Salivation due to lesions in the mouth in a sheep with Bluetongue
Large areas of necrosis with sloughing of the mucosa on the tongue
Diagnosis of Bluetongue in Sheep and Cattle
A presumptive diagnosis of Bluetongue based on clinical and pathological signs can frequently be made. For a definitive diagnosis laboratory confirmation may be required.
The following techniques are available for the definitive diagnosis of Bluetongue infection.
- Direct:
- Virus isolation on embryonated eggs or cell culture
Blood (non-coagulated) or tissue samples; samples need to be cooled but not frozen - Indirect:
- Detection of BT antigen by immunofluorescence
(tissue samples, e.g. spleen and lymphnodes) - Detection of BT RNA by PCR or real time PCR
(Blood (non-coagulated) or tissue samples) - Classic methods like immunodiffusion and hemolysis-inhibition testing are available, but for routine diagnosis, ELISA tests are preferred
- Competitive ELISA (commercially available)
- Blood samples (plasma or serum)
- Indirect ELISA (commercially available)
- Milk samples (individual or pool)
Virus detection
Antibody detection
Accuracy of laboratory tests
The sensitivity of tests may vary between laboratories but in general, viral genome can be detected in blood samples from 3 days after infection onwards (by real time PCR) and positive antibody detection by ELISA can be expected from 5 to 7 days after infection.