Testing of oral swab material of corvids 

Oral swabs collected from corvids are tested for the presence of West Nile virus (WNV) antigen.  A commercial kit, called VecTest^TM West Nile Virus Antigen Assay, developed by Medical Analysis Systems, Inc. (Camarillo, CA), will be used.  The assay is a rapid "immunochromatographic" assay (i.e., a color change is detected when antibodies to WNV bind to virus antigen or protein in the specimen), which takes 5-10 minutes to set up, and allows test results to be read 15 minutes later.  The technique was developed for qualitative detection of WNV antigen in mosquitoes, but has proven to be quite sensitive and specific when used on oral or cloacal swab material from corvid birds.  This assay replaced the immunohistochemical (IHC) staining done in previous years on heart and kidney tissues collected from dead birds.  In addition to obtain results quicker, handling of dead birds and collection of test specimens will be safer for field personnel and laboratory workers with this new surveillance technique.

VecTest reaction:  Weak positive on the left, strong positive in the center, negative on the right.

Immunohistochemistry for non-corvid birds and mammals

For non-corvid birds and mammals, the kidney, heart and brain tissue will be examined for immunohistochemistry (IHC).  The tissues are placed in formalin for 24 hours, and then are embedded in paraffin (wax). Thin sections of the tissues are cut from the paraffin blocks, and then are stained for WNV antigen (protein), using an antibody directed against the virus. A positive reaction is indicated by a reddish brown, granular staining in the cells of the kidney and/or heart.

Positive IHC reaction in kidney tissue from an American crow

Positive IHC reaction in heart tissue from an American crow

To report a sick or dead bird or mammal, please use read the instructions at this webpage: West Nile Virus Sick and Dead Bird Observation Report