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 the Arabian Peninsula, the Middle East, Southeast Asia, India, China and North Africa [11] [12].

The disease principally spreads by direct contact between non-infected animals and infected ones. Extensive breeding systems, seasonal migrations, market and gatherings ease the propagation of the disease. International transhumance is very practiced in the area which brings together the three regions of the North (Far North, North and Adamawa). Indeed, there are several massive movements of breeders and small ruminants from East African countries (Chad, Sudan, Central African Republic), via the three Regions to reach the African countries of West (Nigeria, Benin). The risk of spreading the disease is therefore very high [13]. PPR is a very contagious disease which spreads very fast. The contamination sources are different sick animals’ excretions: nasal and eye secretions, saliva, feces and urine [1] [14] [15]. The infected animals can excrete the virus about 3 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.

A better knowledge of the epidemiological situation of pests of small ruminants and of the risk factor is very important to adjust the control strategy with a view of eradicating this disease in Cameroon. This study is the first nationally to provide prevalence based on the presence of anti-PPR antibodies in the serum analyzed, PPR is present in all Cameroon regions and the serological prevalence rate was 39.6% [CI 95%; 37.6 - 41.6], value appeared rather close to a study carried out in breeding station in the northern zone of the country by Awa et al. Who found a serological prevalence of 29% in sheep and 44% in goats [19]. It is also close to studies carried out in other countries. This is the case in Mali where a prevalence of 42.6% [CI 95%; 40.9 - 44.3] in small ruminants has been found [10] [20].

The northern zone made up of three regions (Adamawa, North and Far North) shows a high prevalence of 52% [CI 95%; 47 - 60] than the southern zone 29% [CI 95%; 11 - 57]. This can be justified by the fact that each of these two large areas includes regions which have a fairly similar geographical location and a method of rearing small ruminants. Thus in the northern part of the country, for deficiency reasons in grazing and watering due to a long period of the dry season, the mode of breeding, transhumance and the gathering of animals in the pastures and common watering, remains the most practiced breeding method. On opposition, in the southern zone, a wetter zone characterized by an abundance of pasture, this zone is at less risk despite the rambling which constitutes a risky practice. However, in the southern regions, there is a high prevalence in the

Littoral, South and West regions with 44%, 54%, and 70.7% respectively. These rates can be explained partly by the traffic of small ruminants from the northern part to the southern part, to conquer the markets of large cities (Yaounde, Douala, Bafoussam, …) and neighboring countries (Gabon, Equatorial Guinea, Nigeria). This argument is consolidated by the results of this study which indicates that the prevalence of animal breeding in the urban/peri-urban area appears in this zone of the country, 5 times more than in the rural areas in comparison to the southern zone where the prevalence between these two areas seems weakly significant with a prevalence report of 1.6 times. The proximity to the market of these cities facilitates the purchase of animals at risk, their introduction into breeding grounds, therefore an increase of this disease in small ruminants found in the urban and peri-urban zones. These results indicate a possible link between these environments where breeding and the disease are implemented [6].

As part of these studies and in order of importance, the five factors of PPR propagation risk are as follows: breeding location, introduction of new animals in the breeding ground, the gathering of animals on pasture or common watering, wandering of animals and transhumance after a poll opinion amongst breeders. The implantation environment appears as one of the most important risk as compared to the other factors. This is explained by the fact that it is an associated factor grouping at least two other factors depending on the zones and breeding methods. The sale of sick animals in livestock market has proven to be a risk factor during the opinion poll, since 68% of breeders questioned their animals at the livestock market when they notice first mortalities in their breeding environments. Those buying can thus in some cases procure sick animals which enter their breeding environments without respecting quarantine measures. This certifies what Singh et al. noticed; the commerce of small ruminants in markets, where animals from different horizons and sources are put in contact with others hence, favors the transmission of PPRV [12].

By the way, imported animals from the northern zone with an unknown sanitary state and sold in markets then introduced in breeding environments, can develop a sickness in their new environment and transmit to other animals. The gathering of animals during pasture constitute a current practice in the northern regions (Adamawa, north and far north) or in particular towns where one person is in charge of collecting the animals in their various concessions each morning, bringing them to common grazing zones and taking them back in the evening. The transhumance equally constitutes a risk factor because of animals which are brought from neighboring countries (Congo; Gabon; RCA; Equatorial Guinea; Nigeria and Chad) researching pastures.

These two risk factors listed are very important in this zone. Conversely, the wandering of animals is a common risky practice, especially in the southern part of the country and particularly in the rural area. However, this breeding method favors gathering and is a risk factor for the diffusion of the disease. We may expect a high prevalence rate in rural areas, except that in the southern zone, the rural landlocked zones and the limitation see absence of introduction of new animals lowers the exposition to the PPR.

The identification periods at risk of outbreaks from inventories of historic outbreaks from 2005 to 2010 through the epidemiological monitoring system put in place by the PACE in 2004 indicates the occurrence of PPR outbreak in goats and sheep at every moment of the year, but with a high frequency appearance of outbreaks between January and April with its peak in February. This has been noticed in India by Singh et al. who noticed the appearance of outbreaks with a great affluence during the dry and cold seasons (January and February) rather than during the rainy seasons [12] [21]. This could be due to the cold-dry season from December to February associated with the mal nutrition of animals since they are brought from place to place in search for grazing and to be commercialized hence favoring the propagation of the PPR [21] [22]. This was later confirmed by Singh and al who think that the epizootic apparition of PPR is related to the movement of animals and climatic factors which favor the survey and propagation of the virus.

International transhumance, which leads to massive movements of breeders and animals, contributes to the spread of the disease. Indeed, the borders are very porous in the zone which gathers the three Regions of the North (Far-north, North and Adamaoua). There is a large movement of small ruminants which have obtained from the countries of East Africa (Chad, Sudan, Central African Republic), crossing the three Regions to go to the countries of West Africa (Nigeria, Benin). The three Regions are therefore areas of transhumance to foreign herds. This may explain, in part, why the average prevalence rate 52% [95% CI; 47 - 60] is higher in this zone which groups together the three Northern Regions compared to the average prevalence rate 29% [95% CI; 11 to 57] in zone which groups together the seven Southern Regions [13]

Similary, the movement of these small ruminants in the country constitutes an important propagation factor of the PPR. This is done for commercial reasons 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]. 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.

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.

We would like to thank all the officials of the Ministry of Livestock, Fisheries and the Animal Industries (MINEPIA), the staff of the National Veterinary Laboratory (Garoua and Yaoundé) and the breeders who contributed to accomplishement this study.

Also, thank you to Doctors Gery Wamba (Mfou National Park) and Matchawe Chelea (Institute of Research Medical and Medicinal Plant Study) for their contributions

The authors declare no conflicts of interest regarding the publication of this paper.

Loul, S., Wade, A. and Nlôga, A.M.N. (2020) Sero-Prevalence and Risk Factors of Diffusion of Peste des Petits Ruminants in Cameroon. Open Journal of Veterinary Medicine, 10, 103-115. https://doi.org/10.4236/ojvm.2020.107009