Bluetongue has once again struck Belgium.
Belgian veterinary authorities reported their suspicions on 17 July to the World Organisation for Animal Health after a single sheep in a flock near Antwerp had shown clinical signs of bluetongue and then died.
The outbreak was confirmed later that day and laboratory tests confirmed the diagnosis.
This follows the re-emergence of bluetongue in Germany during April. On 20 July the German veterinary authorities reported six more cases of bluetongue, four in cattle and two in sheep.
The disease occurred in northern Europe for the first time last summer. The successful spread of this serotype to domestic animals in Belgium, France, Germany, Luxembourg and the Netherlands is believed to have been helped by higher than normal temperatures.
The virus is spread by Culicoides midges, in which the virus replicates. Warm temperatures increase the rate at which the virus grows in midges, and increase the rate at which the midges bite their victims for a blood meal.
It is during this process that the virus is transmitted from midge to ruminant and vice versa. A few years ago other serotypes of bluetongue virus had spread to southern Europe, where they became established. Those serotypes have not spread to northern Europe.
Although all ruminant species can be infected by the bluetongue virus, clinical signs of the disease are usually restricted to domesticated breeds of sheep. Other animals such as goats and cattle rarely show any symptoms.
Bluetongue may therefore spread into new areas without necessarily being noticed. However, a relatively high number of cattle have been affected during the current outbreak in Northern Europe.
In sheep, bluetongue disease is characterised by a fever that may last for several days. The virus mainly affects small blood vessels and this can lead to reddening and swelling of the lips, mouth, nasal linings and eyelids. Swelling of the tongue can lead to a restriction of the blood supply to the tongue, leading to a blue colouration, hence the name of the disease.
Animals may have quickened breathing. Nasal discharges, excess salivation and frothing are common. Lameness may occur. Animals can lose condition rapidly, including muscle degeneration.
There is no treatment for bluetongue. Prevention may be possible by vaccination and by controlling midge populations, but neither is totally successful.