A study was performed in 2008 to estimate the prevalence of tuberculosis and brucellosis in traditionally reared cattle of Southern Province in Zambia in four districts. The single comparative intradermal tuberculin test (SCITT) was used to identify TB reactors, and the Rose Bengal test (RBT), followed by confirmation with competitive enzyme-linked immunosorbent assay (c-ELISA), was used to test for brucellosis. A total of 459 animals were tested for tuberculosis and 395 for brucellosis. The overall prevalence of BTB based on the 4 mm and 3 mm cutoff criteria was 4.8% (95% CI: 2.6–7.0%) and 6.3% (95% CI: 3.8–8.8%), respectively. Change in skin thickness on SCITT was influenced by initial skin-fold thickness at the inoculation site, where animals with thinner skin had a tendency to give a larger tuberculin response. Brucellosis seroprevalence was estimated at 20.7% (95% CI: 17.0–24.4%). Comparison between results from RBT and c-ELISA showed good agreement (84.1%) and revealed subjectivity in RBT test results. Differences in brucellosis and tuberculosis prevalence across districts were attributed to type of husbandry practices and ecological factors. High prevalence of tuberculosis and brucellosis suggests that control control programmes are necessary for improved cattle productivity and reduced public health risk.
Bovine tuberculosis and brucellosis are major zoonotic diseases of worldwide economic and public health importance, especially in developing countries where the diseases are endemic [
Human brucellosis is one of the widely distributed zoonoses, especially in economically disadvantaged livestock keeping communities [
In the light of high HIV/AIDS prevalence in sub-Saharan Africa [
Although the livestock keeping communities are at highest risk of contracting these zoonotic diseases, they are often unaware of these risks. In our earlier reports, we noted that there is generally low awareness among the traditional farmers regarding the risk to
The study was conducted in four districts of Southern Province in 2008. These districts were purposively selected because these were the operational areas of the funding project and also because most cattle under traditional management are found in these areas (Table
Study areas with estimated livestock populations in the study districts (2006).
Areas |
Estimated cattle population | Estimated goat population | Estimated sheep population |
---|---|---|---|
Choma | 78,521 | 31,553 | 2,538 |
Itezhitezhi | 40,250 | 1,385 | 128 |
Monze | 110,000 | 32,340 | 757 |
Namwala | 99,038 | 7,600 | 231 |
The study was conducted as a cross-sectional study to estimate prevalence of antibodies to
Study areas with target herds and cattle sample sizes.
Study area |
Estimated number of herds (approx. herd size = 100 cattle) | Estimated number of herds to be sampled | Estimated number of animals to be tested (10% sampling fraction) |
---|---|---|---|
Choma | 785 | 52 | 520 |
Itezhitezhi | 402 | 26 | 260 |
Monze | 1100 | 72 | 720 |
Namwala | 990 | 65 | 650 |
We assumed that sampling would be done randomly and that there would be low heterogeneity between herds. The detection power was set (
For the determination of the prevalence of BTB in cattle, the single comparative intradermal tuberculin test (SCITT) was applied. The procedure was conducted as earlier described [
Blood samples were collected from pregnant heifers, cows, and bulls, since clinical brucellosis is said to be a disease of sexually mature animals (≥2 years) [
In the laboratory, sera was separated by centrifugation at 2,500 rpm (503 g) for 15 minutes and stored in 2 mL cryovials at −20°C until laboratory tests were performed. Antibodies to
The database was established in Excel before transferring to STATA SE 11 for Windows (StataCorp, College Station, TX).
BTB-positive reactors (mm) and avian-positive reactors (mm) were obtained as earlier described [
Proportions of positive animals, with 95% confidence intervals were estimated for each district and all the districts (
The overall prevalence of BTB based on the 4 mm and 3 mm cut-off criteria was 4.8% (95% CI: 2.6–7.0%) and 6.3% (95% CI: 3.8–8.8%), respectively. TB-reactivity varied according to study area with Monze district recording the highest prevalence (Tables
Distribution of tuberculosis cattle reactors by district at >4 mm cutoff (2008).
District | Total tested | BTB tuberculin reactors (mm) | Avian reactors (4 mm) ((Av72 − Av0) − (Bov72 − Bov0)) | Average skin thickness Bovine site (Bov0) (mm) | ||
---|---|---|---|---|---|---|
((Bov72 − Bov0) − (Av72 − Av0)) | ||||||
Negative |
Inconclusive |
Positive | ||||
Itezhitezhi | 102 | 81.2 |
17.7 |
1.0 |
15.4 |
10.4 |
Monze | 176 | 69.3 |
22.1 |
8.6 |
15.3 |
10.5 |
Namwala | 181 | 84.0 |
14.7 |
1.3 |
38.2 |
11.4 |
All districts | 459 | 76 |
19.2 |
4.8 |
21.6 |
10.8 |
Distribution of tuberculosis cattle reactors by district at ≥3 mm cutoff (2008).
District | Total tested | BTB tuberculin reactors (mm) | Avian reactors (4 mm) ((Av72 − Av0) − (Bov72 − Bov0)) |
Average skin thickness | ||
---|---|---|---|---|---|---|
((Bov72 − Bov0) − (Av72 − Av0)) | ||||||
Negative |
Inconclusive (+1–+2 mm) % | Positive | ||||
Itezhitezhi | 102 | 81.2 |
16.7 |
2.1 |
23.1 |
10.4 |
Monze | 176 | 69.3 |
20.2 |
10.4 |
22.4 |
10.5 |
Namwala | 181 | 84.0 |
13.3 |
2.6 |
41.8 |
11.4 |
All districts | 459 | 76.0 |
17.7 |
6.3 |
28.0 |
10.8 |
The mean initial skin thickness was observed to be different between the three districts (
Scatterplot and regression line showing the relationship between BTB reactivity
Scatterplot and regression line showing the relationship between BTB reactivity
A total of 395 animals from Monze (
Comparison of RBT results from two technicians and c-ELISA results (
Agreement (%) | Expected agreement (%) | Kappa | Std. err. |
|
|
---|---|---|---|---|---|
RBT1_RBT2 | 64.8 | 54.7 | 0.22 | 0.040 | 0.0000 |
RBT1_c-ELISA | 71.2 | 54.1 | 0.37 | 0.044 | 0.0000 |
RBT2_c-ELISA | 84.1 | 69.9 | 0.47 | 0.050 | 0.0000 |
NB: RBT1: RBT test results from an elderly technician (1) with aided sight; RBT2: RBT test results from a young technician without sight defect correction; Std. err.: standard error.
Distribution of
District | Total tested | c-ELISA Seroprevalence |
RBT-1% |
RBT-2% |
---|---|---|---|---|
Itezhitezhi | 101 | 33.7 |
31.0 |
36.3 |
Monze | 176 | 19.3 |
24.5 |
8.18 |
Namwala | 118 | 11.9 |
60.1 |
9.3 |
All districts | 395 | 20.7 |
42.7 |
15.9 |
We estimated the prevalence of tuberculosis and brucellosis in cattle among traditional cattle in Southern Province of Zambia. We could not perform a random survey because sampling was based on operational areas of the project that funded the study. Despite the above shortcoming, the study gives an indication of the situation regarding the two zoonotic diseases in the study areas. Our estimated overall BTB prevalence of 6.3 (95% CI: 3.8–8.8) is similar to that estimated by Munyeme et al. [
Considering that the tuberculin test is not a perfect test, some animals could have been missed resulting in underestimation of the prevalence. There are several seasons why tuberculosis-infected animals may give a false negative result. In endemic areas, delayed hypersensitivity may not develop for a period 3–6 weeks following infection, and in chronically infected animals with severe pathology, the tuberculin test may be unresponsive [
The RBT is a very sensitive test that sometimes gives a positive result because of S19 vaccination or other cross-reactions such as reaction with
The observed
This study has demonstrated that BTB and brucellosis are a problem in the investigated areas and are likely to pose significant public health risk to traditional farmers. There is a need to control the prevalence of these zoonoses in order to protect the general public considering that the investigated diseases are both milk borne. Further studies need to be conducted to determine the actual public health burden on the affected communities.
The authors of this paper declare than none of them have financial or personal relationships with individuals or organizations that would unacceptably bias the content of this paper and, therefore, declare that there is no conflict of interests.
This study was jointly funded by the Government of the Republic of Zambia through the Ministry of Agriculture and Cooperatives and the Japan International Cooperation Agency (JICA).