Seroprevalence and risk factors of Peste des Petits Ruminants in sheep and goats in Sudan

The seroprevalence and risk factors of Peste des Petits Ruminants (PPR) were determined in unvaccinated sheep and goats in Sudan. A total of 480 sera samples were collected from the sheep (n=261) and goats (n=219) of Sennar, Gedarif, River Nile, and North Kordofan states during May, June, and October 2012 and February 2013, respectively. The sera were tested for the presence of antibodies against PPR using competitive Enzyme Linked Immunosorbent Assay. The overall seroprevalence of PPR was recorded as 45.6% (n=219/480); whereas, 57.2% in Sennar, 46.2% in Gedarif, 34.9% in River Nile and 39.8% in North Kordofan. A total of 14 risk factors were investigated using structured questionnaire, of which 9 were found to be associated with PPR seroprevalence (p≤0.05). Among the localities, Abozabad located in North Kordofan had the highest prevalence (91.7%) of PPR followed by Barbar in River Nile. PPR seroprevalence was higher in pastoralists, animals housed in scarp fences, females, and Kwahla sheep. In addition, PPR was higher in the states that had high rainfall and wind-speed. The associated 9 factors were further analyzed multivariably by logistic regression, and finally 5 of them (states, localities, husbandry system, gender, and age) were found to be associated with PPR seroprevalence (p≤0.05).


INTRODUCTION
Peste des Petits Ruminants (PPR) is a highly contagious transboundary animal disease affecting both wild and domestic small ruminants.The disease was first described in 1942 in Cote Devoir (Ivory Coast), and subsequently it spread over large areas in Africa.PPR is now prevalent in broad belt in Sub-Saharan Africa.In Africa, serological evidence of this disease was detected in Niger; however, the existence of PPR virus was confirmed in Ethiopia and Eritrea (Gopilo, 2005).In 2007, PPR was confirmed in Kenya and Uganda, and in 2008, the disease was reported in Tanzania (Karimuribo et al., 2011).
In Sudan, PPR was first reported during 1971 in Southern Gedarif state (Eastern Sudan), then in Central Sudan during [1971][1972].After these reports, PPR outbreaks continued to be reported in Darfur, Central Sudan and Khartoum (Saeed et al., 2004).At present, the disease is considered as an endemic disease in Sudan, similar to other countries of East Africa, with a seroprevalence rate varying from 58.1% to 93.8% (Shuaib, 2011).So far, several studies have been reported on seroprevalence of PPR and isolation of PPR virus in Sudan.However, there are very few reports on epidemiological and environmental factors related to PPR outbreak in small ruminants in Sudan.Also, limited works have been conducted to investigate the risk factors which contribute in the spreading of PPR virus.Therefore, the present study was designed to investigate the seroprevalence of PPR in sheep and goats of Sudan; and to rule out different risk factors that might be associated with PPR seroprevalence in Sudan.

Study area:
The study was conducted in four different states of Sudan; River Nile (in the north), Gedarif (in the east), Sennar (in the center), and North Kordofan (in the west) (Figure 1).

Sample collection:
A total of 480 blood samples were collected from sheep (n=261) and goats (n=219) from Sennar, Gedarif, River Nile, and North Kordofan states in Sudan during the months of May, June and October 2012, and February 2013, respectively (Table 1).

Detection of PPR antibodies using competitive
Enzyme Linked Immunosorbent Assay (cELISA): Sera samples were separated from the blood samples by centrifugation (5,000 rpm) at room temperature, and stored at -20 0 C until used.The sera were tested for PPR antibodies using cELISA kit (CIRAD EMVT, Montpellier, France).The test was performed according to the instructions of the manufacturer.
Data collection: Data on PPR outbreaks, animal census, vaccination and animal movement were collected from the General Directorate of Animal Health and Epizootics Disease Control, and the General Administration of Animal Resources located in the above mentioned four states.Meteorological data were collected from the Sudan Meteorological Authority.The data included rainfall, temperature, wind-speed and relative humidity records during the sampling period.A structured questionnaire was used to collect data during the period of sampling.The questionnaire was designed to record the risk factors via direct questioning to the herd owners, and also some factors were taken from the direct notices and calculations, the Latitude and Longit-ude were taken using Global Positioning Service (GPS).

Data analysis:
Categories of all data have been presented in Table 2.The collected data were analyzed by the Statistical Package for Social Sciences (SPSS) version 17.0.First, an analysis by using 2-tailed Chisquare test was conducted to find out the association between the investigated 14 risk factors and the ELISA positive and negative animals.In the second step, a logistic regression model was used to assess the association between the 9 significant risk factors (p≤0.05) in the univariate analysis and the PPR Abs (+ve) and PPR Abs (-ve).Data and results displayed in tables and Map were produced using GIS software ArcMap 9.3.

Risk factors associated with PPR seropositivity:
Univariate analysis using Chi-square: Fourteen risk factors were assessed using structured questionnaire for every sampled herd.Nine different factors were found to be associated with PPR seroprevalence (p≤0.05).In univariate analysis when analyzed by Chisquare (χ 2 ), Sennar state was found to have the highest prevalence (57.2%), and within localities, Abozabad in Northern Kordofan had the highest prevalence (91.7%) followed by Barbar in River Nile state (70%).PPR was found to be highly prevalent among pastoralists (68.1%) as compared to other husbandry systems.Among the animal housing types, the animals kept in scrap fence houses had the highest PPR seropositivity (100%).Females were found to be more affected with PPR (54.5%).Regarding age groups, animal >12 months had the highest prevalence (57.2%) of PPR (Table 2).Kwahla sheep was mostly affected (83.3%) by PPR as compared to other sheep breeds.Some climatic conditions were found to be associated with PPR prevalence; the states with high rainfall and high windspeed were found to have the highest PPR prevalence (51.6% and 50.2%, respectively) as shown in Table 2.

Multivariate analysis using Logistic regression:
The significant 9 factors, found from univariate analysis, were further subjected to multivariate analysis using Logistic Regression model, and finally 5 risk factors were found to be associated with PPR seroprevalence (p≤0.05);these were states, localities, husbandry system, sex and age as shown in Table 3.

DISCUSSION
Assessment of risk factors is important for effective control and eradication of PPR.Besides climatic factors, seasonal and geographical variations influence PPR outbreak.Our study showed that the overall prevalence (45.6%) of PPR in four states of Sudan was  Shuaib (2011).This variation might be due to the wide-coverage of vaccination against PPR that reached 5,200,190 doses (animals) in 2011 as compared to 2,799,299 doses (animals) in 2010 (Anonymous, 2010(Anonymous, & 2011)).The PPR prevalence was found to be significantly higher in Sennar (57.2%) followed by Gedarif (46.2%) in Eastern Sudan, and North Kordofan (39.8%) in western Sudan; whereas, the lowest prevalence was recorded in River Nile (34.9%) in Northern Sudan.The highest prevalence of PPR in Sennar and Gedarif might be due to the difference in climatic factors as these two states had the highest annual rainfall rates among the states.These findings were agreed with the reports of Saeed et al. (2010), while differed from the findings of Abdalla et al. (2012), andShuaib (2011).This state variation of PPR prevalence might be due to variation in rainfall, humidity and wind-speed among the states.In our study, we found that the states with high rate of rainfall and high wind-speed were significantly affected as compared to the states having low rainfall and slow windspeed.High rainfall cools weather that contributes to PPR spreading, as described by Elnoman et al. (2011), Elhassan et al. (1994), andSaeed et al. (2010).
On the other hand, based on locality, highest prevalence of PPR was found at Abozabad (91.7%) in Northern Kordofan state, followed by Barbar in River Nile state (70%).From these findings, it can be speculated that the prevalence of PPR was varied significantly among the states of Sudan as well as within a state in the country due to the geographical difference; these findings are agreed with the results reported by Shuaib (2011) and Muse et al. (2012).However, the observation reported by Ozkul et al. (2011) differed to our findings.
Sheep and goats of >12 months had a significantly higher seroprevalence, followed by animals with age from 4 to 12 months, while the low prevalence was found in kids aging 1 to 3 months.These results are in support to the findings of Abubakar et al. (2009), who reported that highest PPR seroprevalence was seen in animals aged >2 years.Therefore, adult animals might be more vulnerable to PPR infections as compared to younger animals.However, Sarker and Islam (2011) reported the highest PPR prevalence in young animals reasoning the poor immunity and poor nutrition as responsible factors for the disease prevalence.
Our study revealed that females were affected significantly as compared to males, agreeing with Shuaib (2011), andAbdalla et al. (2012).The present breeding system in Sudan could be the reason as female animals were kept longer time for reproduction purpose.But, it was disagreed with Sarker and Islam (2011) who stated that males are mostly affected by PPR, and this might be due to genetic variation of the animals.
In our study, animals reared with pastoralist system (Transhumance) were mostly infected (68.1%).Low prevalence was found in the animals reared in intensive system.This was similar to the findings of Shuaib (2011).Also, the interaction between sheep and goats in pastoralist system especially in the states with high density of wild animals like Sennar and North Kordofan could affect the PPR prevalence; as the infectivity and role of PPR transmission through wild ruminants is mentioned by Housawi et al. (2004), Zahur et al. (2008) and Gopilo (2005).
PPR seroprevalence was found to be differed significantly between housing categories; animals in scrap fences were mostly affected, followed by animals with no houses.The low prevalence was found in animals kept in modern houses with metal fences.
We also checked the seroprevalence of PPR among the breeds, and we found that Kwahla breed of sheep was significantly affected followed by Gwasma sheep.These two breeds belong to trans-human tribes and trans-human was shown for the highest seroprevalence among husbandry systems.
The association between the positive cases against PPR and the 9 potential risk factors found through univariate analysis was assessed with a multivariate analysis using logistic regression; with confidence interval 95% and p≤0.05.The multivariate analysis revealed an association between the PPR seropositivity and the geographical location in state and locality levels, and that was in line with Shuaib (2011).Sheep and goats from three localities were at high risk for PPR infections; Basonda in Gedarif state (Exp (B)=5.731),Abuhugar (Exp (B)=12.949)and East Sennar (Exp (B)=11.217) in Sennar state.
Regarding the husbandry system, logistic regression revealed significant association between the systems and PPR seropositivity.The animals owned by nomadic pastoralists were at high risk for PPR with Exp (B)=0.073and p=0.018 as compared to other systems.This could be due to vulnerability of small ruminant herds in pastoralists and open grazing systems to infected herds in pastures, and water points.These herds might be arrived from other states particularly, from the states located at country borders like Sennar and Gedarif with high PPR prevalence.This finding is in agreement with the observations of Kihu et al. (2010).

CONCLUSIONS
The overall seroprevalence for PPR was 45.6%.Prevalence of PPR was mostly associated with high rainfall and high wind-speed.Pastoralists and open grazing among the different husbandry systems were most important for PPR outbreaks.On the other hand, PPR was mostly prevalent in female animals, and the animals of >12 months of age.