Diagnosis of Bovine Tuberculosis in Zambia

In Zambia, the diagnosis of BTB in cattle and wildlife is constrained by numerous challenges. The comparative intradermal tuberculin test (CCT) (Table 23.1) (Munyeme et al. 2009a, b), as recommended by the World Organisation for Animal

Table 23.1 Herd prevalence of BTB in cattle determined by cross-sectional studies around the Kafue basin based on comparative intradermal tuberculin testing (CCT)

Table 23.2 Area-based prevalence of BTB using postmortem examination, Ziehl-Neelsen staining, and culture results from Kafue lechwe tissue samples (n = 119) (Munyeme et al.

Health (OIE), is recommended for making an antemortal diagnosis of tuberculosis, but it is not often used in Zambia. Normally, when it is done, employees of the Veterinary Services perform the test. The limited use of the test is due to the reluctance of farmers to allow it to be done since they are not compensated for positive reactors that must be culled. Implementation of a test-and-slaughter policy is not feasible because of this reluctance, and the difficulties of controlling BTB in rural, nomadic cattle pose additional challenges.

Farmers supplying milk to commercial processing companies must screen their animals annually for BTB by using the tuberculin test if they are to have their milk accepted by these companies and they are thus forced to comply. In cattle owned by traditional farmers, BTB is mainly diagnosed by postmortem exanimation to detect the presence of gross lesions compatible with those of BTB in the lungs and/or associated lymph nodes. Whole carcass or partial condemnation is regularly applied depending on the distribution of the lesions. When the lesions are localized, car­casses are according to standard regulations declared fit for human consumption once the organs containing gross lesions have been removed (Gracey et al. 1999).

Laboratory diagnostic techniques such as acid-fast staining, culture, biochemical typing, and PCR molecular typing methods (Munyeme et al. 2010a, b; Hang’ombe et al. 2012) are only available at the Veterinary Research Institutes, and the School of Veterinary Medicine at the University of Zambia in Lusaka (Table 23.2), and have limited value in terms of controlling the disease throughout the country.

23.5 National Bovine Tuberculosis Control Policies and Strategies

Although BTB is a notifiable disease, there is no official control program for the disease in Zambia. The Zambian authorities profess that diseases such as BTB do not have a dramatic effect on livestock populations and have little effect on their international trade, and they consequently allocate financial and human resources to more pressing problems. Unlike in developed countries that control the disease in cattle with consequent benefit to public health, most African countries, including Zambia, argue that BTB is not a disease of national economic importance, and its control is left to individual farmers as they classify it as “a management disease.” The Zambian government only encourages the screening of cattle herds for the presence of BTB and culling of the positive animals (Munyeme et al. 2010a, b). Currently, BTB control is mainly applied in the private dairy sector as the major milk processing factories do not buy milk from cattle herds that are not certified BTB free. For this reason, commercial cattle farmers privately fund the required BTB screening tests, and those animals that test positive are sold off to recover some of the costs.

This approach in Zambia is considered to be poorly justified given the zoonotic risk posed by BTB, the high prevalence of the infection in sectors of the cattle population, the existence of a wildlife maintenance host, and the large-scale consumption of potentially BTB-infected raw milk by a significant proportion of the rural communi­ties. This situation may change in the foreseeable future as the Zambian Government realizing the public health importance of BTB and the need to control it to limit the risk for the at-risk population, is currently developing a National Bovine Tuberculosis Surveillance and Control Program that will be funded by the World Bank.

A general lack of knowledge about the disease is another critical factor in Zambia impeding the control of BTB (Munyeme et al.

Another aspect complicating control of BTB in Zambia is the nature and com­plexity of the natural reservoir hosts other than cattle. It is known that once BTB establishes itself in wildlife populations, the likelihood of controlling and/or eradi­cating it because of the presence of sylvatic reservoir hosts is extremely difficult, if not impossible with the currently available means of controlling the disease (Michel et al. 2010). The extensive livestock/wildlife interface further complicates the situation due to bidirectional transmission of the disease across it and the further likelihood of environmental contamination (Cross et al. 2009). This situation pre­vails in the Kafue basin, where it has been shown that cattle initially introduced the disease to wildlife and that there now is spillback to cattle from wildlife.

A number of key factors that further negatively affect BTB control in Zambia include the different types of cattle farming and pastoral practices (Aranaz et al. 2006). Herd size has an influence on the prevalence of BTB (Ameni et al. 2010), and on the Kafue flats, it is not uncommon to find pastoralists owning over a 1000 head of cattle that allows easy spread of the disease. The spread of the disease is further enhanced by the aggregation of large numbers of cattle at water sources in arid environments and by communal grazing (Oloya et al.

The choice of workable control measures and strategies should take all the various factors dealt with into account. At the livestock/wildlife interface, more detailed studies will be needed to provide data on how the disease is maintained, and how it is spread and transmitted between susceptible hosts to allow an adequate control strategy to be designed.

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