The Hidden Paw

A cluster of nine cases of tuberculosis in cats in Newbury at the end of 2012 and early 2013 spread to their human owners, causing serious lung disease in two of them and infection without disease in another two. Unsurprisingly, when the results of the investigation were published, it became a top news story. It would have been an even bigger one if it hadn’t had to compete with Ebola in Guinea.

TB in domestic cats is not new. It was common in them before the First World War and for many years afterwards. Saucers had been filled with milk from tuberculous cows. The Newbury cats were also infected with bovine TB. But milk is safe today because of pasteurisation and the rigorous control of the disease in dairy herds. The cats caught it from infected wild life, possibly by eating a tuberculous rodent – voles are prime suspects – or by fighting an infected animal, maybe even a badger. The TB strain was also found in cattle on Greenham Common, near Newbury. But the connection between these findings is a mystery. It will remain so.

In the 1970s I used to travel regularly on the Shuggle, the Glasgow Underground (the uriniferous narrow 1886 teak-framed cars creaked and rocked alarmingly between stations), and I have vivid memories of sitting opposite elderly women with necks scarred by the surgery they had had to remove their tuberculous lymph glands. They had been infected as children by drinking contaminated milk. I thought at the time that they were like the ‘mutilés de guerre’ notices on the Paris Metro, reminders of history long gone. After all, wasn’t the eradication of bovine TB in the UK in sight? Not far off for Scotland. But in England and Wales a long-term increase in the number of infected cattle started in 1986. In 2010 the proportion of cattle with TB in Scotland was 0.004 per cent. In England it was 0.46 per cent.

Cat to human transmission of TB has never been recorded before. Contracting TB in the UK is now rare, and cases are investigated in detail using molecular fingerprinting to find the source. But fifty and more years ago fingerprinting had not been developed, and any cat-contracted human cases would have been unremarkable against a background of a relatively high incidence of indigenously acquired TB.