Peste Des Petits Ruminant (PPR) is a serious disease that hampers cross-border trade in many countries including Ethiopia. The small ruminant population of Ethiopia is about 30.70 million sheep and 30.20 million Goats. The potential of animal production remains low valued and one of the main limiting factors is the presence of PPR. The socio-economic impact of PPR results in heavy losses of small ruminant production, and its impact on market access of small livestock are paramount, affecting all players in the sector. Morbidity and mortality rates can be as high as 100 and 90 percent, respectively. In clean flocks, sheep and goats of all ages can be affected during an outbreak. This impact negatively on the livelihoods, food security and socio-economic activities of livestock keepers in affected areas. PPR is among the commonest of the diseases that affect small ruminants entailing a huge economic loss as it is listed trans- boundary diseases affecting the economy of the country through limiting international trade of animals and animal products. Currently, PPR is endemic in Ethiopia and the National Veterinary Institute (NVI) produces live attenuated vaccine using PPR75/1 (LK6 Vero74) strain.

Introduction

The small ruminant population of Ethiopia is about 30.7 million sheep and 30.2 million Goats [1]. Owing to their high fertility, short generation interval and adaptation even in harsh environments, sheep and goats are considered as an important asset of poor farmers. Small ruminants are exploited in the country for diverse purposes. However, small ruminant production and productivity and producers benefits are far below expectations due to diseases and other factors. A Peste Des Detits Ruminantis Virus (PPRV) is among important diseases affecting the productivity of small ruminant [2]. PPR is a highly contagious viral disease of domestic and wild small ruminants characterized by fever, anorexia, necrotic stomatitis, diarrhea, mucopurulent nasal and ocular discharges, enteritis and pneumonia [3].

Morbidity and mortality rates can be as high as 100 and 90 percent, respectively. In clean flocks, sheep and goats of all ages can be affected during an outbreak. This impact negatively on the livelihoods, food security and socio-economic activities of livestock keepers in affected areas. The important direct economic losses caused by PPR are often further aggravated by sanitary measures imposed by authorities in controlling animal movement and trade restrictions on their by-products [2]. The disease has been associated with increased animal movement for commercial and trade purposes, transhumance and nomadic customs, climatic changes and extensive farming practices [3]. The causative agent of this economically important disease of small ruminants is Peste Des Petits Ruminants Virus (PPRV), which is grouped under genus Morbillivirus, of the family Paramyxoviridae [4].

PPR was clinically suspected for the first time in Ethiopia in 1977 in a goat [5] and serological evidence reported in 1984 and later confirmed in 1991 with cDNA probe [4]. PPR is among the commonest of the diseases that affect small ruminants entailing a huge economic loss as it is listed trans-boundary diseases affecting the economy of the country through limiting international trade of animals and animal products [6]. Currently, PPR is endemic in Ethiopia and the National Veterinary Institute (NVI) produces live attenuated vaccine using PPR75/1 (LK6 Vero74) strain [3]. The economic impact and losses in a PPR outbreak can be very high with mortalities among sheep and goats up to 90 percent; for villagers and communities this can be devastating in terms of food security, livelihoods and availability of quality products [7]. Serological investigations of PPRV were conducted in different regions of Ethiopia and revealed that the prevalence of 36.6% in Afar reported by [8], 27.3% in Gambella reported by [2], 24.5% in Benji Maji reported by [9] and 47.5% in Tigray reported by [9]. This was summarized below table 1.

In this regards, comprehensive quantification of the occurrence of the disease and its associated risk factors and assessment of the losses due to this disease would have great contribution to determine the status and socio-economic impacts of the disease which in turn help to design and implement appropriate control strategy.

There for the objective of this review were;

• To indicate the Sero-prevalence and to determine the associated risk factors of PPR and

• To determine socio-economic impacts of PPR in small ruminants.

Epidemiology of PPRV

Distributions of PPRV

Peste des Petits Ruminants virus was long considered to be confined to West Africa but later it has expanded to cover large regions of Africa, the Middle East and Asia [11]. It was first recognized as a disease entity in the Ivory Coast. It started to expand rapidly to other West African countries and continued to spread towards Central and East-Africa [12]. Subsequently, PPR was disseminated outside Africa into Asia and further to Turkey [13]. The disease is now endemic in nearly most of African countries excluding countries south of Tanzania and Angola, in all Arabian- Peninsula and Middle-Eastern countries, in a wide belt of Asia including central, southern and south-eastern countries [14,10]. Within the European continent PPR is currently present only in Turkey [15,16,4,2]. In Northern Africa, PPR has been identified in Tunisia [16] and Algeria [17]. It has now spread north of the Sahara and only Libya has not reported the disease in the region [18]. In addition, PPR outbreaks have also been reported in East and Central African countries like: Ethiopia [19], Democratic Republic of Congo [20] and Kenya and Uganda [21].

Morbidity and mortality

In Ethiopia PPR disease outbreaks are under reported, due to the poor reporting system, an increasing trend has been observed in PPR outbreaks between the years 1996 and 2005 [25]. Periodic outbreaks may be seen in endemic regions, particularly when animals are mixed or new animals are introduced into the herd. Some epizootics are associated with changes in weather, such as the beginning of the rainy season or a cold and dry period [3]. It might circulate sub clinically in small ruminant populations and emerging, when immunity wanes or naive animals are introduced. In endemic regions, animals between three months and two years of age are most severely affected; young animals that are still nursing and older animals tend to be spared [3]. Morbidity and mortality can be as high as 100% and 90%, respectively, when associated with other diseases such as caprioles [14].

Risk factors

There are numerous environmental, husbandry and animal related factors that affect the occurrence of PPRV in small ruminants. In pastoral areas, livestock trade, nomadic herding and the congregation of susceptible populations close to watering points during dry seasons and/or in livestock markets play an important role in spreading the disease [21]. Movement of animals and introduction of newly purchased animals from the market therefore play an important role in transmission and maintenance of the virus [27]. In addition, trade in small ruminants, especially at markets where animals from different sources are brought into close contact with one another increases the opportunities of PPR transmission [28]. It has been reported that in Maghreb countries of North Africa, traditional sacrifices of sheep during major Islamic festivals provide a major opportunity for seasonal clustering of small ruminants of multiple sources whose health status is often unknown, thus creating a favorable environment for the transmission and dissemination of the PPR virus [29].

Age of the animals is also among animal related risk factors known to affects the occurrence of PPR in small ruminants. Kids over four months and under one year of age are most susceptible to the disease. In a particular flock, risk of an outbreak is greatly increased when a new PPR infected stock is introduced or when animals are returned unsold from livestock markets at endemic area. The increase in incidences of PPR outbreaks has been attributed more to an increased number of susceptible small ruminants recruited rather than seasonal upsurges in the viral activity [30]. It has also been reported that the recent PPR disease outbreaks have been attributed to the cessation of rinderpest vaccination and loss of antibody cross protection between the PPR and Rinderpest, leaving the small ruminants fully exposed to PPRV [31].

Among the environmental factors affecting the occurrence of PPR, season is believed to be in the forefront. Low environmental temperatures with high humidity, stress of as well as nutritional deficiencies, are known to influence the occurrence of PPR small ruminants. Limited fodder availability often, leads to nutritional deficiency, resulting in increased susceptibility to infection [32,33]. Furthermore, large numbers of animals become infected during this period and these animals then help to maintain the circulation of the virus throughout the year by frequent animal-to-animal transmission which, play a key role in the transmission of PPR [34]. The seasonal epidemiologic patterns of the PPR disease differ in different ecological systems, geographical areas and are dependent on culture and livelihood patterns of small stock owners [35].

Diagnosis

Since sheep and goat are infected by both PPR and Rinderpest, it is difficult to diagnosis both disease tentatively alone, therefore laboratory techniques should have to be used. The laboratory techniques used for the detection of the virus includes virus isolation, detection of viral antigens, nucleic acid sequencing and detection of specific antibody in serum [36,33].

Virus isolation: Recovery of PPR virus is not always successful. But, virus isolation in cell culture can be attempted with several different cell lines. African green monkey kidney cells (Vero-cell) have been used for a long time as the cells of choice for the isolation and propagation of PPRV [32]. However, some isolates may not grow well in these cells. Recently, transformed monkey cells expressing sheep/goat Signaling Lymphocytic Activation Molecules (SLAM or CD150) have been shown to possess increased sensitivity. Techniques for virus isolation cannot be used as routine diagnostic tests as they are time-consuming and cumbersome. Moreover, the preservation of samples collected under field conditions is not always adequate for successful laboratory results [37].

Antigen detecting methods: Peste des petits ruminates virus antigens can be detected by using an Immune Capture ELISA (ICELISA) [38], Counter Immune Electrophoresis (CIEP) or Agar Gel Immune Diffusion (AGID) [39], haem-agglutination tests [20,39], latex agglutination tests [25] and immune fluorescence [40]. Immuno-capture ELISA and counter immune electrophoresis assays can distinguish between PPRV and RPV. Although AGID test is simple and cheap, it cannot differentiate PPRV and RPV due to its less sensitivity [39]. But, Immuno-capture ELISA is a rapid, sensitive and virus specific test for PPRV antigen detection and it can differentiate between RP and PPR viruses. Moreover, it is more sensitive than AGID [2].

Detection of antibody: The (c-ELISA) based on Monoclonal Antibodies (MAbs) against the N or H proteins and virus neutralization tests [40,13,34] are the most important diagnostic techniques used for the detection of antibodies to PPRV. Currently, competitive ELISA is the most commonly used diagnostic techniques for PPRV antibody detection. The overall specificity of c-ELISA test is 98.4% with a sensitivity of 92.2% when compared with VNT. The diagnostic efficacy of the assay in terms of sensitivity and specificity was calculated using two-sided contingency table. Sensitivity of the assay was taken as proportion of positive samples out of actual positive Sample [40]. The c-ELISA for the detection of antibodies to PPRV in sera from cattle, camel, sheep and goats has been standardized by [2]. In Ethiopia, It is performed strictly as per the protocol outlined in the user manual supplied with the kit where the method is developed [31].

Nucleic acid sequencing: Molecular detection of PPRV is performed by using loop-mediated isothermal amplification techniques [20] and a Real-Time Polymerase Chain Reaction (RT-PCR) assay based on sequence of the N protein gene [9]. From those methods RT-PCR assay based on sequence of the N protein gene is the most and rapid methods for viral Nucleic acid sequencing [9,10].

Prevention and control: Prevention and control of PPR outbreak is based on movement control combined with proper disposal of carcass and the use of vaccine. Restriction on importation of sheep and goats from affected areas or newly introduced animal should be quarantined for three weeks. Additionally, carcass and contact fomites should be buried or burned, Barns, tools and other items that have been in contact with the sick animals must be disinfected with common disinfectants such as phenol, sodium hydroxide 2%, virkon as well as alcohol, ether and detergents. Vaccination should be carried before the start of the rainy season and annually in endemic areas [34].

Socio economic impacts of PPR in Ethiopia

The socio-economic losses associated with PPR mainly result from the high mortality rate that is characteristic of the disease. This negatively affects income from production and value addition in small ruminants marketing chains. PPR disease is a constraint to international trade, although this impact is mitigated in local and regional markets due to wide geographic distribution of the disease at present [41]. However, the direct economic losses caused by the disease are reduced by the sanitary measures imposed by authorities to control animal movement and by trade restrictions on animal by-products [41,42]. Because of the negative economic impact on countries affected by PPR, the disease is one of the priorities among international and regional livestock disease research and control programs [43]. Moreover, it has also been ranked by pastoral communities as one of the top ten diseases of small ruminants [18].

Conclusion and Recommendations

PPR is an important animal disease which now threatens the billion strong ruminant’s population in Africa, the Middle and Near East, South West and Central Asia. PPR is a disease of animals, sheep and goats, which contribute significantly to the livelihoods of rural poor farmers, its control should therefore be considered in programs that aim at alleviating poverty in developing countries. In addition, as disease of public concern and thus its control should benefit from all international concerning organizations. In Ethiopia beside seasonal occurrences of the disease illegal animal movement within and across the borders is a great hindrance for prevention and control of the disease.

Therefore, based on above conclusion the following points are recommended;

∎ Regular mass vaccination should be carried out; tempo-spatial pattern of the disease should purposely have studied to implement proper intervention measures in lining illegal animal movement control.

∎ Awareness on the risk of direct introduction of purchased animals into herds should be created among small ruminant rearing communities.

1. Abebe R, Tatek M, Megersa B, Sheferaw D. Prevalence of small ruminant Ectoparasites and associated risk factors in selected districts of Tigray region, Ethiopia. Global Veterinarian. 2011; 7: 433-437. http://bit.ly/33iq8vA
2. Abraham G, A Sintayehu, G Libeau, E Albina, F Roger, Y Laikemariam, et al. Antibody seroprevalence against Peste Des Pestits Ruminant’s Virus (PPRV) in camels, cattle, goats and sheep in Ethiopia. Preventive Medicine. 2005; 70: 51-57.
3. Abubakar M, Khan HA, Arshed MJ, Hussain M, Ali Q. Peste Des Petits Ruminants (PPR): disease appraisal with global and Pakistan perspective. Small Ruminant Research.2011; 96: 1-10. http://bit.ly/2NFjFUX
4. Albina E, Kwiatek O, Minet C, Lancelot R, Servan de Almeida R, Libeau G. Peste des petits ruminants, the next eradicated animal disease. Vet Microbiol. 2013; 165: 38-44. http://bit.ly/34yaBrs
5. Ayaalet G, Fasil N, Jembere S, Mekonen G, Sori T, Negussie H. Study on immunogenicity of combined sheep and goat pox and peste des petitisruminants vaccines in small ruminants in Ethiopia. African Journal of Microbiology Research. 2012; 6: 7212-7217. http://bit.ly/2Ccr6xB
6. Ayari-Fakhfakh E, Ghram A, Bouattour A, Larbi I, G Dridi, Kwiatek, et al. First serological investigation of peste-des-petits-ruminants and rift valley fever in Tunisia. Vet J.2011; 187: 402-404. http://bit.ly/33fAOeg
7. Bailey D, Banyard A, Dash P, Ozkul A, Barrett T. Full genome sequence of peste des petitsruminants virus, a member of the Morbillivirus genus. Virus Res.2005; 110: 119-124. http://bit.ly/2WJ8L4t
8. Banyard AC, Parida S, Batten C, Oura C, Kwiatek O, Libeau G. Global distribution of peste des petits ruminants’ virus and prospects for improved diagnosis and control. J Gen Virol. 2010; 91: 2885-2897. http://bit.ly/2r6xWlI
9. Batten CA, Banyard AC, King DP, Henstock MR, Edwards L, Sanders A, et al. A real time RT-PCR assay for the specific detection of peste des petitsruminants virus. J Virol Methods. 2011; 171: 401-404. http://bit.ly/36AxGvN
10. Berihun A, Kassaw A, Daniel H. Seroprevalence of peste des petits ruminant’s in goats of southern parts of Tigray region. Global Veterinarian. 2014; 12: 512-516.
11. Agricultural sample survey. Volume 2: report on livestock and livestock characteristics. Federal democratic republic of Ethiopia, Central Statistical Authority. Addis Ababa: central Statistical Authority. 2016/17. https://stanford.io/34zkci3                                               
12. Peste des petits ruminants. CFSPH. Technical Disease Fact Sheets. 2008.
13. Choi KS, Nah JJ, Ko YJ, Kang SY, Jo NI. Rapid competitive enzyme-linked immunosorbent assay for detection of antibodies to peste des petitsruminants virus. Clin Diagn Lab Immunol. 2005; 12: 542-547. http://bit.ly/2NeRDk2
14. Peste des petits ruminants. CIDRAP. 2003. http://bit.ly/2NjniRn
15. MD Nardi, SM Lamin Saleh, C Batten, C Oura, A Di Nardo, D Rossi. First evidence of peste des petits ruminants (PPR) virus circulation in Algeria (Sahrawi territories). Outbreak investigation and virus lineage identification, Transboundary and Emerging Diseases. 2012; 59: 214-222. http://bit.ly/2NfOhxg
16. Delil F, Asfaw Y, Gebreegziabher B. Prevalence of antibodies to peste des petits ruminant’s virus before and during outbreaks of the disease in awash fentale district, Afar, Ethiopia. Tropical Animal Health and Production. 2012. 44: 1329-1330.
17. Dhar P, Sreenivasa BP, Barrett T, Corteyn M, Singh RP, Bandyopadhyay SK. Epidemiology of Peste Des Petitsruminants Virus (PPRV). Vet Microbiol. 2002; 88: 153-159. http://bit.ly/2JPM7Ci
18. Olivier K, Yahia HA, Intisar KS, Abdelmelik IK, Osama IM, Ali AO, et al. Asian lineage of peste des petits ruminants virus in Africa. Emerg Infect Dis. 2011; 17: 1223-1231. http://bit.ly/2CfcTjc
19. Dufour L. The plague of small ruminants: moroccan outbreak of 2008, a danger to Europe? PhD thesis. The Faculty of Medicine, Creteil, National Veterinary School of Alfort. 2010.
20. Ezeibe MC, Okoroafor ON, Ngene AA, Eze JI, Eze IC, Ugonabo JA. Persistent detection of peste des petits ruminant’s antigen in the faeces of recovered goats. Tropical Animal Health and Production. 2008; 40: 517-519. http://bit.ly/2CeJaHa
21. Javier SA, Adama D, Stephane DL, Rocque, Julio P, Samuel T, et al. Peste Des Petits Ruminants (PPR) in Morocco. EMPRES WATCH. 2008; 1-7. http://bit.ly/36BTWVN
22. Gibbs EPJ, Taylor WP, Lawman MPJ, Bryant J. Classification of the peste des petits-ruminants virus as the fourth member of the genus Morbillivirus. Intervirology.1979; 11: 268-274. http://bit.ly/2pGtjyx
23. Girma A. Sero epidemiology of peste des pestes ruminats in small ruminats in Maji destricts, South Western Ethiopia. 2017.
24. Gopilo A. Epidemiology of peste des petits ruminant’s virus in Ethiopia and molecular studies on virulence. 2005. http://bit.ly/2WHurho  
25. Keerti M, Sarma BJ, Reddy YN. Development and application of latex agglutination test for detection of PPR virus. AGRIS. 2009; 86: 234-237. http://bit.ly/36tlih3
26. Khan HA, Siddique M, Abubakar M, Arshad MJ, Hussain M. Prevalence and distribution of peste des petits ruminants virus infection in small ruminants. Small Ruminant Research, 2008; 79: 152-157. http://bit.ly/2rezHxp
27. Lefevre PC, Diallo A. Peste des petits ruminants. Revue Scientifique et Technique. 1990; 9: 935-981. http://bit.ly/2JKYzTV
28. Li L, Bao J, Wu X, Wang Z, Wang J, Gong M, et al. Rapid detection of peste des petits ruminants virus by a reverse transcription loop-mediated isothermal amplification assay. J Virol Methods. 2010; 170: 37-41. http://bit.ly/2oRlmpS
29. Libeau G, Diallo A, Colas F, Guerre L. Rapid differential diagnosis of rinderpest and peste des petits ruminants using an immunocapture ELISA. Vet Rec. 1994;134: 300-304. http://bit.ly/2Ccftqh
30. Libeau G, Diallo A, Parida S. Evolutionary genetics underlying the spread of peste des petits ruminant’s virus. Animal Frontiers. 2014; 4: 14-20. http://bit.ly/2NFLHzx
31. Libeau G, Prehaud C, Lancelot R, Colas F, Guerre L, Bishop DH, et al. Development of a competitive ELISA for detecting antibodies to the peste des petitsruminants virus using a recombinant nucleoprotein. Res Vet Sci. 1995; 58: 50-55. http://bit.ly/34xMcCB
32. Mahapatra M, Parida S, Baron MD, Barrett T. Matrix protein and glycoproteins F and H of peste-des-petits-ruminants virus function better as a homologous complex. J Gen Virol. 2006; 87: 2021-2029. http://bit.ly/2JSieRN
33. Megersa B, Biffa D, Belina T, Debela E, Regassa A, Abunna F, et al. Serological investigation of peste des petits ruminants (PPR) in small ruminants managed under pastoral and agro-pastoral systems in Ethiopia. Small Ruminant Research. 2011; 97: 134-138. http://bit.ly/36yAf1l
34. Munir, Muhammad, Zohari, Siamak, Berg, Mikael. Molecular biology and pathogenesis of peste des petits ruminant’s virus. 1st edn. Heidelberg; Springer-Verlag Berlin Heidelberg: 2013. http://bit.ly/2WHaK9o
35. Murphy FA, Gibbs EPJ, Horzinek MC, Studdert MJ. Classification and nomenclature of viruses. Veterinary Virology. 3rd edn. New York; Academic Press: 1999. http://bit.ly/2Cfx4xs
36. Nyamweya M, Otunga T, Regassa G, Maloo S. Technical brief of peste des petitsruminants virus. 2009
37. Peste des petits ruminants. Manual of Diagnostic Tests and Vaccines or Terrestrial Animals 7th edn. Paris; OIE: 2012. http://bit.ly/32evA0X
38. World Organization for Animal Health. Manual of standards for diagnostic tests and vaccines 6th edn. Paris; OIE: 2008. http://bit.ly/2NgbDCW
39. Osman NA, Rahman ME, Ali AS, Fadol MA. Rapid detection of Peste Des Petits Ruminants (PPR) virus antigen in Sudan by Agar Gel Precipitation (AGPT) and Haemagglutination (HA) tests. Trop Anim Health Prod. 2008; 40: 363-368. http://bit.ly/32fWy8K
40. Singh RP, Saravanan P, Sreenivasa BP, Singh RK, Bandyopadhyay SK. Prevalence and distribution of peste des petits ruminants virus infection in small ruminants in India. Rev Sci Tech. 2004; 23: 807-819. http://bit.ly/2NzXG1m
41. Sumption KJ, Aradom G, Libeau G, Wilsmore AJ. Detection of peste des petits ruminant’s virus antigen in conjunctival smears of goats by indirect immune fluorescence. Veterinary Research. 1998; 142: 421-424.
42. Swai ES, Kapaga A, Kivaria F, Tinuga D, Joshua G, Sanka P. Prevalence and distribution of peste des petitsruminants virus antibodies in various districts of tanzania. Vet Res Commun. 2009; 33: 927-936. http://bit.ly/2PJ7fho
43. Taylor WP, Busaidy SA, Barret T. The epidemiology of peste des petits ruminants in the sultanate of Oman. Vet. Microbiology. 1990; 22: 341-352. http://bit.ly/33ufzFy