Controlling mammalian tuberculosis: An Ethiopian pilot study

In Ethiopia, like many low- and middle-income countries, mammalian tuberculosis (mTB) remains a major concern. The highly contagious and chronic bacterial disease infects cattle and other domesticated animals. In Ethiopia alone, mTB affects around 3.8 million cattle on more than half the country’s farms. This coupled with an estimated 2.4% prevalence of zoonotic tuberculosis in the country, amounts to the region bearing a high burden of mTB. 

The current standard for mTB management is the test and cull method (T&C) consisting of testing animals and — just as it sounds — culling those that are mTB positive. This method has been highly successful in controlling the spread of the disease in both cattle and humans in high-income countries. 

However, for a myriad of reasons, Ethiopia, and many other countries most burdened by the disease have not adopted T&C as an official mTB control strategy. This is due to economic inability, lacking infrastructure, cultural and religious reasons or a combination of these factors. To address this concern, in October 2024 the World Organisation for Animal Health (WOAH) released its Guidelines for the control of mTB complex: Beyond test and slaughter. These guidelines highlight an alternative method of mTB control — test and segregate (T&Sg). Using this method, animals are tested, and positive cattle are completely segregated from the rest of the herd instead of culled.  

Evaluating control methods  

‘In Ethiopia, we have a huge livestock resource.‘ explains Matios Lakew, veterinarian and researcher at the Animal Health Institute in Sebeta, ‘And there is a governmental plan to use it for economic development of the country and food security. We are exporting livestock to other countries and using it for farming.‘

As the livestock industry increases, the risk of disease transmission has become a high priority challenge in the country.  This is due, in part, to a growing population of Holstein-Friesian cattle which have been imported into the country for their high milk production but are at greater risk of becoming infected with mTB than local breads. ‘Knowing this we wanted to see whether these methods of mTB control were effective and feasible,’ he continues, ‘so, we launched a pilot study on four dairy farms.’  

Lakew and his team evaluated T&C and T&Sg for more than a year. After 18 months, using T&C decreased mTB from an 11.3% prevalence at the beginning of the study to 0%. And, using T&Sg, the prevalence of mTB went down from 22.2% to 0% within one year. It was clear from the study that both methods were effective, but the team wanted to evaluate the economic feasibility of each. What they found was surprising. Although less infrastructure was needed for T&C, its total cost of over $38, 000 was nearly three times as expensive as T&Sg.  

For us, in Ethiopia, T&C is not feasible to implement on a larger scale. Not only is it very expensive, but farmers also lose high milk producing animals and they are not compensated for their losses.

Matios Lakew, veterinarian and researcher at the Animal Health Institute in Sebeta.

Using T&Sg, on the other hand, proved feasible for farmers with both high- and low-prevalence herds. ‘In one case, we had a farm with 100% prevalence of mTB. This herd gave rise to a group of calves who mostly remained negative — about 76%.’ he continues, ‘In effect, the 100% positive herd gave rise to its own test-negative, replacement herd.’  

Lessons from the mTB study 

Lakew has a few lessons to share with other countries who would like to implement T&Sg as a mTB control method.

Now that his own pilot study is complete, Lakew, his team and their partners plan on assessing T&Sg at a larger scale, possibly including vaccination. ‘Research is taking place in the United States of America, Canada, India and here in Ethiopia in which vaccination is used in addition to T&Sg,’ he says, ‘to assess where and when vaccination could have a synergistic effect.’