Abstract :
[en] Livestock is an important source of income in most developing countries. In Africa, it often makes up 10% to 20% of the gross national product at level. One of the major constraints to the development of this sector is animal diseases, which sometimes generate significant economic losses with social consequences that are often very burdensome for farmers. They restrict trade between countries. Reducing the impact of these constraints necessarily involves the prevention and the control of diseases. For this purpose, an adequate knowledge of the epidemiology of the diseases is a prerequisite to define a strategy for their prevention and/or the design of appropriate monitoring measures. One of the essential tools of production remains the epidemiological information network for the surveillance of animal diseases. It is also a tool for decision in international trade involving livestock products. For this purpose, its effectiveness is a guarantee for its credibility. An effective network system must be well organized, meet scientific standards and satisfy the efficiency characteristics which are sensitivity, specificity, acceptability, responsiveness and cost.
In west and central Africa, epidemiological surveillance networks of animal diseases are mostly created in the 1990s through the Pan African Program for the Control of Epizootics. A 2004 assessment carried out by this program revealed that these networks are at different stages and found weaknesses in their efficiency.
To contribute to the improvement of these systems, an analysis of some performance parameters of these networks has been conducted and suggestions for improvement were made.
To achieve this overall objective, the following specific objectives were listed: (i) analyze the technical and functional organization of epidemiological surveillance networks in West and Central Africa; (ii) compare the effectiveness of active surveillance and passive surveillance, the two main monitoring methods used by the networks in West and Central Africa using the case study of the epidemiological surveillance network, in Chad, namely REPIMAT; (iii) assess the sensitivity of an epidemiological surveillance network from an approach based on prevalence of a disease such as Foot and Mouth Disease; (iv) develop performance indicators for regular monitoring of the epidemiological surveillance network for animal diseases in West and Central Africa, again by taking the case of REPIMAT; and finally, (v) estimate the cost incurred by an epidemiological surveillance network in West and Central Africa, for example the REPIMAT.
Each of these specific objectives leads to a specific study of which results are presented below:
Organization of epidemiological surveillance networks in West and Central Africa
The survey on technical and institutional organizations networks in west and central Africa was organised on the basis of a written questionnaire. It involved nine networks of which five were in West Africa (Senegal, Burkina Faso, Ivory Coast, Togo, Guinea) and four in Central Africa (Cameroon, Central African Republic, Democratic Republic of Congo and Chad).
The results of this survey showed that the oldest epidemiological surveillance network is that of Chad, REPIMAT. There are more similarities than differences between these networks. In general, network monitoring of animal diseases in west and central Africa are technically and institutionally well formalized. The establishment and operation of the networks surveyed are mainly financed by foreign aid. In general, these are epidemiological surveillance networks that monitor several diseases. All countries surveyed have a central national laboratory for the analysis of samples collected. However, only four countries (Cameroon, Côte d'Ivoire, Guinea and Senegal) can make a diagnosis of all diseases selected for monitoring. The laboratories are considered as partners with surveillance networks in most of the countries surveyed.
All networks use the PID/ARIS for data management. In addition to the latter, countries such as Guinea, DRC, Senegal and Chad use a national database developed with Access®. On average, 26% of veterinary stations on the total networks surveyed are involved in the monitoring. This proportion varies from 7% to 91%. However, insufficient diagnostic capacity of laboratories and inadequate operational steering committees are the two main weaknesses of the networks concerned with this survey.
Comparison between active and passive surveillance within the network of epidemiological surveillance of animal diseases in Chad
The comparison between active and passive surveillance involved 106 REPIMAT surveillance stations randomly divided into 52 active surveillance stations and 54 passive surveillance stations. Vaccination status of nine diseases and their respective prevalence levels are monitored by the network.
A work plan was developed for each station. The stations of active surveillance make monthly visits to four herds (villages) to look for monitored diseases and also organise four information meetings with farmers how to react in case of suspicion of the monitored diseases. Passive surveillance stations only organise, monthly, four information meetings with farmers. Suspicions in each station are recorded on a specific form developed for each disease. The agent mentions if the suspicion is performed following a breeder call, a visit from herds or a sensitization meeting. Monitoring lasted 24 months. The results of this study showed that regardless of the type of surveillance, diseases monitored with the exception of rare diseases (Rinderpest, and Rift Valley fever) are reported by the monitoring agents. However, we note that the number of calls recorded following suspicions of farmers (41%) was significantly higher (p <0.05) than suspicions made during visits to herds (30%) or in meetings (29%).
For moderately prevalent diseases, the suspicions are mainly calls farmers (77%) and regardless of the type of monitoring (73% for active surveillance and 84% for passive surveillance). On the other hand, for FMD, a disease with high prevalence, 37% of suspicions are recorded by visiting farms. Overall, no significant difference was observed between the types of surveillance because of a low rate of disease onset during sensitization meetings by the active surveillance stations. Passive surveillance stimulated by awareness meetings appears to be a mode for surveillance in the conditions of Chad and cheaper. However, for rare diseases, the specific methods of active surveillance (such as, for example, sentinel flocks) seems preferable.
Evaluation of the sensitivity of the animal disease epidemiological surveillance network for Foot and Mouth Disease in Chad
Evaluation of the sensitivity of the animal disease epidemiological surveillance network for Foot and Mouth Disease in Chad
The study on the network sensitivity was carried out in REPIMAT by taking the surveillance of FMD as an example. FMD is the disease most frequently suspected by REPIMAT. However, the reporting of cases is limited to clinical suspicion. The samples for the purpose of laboratory diagnostic for confirmation of these suspicions are not made. In order to assess the sensitivity of REPIMAT for this disease, a serological survey was conducted in eight of the nine regional delegations with the highest cattle population of the country. The samples were analyzed by the National Reference Laboratory for FMD in Brescia (Italy) with the support of the European Commission action against FMD. The 3ABC and SP-ELISA tests were used for the detection of antibodies and the serotype of the virus. The number of FMD suspicions reported within the network was compared with the seroprevalence. Epidemiological information on the disease, including the circulating serotypes in Chad, was also provided.
A total of 796 cattle sera were collected. The seroprevalence rate at individual level was 35.6% (95% CI: 32.2 to 39.0) and that at the herd level was 61.9% (95% CI: 51.9 to 71.2). A strong correlation was observed between the estimated prevalence and number of clinical suspicions reported within REPIMAT. The disease is present in all livestock regional delegations surveyed with a high prevalence in the delegations located in the south, the wettest area, and where cross-border movements are the most important. Serotypes A, O, SAT1and SAT2 were identified.
Development of operating performance indicators of Chad epidemiological surveillance network for animal diseases: REPIMAT
The maintenance and effectiveness of a disease monitoring system requires regular evaluation to identify timely deficiencies that may occur. For this purpose, the performance indicators are essential tools. One approach for developing performance indicators as well as their application in the operation of 43 monitoring stations REPIMAT was carried out. An analysis of the objectives and operation mechanism of REPIMAT allowed retaining three main components, namely the field workers, the animation cell and the laboratory. The activities of each of these components were listed. The analysis of the outcomes of these activities resulted in the development of the performance indicators that can be used in the operation of REPIMAT. The application of these indicators has highlighted the weaknesses of each component.
Estimated cost of a network for animal diseases epidemiological surveillance in Central Africa: the case of Chad network
In sub-Saharan Africa, most of the networks for epidemiological surveillance of animal diseases were temporarily financed by external aid. The sustainability of such decision support tools should have been insured by national public funds. The objective of this study was to estimate the costs involved in running an animal disease epidemiological surveillance network by taking the example of such network in Chad (REPIMAT) and its weight in the state budget. These costs were then compared to those of other epidemiological surveillance in West Africa networks.
The results of this study showed that the total annual operating and implementing cost of REPIMAT is estimated at € 666 349 (437 096 291 FCFA) for the entire system comprising 106 monitoring stations constituting the local level, 26 livestock sectors, nine regional livestock delegations representing the intermediate level and an animation cell constituting the central level. This cost represents only 3% (2% of fixed costs and 1% of variable costs) of the budget allocated by the Chadian Ministry of Livestock. Fixed costs (72%) weighed more than variable costs (28%) regardless of the levels of intervention. This estimate is similar to the estimated costs of epidemiological surveillance networks in Benin, Ghana, Mauritania and Senegal. Considering only the variable costs (operation), the annual cost of operating a surveillance station, the most important entity in the system was only 932 € or 611 352 FCFA.
The surveillance cost is mainly related at the local level (surveillance stations) and intermediate level (livestock sectors and regional livestock delegations) to the cost involved in health surveillance as well as the equipment it requires.
This thesis allowed to analyze some parameters of effectiveness of a surveillance network for animal diseases including general organization, type of surveillance, sensitivity, cost and to develop a tool for continuous monitoring of operating a network. It is difficult to meet all the efficiency criteria of an animal disease surveillance network, however, the few parameters studied which are interrelated will help if they are used properly to improve the efficiency of an epidemiological surveillance system of animal diseases in sub-Saharan Africa.
