Tuberculosis and brucellosis prevalence survey on dairy cattle in Mbarara milk basin (Uganda)

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Abstract

We determined the prevalence of tuberculosis and brucellosis reactors in the dairy herds in the Mbarara district of Uganda in 2002. This is one of the most important dairy-production areas of the country and includes both pastoral and agro-pastoral zones. A total of 340 (of 11,995) randomly selected herds were tested for tuberculosis, using the intradermal tuberculosis-skin test and 315 (of 10,562) herds tested for brucellosis using the serum Rose Bengal test.

The herd prevalence for tuberculosis reactors was 74.1% (95% confidence intervals 69, 78), the individual-animal prevalence was of 6.0% (5.6, 6.5) and within-herd range was 1–50% (up to 100% if suspicious reactors were included).

The herd prevalence for brucellosis was 55.6% (50, 61.2) individual-animal prevalence 15.8% (14.8, 16.7) and within-herd range 1–90%.

The reactor prevalence increased with the age of the animals for both tuberculosis and brucellosis.

Tuberculosis reactor prevalences were higher in animals from the agro-pastoral zone. However, the individual-animal and herd prevalences of brucellosis seroprevalences were higher in the pastoral zone.

Introduction

Milk consumption is increasing in many southern-hemisphere countries and especially in Africa (Delgado et al., 1999, Faye and Alary, 2001). In Central and Eastern Africa, higher milk production is observed around the major towns to supply the urban populations. In Uganda, the highlands around Mbarara in the south-western part of the country have a temperate climate and are particularly well adapted for milk production. A recent survey (Dabusti and Vancauteren, 1998) identified five types of dairy farmers from pastoralists with Ankole cattle (a local breed) in extensive lowlands to modern specialized dairy farmers with pure Holstein cows in the highlands. Most of the farmers between those two groups had diversified activities (primarily coffee or banana).

At the same time, human tuberculosis and brucellosis is increasing in populations with high prevalence of HIV—especially in Africa (Raviglione et al., 1995). TB and brucellosis are the major zoonotic diseases that can be transmitted through the cow's milk. According to the Ugandan Ministry of Health, the mean annual incidence rate of human TB was 1.34/1000 person-years in Uganda for 1995. However, the role of Mycobacterium bovis was not known. The human brucellosis incidence rate was officially 0.7/1000 person-years in 1995. The current tuberculosis and brucellosis status in dairy cattle is not well known in Uganda. We did a prevalence survey of a randomly selected population of dairy farms in a district of Uganda to assess the importance of those zoonotic disease in the milk basin of Mbarara (the main milk-production area in Uganda). The associations of animal characteristics (gender, age, breed) with prevalences of tuberculosis and brucellosis was assessed.

Section snippets

Study area

The Mbarara district represents 5% of the whole area of Uganda (i.e. 10839 km2). This district has a common border with Rwanda and Tanzania in the southern part. Mbarara is located in the south-west part of Uganda and has a mean altitude of 1200 m above sea level. The eastern part of Mbarara district is lowlands and the western part is highlands. The climate is equatorial temperate (especially in the highlands). The mean minimum and maximum annual temperatures are 14.6 and 26.3 °C, respectively.

Tuberculosis

The participation proportion of the survey was 340/396 herds (86%). The difference from the sampled herds was due to (i) the absence of cattle in 26 farms for various reasons (lack of manpower, cattle sold for dowry, moving, deceased), (ii) the lack of time for achieving the survey before the rainy season in 22 farms from the agro-pastoral zone, and (iii) the farmer's refusal in eight farms. In the pastoral zone, 121 herds were tested, and 219 in the agro-pastoral zone.

The size of the herds

Discussion

Because no available or convenient data are published in the Mbarara district on TB and brucellosis prevalence, our data cannot be compared easily with previous studies. The official data from Office International des Epizooties (OIE) mentioned 640 cases of bovine tuberculosis in Uganda in 1997 (OIE, 2003). Unpublished data from the Mbarara slaughterhouse mentioned 76 cases of affected animals with TB i.e. 2.2% of the slaughtered animals in 1997 but 1.07% in 1999. However, no disease control

Conclusion

We found apparent prevalences of infection of 6% and 15.8% (animal-level) for TB and brucellosis in an important dairy-cattle area of Uganda. There were higher prevalences among females than males, and among older than younger animals (all uncorrected for clustering). More than half the herds sampled had positive animals. Positive animals were more typical in the more intensive wetler agro-ecologic zone.

Acknowledgements

The present study was supported by the French Embassy in Uganda. Special thanks are addressed to Mrs Michele Baherle for her support to this programme and to S.E. J.B. Thiant, Ambassador of France in Uganda for his interest in this survey. We are also grateful to the Ugandan partners from local veterinary services and local authorities for their help and contribution, and to the farmers from Mbarara district.

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