The Badger vaccine research project – results to date.
Leigh Corner, Denise Murphy a, Eamon Costello b and Eamonn Gormley a
a
School of Agriculture, Food Science and Veterinary Medicine, University College Dublin
b
Central Veterinary Research Laboratory, Backweston, Co. Kildare
e-mail: leigh.corner@ucd.ie
ABSTRACT
Mycobacterium bovis infection is endemic in badger populations in Ireland and infected
badgers are a reservoir of infection for cattle. Although badgers are a protected wildlife species,
limited badger culling is undertaken to lessen the impact of badger tuberculosis on cattle. Culling
is an interim strategy of pending the development of vaccination as an alternative strategy.
In Ireland, the prevalence of M. bovis infection in culled badgers is 42%, and the true
prevalence, after allowing for false-negatives, is probably ~ 50%. Our estimate is based on
detailed post mortem examination and sensitive bacteriological methods using 347 cull badgers.
Previous reported prevalence of 12 to 15% (using gross pathology only) and 18 - 26%
prevalence (based on limited bacteriological examination (10 tissues/badgers) were severe
underestimates. In our study the “average” infected badger could not be differentiated from noninfected badgers on body weight measurements or the presence of bite wounds. As previously
reported the prevalence of infection in males was significantly greater than in females. We found
53% of infected badgers had no gross lesions, and infected badgers had a mean of 5.9 sites of
infection (range 1 – 29 sites). Those with gross lesions had a mean of 4 (1 – 20) gross lesions.
Only 6.6% of badgers had bite wound and these were evenly distributed between infected and
non-infected badgers. In infected badgers 48% of bite wounds were tuberculous.
Infection was focused on the thoracic cavity, with 54% of infected badgers having lung or
thoracic lymph node infection. We would predict, therefore, that excretion from the respiratory
tract would be more significant in transmission, both between badgers and from badgers to
cattle, as excretion by other routes, e.g., urine and faeces, occurred with low frequency (9% and
3.5% of infected badgers respectively). Although the concentration of bacilli in urine was low
but high in faeces.
The badger BCG vaccine research project commenced in 2001 with the aim of testing if BCG
was protective in badgers, and to provide scientific support for the incorporation of vaccination
into the national programme. The studies have examined pathogenesis of infection, and have
been used for the development and evaluation in vitro diagnostic assays measuring immune
responses to infection, vaccination, and challenge. We have shown that BCG induces protection
when delivered by each of three routes – subcutaneous, mucosal and oral. Protection was still
evident 12 months after oral vaccination. No significant differences were found in the protective
effect of BCG Pasteur and BCG Danish vaccine strains.
The studies have established that BCG induces a protective response, limits the distribution
and severity of tuberculosis in experimentally challenged badgers. A field trial is to be
undertaken, designed to test if BCG is protective in wild badgers under conditions of natural
transmission and to estimate vaccine efficacy. The design of the vaccine field trial will be
described. The field trial and related studies will be used to develop strategies and policies for
using vaccination in the national TB programme.