PCR, M. bovis and badgers - Veterinary Practice
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InFocus

PCR, M. bovis and badgers

RICHARD GARD reports on latest developments in the fight against bovine TB

A VERY short time after taking
office, the new Minister of
Agriculture attended the Devon
County Show and made a statement
about badger culling.

If he was reported correctly, he was
intending to base any action on science
and the detection of TB
in badgers using the “polymerase chain
reaction” (PCR) tool.

The regional press
has recently trumpeted
that the application of
a magic black box is
the way to eradicate
TB in cattle. The idea
being put forward is
that a probe is inserted
into the earth near a
badger hole, or into a
latrine, and the box
indicates whether M.
bovis
is present. If the
organism is identified,
then you shoot the badgers.

Anyone who has worked with the
application of PCR will quickly point
out that there are very great scientific
difficulties with what is being talked up.

A whole raft of information is available (e.g. www.454.com) and in
summary the current situation is
described by Dr Colin Fink of
Micropathology Ltd as there having
been “a quantum leap in sequencing
mixed bacterial or virus samples and
pulling out the quantitation of what pathogens and
commensals are
present in, say, soil
samples or in throat
samples. The new
problem is that the
technology is now so
sophisticated that
information overload is
the new disease.

“There is very
good field technology
for PCR single round
where the pathogen is
single and likely to be
there in large quantities
(foot-and-mouth comes to mind as the
ideal example). The problem is that there are many soil Mycobacteria and
deciding what is M. bovis as an animal
pathogen and what is simply there as
other species is not yet easy to separate.
“This is why there is so much ‘noise’, which is difficult to interpret.
The new technology could be applied to
this problem and I suspect would give
interesting data. It is not suitable for use
in the field.”

A commercial field-based battery-
operated product is being talked up in
farming circles, produced by Enigma
Diagnostics at Porton Down. Further
developments are awaited.

A key aspect for PCR is phrased as
detecting clinically significant material.
The basic result from running a test is a
number. How that number is
interpreted becomes an important issue.
A low level of M. bovis could be residual
on the ground for years. The badger
that left that marker could well be dead
or already evicted from the badger
community and moved on.

The concern then is about “fresh”
samples and significant quantities of the
organism. Maybe this interpretive work
has already been done but if not, linking
scientific detection with badger culling
could raise various challenges. The
indications are that there are badgers
that are not a risk to the cattle.

It has been said at TB meetings that
a single cell of a Mycobacterium is
sufficient to infect a bovine. Is this an
active cell or a passive cell? Does a cell
from the environment have the same
infective ability as a cell from a clinical
source? If such science is available, now
may be a good time to offer clarification
before veterinary practices are asked by
clients to provide advice on
environmental TB detection.

Unrealistic expectations?

Much rests on a means to control TB,
both politically and to reduce the burden
on cattle farmers. If PCR cannot be
currently used accurately in the field,
then an advisory note needs to be sent
out to reduce unrealistic expectations.
Maybe, if enough money and resources
are applied, the problems of
environmental noise may be overcome.

The technical developments for M.
bovis
identification are one obstacle,
interpreting the results a second but an
effective way of culling the badgers is
the third obstacle and fortunately the
easiest to solve.

In endemic TB areas, the virtues of
local badger exterminators are being
extolled: people who, for a fee, will
shoot badgers. In all species, stress and
other ill health are recognised as triggers
for Mycobacteria infectivity.

Disruption of badger communities
by filling in setts, road kill, rat poison,
paracetamol, antifreeze and random
killing are all included in the list of
actions expected to cause badgers to
either move into other territories and
fight, or feel unwell. Both outcomes are expected to increase M. bovis excretion.
Shooting a few badgers on one farm could well increase local badger stress
and bring down the cattle herds at
farms nearby. The idea of simply
reducing the bacterial load by reducing
the badger population only applies if
the M. bovis excretors are removed from
the land.

The Minister is probably now aware
of all the obstacles to the effective
control of TB. He is also aware that it is
practical to identify the location of sick
badgers, living outside healthy badger
communities. Removing them from an
area in one day during the winter is the
way to improve TB in cattle grazing
land that was occupied by badgers.

A practical, cheap, sustainable,
targeted method is gas, used in a way
that matches the realities of badger
accommodations. Unhealthy badgers are
not necessarily in traditional setts.

The sooner the use of carbon
monoxide is approved to cull sick
badgers, and applied in an effective way
in local areas, the sooner a resolution to
TB in cattle can be seriously anticipated.
Vets may wish to encourage urgent
approval for the use of the smoky
tractor, in a controlled, effective way to
best effect, as part of a wildlife
management programme.

A practical, successful and rapid
testing method to assess the
concentration and effectiveness of
carbon monoxide gassing of badgers is
available. Approval need not be a
lengthy or expensive process.

Achieving healthy badgers and
healthy cattle in a local area can be a
reality. Clients expect practices to be
involved in the forthcoming reduction
of herds undergoing 60-day testing with
trading restrictions. It will be important
that the detailed TB records of these
herds are kept up to date.

Where short interval testing is
brought back in-house by DEFRA this
winter, it is hoped that the results of the
tests will be provided to the veterinary
practice that has been carrying out the
testing and may do so again.

The data will become more
important for disease reduction as time
goes on in addition to the role with
disease surveillance and compensation.
Relying on information from the client
may be effective for herds that are
routinely visited but in many counties
the majority will be beef herds and
information may be harder to obtain.

If the disease reduction programme
can be effectively activated, then the
concerns about the DEFRA budget will
be alleviated. During the next three
years significant financial gains can be
made for the farmers and for the TB
budget.

The BCVA congress in Torquay
from 14th to 16th October will provide
an opportunity to define the practical
ways forward.

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