In the autumn of 2006 Bluetongue (serotype 8) was found in the Netherlands, Belgium, Luxemburg, Western Germany and in parts of North Eastern France. The outbreak was identified as a new incursion in the EU. How Bluetongue entered Europe is still subject to investigation.
In August 2008 the first case of Bluetongue serotype 8 was diagnosed in East Anglia in a cow.
Bluetongue was first described in South Africa but has since been recognised in most countries in the tropics and sub-tropics. Since 1999 there have been widespread outbreaks of Bluetongue in Greece, Italy, Corsica (France) and the Balearic Islands (Spain). Cases also occurred in Europe in Bulgaria, Croatia, Macedonia, Kosovo and Yugoslavia. Serotypes 8, 1, 2, 4, 9 and 16 have been involved. These cases have been well north and west of its normal distribution. It appears that the virus has spread from both Turkey and North Africa. Bluetongue does not affect humans. A virus within the Orbivirus genus of the family Reorvirades causes bluetongue. At present 24 distinct serotypes have been identified as a result of serum neutralisation tests.
The virus is transmitted by a small number of species of biting midges of the genus Culicoides. Bluetongue virus cannot naturally be transmitted directly between animals. Virus transmission between animals occurs via the midges. However mechanical transmission of the virus between herds/flocks and within a herd/flock by unhygienic practices (e.g. use of contaminated hypodermic needles) is possible.
When a midge bites an infected animal, the virus passes to the midge in the blood meal and the virus multiples in the midge. The cycle of replication of the virus in the insect vector and in the ruminant host, results in amplification of the amount of virus available to naïve hosts and vectors. Peak populations of vector Culicoides occur in the late summer and autumn and therefore this is the time when Bluetongue is most commonly seen.
Clinical signs can vary by species – although symptoms are generally more severe in sheep, cattle are important in epidemiology of the bluetongue as they act as an often silent source of BTV – a reservoir for disease and keep the infection circulating.
There is a wide variation in the clinical signs seen in cattle:
The initial signs in lactating cows are that the animal becomes slower and stiff with a reduced appetite and a fall in milk yield. There is usually a nasal discharge, clear at first with the mucosa inside the nostril noticeably redder than usual; this is accompanied by red eyes due to the inflammation of the conjunctivae. Over the following days erosions and crusting develop around the entrance to the nose; there may be crusty scabs on the teats. There may be some foamy saliva around the mouth. On opening the mouth there are erosive lesions on the upper gum (dental pad) which develop a yellowy skin of necrotic tissue over them, there may also be lesions on the hard palate and tongue. It is important to note that these are erosive lesions not vesicles as in Foot and Mouth! The lameness is due to a coronitis (i.e. inflammation of the coronary band which runs around the top of the hoof); if the foot is washed and cleaned the coronary band can be seen to be red and inflamed. Sometimes the leg above the coronary band may become secondarily infected and swell up.
There are problems with transplacental infection; pregnant cattle infected with Bluetongue will pass the infection on to their calf in utero. The calf may be aborted, die in the first few days of life or recover. It is believed that colostrum from recovered cows is valuable in helping weak calves to recover. These calves, their placentas and fluids will also act as a focus of infection on the farm, allowing the disease to flare up again in unvaccinated animals. The dams that have carried infected foetuses are likely to have lower milk production and fertility in their next lactation, reinforcing the point that prevention is the key in controlling this disease. If the disease spreads to a herd with a large number of pregnant animals the effects will be much more severe.
Bluetongue UK Situation 2011.
On 12th June 2010, Scotland, England and Wales moved into a Lower Risk Protection Zone (LRZ) for BTV-8.
This LRZ provides some increased protection against imports from higher risk zones and is being viewed as the first move towards disease freedom.
There were no outbreaks of BTV in the UK in 2010 and no evidence of bluetongue virus circulation in the winter of 2009. Further testing was to be carried out in 2010 but the results have not yet been reported.
Between April and October 2010, new outbreaks of BTV were reported in Greece, Cyprus, Italy, Portugal and Spain.
In the UK We must not be complacent. We need to continue to take steps to keep disease out, so that we maintain a good chance of becoming free and removing our BTV zones and trade restrictions.
Vaccination played a key role in keeping us free from circulating bluetongue disease in 2008 – 2010 and will provide the greatest security against loss, should there be a resurgence of disease in 2011.
Vaccination before the start of the risk period or when the midges and disease become active is still being recommended by NFU and DEFRA.. For those who vaccinated last year, a reminder that only a single vaccination booster is required in both cattle and sheep.
It is vital that we continue to remain vigilant for signs of disease. Suspicion of disease must be notified immediately to your local DEFRA Animal Health Office.
Blue tongue latest.
Our thanks to Marcel Van Aert for the use of his photographs.