The source of a cluster of six cases of tuberculosis in central England in 2005 originated from one person’s exposure to bovine TB, strongly suggesting that bovine tuberculosis can be spread by human to human contact, conclude authors of research published in this week’s issue of The Lancet.
Despite a recent resurgence in the incidence of bovine tuberculosis in UK cattle herds, no associated rise in the number of cases in human beings has been noted. Disease due to human Mycobacterium bovis infection usually occurs among older people, in whom drinking unpasteurised milk in the past is the probable source of infection. Person-to-person transmission is very rare.
Jason Evans from the West Midlands Public Health Laboratory, Health Protection Agency, Birmingham, UK, and colleagues did genetic fingerprinting of all tuberculosis cases occurring between 2001 and 2005 in central England. Of the 20 cases identified as M bovis infection, 6 were found to be genetically indistinguishable.
Five patients had pulmonary disease, and one patient died from M bovis meningitis, with four patients possessing factors predisposing to tuberculosis. All patients had common social links through visits to a local bar and city-centre nightclub. With the exception of the source case, there was no exposure to bovine disease (via contact with infected cattle, or consumption of unpasteurised milk), suggesting that person-to-person transmission had occurred.
The cases came to the attention of Health professionals through a combination of epidemiological and laboratory investigations. The local Health Protection Unit conducted contact tracing and no further cases were discovered.
Grace Smith, one of the study authors, states: "This report of several instances of M bovis transmission between people in a modern urban setting emphasises the need to maintain control measures for human and bovine tuberculosis. Transmission and subsequent disease was probably due to a combination of host and environmental factors. Prospective surveillance and DNA fingerprinting identified the cluster, enabling health protection teams to set up control measures and prevent further transmission."
In an accompanying Comment, Charles O Thoen (College of Veterinary Medicine, Iowa State University, USA) concludes: "Investigations are needed to elucidate the relative importance of M bovis in the worldwide tuberculosis problem in human beings, especially in developing countries. Efforts should be concentrated in countries where HIV infection is widespread, since people infected with the virus are more susceptible to M bovis. Eradication of M bovis in cattle and pasteurisation of dairy products are the cornerstones of prevention of human disease. Standard public-health measures used to manage patients with contagious M tuberculosis should be applied to those with contagious M bovis to stop airborne person-to-person spread. Finally, measures should be developed to identify and control M bovis infection in wild animals, which might be an important source of infection for domesticated food-producing animals".
Journal
The Lancet