A recent study by IRTA-CReSA, in collaboration with the Autonomous University of Barcelona (UAB) and the Department of Agriculture, Livestock, Fisheries and Food (DARPA), investigated two recurrent outbreaks of bovine tuberculosis in the same area of Catalonia, nine years apart: the first between 2009 and 2012 and the second between 2021 and 2022. In total, five cattle herds and at least two wild boars were affected, and all herds had to be completely culled—what is known as a sanitary emptying—at some point in the disease eradication process.
Bovine tuberculosis, mainly caused by Mycobacterium bovis, is a chronic infectious disease that can affect both animals and humans. In Catalonia, its incidence is very low and in 2023 the region achieved officially bovine tuberculosis–free status. Nevertheless, occasional sporadic outbreaks are still detected, which may be related to the persistence of the bacterium within herds or its transmission from other species such as wild boar or goats. This complexity, involving several hosts and a slowly progressing infection, makes complete eradication a truly challenging goal.
Through whole-genome sequencing of M. bovis isolates and epidemiological analysis of the outbreaks, the study identified a long-term residual infection within a cattle herd that had acted as a bridge between the two outbreaks and also as a source of transmission to wild boar (with a very low prevalence, around 2% of the animals analysed).
The so-called residual infection refers to the continued presence of infected animals that are not detected by routine diagnostic methods. It is an umbrella term that includes:
Residual infection is a major obstacle to disease eradication, as the bacterium can persist and circulate within a herd without being detected in time, causing new outbreaks—even years later. This study highlights the importance of conducting thorough epidemiological investigations in recurrent tuberculosis cases, in order to detect weaknesses in control measures and better understand how infection is maintained and transmitted. In this regard, genomic surveillance using high-throughput sequencing technologies is a valuable tool for understanding transmission chains and improving risk assessments.
Overall, with the aim of reducing the likelihood of recurrence of this persistent infection, the study emphasises the need to apply risk-based surveillance strategies, including measures such as:
This study has been published in English in open access in the journal Transboundary and Emerging Diseases:
The work was funded by the INNOTUB II – EFA115/04 project of the Interreg POCTEFA 2021–2027 programme and by the DARPA’s service agreement with IRTA-CReSA.
