Systematic Veterinary Virology

LABORATORY DIAGNOSIS

Isolation and identification

• Clinical materials
• Sterile heparinized blood samples from animals with clinical signs or spleen or bone marrow, or both, from dead animals are the clinical materials of choice. Samples from aborted and congenitally infected newborn animals should include heparinized blood and, if possible, spleen, lung, brain, and serum. Specimens should be shipped refrigerated, not frozen. Freezing makes virus isolation difficult.
• Isolation systems
• Chicken embryos and cell cultures like baby hamster kidney (BHK)-21, African green monkey kidney (Vero) and Aedes albopictus (AA) cells.
• Immunological tests
• Serogrouping: BTV are serogrouped on the basis of their reactivity with specific standard antisera that detect proteins, such as VP7 that are specific within each serogroup. Monoclonal antibodies specific for VP7 are used in the assay. The immunological assays that are performed using monoclonal antibodies against VP7 protein are immunofluorescense, antigen capture ELISA and immunospot test (dot ELISA).
• Serotyping: Serotyping of BTV is carried out using serum specific for each of 24 serotypes. Virus neutralization assays are performed to serotype BTV. Four different types neutralization assays are performed in BHK21, Vero and L929 cells. These tests are plaque reduction test, plaque inhibition test, microtitre neutralization and fluorescent inhibition test.
• Nucleic acid detection methods: Polymerase chain reaction (PCR) is an accepted test for international trade. Serotyping is also possible in PCR.