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The Bluetongue virus threat
to UK livestock this summer
Teviot Scientific. Cultybraggan Farm, Comrie,
Filed 12 Apr 07
Bluetongue is a viral infection
that mainly affects sheep, but also cattle, goats and deer. It does
not affect man. The Bluetongue virus (BTV) is transmitted by midges
(Culicoides). If the disease gets into a flock of sheep
the morbidity and mortality rates can be high, depending on the
type of the infecting virus. In highly susceptible sheep the mortality
can be as high as 70% (1).
The disease in cattle may not be
so severe, but again can be serious according to the type of BTV.
There are 24 types of BTV. There is no treatment for Bluetongue
Disease, but antibiotics can be used to counter bacterial secondary
infections that may occur.
BTV has long been a problem globally,
particularly in Africa and southern Europe, existing in a broad
band from about 40 degrees north to about 35 degrees south. In recent
years it has spread further north in Europe. The reason is thought
to be related to climate change, allowing midges carrying the virus
to survive in more northerly latitudes. In the last five years outbreaks
have occurred, reaching 44 degrees north. That is some 800km further
north than previously recorded.
Late in the summer of 2006 the
disease was identified in the Netherlands, followed by Germany,
Belgium, Luxembourg and parts of northern France.
Photograph kindly provided
Head of Entomology and Mathematical Modelling,
Institute for Animal Health, Woking, Surrey, UK
(To enlarge photo Click
As everyone in Scotland knows, midges are not confined to southern
climes. What is particularly worrying is that the midge species
in the affected areas, Culicoides imicola, can pass the
virus on to other types of midge, such as the Culicoides obsoletus
group and Culicoides pulicaris. Whether, if given the opportunity,
the virus could also be passed on to the common biting midge of
Scotland, Culicoides impuctatus, must be a matter of concern.
Certainly within some types of
midges the virus can be passed on from one type to another, rather
like passing a baton in a relay race.
Although Bluetongue Disease is
not contagious, once the virus gets lodged in organic matter it
can survive for prolonged periods.
Midges are spread by the wind,
but are killed off by low temperatures. If the disease becomes active
again this summer in northern continental Europe it is possible
that midges bearing the virus could be blown across the Channel
to Kent, which has a high population of sheep.
Midges infected with BTV could
also be transported to areas far beyond their normal territory in
aeroplanes, in lorries or on the person of travellers. They could
also be carried on plants, or other materials that are being imported.
A species of midge carrying the virus could then pass it on to another
species of midge that is common in the hitherto unaffected geographical
The virus can be spread through
the import of livestock from areas that are infected, or which have
passed through such areas. It is illegal to import cattle or other
susceptible livestock if they have originated from, or travelled
through, a restricted BTV zone. Currently, BTV restricted zones
include all of Belgium, the Netherlands and Luxembourg, as well
as parts of Western Germany and Northern France (including the export
centres of Calais and Dunkirk).
According to the National Beef
Association (NBA) at least three recent instances have occurred
where cattle had travelled through BTV restricted zones and subsequently
entered the UK. The NBA documents an instance when 70 continental
cattle, brought together in a single load, by various buyers in
Scotland and England, in January 2007. The route the lorry took
went through an area where the animals could have attracted biting
midges carrying BTV. Fortunately, subsequent testing showed the
cattle to be negative for BTV, but the risk was real.
Not only should the importers have
known the rules but the border checks should have been more rigorous
- a frequent and long standing complaint of the UK's livestock industry
and of the EU's approach to the control of spread of diseases affecting
An electron micrograph of
the prominent biting midge of Scotland
Photograph kindly provided
Dr Alison Blackwell, Advanced Pest Solutions Ltd,
University of Edinburgh.
The type of BTV that is closest
to the shore of the UK is currently V8. In southern Europe the types
involved are V2 and 4. However, from what has been described above,
there is the potential for the UK to be hit by a wider range of
types of BTV, although V8 is the most likely.
There are fears that the BTV may
have survived last winter in parts of northern Europe - possibly
in both the host and the vector. With climate change, milder but
wetter winters are predicted for the UK.
There is, therefore, a very real
threat to the UK's livestock this summer from Bluetongue - a disease
that hitherto has not been seen in Britain. With the current early
and unusually warm Spring, the infected midge may arrive on UK shores
earlier than the authorities may lead us to believe.
Symptoms and signs of Bluetongue
The most prominent signs of BTV8
infection in sheep as recorded in the recent outbreaks in north
western Europe (2, 3,
fever, salivation, erosions of
the oral cavity, facial oedema, dysphagia and, apathy and tiredness,
congestion, erythema, redness of oral mucous membranes and lameness.
In cattle BTV8 caused:
crusts/lesions of nasal mucous
membrane, salivation, fever, conjunctivitis, dysphagia, serous
nasal discharge, apathy and/or tiredness, hyperaemic/purple colouration,
lesions of teats, lameness and coronitis.
This is in contrast with previous
experience that BTV does not produce more than transient and mild,
if any, clinical signs in cattle. The recent experience in northwest
Europe with BTV8 has shown that a few cattle within a herd can show
distinct clinical signs. This is borne out by the experience of
Sabine Zentis who runs a pedigree herd of Longhorns in Germany,
who states (5) that
"Cattle infected with V8 and
showing clinical signs are really ill. If treated properly
they will survive, but beside the short term lesions of the mouth,
tongue or teats, they suffer from laminitis for quite a time.
The longterm effects of calves born to dams infected during pregnancy
have not yet been investigated, nor a suspected reduction of fertility
or milk yield after infection."
In sheep, BTV8 clinical signs
and mortality are much more prominent than in cattle.
Differential diagnosis of Bluetongue
With such non-specific clinical signs
in both sheep and cattle, it is essential that an accurate and rapid
diagnosis can be made. This is where it is greatly disappointing
that the lessons that should have been learned from FMD UK2001 apparently
have not been learned.
According to the latest version of
the UK BT Contingency Plan, blood samples taken from anywhere throughout
the UK have to go to Pirbright, Surrey in the south of England for
testing. While this may be fine for establishing the serotype of
the first case, it is far from satisfactory when it comes to checking
whether a beast on a farm is suffering from BTV or from some other
condition. What is required is rapid on-farm tests that can be done
within a few hours, not a few days. RT-PCR technology is available
for that internationally, but for some reason the UK authorities
do not wish to use it. There must surely have been abundant opportunity
to "validate" such tests if there was a will to do so.
It should also be remembered that
rapid on-farm slide tests were available during FMD UK2001 but were
Modern RT-PCR testing should be able
to rapidly test for a spectrum of diseases all in one go, on farm.
How can BTV be controlled?
As every Scot knows who has taken
a summer holiday on the West Coast, it is very difficult to control
midges. As mentioned above, they are carried on the wind and by
other means. They can be very prevalent even in the absence of livestock
or dung heaps.
By the time a case of BTV is diagnosed
in farm livestock there are likely to have been many beasts that
have been subclinically infected for a considerably period on that
farm, and possibly other farms in he area. The vector midges will
be all over the vicinity and beyond. It is the area that is infected,
not just the particular farm where the disease was first found.
There would, therefore, be little point in slaughtering the identified
host in a rather forlorn attempt to reduce the viral load. The host
beast is likely to survive and to develop immunity to future infection,
at least to that particular BTV type.
It would appear patently obvious
that the only way to control the spread of BTV is through an effective
vaccination policy. Science is perfectly capable of producing BTV
vaccines that are sufficiently effective to be useful in the field,
but there is a clear lack of an effective integrated policy within
Europe to achieve this essential objective (6,
We are told that Merial may have
a BTV8 vaccine by 2008 or 2009. But vaccine manufacturers will only
produce vaccines if they are contracted and paid to do so. What
the Chinese managed to do in relation to vaccine production for
Avian Influenza was impressive in its timescale and effectiveness.
There is a European vaccine bank
that allegedly holds some millions of doses of combined vaccine
against BTV2&4, and which has been used for the past 2-3 years
in Spain. It would be interesting to discover how effective it has
been, and what complications may have arisen. The fact that the
vaccination policy is allegedly continuing in southern Europe would
suggest that there is confidence in its success.
But in the UK, DEFRA reiterates the
same message that it had during the disastrous management of FMD
"In the event of a decision to vaccinate against
Bluetongue, supplies of vaccine would be ordered by the CVO from
the European Bluetongue Vaccine Bank. In a worse case scenario
around 7.4 million doses of vaccine might be required.
"At present the UK does not hold a marketing
authorisation for use of such vaccines. Vaccination could could
therefore only be used on a vaccinate to kill basis.If such a
policy was adopted further details would be issued to holders
of the contingency plan concerning the quantity of vaccines necessary"
This makes most depressing reading.
Why is DEFRA stuck in the mindset of not getting a marketing licence
because it has not asked for it? Does the vaccination programme
in Spain rely on a vaccinate to kill basis? It would hardly make
Warnings are also made about the
possible teratogenic effect that vaccines may have, and the risk
of viruses adapting to vaccines that are only partially effective
to create new virulent strains that could possibly escalate rather
than help the situation. But are these warning based on experience
in the field, or just on theoretical fears of academics? Surely,
with the extensive experience with BTV vaccines around the world
there should be some reasonably objective assessment of these risks.
How much funding has the UK government
put into EU collaboration - or indeed wider international collaboration
- directed at producing BTV vaccines that are relevant and promptly
available? Or do they simply leave such matters to market forces,
whilst proclaiming their devout interest in animal health and welfare?
There is deep suspicion that DEFRA
may be taking the same , largely misguided, advice from the same
group of vets (or indeed from those without any relevant veterinary
experience) that advised them so poorly in FMD UK2001, and again
with regard to the threat to the UK of Avian Influenza H5N1 (8).
The reality is that, through lack
of applying science fast enough, the UK this summer is highly vulnerable
to BTV arrriving on virgin territory - and we are virtually defenceless
to do anything about it before it gets a grip.
1. DEFRA (2007).
Technical review - Bluetongue
(Accessed 10th April 07)
2. Institute of
Animal Health (2007). Clinical signs of Bluetongue in sheep (pdf)
http://www.iah.bbsrc.ac.uk/virus/Reoviridae (Accessed April 07,
3. O.I.E. (2006).
Bluetongue detected for the first time in northern Europe.
http://www.oie.int/eng/press/en_060823.htm (Accessed April 07, 2007)
4. European Food
Safety Authority (2007). Report on the epidemiological analysis
of the 2006 bluetongue virus serotype 8 epidemic in north-western
Europe: provisional findings through 31January 2007.
5. Zentis, Sabine (2007). "Gluing fly swats
to cattle's tails didn't do the trick"
http://www.warmwell.com - See April 10, 2007 entry.
Brooks (2007). Europe's bio-threat readiness questioned.ISN Report
Apr 11th, 2007
http://www.isn.ethz.ch (accessed April 12th, 2007)
7. European Commission:
Scientific Committee on Animal Health and Welfare (2000).
Possible use of vaccination against Bluetongue in Europe.
8. Irvine, James
(2007). DEFRA statements on the role of vaccination in the control
of virulent livestock viruses could make better informed people
See SCIENCE Homepage, filed 12 Feb 07, www.land-care.org.uk
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