How is bovine tuberculosis transmitted?
Bovine tuberculosis is most commonly transmitted by airway, although the digestive tract may also exist. Domestic cattle are the primary maintenance hosts of infection to M. bovis (except in exceptional cases), i.e. the disease is transmitted first and foremost from infected cattle to healthy cattle. Maintenance hosts are able to maintain infection between individuals of the same species within the same population, without an external source, and to transmit it to other susceptible species. The eradication of bovine tuberculosis depends above all on the fight once morest this infection in breeding.
Cattle can in some cases excrete the bacteria and contaminate humans, as well as other mammals, directly (aerosols), but also indirectly because the bacterium can survive for several months in the environment under certain conditions. Thus, wild animals, in particular wild boars, badgers and deer, can also contract the infection, and are likely to contaminate farms in turn. Apart from exceptional cases, however, these wild populations are considered to play the role binding hostsunable to maintain the infection in a perennial manner without an external source of contamination, but nevertheless capable of transmitting it to another population, domestic or wild.
Highlighting the importance of wildlife in the transmission of the disease has led to a strengthening of the screening for infection in these populations around domestic outbreaks. Wildlife surveillance, via the surveillance network Sylvatubis carried out in order to implement control measures and prevent the infection from persisting in these populations, or that some of them may play a role of maintenance host, as has been observed in d other countries (for example, badger populations in Great Britain, and wild boar populations in certain areas of Spain).
ANSES’s work on bovine tuberculosis
Learn more regarding bovine tuberculosis and how it is transmitted
ANSES laboratories carry out major research work on bovine tuberculosis. These are the Rabies and Wildlife Laboratory in Nancy and the Animal Health Laboratory in Maisons-Alfort where the National Reference Laboratory for Tuberculosis (NRL) is located. The NRL is in particular responsible for developing analytical methods for monitoring this disease, and for transferring these methods to the network of approved laboratories that it coordinates on French territory.
The main research work carried out by the Agency is aimed at improving knowledge of infection with M. bovis in the domestic population and wildlife in order to understand the transmission networks between these two types of populations:
- studies of the roles of different species of wildlife in maintaining infection and direct transmission between animals or indirect by contamination of the environment;
- modeling of the interactions between the different infected species and their environment, to improve disease control in animals;
- characterization of possible differences in virulence between the strains of Mycobacterium bovis in the affected regions.
Among the work carried out, the NRL for tuberculosis has been participating in the project since June 2020. Innotub Poctefa (Trans-Pyrenean Network for Research and Development of Innovative Tools for the Control of Animal Tuberculosis), funded by the European Program Interreg Poctefa and the European Regional Development Funds (ERDF), within the framework of cross-border cooperation projects between Spain, France and Andorra. The objective of the project is to create a scientific network of excellence across the Pyrenees, to improve the control and surveillance of tuberculosis in farm animals and wildlife.
ANSES also contributes to research work on the development of a oral vaccine for badgers as a preventative measure to control wildlife infection under certain conditions. This work is carried out in collaboration with teams in the United Kingdom, Spain and the United States.
Assess risks and monitoring and control measures
For several years, the Agency has also been carrying out risk assessment and regulatory support work for the public authorities with regard to this disease. Since 2005, more than twenty opinions and reports on bovine tuberculosis have been published. Among its expert appraisals, in 2011 the Agency published a report on bovine tuberculosis and wildlife (PDF) with recommendations for the management of wild animals infected with bovine tuberculosis, in particular on the methods of trapping and/or destruction of badger burrows. In 2019, the Agency was contacted by four nature protection associations regarding the management of badger populations in the fight once morest bovine tuberculosis (PDF). After analyzing all of the available data, both on badger populations and on their health status, the Agency stressed that the current regulations provide a precise framework for surveillance and control measures leading to the elimination of animals wild, depending on infection levels and areas. As such, control measures in badgers can only be implemented in a delimited area, determined on the basis of surveillance data, over a given period and regularly reassessed according to the results of surveillance. These measures only concern areas at risk in a few departments in France, which represents less than 4% of the metropolitan territory. Nationally, these measures do not threaten the species.
Following a referral from the DGAL, ANSES issued an opinion in February 2021 on the role of the fox in the transmission of bovine tuberculosis (PDF). The Agency concluded that this animal species can indeed contribute to the transmission of the disease, but that because of its way of life and the rapid turnover of its population, its role is probably less important than that of other wild species, such as badger or wild boar. Management measures are to be taken on a case-by-case basis and locally, in the immediate vicinity of contaminated farms. This opinion specifies that the preventive elimination of foxes, like badgers or other wild species, cannot in any case be justified on the grounds of the fight once morest tuberculosis.
