The recent bluetongue epidemic in northern Europe began in the summer
(August) of 2006 and cases have been detected up until January 2007. The
outbreak has been caused by serotype 8 of the virus and of the 2124, 695 cases
were reported from Belgium, 7 from France, 952 from Germany, 460 from the
Netherlands, and 8 from Luxembourg. 1111 of the cases were in cattle, 951
in small ruminants, and 47 in wild animals.
This epidemic is unusual for a few reasons. It is very unusual for an outbreak to occur so far north. There has been concern for a number of years that the virus could spread from North Africa to Europe, and cases have been detected in southern Europe, mainly in Italy and Spain. As the disease is spread by Culicoides midges it is unusual that the outbreaks would continue throughout the winter months of December and January. Concern about the spread of the disease have been heightened by the prospect of climate change and the possibility of the vector species moving northwards. Another unusual feature of this epidemic is the fact that so many cattle have been affected clinically, as the disease normally only clinically affects sheep.
Bluetongue is caused by a virus within the Orbivirus genus of the family Reorvirades. 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. These vectors - insects that carry the disease- prefer to feed on large animals. The main transmission cycle is between the Culicoides midge and cattle, with sheep being infected when cattle are not present or the midge population is high. Thus, cattle can be used to detect the presence of the virus. Peak populations of vector Culicoides occur in the late summer and autumn and therefore this is the time when Bluetongue is most commonly seen.
Only about 20 of the more than 1,400 Culicoides species worldwide are actual or possible vectors of bluetongue virus. Continued cycling of the virus among competent Culicoides vectors and susceptible ruminants is critical to viral ecology. In the USA, the principal biological vector is C. variipennis sonorensis , which limits distribution of the virus to southern and western regions. In Australia the principal vector is C. brevitarsis , while in Africa, Europe, and the Middle East it is C. imicola .
Infection with the bluetongue virus causes inflammation, swelling, and haemorrhage of the mucous membranes of the mouth, nose, and tongue. It can also cause inflammation and soreness of the feet. In sheep, the tongue and mucous membranes of the mouth become swollen, haemorrhagic, and may look red or dirty blue in colour, which gives the disease the name bluetongue. Affected sheep may die after acute or chronic disease, or may recover with weight loss and/or wool breaks.
Bluetongue can cause spectacular disease outbreaks and is classified by the Office International des Epizooties (OIE) as having the potential for rapid spread and has important implications for international trade.
The disease was first described in South Africa after Merino sheep from Europe were introduced in the late eighteenth century. It was thought to be confined to South Africa and for many years the research into the virus and the disease were exclusively undertaken in that country, mostly at the Onderstepoort Veterinary Institute. The viral nature of the disease was established, as was its insect-borne spread and multiple virus serotypes.
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. The infection is therefore mostly 'silent'.
The Northern European epidemic is another example of a disease or disease agent behaving in new and un-typical ways. As viruses, vectors and other disease agents can change their range and behaviour it means that it is very important for scientists and veterinarians to keep an eye on the international situation and watch out for any new developments. An understanding of the reasons for these differences will be important for controlling outbreaks that may occur in summer and autumn 2007.
This epidemic is unusual for a few reasons. It is very unusual for an outbreak to occur so far north. There has been concern for a number of years that the virus could spread from North Africa to Europe, and cases have been detected in southern Europe, mainly in Italy and Spain. As the disease is spread by Culicoides midges it is unusual that the outbreaks would continue throughout the winter months of December and January. Concern about the spread of the disease have been heightened by the prospect of climate change and the possibility of the vector species moving northwards. Another unusual feature of this epidemic is the fact that so many cattle have been affected clinically, as the disease normally only clinically affects sheep.
Bluetongue is caused by a virus within the Orbivirus genus of the family Reorvirades. 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. These vectors - insects that carry the disease- prefer to feed on large animals. The main transmission cycle is between the Culicoides midge and cattle, with sheep being infected when cattle are not present or the midge population is high. Thus, cattle can be used to detect the presence of the virus. Peak populations of vector Culicoides occur in the late summer and autumn and therefore this is the time when Bluetongue is most commonly seen.
Only about 20 of the more than 1,400 Culicoides species worldwide are actual or possible vectors of bluetongue virus. Continued cycling of the virus among competent Culicoides vectors and susceptible ruminants is critical to viral ecology. In the USA, the principal biological vector is C. variipennis sonorensis , which limits distribution of the virus to southern and western regions. In Australia the principal vector is C. brevitarsis , while in Africa, Europe, and the Middle East it is C. imicola .
Infection with the bluetongue virus causes inflammation, swelling, and haemorrhage of the mucous membranes of the mouth, nose, and tongue. It can also cause inflammation and soreness of the feet. In sheep, the tongue and mucous membranes of the mouth become swollen, haemorrhagic, and may look red or dirty blue in colour, which gives the disease the name bluetongue. Affected sheep may die after acute or chronic disease, or may recover with weight loss and/or wool breaks.
Bluetongue can cause spectacular disease outbreaks and is classified by the Office International des Epizooties (OIE) as having the potential for rapid spread and has important implications for international trade.
The disease was first described in South Africa after Merino sheep from Europe were introduced in the late eighteenth century. It was thought to be confined to South Africa and for many years the research into the virus and the disease were exclusively undertaken in that country, mostly at the Onderstepoort Veterinary Institute. The viral nature of the disease was established, as was its insect-borne spread and multiple virus serotypes.
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. The infection is therefore mostly 'silent'.
The Northern European epidemic is another example of a disease or disease agent behaving in new and un-typical ways. As viruses, vectors and other disease agents can change their range and behaviour it means that it is very important for scientists and veterinarians to keep an eye on the international situation and watch out for any new developments. An understanding of the reasons for these differences will be important for controlling outbreaks that may occur in summer and autumn 2007.
[To see more information see CAB Abstracts Database which has more than 2000 references on this important disease]
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