Peste des petits ruminants (PPR) is a highly infectious viral disease of domesticated small ruminants (Gibbs et al., 1979) characterized by various clinical manifestations of respiratory and digestive nature (Libeau et al., 2014) which are mostly accompanied by ulcerative inflammations and high morbidity and mortality rates (Hammouchi et al., 2012).
The etiology of the disease PPR virus (PPRV) belongs to the genus Morbillivirus under the family Praramyxoviridae (Adams et al., 2017). The virus is enveloped, non-segmented, negative sense and single-stranded. The genomes of different isolates are of variable lengths (Chard et al., 2008). However, isolates that have genes organized in the order 3’ N–P/C/V–M–F–H–L 5’ code for 6 structural and 2 non-structural viral proteins (Bailey et al., 2005). Transmission of the virus is through the respiratory route. Infection is initiated by the surface spike-like H and F structural glycoproteins to induce virus attachment and fusion, respectively (Diallo, 1990). With the aid of the signaling activation lymphocyte molecules (SLAM, CD150) and Nectin-4 (PVRL-4) surface receptors, PPRV exploits the lymphatic and epithelial pathways to establish in vivo or in vitro replication (Pawar et al., 2008; Birch et al., 2013). However, recently, a third endothelial endocytosis pathway was described where the virus replicates potentially to deregulate 146 genes 1-hour post viral attachment and entry (Yang et al., 2018). Distinct from the other members of the group, PPRV is classified with rinderpest virus, dolphin morbillivirus, canine distemper virus, phocid distemper virus, porpoise morbillivirus and human measles morbillivirus (Barrett et al., 1991).
Primarily infecting sheep and goats, several infections and outbreaks were also reported among other host species. Infections among wild ungulates were early observed by Furley et al., 1987; Elzein et al., 2004; Kinne et al., 2010; Abubakar et al., 2011 and Bao et al., 2011. Recent outbreaks in Sagia and naïve unknown PPR-infecting wild ruminants were also reported (Pruvot et al., 2020). Apparently healthy ruminants including Oryx (Frölich et al, 2005), cattle (Anderson and McKay, 1994, El Amin and Hassan, 1999; Haroun et al., 2002; Herzog et al., 2019; Rasooli et al., 2019), buffaloes (Govindarajan et al., 1997; Balamurugan et al., 2014), camels (Ismail et al, 1992; Roger et al., 2001; Haroun et al., 2002, Abraham et al., 2005) and yaks (Li et al., 2018) were also shown positive for blood serum PPRV antibodies (Ab) suggesting natural exposure of these animals to circulating PPRV field strains. Several studies have demonstrated retrieval of the virus RNA from tissues of clinically PPR-suspected one-humped camels (Camelus dromedaries) assuming natural exposure to the virus (Khalafalla et al., 2010; Kwiatek et al., 2011; Albina et al., 2013; Zakian et al., 2016, Omani et al., 2018). Records also indicated detection of viral nucleic acid among unnatural hosts including dogs (Ratta et al., 2016); Asiatic lion (Balamurugan et al., 2012) and biting midges (Sevik and Oz, 2015) were also evidenced. Successful establishment of clinical and subclinical infections were also reported among experimentally PPRV-infected animals including camels (Fakri et al., 2018), cattle (Couacy-Hymann et al., 2007a; Sen et al., 2014) and pigs (Nawathe and Taylor, 1979; Schultz et al., 2018). In vitro, PPRV isolates have shown to have high affinity to potentially replicate into many cell cultures and cell lines including lamb kidney cell culture (Begum et al, 2020), Vero cell lines (Kumar et al., 2016), Marmoset B95a cell lines (Sreenivasa et al., 2006), Monkey CV1 cell lines (Adombi et al., 2011), and murine 10T1/2 cell lines (Comerlato et al., 2020). However, with a characteristic to only support replication of virulent isolates, 10T1/2 is recommended a tool to differentiate attenuated strains from virulent isolates (Comerlato et al., 2020).
Recognized single serotype in nature, molecular phylogenic analysis of the small region of the viral N/F gene identified four worldwide distinct PPRV genetic lineages (Banyard and Parida, 2015); lineage I and II in West Africa, lineage III in Arabia and East Africa and lineage IV in Asia and the Middle East (Dhar et al., 2000, Kinne et al, 2010), all of which were diverged from the West African ancestor (Padhi and Ma, 2014). This finding purports to facilitate the geographic speciation of the disease in general and the rapid spread of lineage IV across Asia and Africa. Respected originating in West Africa and endemic in South Asia, the first known breakthrough of PPR to European Turkey was in 2016 (Banyard et al., 2010). Shortly after occurrence of the disease in Turkey in 2018 nearby the European Union boarders, PPR was reported in Bulgaria in 2018 recording the first occurrence of the disease in the European Union (Altan et al., 2018). In the Middle East, PPR was reported in most of the Arabian Peninsula countries including Oman (Hedger et al., 1980; Taylor et al., 1990), the United Arab Emirates (Furley et al., 1987) and Saudi Arabia (Abu-Elzein et al., 1990; Elzein et al., 2004; Al-Dubaib, 2009). Despite no conventional or molecular evidences indicating existence of the disease in Qatar, serum anti-PPRV antibodies were repeatedly detected among clinically suspected animals (DAR, 2013).
In Qatar, the total population of PPR susceptible animal species is estimated to be 1,777, 207 (DAR, 2021), 62% (n= 1,115,293) of which are sheep, 26% (n= 464,980) goats, 8% (n=135,976) camels, 3% cattle (n=45958) and 1% (n= 15,000) are wild ruminants. Due to the limited grazing areas in the country, most of the animal species are raised within mixed closures of open farming system, however, each occupies a separate unit. Of the total wild ruminants species, Oryx represents 82% (n=12,400) of the species. These are kept into 3 different separate natural reservation units supervised by the governmental Wild Ruminants Reservation Authority. The fem reminders and the rest of the wild ruminants species are owned by the private sectors and kept in the same manner described for the other animal species.
Recognized animal food importing country, the quarantine veterinary section at of the veterinary authority in Qatar is routinely checking the vaccination certification upon importation from PPR suspected or endemic countries. As a practice, the animal health section used to vaccinate susceptible animals against PPR using the live attenuated PPRV 75-1 Nigerian strain. Usually vaccinations are performed at the discretion of the animal owner, complementation with the animal movement regulations or response to a reported regional PPR outbreak. However, the first incident of PPR in Qatar was reported by Banyard and Parida, 2015; based on viral RNA that had been retrieved from samples collected in 2010 from goats and deer. Nonetheless, to date, there is no single official national or international declaration indicating existence of PPR in Qatar.
With respect to the recent global movement towards preventing, controlling and eradicating PPR, there is a crucial need to raise the global awareness about the disease benefiting from the regulations set forth in the national feedback platforms (FAO, 2015a). Taking this into consideration, it is obvious that there are huge gaps in knowledge concerning the epidemiology of the PPR in Qatar. These gaps include the following questions: 1. Does PPR exist in Qatar? 2. And if so, what is the extent of the disease perpetuation among the susceptible domesticated and captivated wildlife hosts? 3. What are the lineages of the viruses that are circulating among the susceptible animals? 3. And finally, what are the possible factors that are potentially influencing the disease to perpetuate among these animals?
Since PPR is on the World Organization for Animal Health (OIE) list of the notifiable diseases, and it’s currently a global thread to animal industry, it needs more attention. The aforementioned setbacks observed in Qatar coupled with the animal species existing in the country, the rearing pattern practiced in the country with the absence of previous vaccination records; have promoted the authors to conduct a first retrospective investigation about the prevalence of the disease. Answers given to the previously raised questions would expect to offer baseline data on the disease and help establishment of an effective sustainable preventive and control programmes.