashmi et al., 2017).
the possibility of animals passing through the area is high. Then the
landscape unit is regarded as a corridor (migration paths)(F. et al.,
2003). We assume that there are natural migration paths for wild and
domestic ruminants in the N 29°54’-44°32’section of the western border
of China, and transboundary spreading of PPRV exist. Therefore, this
study mainly focuses on the risk analysis of PPR and the verification of
transboundary paths in the above-mentioned multinational border areas,
and try to block the local transboundary communication of PPR, so as to
provide valuable suggestions for the prevention and control for border
areas worldwide.