Bovine Tuberculosis (BTB) in selected areas of Northwestern Tigray, Northern Ethiopia: Prevalence, Risk Factors, and Public Health Implication

In the highlands of northern Ethiopia, cattle are more than just livestock; they are the backbone of family livelihoods and a critical source of nutrition. Yet, these herds face a silent, persistent threat: bovine tuberculosis. This is a chronic bacterial disease that primarily affects cattle but can jump to humans, making it a classic example of a zoonotic illness where the health of animals and people are inextricably linked. The bacteria that causes it, Mycobacterium bovis, travels through the air when infected animals cough or sneeze, and it can also spread through contaminated milk and meat. Because the disease often hides without showing obvious symptoms in its early stages, it can quietly weaken a herd, reduce milk production, and pose a serious health risk to the families who live and work alongside the animals. Understanding how widespread this infection is, and what makes it more likely to spread, is essential for protecting both the local economy and public health.

A team of researchers recently set out to map this invisible threat in the northwestern Tigray region, focusing on the area around Shire Indasilase and the nearby Tahtay Koraro district. Between late 2018 and mid-2019, they visited 109 dairy farms, examining a total of 382 cows. To detect the infection, they used a standard skin test where a small amount of protein from the bacteria is injected under the skin; if the animal's immune system recognizes the invader, a swelling appears at the injection site after three days. The team also spoke with the farm owners and interviewed patients who had been diagnosed with a specific type of tuberculosis affecting the lymph nodes, asking them about their daily habits and what they knew about the disease.

The investigation revealed that the disease is indeed present and active in the region. At the individual animal level, about 10 percent of the cows tested positive for the infection. When looking at the farms as a whole, the situation was even more pronounced: more than a quarter of the farms had at least one infected animal. The researchers found that the risk of infection was not spread evenly across the herd. Certain groups of animals were significantly more likely to carry the disease. Crossbred cattle, which are a mix of local and foreign breeds, were more than twice as likely to be infected compared to local breeds. Pregnancy also played a role, with pregnant cows showing a much higher rate of infection than non-pregnant ones. Additionally, cows that were in poor physical condition or were currently producing milk faced higher risks, suggesting that the physical stress of these life stages may make the animals more vulnerable.

The study also highlighted how the way cattle are kept influences the spread of the disease. Farms with larger numbers of animals and those using intensive management systems, where cows are kept in close confinement, saw much higher rates of infection. This makes sense, as crowded conditions and shared feeding areas provide more opportunities for the bacteria to move from one animal to another. Interestingly, the location mattered too; the town of Shire Indasilase showed higher infection rates than the surrounding rural district, likely due to the higher density of dairy operations in the town.

Perhaps the most concerning finding was the gap in knowledge among the people living with these animals. When the researchers asked farm owners if they knew that cattle could get tuberculosis and pass it to humans, fewer than one in five said yes. This lack of awareness was matched by risky daily habits. Nearly half of the people interviewed admitted to drinking raw milk, and a significant portion ate raw meat. These practices are dangerous because the bacteria can survive in uncooked animal products. The connection between animal and human health was further underscored by the fact that in 13 percent of the households that owned infected cows, a family member was also suffering from tuberculosis. While the study cannot prove that the human cases came directly from the cows, the overlap is strong enough to suggest a clear link.

The researchers concluded that bovine tuberculosis remains a significant challenge in this part of Ethiopia, driven by a mix of animal biology, farming practices, and human behavior. The disease thrives in crowded, intensive farming systems and spreads easily when people are unaware of the risks or continue to consume unpasteurized products. To stop the cycle, the authors suggest that efforts must go beyond just treating sick animals. They recommend better biosecurity on farms, stricter screening for larger herds, and a major push to educate the public about the dangers of raw milk and the importance of cooking meat thoroughly. By treating the health of the cattle and the health of the community as one connected issue, it may be possible to reduce the spread of this ancient disease and protect the future of the region's dairy farmers and their families.