The host range includes above all ruminants (e.g. cattle, sheep, goats), wild ruminants (e.g. deer, ibex, chamois) and camelids (e.g. alpaca). The most susceptible species is the sheep, although there are differences in susceptibility between different individual breeds. For humans there is no risk of infection. There is no risk of BLUETONGUE DISEASE spreading or being transmitted via meat or milk.
Infected animals have a low fatality rate and high morbidity.  Mortality (= the proportion of the susceptible animal population that dies of the disease) is reported as 1 % to 5 % in sheep, and up to 1.5 % in goats and cattle.

Transmission of the pathogen takes place via biting midges (Culicoides spp.), meaning there is no direct transmission path from mammal to mammal. Since midges are involved in the proliferation of the viruses, the disease is seasonally bound to the activity of Culicoides midges. Cases of the disease occur seasonally, mostly in late summer and autumn. In Austria too, the occurrence of insect vectors in large numbers was detected as part of the “Bluetongue Monitoring 2007-2010” project. The Culicoides midge ingests blood containing the BT virus when sucking the blood of the infected animal. The BLUETONGUE VIRUS (BTV) first reaches the intestine of the Culicoides midge and from there enters the salivary glands. The next time blood is sucked, saliva containing the BT virus is introduced into the bloodstream of the mammal (ruminant). There the BT virus replicates and spreads to all organs. The mammal then produces an immune response (formation of anti-bodies) to counter the pathogen. The BT virus can be detected in midges for up to approximately 28 days, in sheep for up to approximately 60 days and in cattle for up to approximately 150 days.

Bluetongue is a cyclical disease. The incubation period is 10 days. Being bitten by an infected midge leads to viraemia in the susceptible host with fever and clinical symptoms. The clinical picture in cattle is similar to FMD, while in sheep lameness is usually the most noticeable symptom.

The most frequent form of the disease is the unapparent one. Different forms of the disease have been observed in sick animals: acute, subacute and abortive, all beginning with a raised temperature.

The symptoms are:

• Fever (40-42 °C)
• Hyperaemia of the oral and nasal mucous membranes
• Lip oedema
• Hoof inflammation: hyperaemia of the coronary band area
• Spontaneous abortions
• Changes in the skeletal musculature

In terms of differential diagnosis, FMD, MCF, BHV1, BVD, PI3, VS (vesicular stomatitis), EHD, ORF, circulatory disorders of other genesis etc. come into consideration.

Suitable sample materials are:

• Blood (EDTA/serum)
• Milk
• Organs
• Midges

Verification of BTV from the above-mentioned materials is possible with the following procedures:

• Serological test procedures for antibody detection: ELISA (serum and milk) and serum neutralisation test (serum)
• Molecular biological identification (EDTA blood, organs and midges)
• BT virus replication (EDTA blood, organs, possibly midges)

Information on the testing laboratories:

AGES-Institute for veterinary Disease Control, Mödling
Nationales Referenzlabor

Contact: Dr. Angelika Loitsch, angelika.loitschno@Spam@agesno.Spam.at

Other AGES testing laboratories:
AGES Institute for Veterinary Disease Control, Linz
AGES Institute for Veterinary Disease Control, Innsbruck