Individuals with symptoms consistent with West Nile virus (high fever, confusion, muscles weakness, severe headache) should contact their physician. The physician may suspect WNV infection based on clinical signs, travel history, age and medical history, however a cerebral spinal fluid (CSF) sample submitted to the Michigan Department of Community Health (MDCH), Bureau of Laboratories (BOL) is required for confirmation.
The MDCH, BOL conducts testing for the 4 mosquito-borne viruses that can cause illness in humans in Michigan. This Arbovirus Serology panel includes West Nile virus (WNV), St. Louis encephalitis virus (SLE), La Crosse encephalitis virus (LC), and Eastern Equine encephalitis virus (EEE).
The laboratory test most commonly used for WNV measures antibodies (IgM antibodies) that are produced at an early stage in a person infected with WNV. These IgM antibodies can be measured in blood serum or in cerebral spinal fluid (the fluid surrounding the brain and spinal cord). Because IgM antibodies have been detected in serum for up to 500 days, cerebral spinal fluid is the preferred specimen for testing. The initial testing takes two days to perform and is repeated in duplicate if a positive result is obtained.
Additional testing on an IgM positive sample may be performed by Plaque Reduction Neutralization Test (PRNT) to rule out cross reactions between WNV and other arboviruses, to confirm a state's first positive human case, or if IgM results cannot be determined based on the sample.
See the Human Health Issues Section, Laboratory Testing for more information.
Algorithm for Local Health Department Reporting of West Nile Virus
Diagnosis of WNV infection in live horses with neurologic signs is made by testing blood or cerebrospinal fluid for antibodies against the virus at the Michigan State University (MSU) Diagnostic Center for Population and Animal Health (DCPAH). Both DCPAH’s Immunodiagnostics/Parasitology and Virology sections perform diagnostics for WNV. Testing for acutely infected and non-vaccinated horses is done by West Nile Virus IgM Capture ELISA (enzyme-linked immunosorbent assay). Positive results by this assay, in conjunction with compatible clinical signs, is strong support for WNV as the causative agent. For vaccinated horses, the West Nile Virus Neutralization (VN) test is preferred. It is important that vaccination history for WNV is provided. Either of those tests is performed as part of the Equine Neurologic Disease Core Panel. West Nile Virus Isolation and West Nile VN tests are available for all species. Polymerase chain reaction (PCR) tests are available for cerebrospinal fluid, fresh frozen tissues, and formalin fixed-paraffin embedded tissues.
Horses and other equidae with acute neurologic signs that die or are euthanized are tested not only for WNV infection, but also for rabies virus, and eastern equine encephalitis (EEE) virus, and possibly other diseases. At DCPAH, brain tissue is first collected and submitted to the MDCH for rabies testing. At the same time, brain and possibly spinal cord tissues are examined microscopically for evidence of disease. If rabies results are negative, and arbovirus encephalitis (caused by WNV or EEE) is suspected following microscopic examination, then the nervous tissue is tested by reverse transcription-polymerase chain reaction (RT-PCR) for these viruses.
See the Horse Health Issues Section, Laboratory Testing for more information.
Currently, testing of samples from living non-equine species for evidence of WNV infection is limited. At DCPAH, West Nile Virus Isolation and West Nile VN tests are available for all species. PCR tests are available for cerebrospinal fluid, fresh frozen tissues, and formalin fixed-paraffin embedded tissues.
See the Pet Health Issues Section, Laboratory Testing for more information.
Birds and Mammals
Corvids (crows, blue jays and ravens) are reported by the public, local health departments and local DNR offices if found dead or observed displaying symptoms consistent with WNV infection. Trained personnel from local health departments or other state or local agencies conducting WNV surveillance may collect an oral swab from the bird, which can be submitted to DCPAH where the oral swabs are tested for the presence of West Nile virus (WNV) via PCR.
Non-corvid birds and mammals observed alive prior to death with signs of a central nervous system disorder can be reported to the Michigan Department of Natural Resources via the "How to Report a Dead Bird or Mammal" link on this site.
See the Wildlife Issues Section, Laboratory Testing for more information.