Not a sexy disease
Recently, a new disease, BNP, has
become a major source of interest in
cattle veterinary circles. The acronym
is not referring to a political party but
to bovine neonatal polycytopaenia.
Large amounts of money, time and
effort have been spent
in the last year on a
disease, which at best
has only affected a
few thousand calves
worldwide.
If a quarter of the
time and expertise
were being spent on
more common
diseases such as
coccidiosis it might
produce a much more
cost-efficient return
on a ubiquitous
problem which can produce
widespread clinical signs and welfare
problems.
Thoughts on coccidiosis change
In the1960s and before, coccidiosis in
farm animals (cattle, sheep, goats, pigs)
was thought to be almost completely
self-limiting. However, as time has
gone on, many severe outbreaks have
occurred and almost every animal
reared inside or out will become
infected.
Luckily, unlike BNP, most animals
are exposed to the parasite and
become immune without disease signs developing. On occasions, however,
major problems occur on farm and,
despite infection being known about
for so many years, it is not always
possible to understand why an outbreak has arisen.
It was also seen that there was a
marked rise in the
number of cattle
problems in the mid-
1990s and to a lesser
extent in sheep.
This article will try
and remind the reader
of some features
about the infection in
cattle, sheep, goats
and pigs. It is not
possible in this short
piece to do justice to
this important
infection but a few highlights will be given.
CATTLE
Occurrence
Coccidiosis has been known about in
cattle since early in the 1940s. Whilst
several species affect cattle, two appear
to be the main pathogens Eimeria bovis
and E. zuernii. It is primarily a disease
of young cattle, both indoors and
outside.
In a NADIS study it was the third
highest cause of diarrhoea in
unweaned calves as well as the most
common problem found between
three and 12 weeks old (Otter and
Cranwell 2007). It was also found to
be the most common cause of poor
growth in calves which were “poor
doers” and which did not show
diarrhoea or respiratory signs.
Thus, it is undoubtedly a major
cause of economic loss in cattle. The
infection is seen occasionally in cattle
going to grass for the first time (often
due to E. alabamensis) and it rarely
occurs in older animals.
The Veterinary Investigation
Surveillance (VIDA) data for Great
Britain for diagnoses from faecal
samples showed a rapid rise in positive
levels for coccidiosis from 1993 to
1997. Levels that were found positive
doubled.
This suggested that some factor
changed rapidly in the mid 1990s and
it has previously been suggested that
this was the result of antimicrobial
growth promoter (AGP) removal by
most feed manufacturers (Andrews
2008).
The disease is more common in the warmer months of the year (May
to November) and less from
December to April with overall most
cases occurring in June and the least
being in February.
Diagnosis
Diagnosis of outbreaks is often
difficult because it is usually based on
oocyst counts with levels over 5,000 opg (oocysts per gram of faeces).
From my investigations this figure
appears to be based on a paper by
Boughton in 1945.
In it he states: “In the writer’s
experience with both experimental and
natural infections in dairy calves one to
three months old, oocyst counts on
the order of 5,000 to 10,000 per gram of faeces were nearly always associated
either with outright clinical coccidiosis
or with severe infections characterised
by diarrhoea, enteritis, and general
unthriftiness.”
Unfortunately, the paper itself does
not provide the results upon which
this statement has been based. In the
experience of many clinicians, they
have found using this number
misleading as cases appear to occur
when the oocyst count is lower.
One major problem is when any
faecal samples are taken. The oocyst
counts are only very high for a short
period although usually diarrhoea lasts
two or three times as long.
Frequently, faecal sampling is
undertaken after, or occasionally
before, the period of maximum oocyst
shedding; therefore, when undertaking
faecal sampling it is important to take
samples from several animals within
the group and not just those with
signs.
Various criteria have been
suggested to assist in diagnosis besides
just relying on a faecal oocyst count
and are shown in Table 1.
Economics
The cost of any disease is hard to
estimate. One problem is that in
Britain it is not usually ethically
possible to leave untreated affected controls. In addition, most of the
treatments used have some growth
promoting properties and thus an
enhanced growth performance may
result from their use.
However, in some USA studies on
the efficacy of coccidiostats in cattle,
two types of controls were used,
namely experimentally infected and
uninfected controls. These showed the
effects of infection as well as allowing
both groups to later be exposed to any
natural infection in their environment,
both inside and then out of doors.
Figure 1 shows that infection
caused a reduction in weight gain after
infection. Although weight gain later
improved in these infected animals, the
weight difference caused by coccidia
remained until the end of the trial.
These reductions in weight gain
and other influences on affected
animals probably currently amount to
between at least £24.50 to £59.25 per
animal, not including the cost of any
treatment.
SHEEP
Again, the disease appears to be more
common than some years ago. There
are two main pathogens recognised,
namely E. crandallis and E. ovinoidalis.
Diagnoses of coccidiosis from
VIDA data do not show the same
pattern as in cattle but there were high levels of infection from the mid-1990s
including 2000 but since then they
have reduced in most years.
Again there are problems with
diagnosis but in general using the
criteria presented in Table 1 will assist
with diagnosis.
GOATS
At one time, several of the coccidial
species found in goats were considered
to be the same as sheep but now those
in both sheep and goats are considered
relatively species specific. E. arloingi
and E. ninakohlyakimovae are considered
the main pathogens.
The number of diagnoses in VIDA
data is small but again there was a
trend to higher infections from the
mid 90s to 2000, but then remaining
low. However, coccidiosis is often
considered the most important cause
of diarrhoea in goats greater than four
weeks old.
PIGS
In many ways coccidiosis in pigs is
very different to the condition in
ruminants. It involves a different coccidial genus to ruminants, namely
Isospora, and the infection mainly
involves I. suis.
The pre-patent period is much less
than for the ruminant species and so
signs can occur towards the end of the
piglet’s first week of life with yellow
watery diarrhoea. The animals may be
indoors or outside. This early
occurrence can catch out the unwary
unless attempts are made to make a
proper diagnosis.
The VLA data show a relatively
high level of diagnoses in the mid to
late 1990s but after 1999 they have
been low.
The treatment of coccidiosis
There are three main chemical
preparations available for treating
coccidiosis and most of the companies
marketing them are mentioned in
Table 2. The products are best used at
the start of signs or prior to their
predicted development.
An indication of how to use them
as indicated in the data sheets is also
included in the Table. However, always
check details with the data sheet as they do change, but also always tailor-
make your recommendations to the
specific farm and its management as
well as any specific problem present.
Effective use does depend on
understanding the epidemiology of the
disease, the production of immunity and the
management
system on the
farm.
Ideally, the
timing of any treatment is to
prevent clinical
disease but also
allow the
development of
protective
immunity.
Some
indications for
their use in cattle have recently been made (Taylor and other, 2010).
Conclusion
In all the main species of farm animals
coccidiosis should always be
considered in young animals not only
because of the clinical signs that the
infection can produce but also because
it can result in reduced immunity to
other diseases, reduce normal growth
and also possibly increase signs of
other diseases.
References
Andrews, A. H. (2004) The diagnosis of clinical coccidiosis in calves. UK Vet 9 (1):
45-47.
Andrews, A. H. (2008) Coccidiosis – new
thoughts on an old disease. Cattle Practice 16
(2): 156-164.
Boughton, D. C. (1945) Bovine coccidiosis:
from carrier to clinical case. North American
Veterinarian 26 (3): 147-153.
Fitzgerald, P. R. (1972) The economics of
bovine coccidiosis. Feedstuffs 44: 28-30.
Otter, A. and Cranwell, M. (2007)
Differential diagnosis of diarrhoea in adult
cattle. In Practice 29 (1): 19.
Taylor, M. (2000) Protozoal disease in cattle and sheep. In Practice 22 (10): 604-617.
Taylor, M. A., Andrews, A. H., Alzieu, J. P.,
Holzhauen, M., Kakse, M. and Willemsen,
M. (2010) Role of immunity in the
management and control of bovine
coccidiosis. Veterinary Record 166 (26) 831-
832.
VIDA (1975 to 2008) Veterinary
Investigation Surveillance Reports. A
tabulated summary of diagnoses
recorded at Veterinary Laboratories
Agency Regional Laboratories in
England and Wales and Disease
Surveillance Centres in Scotland.
