Bovine tuberculosis in cattle and badgers
What is the problem?
The story so
- Mycobacterium bovis is a bacterium which is closely
related to the human form (Mycobacterium tuberculosis) and
the avian form (Mycobacterium avium).
- It primarily infects
- All types of mycobacterium cause tuberculosis or
TB. In the 1930s there were 50,000 cases of human TB each year. 4000 of
these were caused by Mycobacterium bovis, resulting in 2000 human
Milk was tested and sick cattle were slaughtered, however this
didn't prove too successful in combating the
Testing of cattle was carried out by injecting tuberculin
antigen into each cow. The individuals carrying the disease would react to
the antigen-these animals were slaughtered.
An investigation then began to see how widespread the
disease was in the Badger population :
Badgers are most numerous in the south-west of
England, as are cattle. Due to this, bovine tuberculosis in Badgers
is mainly a south-west problem, it isn't as serious in the rest of
Badgers could only be checked for TB at post mortem,
so unfortunately all Badgers both infected and uninfected were
culled. Gassing (by cyanide) was an efficient way to kill them, but
the Badgers died in their setts and could not be tested for TB.
Cyanide poisoning was later checked, and was found to take a long
time to kill the badgers so was banned because cruel. Cage trapping
the Badgers is less cruel, but requires more time and man power, so
is less efficient as a control method.
When Badgers were killed, the incidence of TB in
cattle decreased. When no Badgers were being killed, the incidence
of TB in cattle increased. How was TB being spread between cattle
The success of eradicating bovine TB in Britain was not
universal. Especially in SW England there were regular outbreaks. These
were not only new cases but repeat cases in farms where cattle herds were
thought to be have been
A badger was found dead in the open in Gloucestershire, on a
farm where there had recently been bovine TB. An autopsy was carried out
on the Badger, and bovine TB was discovered. Other Badgers too were
examined - 22% of Badgers in the area had bovine
Of a large sample of Badgers from the south-west, 14%
had TB. However, this was not representative of the whole of the UK,
as the area was where there were known to be outbreaks previously.
The roles of other wildlife in bovine tuberculosis is
not known so well. Other carriers of the disease may be mink, fox,
mole, rat, ferret and wild deer.
- TB isn't very infectious in Badgers and isn't
always fatal. It also tends to stay within a Badger
- TB is not a major cause of death in Badgers-52% of
Badgers die in road traffic accidents.
- The main mode of TB transmission is respiratory -
especially from mothers to cubs within setts.
The situation in the south-west still wasn't much better. In
the early 1980s, each TB breakout had cost £5,700. However, when the
Badgers were killed, the maximum saving was £1.9 million, but it cost MAFF
(i.e. the taxpayers) £11.3 million. Thus Badger control is not economic.
- It is still uncertain how TB spreads between
Badgers and cattle, and in which direction it
- With humans, TB is more prevalent in dense
populations. This doesn't appear to be the case with Badgers. The
incidence of TB is not related to Badger
- It is not necessarily the Badgers that need to
controlled - a better option would be more secure housing for cattle (to
ensure Badgers can't mix with them), better ways of feeding them (so
Badgers can't raid their feed troughs), and keeping cattle away from