THE first ever global conference on
bovine mycoplasmas was held last
July at the University of Saskatoon
in Canada. The importance of this
conference to UK cattle farming is
evident from a recent independent
survey of UK vets in which 85% said
Mycoplasma bovis was becoming
more widespread, and 79%
recognised it as one of the four main
bacterial respiratory disease
pathogens.
Clinically, the M.
bovis bacterium has
been diagnosed
increasingly in cattle
over the last decade.
Among other
conditions, it has been
identified as a cause of
mastitis, lameness and
respiratory disease and
is now considered one
of the most important
causes of calf
pneumonia
worldwide.2 Yet the
exact level of M. bovis
in UK beef and dairy
herds remains widely underestimated.
This is because (1) many
laboratories do not routinely check for
Mycoplasma in respiratory samples and
(2) the more common bacteria such as
Pasteurella spp are usually isolated first.
Estimates suggest that up to half of
pneumonia-affected herds have
evidence of M. bovis infection.
It is known to be a primary disease
pathogen, carried commensally by many
adult animals with the consequence that
calves can become infected at an early
age, though they may well be
asymptomatic until stress factors,
typically changes in feeding or grouping,
come into play.
The combination of more
widespread awareness of the pathogen
among vets and the availability of better
diagnostics are almost certainly relevant
factors behind the statistics with which
this article begins. Indeed, it is believed
that more vets are asking for M. bovis
when they seek diagnostic investigations
of respiratory disease outbreaks and, in
the fairly near future, this may become
the norm.
On farm, respiratory disease caused
by Mycoplasma bovis is typically fairly mild
in its symptoms. Body temperature is
more likely to be 102-103°C than above
104. There will probably be nasal discharge, but this may be clear and
runny rather than purulent and viscous.
Once established, infection can
spread rapidly among a group, so early
intervention and metaphylactic
antimicrobial therapy should be
considered. However, the initial mild
symptoms mean a sense of urgency in
clients’ minds may not develop until the
severity escalates due to secondary
infections. By this time, the resulting
outbreak can have a devastating impact and adversely affect
weight gain and time to
market as well as other
financial implications
such as treatment and
labour cost.
Consequently,
client education about
early identification of
respiratory infections
and the importance of
appropriate early
treatment is essential in
limiting on-farm losses
and costs. With this in
mind, data published recently showed that
dairy heifers which had to be treated for
pneumonia in their first year of life gave significantly less milk than other heifers
in the same herd which had never
required treatment.3
If pneumonia was diagnosed before
weaning, the first lactation loss was
254kg/head of milk, worth about
£60/heifer at 24p/litre. When disease
occurred post-weaning, the losses per
heifer nearly doubled to 433kg at a value
of £104 (see Table 1).
Strategic focus
There is no reason to believe that beef
animals wouldn’t be similarly affected
and demonstrate slower growth and
therefore take longer to reach target
weight or be sold at lower weights. As a
result, innovative and progressive
farmers have become quite strategic in
their focus on prevention. Hence, more
farmers vaccinate for viral pneumonia
now than in the past, but even so there
are times when vaccination alone is not
able to combat the disease.
Apart from small scale autogenous
vaccines that the VLA has been known
to create for specific problem
situations,4 there is no commercially
available vaccine against M. bovis. Clearly,
this places the emphasis on routine
observation and early intervention
where required with effective
antimicrobial therapy.
One particular concern is that beef
finishers will often buy cattle from
different sources, and cases of
pneumonia may be seen within a few
days of arrival on the home farm,
particularly in the autumn and early
winter.
On diagnosing transit fever, the
farm’s veterinary surgeon may then
advise treating the whole batch with an
antibiotic if disease is confirmed in
more than 10% of the group. Such
metaphylactic treatment of “at risk” or
“in contact” animals has been shown to
increase treatment success and can
lessen the likelihood or extent of a
prolonged pneumonia outbreak.
Critically, as far as the responsible
use of medicines is concerned, it may
also reduce overall antibiotic use
compared with waiting until animals
become clinically sick before treating
them.
Two possible sequellae to M. bovis
related respiratory disease are limb
arthritis or vestibular syndrome due to
middle ear infection. In other countries,
notably the USA and Canada, the
organism is better known to cause
mastitis rather than respiratory disease.
Serious questions
When it comes to treatment choice, the
absence of a cell wall from the M. bovis
organism poses serious questions. Many
antibiotics frequently used to treat
pneumonia (e.g. penicillins and
cephalosporins) do so by disrupting the
pathogen’s cell wall and therefore M.
bovis is intrinsically resistant to these.
While respiratory infections caused
by Pasteurella multocida, Mannheimia
haemolytica and Histophilus somni will
usually respond quite well to any one of
several antibiotics, when M. bovis is
present it is critical that the prescribed
antibiotic’s product licence includes
specific cover against that organism for
treatment.
Failure to observe this guideline may
explain why the most common
bacterium identified in feedlot cattle
affected by chronic unresponsive
pneumonia was confirmed as M. bovis in
studies published in 2001.7 Whatever
the production system, early and
aggressive treatment of M. bovis
pneumonia with an effective antibiotic is
crucial for a successful outcome.
At the Saskatoon event, one of the
main talking points was assessment of
the effectiveness of antimicrobials
against the pathogen. It seems that
laboratory-established minimum
inhibitory concentrations (MICs) on
their own do not necessarily correlate
with treatment success.
There are many other factors, including duration, that drive treatment
outcome and basing decisions solely on
MIC values in vitro are not applicable.
One of the proponents of the duration
hypothesis was Dr Mike Apley from
Kansas State University’s College of
Veterinary Medicine.
He said, “My opinion is that in cases
of bovine respiratory disease where M.
bovis is involved, duration of therapy is
likely to be as important as the selection
of an effective antimicrobial.” When it
comes to the M. bovis-specific licence
claim for the active ingredient
tulathromycin (trade name, Draxxin),
the manufacturer’s application included
both laboratory data and extensive field
evidence of treatment success in
practice.
Economically, it has been estimated
that respiratory disease costs the UK
cattle industry £54 million annually.8
Internationally renowned Mycoplasma
bovis expert, Dr Robin Nicholas from
the VLA in Surrey, who addressed the
Saskatoon conference, has published
papers indicating that M. bovis is
responsible for at least one-quarter to
one-third of these losses.
In spite of growing awareness and
better diagnostics, the mild symptoms
of respiratory disease due to M. bovis
mean it is likely to remain an under-
diagnosed yet critical BRD pathogen.
Effective management requires early
recognition by farm staff, which clearly
depends on educating clients about its
importance and what to look for. The
vet’s selection of an appropriate
antibiotic, effective against M. bovis, is
also key for treatment success.
Whatever the pathogen, it is widely
acknowledged that damaged lung tissue may take at least seven to 10 days to
heal completely. During this window
of susceptibility, cattle are very
vulnerable to further bacterial
infection and relapse. So there is a
strong case that a general purpose,
first line pneumonia treatment needs
to be long duration, broad-spectrum
and licensed for M. bovis.
References
- bio’sat, March 2009. Tracking
Injectable Antimicrobials for Cattle.
Data on file. - Nicholas, R. A. J. and Ayling, R. D.
(2003) Mycoplasma bovis: disease,
diagnosis, and control. Research in
Veterinary Science 74: 105-112. - AFBI Hillsborough data, autumn
2003 to spring 2005. - Nicholas, R. A. J. (2009) Personal
communication with author, June:
VLA, Weybridge, Surrey, UK. - Griffin (1997) VCNA Food Anim
Prac 13 (3). - Lauridsen, B. H. et al, (1996) Proc
XVIII WBC 1: 7,130-7,160. - Haines et al 2001.
8. Reeve-Johnson, 1999.
9. Nicholas, R. A. J., Baker, S., Ayling,
R. D. and Stipkovits, L. (2000)
Mycoplasma infections in growing
cattle. Cattle Practice 8: 115–118
