Badger culling as part of bovine TB control

YET again badgers are being vilified as being a major cause of Mycobacterium bovis infection in cattle. Akhmetova and colleagues1 carried out an extensive government-commissioned study in a 100 km2 historic hotspot in Northern Ireland with a high density of dairy herds and badgers. They found that badger-to-badger transmission was negligible, and that cases of cattle-to-cattle transmission greatly outnumbered badger-to-cattle transmission. Cattle-to-cattle transmission was by far the most common. In a similar study using genomic testing by Crispell and others2 around Woodchester Park in Gloucestershire, cattle-derived isolates of spoligotype SB0263 were selected from the archive, and only those that were the same spoligotype as badger isolates from the area were included; hence the paper's conclusions that, although badger to cattle transmission did occur, the percentage of cattle infections originating from badgers v cattle will be underestimating the number of cattle infections derived from other cattle. Moreover, the cattle area differed from the badger area tested. In some outbreaks that would historically have been attributed to badger-to-cattle transmission, genomic testing has demonstrated that infected cattle purchased several years previously can go undetected and seed bovine TB (bTB) into a new herd (unpublished communication, APHA 2024). In view of a premovement test with a sensitivity between 50 and 80 per cent, this is hardly surprising. It has been demonstrated time and time again that other cattle are the main source of bTB in cattle; the GOV UK website notes that ‘the main source of M bovis in the UK is infected cattle, which act as the primary reservoir and source of infections for new herd breakdowns through the movement of undetected infected animals’.3 If we wish to control bTB in cattle, let's focus on cattle-to-cattle transmission – direct or indirect. The start of cattle vaccination is fantastic news. We should investigate the role of slurry, water troughs and other vectors. How are cows infected? Does oral transmission play a role? Why are dairy herds at greater risk than beef herds, despite usually spending less time at pasture? Do skin and gamma tests detect cattle that are infectious or ones that have merely been exposed in the past? Despite most cattle infections originating from other cattle, TBAS training remains very badger focused. Ditto the TB Hub's five key points to prevent bTB4: the first two points focus on badgers, with only point number five mentioning cattle sourcing and equipment sharing. This grossly distorted messaging needs to be urgently addressed. Badger vaccination will protect badgers from bTB infection, but it is unlikely to reduce cattle bTB. There is no firm evidence that badger culling in the absence of increased cattle testing (eg, gamma interferon testing) and increased biosecurity (a condition of every badger culling licence) has reduced cattle bTB infections. There has however been published evidence that the effect of badger culling on cattle bTB has been negligible.6 The focus on addressing bTB in badgers, either though culling or through vaccination, needs to change. Regarding the culling of deer, as Drouin also discusses in his letter, although Castle Cary, Somerset, reportedly used to have a Badger Roast Festival in the 1950s, the species is not usually shot for meat. Badgers were relentlessly persecuted, hence they were declared a protected species. Deer are not a protected species and their carcases are often used for meat. The role of deer in bTB transmission is unclear at present. The APHA considers deer as ‘spillover’ hosts, but to my knowledge no work has been done to establish direction of transmission. “Wildlife population control for reasons other than animal disease and welfare is not within our remit nor within our expertise