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.

Virus detection

• 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)

Antibody detection

• 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)

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.

Salivation due to lesions in the mouth in a sheep with Bluetongue

Large areas of necrosis with sloughing of the mucosa on the tongue