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Serological investigation of Peste des Petits Ruminants (PPR) in small ruminants managed under pastoral and agro-pastoral systems in Ethiopia
Small Ruminant Research 97 (2011) 134–138
Contents lists available at ScienceDirect
Small Ruminant Research journal homepage: www.elsevier.com/locate/smallrumres
Serological investigation of Peste des Petits Ruminants (PPR) in small ruminants managed under pastoral and agro-pastoral systems in Ethiopia B. Megersa a,b,∗ , D. Biffa a,b , T. Belina a , E. Debela a , A. Regassa a , F. Abunna a , T. Rufael c , S.M. Stubsjøen d , E. Skjerve b a b c d
Hawassa University, School of Veterinary Medicine, P.O. Box 05, Hawassa, Ethiopia Center for Epidemiology and Biostatistics, Norwegian School of Veterinary Science, P.O. Box 8146 Dep., 0033 Oslo, Norway National Animal Health Diagnostic and Investigation Centre, P.O. Box 04, Sebeta, Ethiopia Norwegian School of Veterinary Science, Department of Production Animal Clinical Sciences, P.O. Box 8146 Dep., NO-0033 Oslo, Norway
a r t i c l e
i n f o
Article history: Received 9 August 2010 Received in revised form 25 February 2011 Accepted 2 March 2011 Available online 31 March 2011 Keywords: Peste des Petits Ruminants Seroprevalence Small ruminant Ethiopia
a b s t r a c t A cross-sectional study to investigate Peste des Petits Ruminants (PPR) seroprevalence was conducted between October 2009 and April 2010 in Gambella and Afar regions of Ethiopia. A total of 1163 serum samples were collected from 251 sheep and 912 goats. Competitive Enzyme Linked Immunosorbent Assay (c-ELISA) was used to detect the presence of antibodies in the sera of animals as indicator of exposure to the PPR virus. The results showed an overall individual animal seroprevalence of 30.9% (359/1163) with 29.5% in sheep and 31.3% in goats. The disease affected 96.9% (22/23) of the villages in Gambella and all the villages (9/9) in the Afar regions. The intra-village prevalence records range was 8.3–42.9% and 32.6–54.8%, and 0–66.7% and 0–71.4% for sheep and goats in Afar and Gambella regions, respectively. The high village-level seroprevalence of PPR illustrates a remarkable contagious nature of the disease. Multivariable logistic regression analysis of exposure variables revealed a significant association of PPR seroprevalence with districts and sex. Accordingly, seroprevalence was significantly higher in Adaar district of Afar (OR = 1.7, 95% CI: 1.1, 2.6) when compared to districts of Gambella region. Likewise, females were more likely to be seropositive (OR = 1.9, 95% CI: 1.2, 3.0) than their male counterparts. In conclusion, this study revealed a high seroprevalence and subsequent endemic establishment of PPR in small ruminants in the selected study areas. This disease is detrimental to small ruminant welfare and causes substantial economic losses, thereby affecting the livelihood of poor farmers and pastoralists. The need for implementing feasible control measures is, therefore, eminent to minimize the losses associated with the disease. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Small ruminants are an integral part of the livelihood of the large majority of the rural population in Ethiopia,
∗ Corresponding author at: Hawassa University, School of Veterinary Medicine, P.O. Box 05, Hawassa, Ethiopia. Tel.: +251 911842294. E-mail address: [email protected] (B. Megersa). 0921-4488/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2011.03.003
and significantly contribute to the income generation and food security of households, supplying about 23–39% of the farm cash income (Legesse et al., 2010). Next to camels, small ruminants are the most important species capable of surviving unfavourable climatic situation of arid and semi-arid environments and hence, are species of choice by pastoralists. In view of a high reproduction rate, they often constitute immediate sources of cash income, and source of meat and milk for home consumption (Tolera and Abebe, 2007).
B. Megersa et al. / Small Ruminant Research 97 (2011) 134–138
According to the Ethiopian Central Statistical Authority (2008), the population of sheep and goats in Ethiopia is estimated to be 26.3 and 23.3 million, respectively. They are widely distributed across different agro-ecological zones and production systems, being an integral part of livelihood of rural households and a source of export earning for the country. However, the productivity of sheep and goats is often hampered by multifaceted problems of which animal disease is the major one. Peste des Petits Ruminants (PPR), a severe and highly contagious trans-boundary animal disease of sheep and goats, is caused by a virus belonging to the genus Morbillivirus of the family Paramyxoviridae (Radostitts et al., 2007). Of the four known lineages of PPR virus, lineage 1 and 2 viruses have been found exclusively in West Africa. Lineage 3 has been found in east Africa, identified in the outbreak of 1996 in Ethiopia, also in the Arabian Peninsula and southern India (Dhar et al., 2002). In the past 8 years, virus exclusively of the fourth lineage has spread across the Middle East and the Asian sub-continent, reaching east as far as Nepal and Bangladesh (Dhar et al., 2002; Diallo et al., 2007). The typical clinical form of PPR is the acute form which is characterized by sudden depression, high fever, anorexia, nasal and ocular discharge, mouth erosive lesion, pneumonia and severe diarrhoea. It is considered as one of the main constraints hindering the productivity of small ruminants in enzootic regions of Africa, Asia and the Middle East (Dhar et al., 2002). In susceptible populations, morbidity may range from 10 to 100% and mortality from 0 to 90% (Dhar et al., 2002; Radostitts et al., 2007). Roeder et al. (1994) estimated an overall mortality rate of 60% in a PPR outbreak in Ethiopian goats, while morbidity of 76% and case fatality of 18% were reported from a respiratory disease outbreak in sheep in central Ethiopia (Tibbo et al., 2001). Evidences of PPR occurrence in small ruminants as well as in cattle and camels have been serologically demonstrated in Ethiopia (Abraham et al., 2005; Waret-Szkuta et al., 2008). After the first confirmed cases of PPR in Ethiopia, the disease is continuously affecting small ruminant production and thus contributing to food insecurity, particularly, in vulnerable regions of the country. There have been no substantial studies carried out on the disease in the pastoral and agro-pastoral regions of the country, giving raise to paucity of information regarding its prevalence. The present study was, therefore, aimed at investigating the current status of PPR in small ruminants of Afar and Gambella regions.
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day time and kept mainly in open enclosure during the night. The study animals were sheep and goats above 6 months of age with no vaccination history for PPR since 2006. 2.2. Study design and sampling procedure A cross-sectional four stage sampling technique (region–district– village–flock) was employed to investigate the prevalence of PPR in small ruminants in the study areas. Selection of the study unit at each stage was based on mixed design of convenience and random samplings. Regions and districts were conveniently selected based on geographical proximity and accessibility by vehicle, whereas villages and flocks were randomly selected from each area following a randomization of the villages and herd owners based on lists obtained from respective districts. In some circumstances when this was not possible, flocks were sampled conveniently in consultation with animal owners. With the limitation of establishing sample frame, sample size for detection of disease (Dohoo et al., 2009) was used to estimate the required number of animals to be sampled per village. A 95% sensitivity of finding at least a positive animal in a finite population and an expected prevalence of 10% (Abraham et al., 2005) were assumed, with a sample size of at least 30 units. The number of animals sampled from each village could vary according to flock population, accessibility by transportation and availability of logistic facilities. We intended to establish a comparable sample size covering about 36 villages (18 per region). Accordingly, a total of 1163 animals (251 sheep and 912 goats) were sampled from 32 villages in both regions. Information on potential risk factors such as geographic location, animal factors, and husbandry practices was recorded during blood sampling. 2.3. Serum collection and testing Blood samples were aseptically collected by puncturing the jugular vein using venoject needles and plain vacutainer tubes. Each sample was labelled with an individual identification code, and the descriptions were recorded on the questionnaire format. Blood samples were kept overnight in cold boxes to allow clotting and subsequent separation of serum. Sera were then collected in sterile tubes and transported to the laboratory using an ice box where temporary storage was made at −20 ◦ C until tested. Serum samples were analyzed at the National Animal Health Diagnostic and Investigation Center (NAHDIC, Sebeta, Ethiopia) using a competitive ELISA kit following the instructions of the manufacturer (Institute for Animal Health, Pirbright Laboratory, UK) according to Anderson et al. (1991). The test depends on inhibition of the binding of anti-H protein monoclonal antibody (MAb) to a PPR virus specific epitope in the presence of antibodies in the serum samples. Inhibition is detected as reduction in the optic density (OD) reading obtained with the monoclonal antibody alone following the addition of peroxidase labelled anti-mouse conjugate and substrate (chromogen mixture). The ELISA micro-plates were read with an Immunoskan reader (Flow laboratories, UK) with an inference filter of 492 nm. The reader was connected to a computer loaded with ELISA Data Information (EDI) software (FAO/IAEA, Vienna, Austria), which was used to automate the reading and calculation of percentage of inhibition (PI) values. The OD values were converted to percentage inhibition (PI) using the following formula: PI = 100 −
(OD control or test serum) × 100 (OD monoclonal control)
Samples with PI > 50%, a cut-off point, were considered as positives. 2.4. Data management and analysis
2. Materials and methods 2.1. Study area and study population The study was conducted from October 2009 to April 2010 in selected districts of two regions, namely Gambella (Abobo, Gambella, Lare and Itang districts) and Afar (Adaar district), which are characterized by pastoral or agro-pastoral production systems. The Gambella region is located in the South-western part of the country with an altitude range of 350–500 m above sea level in the Western part and 500–2000 altitude in the Eastern and South-eastern part of the region. The Afar region is located in the North-eastern part of the country with an altitude ranging from 1000 to 1500 m above sea level. Small ruminant production is predominantly traditional, where animals are allowed to graze freely during
Data were stored in a Microsoft Excel® Spread Sheet and data analysis was performed using Stata version 11.0 for windows SE (Stata Corp. College Station, TX). Descriptive statistics of the recorded variables were summarized per different study units (stages) using tabulate command in Stata. Individual level prevalence was calculated at different stages by using the survey command in Stata, with village as the primary sampling unit. Logistic regression analysis was used to investigate the potential association of recorded exposure variables with the disease prevalence. The degree of association between potential risk factors and seroprevalence was computed using the odds ratio. The final multivariable model was established using a backward selection procedure of variables, using village as clustering effect. The model was checked for fit using the Hosmer–Lemeshow goodness of fit test.
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Table 1 Individual animal PPR seropositivity at animal and village levels stratified by region. Gambella
Animal level Goat Sheep Subtotal Village level Goat Sheep Subtotal
Afar
Total
No
Positive (%)
No
Positive (%)
No
Positive (%)
617 162 779
162 (26.3) 51 (31.0) 213 (27.3)
295 89 384
123 (41.7) 24 (27.0) 147 (38.3)
912 251 1163
284 (31.1) 75 (29.9) 359 (30.9)
23 18 23
22 (95.7) 15 (83.3) 22 (95.9)
9 9 9
9 (100) 9 (100) 9 (100)
32 27 32
31 (96.9) 24 (88.9) 31 (96.9)
Table 2 Intra-village levels of seropositivity in sheep and goats in the studied villages over prevalence groups. Regions
Districts
Gambella
Abobo Gambella Lare Itang Adaar
Afar Subtotal a
0%
1–10%
11–20%
21–30%
1 (51)
2 (37) 1 (61)
1 (51)
3 (98)
4 (160) 3 (135) 2 (43) 1 (45) 2 (103) 12 (486)
1 (13)
1 (13)
31–40%
>40%
1 (50) 3 (61)
2 (87) 2 (36)
4 (164) 8 (275)
3 (117) 7 (240)
Total 5 (210)a 5 (222) 10 (190) 3 (157) 9 (384) 32 (1163)
Numbers outside and inside the brackets indicate number of sampled villages and animals, respectively.
3. Results Of the total serum samples tested, 30.9% (359/1163) were found positive for PPR antibodies. The seropositivity ranged from 14.6% in Itang district of the Gambella region to 38.3% in Adaar district of the Afar region. The disease showed a widespread spatial distribution covering 96.9% (22/23) of the villages in Gambella and all the studied villages (9/9) in the Afar region. Table 1 gives the seroprevalence of PPR at animal and village levels stratified by study region. Within-village seroprevalence values ranged from 8.3 to 42.9% and 32.6 to 54.8% (Afar) and from 0 to 66.7% and 0 to 71.4% (Gambella) for sheep and goats, respectively. The intra-village level of seropositivity in pooled samples of sheep and goats is presented in Table 2. Seroprevalence records were uniformly above 30% in most villages of the Afar region, while marked variation in prevalence distributions, ranging from 0 to over 71.4%, were recorded in villages of Gambella. The overall seroprevalence distribution of PPR in the study areas with respect to exposure variables is shown
in Table 3. A significantly higher seroprevalence (38.3%) was found in Afar than Gambella (27.6%). The lowest prevalence was recorded in Itang district (14.7%) of the Gambella region. The multivariable logistic regression analysis (Table 4) showed that geographical locality and sex as being risk factors for seropositivity to PPR. Seroprevalence was significantly higher in Adaar district of Afar (OR = 1.7, 95% CI: 1.1, 2.6) when compared to the prevalence records in districts of Gambella. Likewise, females were more likely seropositive (OR = 1.9, 95% CI: 1.2, 3.0) than their male counterparts. Post estimation statistics (Hosmer–Lemeshow goodness of fit test) shows fit of the model to the observed data (2 = 7.3, P = 0.122). 4. Discussion The study showed that PPR was widely prevalent in small ruminants in the study areas. All villages, except one in Gambella, had seropositive cases. Such a high prevalence in most of the villages (more than 30%) suggests a remarkable contagious nature of the disease, covering
Table 3 Univariable analysis of exposure variables and PPR prevalence in sheep and goats, showing prevalence levels split on variable levels and P-values from univariable statistical analyses. Variables
Levels
Number examined
Positive
Prevalence (95% CI)
Region
Gambella Afar Abobo Gambella Lare Itang Adaar Goat Sheep Male Female Young Adult
779 384 210 222 190 157 384 912 251 154 1009 316 847
212 147 56 78 55 23 147 285 74 34 325 104 255
27.2 (24.1, 30.3) 38.3 (33.4, 43.2) 26.7 (20.7, 32.7) 35.1 (28.8, 41.4) 28.9 (22.5, 35.4) 14.6 (9.1, 20.2) 38.3 (33.4, 43.2) 31.3 (28.2, 34.3) 29.5 (23.8, 35.1) 22.1 (15.5, 28.7) 32.2 (29.3, 35.1) 32.9 (27.7, 38.1) 30.1 (29.3, 35.1)
Districts
Species Sex Age CI, confidence interval.
P-value – 0.000 – 0.117 0.537 0.005 0.006 – 0.591 – 0.012 – 0.357
B. Megersa et al. / Small Ruminant Research 97 (2011) 134–138
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Table 4 Multivariable analysis of exposure variables and PPR seropositivity in sheep and goats. Variablesa
Levels
No (%)
OR (95%CI)
P-value
Districts
Abobo Gambella Lare Itang Ada‘ar Male Female Young Adult
210 (26.7) 222 (35.1) 190 (28.9) 157 (14.6) 384 (38.3) 154 (22.1) 1009 (32.2) 316 (32.9) 847 (30.1)
1.0 (–) 1.5 (0.9, 2.6) 1.1 (0.7, 2.0) 0.5 (0.2, 1.1) 1.7 (1.1, 2.6) 1.0 (–) 1.9 (1.2, 3.0) 1.0 (–) 0.7 (0.5, 1.1)
– 0.137 0.647 0.094 0.009 – 0.006 – 0.102
Sex Age
a Region was not included in multivariable analysis due to collinearity. OR, odds ratio; CI, confidence interval; Hosmer–Lemeshow goodness of fit test (2 = 7.3, P = 0.122) shows the model fitted the data.
wide geographic areas and infecting perhaps most of the susceptible animals in affected villages. The overall seroprevalence (30.5%) of this study (Table 1) is much higher than the findings in previous studies carried out in the country; 6.8% by Abraham et al. (2005) and 6.4% by WaretSzkuta et al. (2008). This could be attributed to the nature of production systems, large flock size, uncontrolled animal movement and frequent contact between flocks. Mobile pastoral herds may often come into contact with local sheep and goats, and facilitate contact transmission of PPRV from infected to susceptible animals. Likewise, infected migratory animals may transmit the virus to susceptible small ruminant population, and, therefore, the movement of animals plays an important role in the transmission and maintenance of PPRV in nature (Abubakar et al., 2009). This is in accordance with the work done by Al-Majali et al. (2008) which recorded a higher seroprevalence of PPR in regions with free animal movement than other areas in Jordan. Furthermore, limited fodder availability, especially during drought and long dry season, further leads to nutritional deficiency and increased susceptibility to infection in addition to animal movements. Consequently, large numbers of animals become infected during this period, giving raise to establishment of disease endemicity and continued year round circulation of the virus enhanced by frequent animal-to-animal contacts (Abubakar et al., 2009). Targeting these factors in disease control programme may play a key role in limiting the transmission of PPR infection and augmenting effective disease control programmes. Poor animal health services, a common constraint in peripheries and pastoral areas of the country, could also contribute to the wide prevalence and endemic establishment of the disease. The Afar region had a higher PPR seroprevalence than the Gambella region, which could be linked to differences in animal husbandry system. Afar is characterized by pastoral production systems where large flocks are kept mixed with cattle and camels, coupled with unrestricted animal movements. In comparison, the Gambella region is more of an agropastoral region. The dynamics and frequent mobility of flocks in pastoral areas increase the chance of coming into contact with other potentially infected flocks or herds. In agreement with our study, previous researchers also documented higher seroprevalence of the disease in pastoral regions compared to other areas of the country (Abraham et al., 2005; Waret-Szkuta et al., 2008). Likewise, a study by Al-Majali et al. (2008) showed an association of large flock
sizes and mixed farming with PPR seropositivity in Jordan. Antibodies to PPRV have been demonstrated in cattle and camels sharing common ecozones with small ruminants in Ethiopia (Abraham et al., 2005), suggesting possible reservoir role of these animals in multiple species holdings. Comparison of village level seroprevalence between the Gambella and Afar regions, revealed a uniformly higher seroprevalence in the latter, while wide variation of prevalence distribution (from 0 to 71.4%) was observed in the former, which could be related to difference in production systems (Table 2). Although the seropositivity difference between sheep and goats remains controversial in the literature, the current prevalence between the two species (sheep 29.5% and goats 31.3%) was comparable (Table 2). Some authors (AlMajali et al., 2008; Waret-Szkuta et al., 2008; Swai et al., 2009) reported a higher seroprevalence in goats than in sheep and linked it to higher fecundity in goats compared to sheep. It was suggested that new born kids account for a large proportion of the goat flock each year, which increase the size of susceptible population. Others reported higher seroprevalence in sheep than goats (Abraham et al., 2005; Khan et al., 2008; Saeed et al., 2010). This was either related to a relatively lower number of sheep sampled in some of these studies or due to the fact that goats are often affected more severely by peracute and acute form of the disease, and might die prior to sampling. Hence, further investigations are required to determine the variation in the relative host susceptibility and pathogenicity of PPRV between the two species. Similar to the findings of Waret-Szkuta et al. (2008) and Khan et al. (2008), a significantly higher seroprevalence of PPR was observed in females compared to males in our study. This could be related to the physiological differences between the two subjects where females reveal some degree of infection preponderance as a result of production and reproduction related stresses. Association of seropositivity with age was not significant in the logistic regression analysis. This contradicts the findings of Abubaker et al. (2009), who reported a progressive increase of seroprevalence with increasing age and related it to the accumulation of recovered convalescent over time where animals maintained in the flock for production purposes. In conclusion, the results of this study documented serological evidence for widespread distribution and endemic establishment of PPR in small ruminant population of the study areas. The disease severely hampers the economic
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contributions, welfare and productivity of the animals. The establishment of early warning systems and proper implementation of control measures are needed, including regular surveillance and vaccination, to improve animal welfare and reduce economic losses associated with episodes of the disease outbreak. Acknowledgements The research was supported by Hawassa University and the National Animal Health Diagnostic and Investigation Center (NAHDIC). All contributions are warmly acknowledged. References Abraham, G., Sintayehu, A., Libeau, G., Albina, E., Roger, F., Laekemariam, Y., Abayneh, D., Awake, K.M., 2005. Antibody seroprevalence against PPR virus in camel, cattle, goats and sheep in Ethiopia. Preventive Veterinary Medicine 70, 51–57. Abubakar, M., Jamal, S.M., Arshed, M.J., Hussain, M., Ali, Q., 2009. Peste des petits ruminants virus (PPRV) infection; its association with species, seasonal variations and geography. Tropical Animal Health Production 41, 197–1202. Al-Majali, A.M., Hussain, N.O., Amarin, N.M., Majok, A.A., 2008. Seroprevalence of, and risk factors for PPR in sheep and goats in Northern Jordan. Preventive Veterinary Medicine 85, 1–8. Anderson, J., McKay, J.A., Butcher, R.N., 1991. The use of monoclonal antibodies in competitive ELISA for the detection of antibodies against Rinderpest and Peste des Petits Ruminants virus. In: The proceedings of the final research coordination, in the seromonitering of Rinderpest throughout Africa, Phase I , International Atomic Energy Agency, Vienna, Austria, pp. 43–53. Central Statistical Authority, 2008. The Federal Democratic Republic of Ethiopia; central statistical authority. Agricultural sample sur-
vey 2007/08. Report on livestock and livestock characteristics. Addis Ababa, Statistical Bulletin 2, 38–47. Dhar, P., Sreenivasa, B.P., Barrett, T., Corteyn, M., Singh, R.P., Bandyopadhyay, S.K., 2002. Recent epidemiology of peste des petits ruminants virus. Veterinary Microbiology 88, 153–159. Diallo, A., Minet, C., Le Goff, C., Berhe, G., Albina, E., Libeau, G., Barrett, T., 2007. The threat of peste des petits ruminants: progress in vaccine development for disease control. Vaccine 25, 5591–5597. Dohoo, I., Martin, W., Stryhn, H., 2009. Veterinary Epidemiologic Research, 2nd ed. AVC Inc., Charlottetown, Prince Edward Island. Khan, H.A., Siddique, M., Abubakar, M., Arshad, M.J., Hussain, M., 2008. Prevalence and distribution of PPRV infection in small ruminants. Small Ruminants Research 79, 152–157. Legesse, G., Siegmund-Schultze, M., Abebe, G., Valle Zárate, A., 2010. Economic performance of small ruminants in mixed-farming systems of Southern Ethiopia. Tropical Animal Health and Production 42, 1531–1539. Radostitts, O.M., Gay, C.C., Hinchdiff, K.W., Constable, P.D., 2007. Veterinary Medicine, Text Book of Cattle, Horses, Sheep, Pig and Goats, 10th ed. W.B. Saunders Company Ltd., London, pp. 1242–1244. Roeder, P.L., Abraham, G., Kenfe, G., Barrett, T., 1994. Peste des petits ruminants in Ethiopian goats. Tropical Animal Health and Production 26, 69–73. Saeed, I.K., Ali, Y.H., Khalafalla, A.I., Rahman-Mahasin, E.A., 2010. Current situation of peste des petits ruminants (PPR) in the Sudan. Tropical Animal Health and Production 42, 89–93. Swai, E.S., Kapaga, A., Kivaria, F., Tinuga, D., Joshua, G., Sanka, P., 2009. Prevalence and distribution of PPRV antibodies in various districts of Tanzania. Veterinary Research Communication 33, 927–936. Tibbo, M., Woldemeskel, M., Gopilo, A., 2001. An outbreak of respiratory disease complex in sheep in central Ethiopia. Tropical Animal Health and Production 33, 355–365. Tolera, A., Abebe, A., 2007. Livestock production in pastoral and agropastoral production systems of southern Ethiopia. Livestock Research for Rural Development 19, 1–13. Waret-Szkuta, A., Roger, F., Chavernanc, D., Yigezu, L., Libeau, G., Pfeiffer, D.U., Guitian, J., 2008. Peste des petits ruminants (PPR) in Ethiopia: analysis of a national serological survey. BMC Veterinary Research 4, 112–115.
Contents lists available at ScienceDirect
Small Ruminant Research journal homepage: www.elsevier.com/locate/smallrumres
Serological investigation of Peste des Petits Ruminants (PPR) in small ruminants managed under pastoral and agro-pastoral systems in Ethiopia B. Megersa a,b,∗ , D. Biffa a,b , T. Belina a , E. Debela a , A. Regassa a , F. Abunna a , T. Rufael c , S.M. Stubsjøen d , E. Skjerve b a b c d
Hawassa University, School of Veterinary Medicine, P.O. Box 05, Hawassa, Ethiopia Center for Epidemiology and Biostatistics, Norwegian School of Veterinary Science, P.O. Box 8146 Dep., 0033 Oslo, Norway National Animal Health Diagnostic and Investigation Centre, P.O. Box 04, Sebeta, Ethiopia Norwegian School of Veterinary Science, Department of Production Animal Clinical Sciences, P.O. Box 8146 Dep., NO-0033 Oslo, Norway
a r t i c l e
i n f o
Article history: Received 9 August 2010 Received in revised form 25 February 2011 Accepted 2 March 2011 Available online 31 March 2011 Keywords: Peste des Petits Ruminants Seroprevalence Small ruminant Ethiopia
a b s t r a c t A cross-sectional study to investigate Peste des Petits Ruminants (PPR) seroprevalence was conducted between October 2009 and April 2010 in Gambella and Afar regions of Ethiopia. A total of 1163 serum samples were collected from 251 sheep and 912 goats. Competitive Enzyme Linked Immunosorbent Assay (c-ELISA) was used to detect the presence of antibodies in the sera of animals as indicator of exposure to the PPR virus. The results showed an overall individual animal seroprevalence of 30.9% (359/1163) with 29.5% in sheep and 31.3% in goats. The disease affected 96.9% (22/23) of the villages in Gambella and all the villages (9/9) in the Afar regions. The intra-village prevalence records range was 8.3–42.9% and 32.6–54.8%, and 0–66.7% and 0–71.4% for sheep and goats in Afar and Gambella regions, respectively. The high village-level seroprevalence of PPR illustrates a remarkable contagious nature of the disease. Multivariable logistic regression analysis of exposure variables revealed a significant association of PPR seroprevalence with districts and sex. Accordingly, seroprevalence was significantly higher in Adaar district of Afar (OR = 1.7, 95% CI: 1.1, 2.6) when compared to districts of Gambella region. Likewise, females were more likely to be seropositive (OR = 1.9, 95% CI: 1.2, 3.0) than their male counterparts. In conclusion, this study revealed a high seroprevalence and subsequent endemic establishment of PPR in small ruminants in the selected study areas. This disease is detrimental to small ruminant welfare and causes substantial economic losses, thereby affecting the livelihood of poor farmers and pastoralists. The need for implementing feasible control measures is, therefore, eminent to minimize the losses associated with the disease. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Small ruminants are an integral part of the livelihood of the large majority of the rural population in Ethiopia,
∗ Corresponding author at: Hawassa University, School of Veterinary Medicine, P.O. Box 05, Hawassa, Ethiopia. Tel.: +251 911842294. E-mail address: [email protected] (B. Megersa). 0921-4488/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2011.03.003
and significantly contribute to the income generation and food security of households, supplying about 23–39% of the farm cash income (Legesse et al., 2010). Next to camels, small ruminants are the most important species capable of surviving unfavourable climatic situation of arid and semi-arid environments and hence, are species of choice by pastoralists. In view of a high reproduction rate, they often constitute immediate sources of cash income, and source of meat and milk for home consumption (Tolera and Abebe, 2007).
B. Megersa et al. / Small Ruminant Research 97 (2011) 134–138
According to the Ethiopian Central Statistical Authority (2008), the population of sheep and goats in Ethiopia is estimated to be 26.3 and 23.3 million, respectively. They are widely distributed across different agro-ecological zones and production systems, being an integral part of livelihood of rural households and a source of export earning for the country. However, the productivity of sheep and goats is often hampered by multifaceted problems of which animal disease is the major one. Peste des Petits Ruminants (PPR), a severe and highly contagious trans-boundary animal disease of sheep and goats, is caused by a virus belonging to the genus Morbillivirus of the family Paramyxoviridae (Radostitts et al., 2007). Of the four known lineages of PPR virus, lineage 1 and 2 viruses have been found exclusively in West Africa. Lineage 3 has been found in east Africa, identified in the outbreak of 1996 in Ethiopia, also in the Arabian Peninsula and southern India (Dhar et al., 2002). In the past 8 years, virus exclusively of the fourth lineage has spread across the Middle East and the Asian sub-continent, reaching east as far as Nepal and Bangladesh (Dhar et al., 2002; Diallo et al., 2007). The typical clinical form of PPR is the acute form which is characterized by sudden depression, high fever, anorexia, nasal and ocular discharge, mouth erosive lesion, pneumonia and severe diarrhoea. It is considered as one of the main constraints hindering the productivity of small ruminants in enzootic regions of Africa, Asia and the Middle East (Dhar et al., 2002). In susceptible populations, morbidity may range from 10 to 100% and mortality from 0 to 90% (Dhar et al., 2002; Radostitts et al., 2007). Roeder et al. (1994) estimated an overall mortality rate of 60% in a PPR outbreak in Ethiopian goats, while morbidity of 76% and case fatality of 18% were reported from a respiratory disease outbreak in sheep in central Ethiopia (Tibbo et al., 2001). Evidences of PPR occurrence in small ruminants as well as in cattle and camels have been serologically demonstrated in Ethiopia (Abraham et al., 2005; Waret-Szkuta et al., 2008). After the first confirmed cases of PPR in Ethiopia, the disease is continuously affecting small ruminant production and thus contributing to food insecurity, particularly, in vulnerable regions of the country. There have been no substantial studies carried out on the disease in the pastoral and agro-pastoral regions of the country, giving raise to paucity of information regarding its prevalence. The present study was, therefore, aimed at investigating the current status of PPR in small ruminants of Afar and Gambella regions.
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day time and kept mainly in open enclosure during the night. The study animals were sheep and goats above 6 months of age with no vaccination history for PPR since 2006. 2.2. Study design and sampling procedure A cross-sectional four stage sampling technique (region–district– village–flock) was employed to investigate the prevalence of PPR in small ruminants in the study areas. Selection of the study unit at each stage was based on mixed design of convenience and random samplings. Regions and districts were conveniently selected based on geographical proximity and accessibility by vehicle, whereas villages and flocks were randomly selected from each area following a randomization of the villages and herd owners based on lists obtained from respective districts. In some circumstances when this was not possible, flocks were sampled conveniently in consultation with animal owners. With the limitation of establishing sample frame, sample size for detection of disease (Dohoo et al., 2009) was used to estimate the required number of animals to be sampled per village. A 95% sensitivity of finding at least a positive animal in a finite population and an expected prevalence of 10% (Abraham et al., 2005) were assumed, with a sample size of at least 30 units. The number of animals sampled from each village could vary according to flock population, accessibility by transportation and availability of logistic facilities. We intended to establish a comparable sample size covering about 36 villages (18 per region). Accordingly, a total of 1163 animals (251 sheep and 912 goats) were sampled from 32 villages in both regions. Information on potential risk factors such as geographic location, animal factors, and husbandry practices was recorded during blood sampling. 2.3. Serum collection and testing Blood samples were aseptically collected by puncturing the jugular vein using venoject needles and plain vacutainer tubes. Each sample was labelled with an individual identification code, and the descriptions were recorded on the questionnaire format. Blood samples were kept overnight in cold boxes to allow clotting and subsequent separation of serum. Sera were then collected in sterile tubes and transported to the laboratory using an ice box where temporary storage was made at −20 ◦ C until tested. Serum samples were analyzed at the National Animal Health Diagnostic and Investigation Center (NAHDIC, Sebeta, Ethiopia) using a competitive ELISA kit following the instructions of the manufacturer (Institute for Animal Health, Pirbright Laboratory, UK) according to Anderson et al. (1991). The test depends on inhibition of the binding of anti-H protein monoclonal antibody (MAb) to a PPR virus specific epitope in the presence of antibodies in the serum samples. Inhibition is detected as reduction in the optic density (OD) reading obtained with the monoclonal antibody alone following the addition of peroxidase labelled anti-mouse conjugate and substrate (chromogen mixture). The ELISA micro-plates were read with an Immunoskan reader (Flow laboratories, UK) with an inference filter of 492 nm. The reader was connected to a computer loaded with ELISA Data Information (EDI) software (FAO/IAEA, Vienna, Austria), which was used to automate the reading and calculation of percentage of inhibition (PI) values. The OD values were converted to percentage inhibition (PI) using the following formula: PI = 100 −
(OD control or test serum) × 100 (OD monoclonal control)
Samples with PI > 50%, a cut-off point, were considered as positives. 2.4. Data management and analysis
2. Materials and methods 2.1. Study area and study population The study was conducted from October 2009 to April 2010 in selected districts of two regions, namely Gambella (Abobo, Gambella, Lare and Itang districts) and Afar (Adaar district), which are characterized by pastoral or agro-pastoral production systems. The Gambella region is located in the South-western part of the country with an altitude range of 350–500 m above sea level in the Western part and 500–2000 altitude in the Eastern and South-eastern part of the region. The Afar region is located in the North-eastern part of the country with an altitude ranging from 1000 to 1500 m above sea level. Small ruminant production is predominantly traditional, where animals are allowed to graze freely during
Data were stored in a Microsoft Excel® Spread Sheet and data analysis was performed using Stata version 11.0 for windows SE (Stata Corp. College Station, TX). Descriptive statistics of the recorded variables were summarized per different study units (stages) using tabulate command in Stata. Individual level prevalence was calculated at different stages by using the survey command in Stata, with village as the primary sampling unit. Logistic regression analysis was used to investigate the potential association of recorded exposure variables with the disease prevalence. The degree of association between potential risk factors and seroprevalence was computed using the odds ratio. The final multivariable model was established using a backward selection procedure of variables, using village as clustering effect. The model was checked for fit using the Hosmer–Lemeshow goodness of fit test.
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Table 1 Individual animal PPR seropositivity at animal and village levels stratified by region. Gambella
Animal level Goat Sheep Subtotal Village level Goat Sheep Subtotal
Afar
Total
No
Positive (%)
No
Positive (%)
No
Positive (%)
617 162 779
162 (26.3) 51 (31.0) 213 (27.3)
295 89 384
123 (41.7) 24 (27.0) 147 (38.3)
912 251 1163
284 (31.1) 75 (29.9) 359 (30.9)
23 18 23
22 (95.7) 15 (83.3) 22 (95.9)
9 9 9
9 (100) 9 (100) 9 (100)
32 27 32
31 (96.9) 24 (88.9) 31 (96.9)
Table 2 Intra-village levels of seropositivity in sheep and goats in the studied villages over prevalence groups. Regions
Districts
Gambella
Abobo Gambella Lare Itang Adaar
Afar Subtotal a
0%
1–10%
11–20%
21–30%
1 (51)
2 (37) 1 (61)
1 (51)
3 (98)
4 (160) 3 (135) 2 (43) 1 (45) 2 (103) 12 (486)
1 (13)
1 (13)
31–40%
>40%
1 (50) 3 (61)
2 (87) 2 (36)
4 (164) 8 (275)
3 (117) 7 (240)
Total 5 (210)a 5 (222) 10 (190) 3 (157) 9 (384) 32 (1163)
Numbers outside and inside the brackets indicate number of sampled villages and animals, respectively.
3. Results Of the total serum samples tested, 30.9% (359/1163) were found positive for PPR antibodies. The seropositivity ranged from 14.6% in Itang district of the Gambella region to 38.3% in Adaar district of the Afar region. The disease showed a widespread spatial distribution covering 96.9% (22/23) of the villages in Gambella and all the studied villages (9/9) in the Afar region. Table 1 gives the seroprevalence of PPR at animal and village levels stratified by study region. Within-village seroprevalence values ranged from 8.3 to 42.9% and 32.6 to 54.8% (Afar) and from 0 to 66.7% and 0 to 71.4% (Gambella) for sheep and goats, respectively. The intra-village level of seropositivity in pooled samples of sheep and goats is presented in Table 2. Seroprevalence records were uniformly above 30% in most villages of the Afar region, while marked variation in prevalence distributions, ranging from 0 to over 71.4%, were recorded in villages of Gambella. The overall seroprevalence distribution of PPR in the study areas with respect to exposure variables is shown
in Table 3. A significantly higher seroprevalence (38.3%) was found in Afar than Gambella (27.6%). The lowest prevalence was recorded in Itang district (14.7%) of the Gambella region. The multivariable logistic regression analysis (Table 4) showed that geographical locality and sex as being risk factors for seropositivity to PPR. Seroprevalence was significantly higher in Adaar district of Afar (OR = 1.7, 95% CI: 1.1, 2.6) when compared to the prevalence records in districts of Gambella. Likewise, females were more likely seropositive (OR = 1.9, 95% CI: 1.2, 3.0) than their male counterparts. Post estimation statistics (Hosmer–Lemeshow goodness of fit test) shows fit of the model to the observed data (2 = 7.3, P = 0.122). 4. Discussion The study showed that PPR was widely prevalent in small ruminants in the study areas. All villages, except one in Gambella, had seropositive cases. Such a high prevalence in most of the villages (more than 30%) suggests a remarkable contagious nature of the disease, covering
Table 3 Univariable analysis of exposure variables and PPR prevalence in sheep and goats, showing prevalence levels split on variable levels and P-values from univariable statistical analyses. Variables
Levels
Number examined
Positive
Prevalence (95% CI)
Region
Gambella Afar Abobo Gambella Lare Itang Adaar Goat Sheep Male Female Young Adult
779 384 210 222 190 157 384 912 251 154 1009 316 847
212 147 56 78 55 23 147 285 74 34 325 104 255
27.2 (24.1, 30.3) 38.3 (33.4, 43.2) 26.7 (20.7, 32.7) 35.1 (28.8, 41.4) 28.9 (22.5, 35.4) 14.6 (9.1, 20.2) 38.3 (33.4, 43.2) 31.3 (28.2, 34.3) 29.5 (23.8, 35.1) 22.1 (15.5, 28.7) 32.2 (29.3, 35.1) 32.9 (27.7, 38.1) 30.1 (29.3, 35.1)
Districts
Species Sex Age CI, confidence interval.
P-value – 0.000 – 0.117 0.537 0.005 0.006 – 0.591 – 0.012 – 0.357
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Table 4 Multivariable analysis of exposure variables and PPR seropositivity in sheep and goats. Variablesa
Levels
No (%)
OR (95%CI)
P-value
Districts
Abobo Gambella Lare Itang Ada‘ar Male Female Young Adult
210 (26.7) 222 (35.1) 190 (28.9) 157 (14.6) 384 (38.3) 154 (22.1) 1009 (32.2) 316 (32.9) 847 (30.1)
1.0 (–) 1.5 (0.9, 2.6) 1.1 (0.7, 2.0) 0.5 (0.2, 1.1) 1.7 (1.1, 2.6) 1.0 (–) 1.9 (1.2, 3.0) 1.0 (–) 0.7 (0.5, 1.1)
– 0.137 0.647 0.094 0.009 – 0.006 – 0.102
Sex Age
a Region was not included in multivariable analysis due to collinearity. OR, odds ratio; CI, confidence interval; Hosmer–Lemeshow goodness of fit test (2 = 7.3, P = 0.122) shows the model fitted the data.
wide geographic areas and infecting perhaps most of the susceptible animals in affected villages. The overall seroprevalence (30.5%) of this study (Table 1) is much higher than the findings in previous studies carried out in the country; 6.8% by Abraham et al. (2005) and 6.4% by WaretSzkuta et al. (2008). This could be attributed to the nature of production systems, large flock size, uncontrolled animal movement and frequent contact between flocks. Mobile pastoral herds may often come into contact with local sheep and goats, and facilitate contact transmission of PPRV from infected to susceptible animals. Likewise, infected migratory animals may transmit the virus to susceptible small ruminant population, and, therefore, the movement of animals plays an important role in the transmission and maintenance of PPRV in nature (Abubakar et al., 2009). This is in accordance with the work done by Al-Majali et al. (2008) which recorded a higher seroprevalence of PPR in regions with free animal movement than other areas in Jordan. Furthermore, limited fodder availability, especially during drought and long dry season, further leads to nutritional deficiency and increased susceptibility to infection in addition to animal movements. Consequently, large numbers of animals become infected during this period, giving raise to establishment of disease endemicity and continued year round circulation of the virus enhanced by frequent animal-to-animal contacts (Abubakar et al., 2009). Targeting these factors in disease control programme may play a key role in limiting the transmission of PPR infection and augmenting effective disease control programmes. Poor animal health services, a common constraint in peripheries and pastoral areas of the country, could also contribute to the wide prevalence and endemic establishment of the disease. The Afar region had a higher PPR seroprevalence than the Gambella region, which could be linked to differences in animal husbandry system. Afar is characterized by pastoral production systems where large flocks are kept mixed with cattle and camels, coupled with unrestricted animal movements. In comparison, the Gambella region is more of an agropastoral region. The dynamics and frequent mobility of flocks in pastoral areas increase the chance of coming into contact with other potentially infected flocks or herds. In agreement with our study, previous researchers also documented higher seroprevalence of the disease in pastoral regions compared to other areas of the country (Abraham et al., 2005; Waret-Szkuta et al., 2008). Likewise, a study by Al-Majali et al. (2008) showed an association of large flock
sizes and mixed farming with PPR seropositivity in Jordan. Antibodies to PPRV have been demonstrated in cattle and camels sharing common ecozones with small ruminants in Ethiopia (Abraham et al., 2005), suggesting possible reservoir role of these animals in multiple species holdings. Comparison of village level seroprevalence between the Gambella and Afar regions, revealed a uniformly higher seroprevalence in the latter, while wide variation of prevalence distribution (from 0 to 71.4%) was observed in the former, which could be related to difference in production systems (Table 2). Although the seropositivity difference between sheep and goats remains controversial in the literature, the current prevalence between the two species (sheep 29.5% and goats 31.3%) was comparable (Table 2). Some authors (AlMajali et al., 2008; Waret-Szkuta et al., 2008; Swai et al., 2009) reported a higher seroprevalence in goats than in sheep and linked it to higher fecundity in goats compared to sheep. It was suggested that new born kids account for a large proportion of the goat flock each year, which increase the size of susceptible population. Others reported higher seroprevalence in sheep than goats (Abraham et al., 2005; Khan et al., 2008; Saeed et al., 2010). This was either related to a relatively lower number of sheep sampled in some of these studies or due to the fact that goats are often affected more severely by peracute and acute form of the disease, and might die prior to sampling. Hence, further investigations are required to determine the variation in the relative host susceptibility and pathogenicity of PPRV between the two species. Similar to the findings of Waret-Szkuta et al. (2008) and Khan et al. (2008), a significantly higher seroprevalence of PPR was observed in females compared to males in our study. This could be related to the physiological differences between the two subjects where females reveal some degree of infection preponderance as a result of production and reproduction related stresses. Association of seropositivity with age was not significant in the logistic regression analysis. This contradicts the findings of Abubaker et al. (2009), who reported a progressive increase of seroprevalence with increasing age and related it to the accumulation of recovered convalescent over time where animals maintained in the flock for production purposes. In conclusion, the results of this study documented serological evidence for widespread distribution and endemic establishment of PPR in small ruminant population of the study areas. The disease severely hampers the economic
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contributions, welfare and productivity of the animals. The establishment of early warning systems and proper implementation of control measures are needed, including regular surveillance and vaccination, to improve animal welfare and reduce economic losses associated with episodes of the disease outbreak. Acknowledgements The research was supported by Hawassa University and the National Animal Health Diagnostic and Investigation Center (NAHDIC). All contributions are warmly acknowledged. References Abraham, G., Sintayehu, A., Libeau, G., Albina, E., Roger, F., Laekemariam, Y., Abayneh, D., Awake, K.M., 2005. Antibody seroprevalence against PPR virus in camel, cattle, goats and sheep in Ethiopia. Preventive Veterinary Medicine 70, 51–57. Abubakar, M., Jamal, S.M., Arshed, M.J., Hussain, M., Ali, Q., 2009. Peste des petits ruminants virus (PPRV) infection; its association with species, seasonal variations and geography. Tropical Animal Health Production 41, 197–1202. Al-Majali, A.M., Hussain, N.O., Amarin, N.M., Majok, A.A., 2008. Seroprevalence of, and risk factors for PPR in sheep and goats in Northern Jordan. Preventive Veterinary Medicine 85, 1–8. Anderson, J., McKay, J.A., Butcher, R.N., 1991. The use of monoclonal antibodies in competitive ELISA for the detection of antibodies against Rinderpest and Peste des Petits Ruminants virus. In: The proceedings of the final research coordination, in the seromonitering of Rinderpest throughout Africa, Phase I , International Atomic Energy Agency, Vienna, Austria, pp. 43–53. Central Statistical Authority, 2008. The Federal Democratic Republic of Ethiopia; central statistical authority. Agricultural sample sur-
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