A case of bluetongue virus was confirmed in a single cow in the southeast of England and farmers in the UK and Ireland have been warned to remain vigilant for signs of the disease.
As a result of the case in Kent, movements of ruminant animals from Great Britain to Northern Ireland have been suspended.
In order to reduce transmission, farmers must know what bluetongue is, how it spreads and what its signs and symptoms are.
Bluetongue virus
The bluetongue virus (BTV) is a notifiable exotic disease transmitted by midge bites. It affects ruminants like sheep, cattle, deer and goats. It also affects camelids (e.g. llamas).
The case confirmed in Kent was serotype 3. BTV-3, BTV-4 and BTV-8 are the strains of the disease that are currently circulating in Europe.
The virus does not affect people or food safety, but outbreaks can result in prolonged animal movement and trade restrictions.
The midges are most active between the months of April and November. There are currently no vaccines which are effective against the type of bluetongue virus confirmed in England.
The predisposing risks for this disease spreading include infected midges being carried over from infected areas by the wind and infected animals, blood, or germinal products being imported from countries where bluetongue is prevalent.
How the disease spreads
Bluetongue virus is mostly spread by certain species of biting midges (culicoides species), many of which can be found throughout Great Britain.
Midges are infected with the virus when they bite an infected animal and the virus spreads when the infected midge then bites an uninfected susceptible animal. Once a midge has picked up the bluetongue virus it will be a carrier for the rest of its life.
The time of year, weather conditions and the proximity and density of neighbouring farms with susceptible animals are significant factors in a potential incursion and on how quickly, and how far midges can spread the disease.
Bluetongue virus can also be spread through biological products such as blood, germinal products (semen or embryos), or the movement of infected animals.
Infected pregnant animals can, under certain circumstances, transmit the virus to their unborn offspring. Once born, the infected offspring could act as a source of bluetongue virus.
Preventative measures
As well as biting midges, bluetongue can also be transmitted through dirty needles.
Animal keepers and vets are advised to follow good practice when treating and vaccinating animals at risk of being infected with the virus.
Farmers and vets can help prevent the disease by vaccinating animals with a suitable and authorised vaccine, responsibly sourcing livestock, practising good biosecurity on your premises and remaining vigilant.
Those planning to import animals are advised to speak to their vet before importing.
Signs and symptoms
The impacts on susceptible animals can vary considerably. Some show no symptoms or effects at all, while other animals will experience productivity issues such as reduced milk yield.
Sheep are more likely to show obvious clinical signs of bluetongue than cattle.
Signs of bluetongue in sheep includes:
- Ulcers or sores in the mouth and nose;
- Discharge from the eyes or nose and drooling from mouth;
- Swelling of the lips, tongue, head and neck and the coronary band (where the skin of the leg meets the horn of the foot).
Other clinical signs include red skin, fever, lameness, breathing problems, abortion and death.
Adult cattle may serve as a source of virus for several weeks while displaying little or no clinical signs of disease and are often the preferred host for insect vectors.
In cattle, signs of the disease include:
- Lethargy;
- Crusty erosions around the nostrils and muzzle;
- Redness of the mouth, eyes, nose;
- Reddening of the skin above the hoof;
- Nasal discharge;
- Reddening and erosions on the teats;
- Fever;
- Milk drop;
- Not eating;
- Abortion.
Calves can become infected with bluetongue (BTV-8) before birth if the mother is infected while pregnant.
Signs of the infection include calves born small, weak, deformed or blind; death of calves within a few days or birth; and abortions.
The UK government said livestock keepers and vets should consider bluetongue as a possible cause for calves showing these signs.
