Sero-Prevalence and Risk Factors of Diffusion of Peste des Petits Ruminants in Cameroon

The present study was carried out between April 2015 and January 2016 to estimate the sero-prevalence and identify the risk factors of the peste des petits ruminants (PPR) in Cameroon. A total of 269 herds randomly sampled across the country have been studied and 1622 samples of serum have been levied on the sheep and goat. The c-ELISA has been studied in order to detect the presence of antibodies in small ruminants like an indicator of exposition to PPRV. The results revealed the circulation of PPRV in the country with a total sero-prevalence of 39% [95%CI; 37 - 41] and a sero-prevalence of 63.2% [95%CI; 57.2 - 69.2] at the herd level. Sero-prevalence was variable in the ten regions ranging from 7% [95% CI; 6.2 - 8.4] to 73% [95% CI; 62 - 84] with the northern zone (Adamawa, North and Far-North) having 52.3% [95% CI; 37 60] and southern zone (including the remaining seven regions) recording 29% [95% CI; 11 - 57]. Similarly, it was higher in animals found in ur-ban/peri-urban areas than in rural areas with prevalence ratio of 2.9 [95% CI 2.54 - 3.4; p < 0.001] i.e. 3 times more,


Introduction
The peste des Petits ruminants (PPR) is an infectious disease which is very contagious due to a virus (PPRV), belonging to the gender Morbillivirus of the family of paramyxoviridae [1]. It affects small domestic (goats and sheep) and wild ruminants and is characterized by a feverish invasion, respiratory and digestive involvements and ulcerative and necrotic lesions of the mucous membrane. The PPR has been identified by the World Organization for Animal Health (OIE) as a cross-border viral disease with a mandatory reporting under the conditions in out in the health code for terrestrial animals of the OIE and economically important in sheep and goat due to the high mortality and morbidity in these species [2].
Following the rinderpest eradication and for its epidemiological and economical importance, FAO and L'OIE, choose PPR as a priority in terms of eradication control in the world. Very effective licensed PPR vaccines have been developed and more than 20 laboratories produce these vaccines in Africa [3] [4].
The causal agent, the PPR virus (PPRV), is genetically grouped into (I, II, III, IV) four lineages based on a partial sequence analysis of the gene. The cloned colonies I to III circulate in Africa while lineage IV is in Asia [5]. However Kadidia TOUNKARA discovered the presence of lineages IV in the Southern of Niger [6] and the same cloned colony had already been discovered in Cameroon in 1997, in Gabon [7] and recently in Nigeria by 2018 [8]. These results suggest that lineage IV of Asian origin spreads from East and Central Africa to West Africa where the lineage II is currently predominant [9].
A recent apparition of the lineages IV was associated with a significant epizootic in Morocco, and posed a probable risk of introduction into Europe [9] [10].
The PPR was first described in 1942, in Ivory Coast [6]. From its African candle located between the equator and the Sahara, the disease has spread to reach days before the beginning of the sickness [15].
In Cameroon, the PPR is a legally contagious disease with a compulsory declaration throughout the territory [16]. Although recognized as being the source of a significant economic loss in small ruminant production system, its epidemiological situation remains poorly assessed epidemiological situation [17]. The Panafrican control of epizootics (PACE) had put in place a control epidemiological network of animal disease in many African countries like Cameroon. The reporting of clinical suspicions of the PPR from 2005 to 2010 by this network permitted to note that the pest of small ruminants was enzootic in Cameroon due to its presence on the national territory [2] [17].
In this study, we analyze the results of serological investigations carried across the country in order to establish the sero-prevalence of the PPR in sheep and goats and to evaluate the risk propagation factors of the disease.

Area and Type of Study
The study took place on the ten regions of the Country: Far North, North, Ada-

Specimens and Samples
During these transverse investigations, the none-vaccinated herds with PPR with less than 10 animals (sheep and goats) were selected by simple random sampling. Totally, 269 herds were chosen by random selection. Four to five animals aged with more than 6 months (owners' notice and confirmation by observation of the dentition) in each herd were drawn regardless of gender and samples were taken. For each herd which disposed of less than six animals which respect the minimal age, they were all collected. Totally, 1622 samples of small ruminants have been done. Blood was taken from the jugular vein by a 10 ml syringe and introduced into a marked tube with the breeding code and serial number. All the samples were transported in a cooler every evening; they were centrifuged and transferred to cryotubes marked with regional codes, the department, district and direct debit number. These serums were conserved in freezers of departmental delegations, and then transported to the National Veterinary Laboratory (LANAVET) under ice, where they were stocked at temperatures of −20˚C.

Serological Test
The samples were diagnosed at the national veterinary laboratory (LANAVET)

Opinion Poll among Breeders
In addition to the sample taken from each herd, an opinion poll (survey) on the behavior, attitude and practicals have been administered to every breeder in order to evaluate the transmission and diffusion risks of the disease. The following points have been mentioned in this questionnaire: breeding mode, implantation and breeding ground, purchase or sale of animals, sanitary state, vaccination and herd conduct.

Statistical Analysis
Data has been saved in excel and the STATA software (version 10.0) has been used to determine the national sero-prevalence then, that of each region. The csi function has been used to have an estimation of the RR. The QGIS software (version 2.12.0) has been used for the cartographic representation of results.

Determination of Risk Factors for the Spread of PPR
The opinion poll of 267 breeders made it possible to identify, in order of importance, five key risk factors, namely; the environment in which the breeding ground was established, the introduction of new animals into the breeding grounds, the gathering of animals grazing or common watering, wandering animals and transhumance with respective opinion percentages of 54%, 33%, 27%, 22% and 7%. The environment in which the breeding ground is located, appeared to be the most important associated risk factor of the five and has a significant impact in the southern zone compared to the northern zone. Transhumance and the gathering of animals in a common pasture or watering is more practiced in the northern zone than in the southern zone where straying constitutes the dominant mode of breeding. The difference was not so significant in the two areas at the Open Journal of Veterinary Medicine risky practice of introducing new animals into the breeding grounds (Figure 1).
For other parameters mentioned during the interviews, our results indicate that 49% of animals sampled were in urban/peri-urban areas, all the farms in our sample were intended to produce meat (no milk production), vaccinated herds were excluded from the survey.

Determination of Prevalence on Breeding Grounds Located in Urban/Peri-Urban and Rural Areas
To measure the risk of exposure of the disease in relation to the setup of breeding grounds either in urban/peri-urban or in rural areas, we calculated the sero-prevalence between animals raised in urban/peri-urban areas with those in rural areas. Overall, the prevalence in herds raised in urban/peri-urban areas is three times higher than in herds raised in rural areas. The prevalence ratio is 2.9; [95% CI 2.54 -3.4; p < 0.0001] ( Table 4). There is a significant difference between the exposures of the infection in the urban/peri-urban area compared to the rural area. The urban/peri-urban environment appears more exposed to the disease than the rural area.
At the national level, the sero-prevalence of PPR appears to be 3 times higher in animals in urban/ peri-urban breeding grounds as compared to animals in rural area breeding grounds. The urban/peri-urban areas seem to constitute an environment at high risk of exposure to the transmission and diffusion of PPR in small ruminants. However, the prevalence ratio (PR) of PPR between urban/peri-urban and rural areas is lower in the northern area (Adamawa, North  2). Animals from urban breeding grounds in the Northern zone and the Southern zones are respectively 1.6 and 5 times more exposed to PPR as compared to animals from rural breeding grounds. The urban/peri-urban environment or area seems to constitute an associated risk factor which facilitates the spread of Figure 2. Determination of the level of risk between the urban/peri-urban and the rural areas.     Similary, the movement of these small ruminants in the country constitutes an important propagation factor of the PPR. This is done for commercial reasons Open Journal of Veterinary Medicine especially during religious feasts (Tabaski) where, an important number of ruminants are transported to urban centers. Thousands of heads leave the northern zone to the southern zone. Big towns like Yaounde and Douala constitute the essential laying point of these animals. A great number is sent to neighboring countries like Gabon, Equatorial Guinea and Nigeria. Veterinary services lack enough human resources to control this animal circulation within the territory and in frontal zones. When animals are displaced, some infected ones escape from veterinary control and are hence at the origin of local livestock contamination [22]. Moreover, during their displacement from the northern to southern zones, animals can develop a disease then get other animals infected during their transport. This can be one of the reasons of a higher PPR epizootic frequency. Some similar observations have been done throughout the study of the PPR in the tropical humid zone of south Nigeria [23] and in India [12] [24].

Discussion
Therefore, breeding practices, agro-climatic conditions and geographic locations have an impact on the seasonal distribution of the disease. The movements of animals therefore play an important role in the maintenance and transmission of the PPRV in the nature [23]. Mass vaccination campaigns have to be scheduled taking into account this period.

Conclusion
This study has permitted us to notice that the PPR is endemic in the whole country and is spread by different breeding modes of different geographic zones, livestock migration, agro-climatic conditions and identified risk factors especially the implantation breeding location in urban/peri-urban areas. The existence of a probable link between the implemented breeding in urban/peri-urban areas and the illness was suspected indicating the interest of purchasing an analytic study for the verification of this probable association.