Alistair and myself attended talks on Bluetongue this week, given by a member of the Institute for Animal Health and a Dutch vet, who has first hand experience of the tragic consequences of endemic BTV in Holland. The overriding impression that we both got is that we must take Bluetongue very seriously as it is likely to be a lot worse than we are expecting and we can only stave off the worst if we can get as close to 100% of ruminants vaccinated in the UK as possible.

Without being alarmist or exaggerating the vet from Holland said that Bluetongue has ripped the heart out of agriculture in Europe, and urges us to be vigilant for the disease and proactive in vaccination policy.

What is Causing Bluetongue?

Bluetongue Virus (BTV); there are 24 serotypes, which can cause slightly different severity and symptoms of disease. The serotype causing disease in North East Europe and in the UK is serotype BTV-8.

There is a large area in South West Europe (French/Spanish border) where there is an outbreak caused by serotype BTV-1. Both serotypes are spread by the same population of midge, so it is likely we will soon encounter the effects of serotype BTV-1 in the UK as well as those starting to be cause by BTV-8.

What is Spreading it?

The virus is spread by midges, so an enormous, uncontrollable population of vectors. The virus replicates within the midge in warm weather and can pass from one generation of midge to the next (“transovarian transmission”).

Midges are surviving overwinter, due to a number of factors, including shorter warmer winters, ability to survive in faeces and bedding and available shelter such as livestock buildings. The virus can infect any ruminant animal, so as well as cattle, sheep and goats, camelids and deer can be infected, leading to a large wildlife reservoir in the case of deer.

Infected cattle are known to have blood borne virus for 30-60 days following infection. Research from cases of BTV-8 in Holland during 2007 have shown that the virus can persist for up to 150 days in infected cattle. This means an animal that has recovered from Bluetongue remains a potential source of infection for some time.

It is now known that BTV is transmitted transplacentally; from cow to calf in uterus. Cleansing from aborted ruminants could potentially be a source of infection.

The transfer of blood from one animal to another is a potential mechanical means of Bluetongue spread. Importantly, using the same needle for more than one animal without sterilizing the needle is a way of spreading the virus rapidly in a group of animals if any are already infected.

What is the Effect of Bluetongue Virus?

Based on the effect of that the strain we have in the UK had on livestock in Holland in from 2006 onwards;

	Cattle	Sheep
Morbidity	6.6%	27.3%
Mortality	0.6%	11%
Case Fatality	18%	42%

Morbidity = percentage of animals with disease symptoms out an infected herd/flock.
Mortality = percentage of animals from an infected herd/flock dying as directed result of disease symptoms.
Case Fatality = percentage of animals with disease symptoms which die, including those culled, as a result of having had bluetongue, but not as a direct result of the initial disease symptoms.

What are the Symptoms of Bluetongue?

Fever and lethargy
Inappetance, not eating for up to a week
Crusty lesion on nose
Nasal discharge
Conjunctivitis
Drooling
Lameness, lying down
Swollen puffy feet, red coronary band
Sores in mouth and on tongue

Any or none of these symptoms may be seen in cattle, making it a difficult disease to pick up in many cases. A colleague from Holland has found the crusting on the nose and drooling are the most common and noticeable early signs in cattle.

More obvious than in cattle
Swollen lips and possibly face, with crusty lesions on nose
Inflammation inside mouth
Drooling
Lameness
Swollen puffy feet
Difficulty swallowing
Difficulty breathing, with loud audible breaths

Again, sheep may present with any or none of the above signs. The experience of the Dutch vets is that the loud, laboured breathing is the most striking sign.

Cattle:
With the unwillingness to eat for several days there is weight loss and milk drop. Not eating is also a major predisposing factor to LDA's (twisted stomach).

Decreased fertility – abortions at any stage of pregnancy
Still births and weak calves
Prolonged herd lameness
Mastitis - greatly increased prevalence and severity, more unresponsive cases
Premature calving and retained cleansings
Prolonged weight loss and wasting in some individuals, some resulting in death

In the Netherlands the company responsible for collection of animal carcasses recorded an increase in collection of dead cows by 24% and collection of dead sheep by 26% between 2006 and 2007, resulting from BTV-8.

Major Differentials:

What control measures are there?

As well as vaccination (below) several preventative control measures have been tried in Europe;

Housing stock at peak midge activity, early morning and dusk
Using insecticides
Keeping ill stock housed to reduce possible midge uptake of virus from infected animals
Relying on natural immunity – very unpredictable

However, these control measures have had MINIMAL effect in Europe, making vaccination the only viable option for disease control and as such an ESSENTIAL measure. Using insecticides on your livestock such as deltamethrin may be advantageous in that it kills feeding midges before they can take another blood meal, so although it wont stop an animal contracting the disease it will stop the disease being spread by midges from an infected animal.

Vaccination:

A “killed” vaccine against BTV-8, which has shown to be highly effective in field trials will be available from May this year. DEFRA has ordered 22million doses of the vaccine for the UK. 20,000 doses are expected in the first batch in May, and supply is limited by speed of production, which will hopefully increase throughout 2008. It is currently illegal to vaccinate animals outside the protection zone. The protection zone will clearly spread with any further cases, but will also be enlarged to cover the rest of the UK as and when sufficient vaccine is available to ensure adequate coverage of livestock.

Vaccination will be voluntary, however;
IT IS ESSENTIAL THAT ALL RUMINANT LIVESTOCK ARE VACCINATED. Having heard reports from Corsica where a similar voluntary scheme was in place this point is reinforced strongly - only 60% of animals were vaccinated in Corsica resulting in Bluetongue returning after only 2 months of being clear and devastating many more farms. Only when the percentage of vaccinated animals reached 80% did Corsica become and remain Bluetongue-free.

As there is a large population of deer in the UK as well as some wild sheep and goats, many of which cannot practically be vaccinated, it is ESSENTIAL that 100% of livestock are vaccinated to ensure 80% coverage of ruminants in the UK. This includes all young stock, breeding animals, cull animals, fat animals and any other groups.

Vaccination consists of 1ml annual dose for sheep and in cattle is 2 doses of 1ml 3 weeks apart for 1st year, followed by an annual booster. It will be important for the UK to vaccinate for at least 3 years. Although data is not available for very young stock, the advice is to vaccinate everything from 3 weeks of age.

How do you deal with infected animals? Treatment of Diseased Animals:

It is extremely unlikely that there will be mandatory slaughter of animals with BTV, largely due to the massive number of animals likely to be affected. A fair proportion of animals will recover well with palliative treatment as detailed below, but there will be individuals which will need to be euthanased, and these should be identified as early as possible.

Within the acute phase of the disease, corticosteroids can be used, in non-pregnant animals.
Thereafter/alternatively NSAIDs should be used for a week's cover.
Broad spectrum antibiotics such as long-acting Oxytetracyclines or Cephalosporins are advisable.
Diuretics where oedema is present, especially if causing dyspnoea.
Oral rehydration or IV fluids if required.

We will investigate the possibility of using an appetite stimulant (“Mederantil”) which is not licensed in the UK but used to good effect in Holland.

Nursing care, comfortable bedding, palatable soft foods, easily reachable water supply and shelter are essential for sick animals, and housing them may help to reduce feeding midges taking on more virus to spread further.