10 September 2025

4 minute read

By: Chris Wright

Editor's note: The following is an excerpt of a report by the World Organization for Animal Health: The State of the World’s Animal Health 2025^1.

Mammalian tuberculosis (mTB), primarily caused by Mycobacterium bovis, is far more than a veterinary concern: it is a global health issue in the truest sense. While mTB affects a wide range of species, bovine tuberculosis sits at the center of the problem. It is the primary form of mTB in domestic livestock and acts as a critical reservoir for cross-species transmission, including to wildlife and humans. As such, controlling bovine TB is not only essential for protecting cattle, but also for breaking wider transmission chains within ecosystems and communities.

Much of the global research, surveillance and policy effort around mTB focuses on cattle as a strategic point of intervention. Its management has historically relied on rigorous testing and culling, movement restrictions and painstaking biosecurity efforts. But now, a new chapter may be on the horizon, one in which vaccination could turn the tide.

Globally, mTB results in billions of US dollars in economic losses annually due to cattle condemnations, trade restrictions, reduced productivity, and the cost of control measures. In low- and middle-income countries, where ‘test and slaughter’ strategies are often unfeasible, the disease is not only endemic but neglected.

In India, the world’s largest milk producer with over 300 million cattle and buffaloes, it is estimated that 7% of dairy cattle are infected. In sub-Saharan Africa, where livestock and human interactions are intimately intertwined, studies show that zoonotic TB represents a significant share of the human TB burden. Even in high-income countries with long-standing control programs, such as the United Kingdom (UK) and Ireland, wildlife reservoirs complicate eradication efforts.

A vaccine for cattle

The idea of vaccinating cattle against TB is not new. The bacille Calmette-Guérin vaccine (BCG) – a live, attenuated strain of M. bovis – has been administered to humans for over a century. Its potential use in cattle, however, has been fraught with complications. Chief among them: BCG interferes with the current tuberculin skin test, making it difficult to distinguish infected animals from vaccinated ones, representing a major barrier to surveillance and trade.

But recent breakthroughs are changing that. Over several years the UK’s Animal and Plant Health Agency, alongside international collaborators, has developed a new differentiate infected among vaccinated animals (DIVA) skin test. This test induces an immune response in M. bovis infected animals (and therefore results in a positive skin test result) but not in uninfected BCG vaccinates.

The DIVA advances are ‘game-changing,’ and trials supported by the UK Government have continued across multiple sites. The DIVA test uses antigens absent from BCG strains but present in wild-type M. bovis, allowing the test to remain effective even in vaccinated animals. This combination overcomes one of the major historical hurdles to cattle vaccination. Recent international studies investigating the full extent of BCG protection in natural conditions have also found a total efficacy of 89%, providing further evidence of the positive potential if it can be coupled with an effective DIVA test.

The commercial licensing of a BCG-based vaccine for cattle would be revolutionary, with implications across several domains. In terms of public health, reduced infection in cattle would lead to fewer zoonotic transmissions to humans, particularly in countries where raw milk is still widely consumed. From an animal welfare perspective, the availability of a vaccine could significantly decrease the need for culling, which is often a distressing and controversial component of TB control.

Regarding trade and the economy, once DIVA-compatible vaccines and diagnostic tests are standardized, international trade regulations could be revised, enabling countries where TB is endemic to gain access to new markets. It also aligns with One Health principles by addressing the disease at its animal source before it spills over to humans or wildlife.

However, implementation will not be without challenges. Vaccine delivery systems, cold-chain logistics, regulatory harmonization, and cost-sharing between public and private sectors will require international coordination.

Reference

¹World Organization for Animal Health (2025). – The State of the World’s Animal Health 2025. Paris, 120pp. https://doi.org/10.20506/woah..... License: CC BY-SA 3.0 IGO.