The author is Animal Health Officer (Bacteriology), Animal Production
and Health Division, FAO, Rome. Tel. +39 6 570 52681; fax: +39 6 570 53500;
e-mail: [email protected]
La tuberculose bovine est très répandue dans l'ensemble de l'Afrique. Cependant, à l'exception d'un petit nombre de pays, l'incidence et la prévalence de la maladie restent très mal connues. La plupart des pays africains sont aussi frappés par d'autres maladies justifiant des mesures d'urgence, ce qui fait que les services vétérinaires affectent leurs ressources déjà maigres à la lutte contre ces maladies. Par ailleurs, les pays sont conscients des pertes économiques causées par la tuberculose bovine et de ses conséquences pour la santé publique, mais ils sont souvent peu incités à faire des efforts concertés en raison de l'absence de vaccin efficace à usage animal et de l'importance des ressources humaines et financières nécessaires pour maîtriser la maladie.
La tuberculosis bovina está extendida por toda África. Sin embargo, con la excepción de un pequeño número de países es muy poco lo que se conoce de la incidencia y la prevalencia de la enfermedad. La mayoría de los países africanos se ven también afectados por otras enfermedades muy prioritarias, por lo que las autoridades veterinarias destinan sus ya escasos recursos a combatirlas. Además, aunque los países son conscientes de las pérdidas ocasionadas por la tuberculosis bovina y de sus efectos en la salud pública, a menudo no se ven animados a adoptar ninguna medida concertada debido a la falta de una vacuna eficaz para utilizar en los animales y al volumen considerable de recursos humanos y financieros que se necesita para combatir la enfermedad.
Bovine tuberculosis (TB) is classified by FAO and OIE as a "List B" disease. This category includes all animal diseases which are considered important because of their socio-economic and/or public health impact.
The FAO/OIE/WHO Animal Health Yearbook (FAO, 1993) and World
Animal Health (OIE, 1988-1992) both report on the incidence of bovine TB, as
communicated annually by member countries.
An analysis of the reports received over the last five years confirms that bovine TB is present in the majority of African countries. However, in most cases the information is only sufficient to indicate the presence or absence of the disease and does not allow for an analysis in a spatial or prevalence context, without seeking explicit clarification from the national veterinary authorities.
Generally speaking, there is a lack of reliable field survey data on animal diseases in Africa. This is demonstrated by an analysis of the above-mentioned disease data sources which indicate that when comparing national reports with the presence of bovine TB as shown in Figure 1, there are large variations which cannot be explained by epidemiological factors only.
The extent of bovine turberculosis in Africa and the Near East in 1993
Situation de la tuberculose bovine en Afrique et au Moyen-Orient en 1993
Situación de la tuberculosis bovina en África y el Medio Oriente en 1993
For example, in 1993, the presence of bovine TB at herd level was
reported by only five countries: South Africa (34 outbreaks), Algeria, Morocco, Ghana and
Madagascar. Most of these figures originate from records of slaughtered animals and
concern mainly young males.
Bovine TB is responsible for the condemnation of a significant amount of all meat inspected. In 1991, Egypt condemned meat and viscera estimated at a value of nearly US$5 million (El-Taweel, 1992). Similarly, in Côte d'Ivoire, in 1992 nearly 50 percent of all whole bovine carcasses condemned and 46 percent of all partial carcass condemnations were attributed to TB contamination, while during the same year only one outbreak of the disease was officially reported.
An analysis of more than 300 Mycobacterium strains originating from human sputum was conducted in Egypt to estimate the presence of Mycobacterium bovis in human TB (El-Sabban et al., 1992). Nearly 5 percent of these strains were found to be M. bovis. This relatively high incidence of the bovine type was attributed to the fact that most of the patients lived near the Cairo abattoir and some were actually abattoir employees.
From the information available it is possible to make some general observations on the epidemiological situation concerning bovine TB in Africa.
In terms of susceptibility, it is established that Zebu cattle are more resistant to TB than imported European breeds of higher productivity. Also, as shown elsewhere, the prevalence of TB is higher in dairy than in beef cattle. This may be a consequence of closer confinement, longer life spans and the stress demanded of greater productivity among dairy cows.
In the dissemination of the disease one can assume that, since the extensive methods of animal husbandry are overwhelming in Africa, intimate contact is reduced and the spread of infection tends to be prevented. Consequently, disease incidence is maintained at a low endemic level and fails to provide the motivation for the authorities to apply the complex measures required for eradication.
The number of countries making use of tuberculin testing, even on a voluntary basis, is rather low (only 11 out of 43 in 1993).
The reports contained in FAO (1993) show that treatment of bovine TB (which normally should be forbidden) is practised in as many as four countries. Only two of these countries, namely South Africa and Tunisia, have ongoing national control programmes while the other two, Morocco and Mozambique, have specifically targeted the dairy sector. Overall, there is an obvious need to strengthen policy measures concerning bovine TB, which is at present a notifiable disease in only 16 countries in Africa (Fig. 2).
Notification of bovine tuberculosis in Africa and the Near East
Déclaration obligatoire de la tuberculose bovine en Afrique et au Proche-Orient
Notificación obligatoria de la tuberculosis bovina en África y el Medio Oriente
It is generally agreed that the accepted method of control, based on test
and slaughter (i.e. proper use of the tuberculin test), although drastic, may lead to
eradication of infection. Essentially the problem is one of mobilizing the available
veterinary human resources and encouraging farmers to cooperate by presenting their
animals for testing. Regarding the veterinary requirements, it is appreciated that there
is often a scarcity of veterinarians and related technical support staff to implement
adequate surveillance and control of the disease. There may also be a lack of adequate
legislation or a failure to implement that which does exist.
Realistic incentives must be given to farmers if they are to comply with control and eradication programmes, either through a compensation scheme (at the real price of slaughtered animals) or by one which ensures the replacement of slaughtered animals.
Where the policy of test and slaughter is applied it is not always vigorously pursued, and animals reacting positively may not be effectively quarantined. Hence, the result may be the opposite to that intended, leading to the spread of the disease through the sale of reactors. A further complicating factor is that abattoirs often sell non-condemned meat from tuberculous carcasses at very low and attractive prices. Replacing compulsory slaughtered animals may also present problems, especially if they are imported stock. This has to be taken into account when calculating compensation. Some incentives must be provided to farmers who adhere to the eradication programme, such as offering guaranteed milk prices and setting favourable subsidies.
In many countries the epidemiological situation of bovine TB is unknown,
with no surveillance or control implemented. This is despite the fact that the
intensification of livestock production, particularly where regulations governing
livestock importation are weak or poorly enforced, may lead to an increase of the disease
incidence. It is therefore essential that the threat be recognized and that vigorous
control and eradication programmes be undertaken using the appropriate and recommended
methods. While it is appreciated that major epidemic diseases such as rinderpest and
contagious bovine pleuropneumonia (CBPP) and, to a lesser degree, dermatophilosis,
haemorrhagic septicaemia, heartwater, lumpy skin disease, etc., are still widespread in
Africa and command the attention and limited resources of veterinary authorities, it is
also important that the public health risks of bovine TB be fully assessed and be afforded
the appropriate priority.
Despite these difficulties, there are nevertheless some encouraging signs for the future. These primarily comprise governments' growing awareness of the need for improved control of major zoonoses, including bovine TB, and the increasing interest shown by countries for the development of effective epidemiological services.
El-Sabban, M.S., Lotfy, O., Awad, W.M. & Soufi, H.S. 1992.
Bovine tuberculosis and its extent of spread as a source of infection to man and animals
in Arab Republic of Egypt. Proc. Int. Conf. on Animal Tuberculosis in Africa and the
Middle East, 28-30 April, 1992, p. 198-211.
El-Taweel, A. 1992. Status of bovine tuberculosis in Egypt. Proc. Int. Conf. on Animal Tuberculosis in Africa and the Middle East, 28-30 April 1992, p. 296-311.
FAO. 1993. FAO/OIE/WHO Animal Health Yearbook. Rome.
OIE. 1988-1992. World Animal Health; Part 1: Reports & Statistics; Part 2: Tables. Geneva.