West Nile Virus seems to be particularly virulent this year. We are seeing an increase in neurologic cases - some confirmed and some assumed to be caused by WNV.
Here are some commonly asked questions about the virus:
What is West Nile Virus? West Nile virus (WNV) belongs to a family of viruses, the flaviviridae, many of which can cause encephalitis, a potentially fatal inflammation of the brain and spinal cord. It is known to affect birds, horses, and humans - and occasionally other mammals. West Nile has been identified in 138 species of birds, with blue jays and crows seeming to be especially susceptible, but most species of raptors are severely affected, as well. It has been reported in raptors in the US since 2002.
How is it spread? The virus is spread by mosquitoes from infected birds and animals to other birds and animals. The virus is zoonotic, but there are no known cases of transmission from person to person or from birds or mammals to humans. There was, however, a report of the virus being spread through a blood transfusion.
What are the symptoms of WNV in raptors? Clinical Signs of WNV in raptors seem to occur in three phases:
Phase 1: Depression, anorexia, weight loss (in proportion to duration of starvation), sleeping, pinched off blood feathers, elevated white blood cell count
Phase 2: In addition to the above, head tremors, green urates (indicating liver necrosis), mental dullness/central blindness and general lack of awareness of surroundings, ataxia (clumsiness or poor equilibrium), weakness in legs, exaggerated aggression, very high fever, polio-like flaccid paralysis, excessive sleeping, detached retinas.
Phase 3: More severe tremors, seizures, and death
What is the treatment and prognosis? There is no prescribed treatment, just supportive care (fluids, warmth, nutrition, and high doses of non-steroidal anti-inflammatories). The chance of recovery depends on what phase the bird is in. Phase 1 birds respond reasonably well to supportive care. Once they reach Phase 2, some birds respond to supportive care, but others do not and proceed to Phase 3. Complete recovery is uncertain but they are typically close to death. Unfortunately, it is not known if they will have permanent neurological damage, even if they have survived the virus infection.
Is it preventable? A couple of equine vaccines (one made by Fort Dodge and one by Merial) have been used in birds but we do not know how well they actually work. We have vaccinated some of our resident birds with the Fort Dodge vaccine and no side effects were seen. Other than that, it is just trying to protect the birds from mosquito bites. This can be difficult when you are housed outside. We use fine mesh netting on our enclosures to try to help with this. We try to reduce the amount of standing water. Mosquito control is key.
Although the infected birds we admit at the clinic are from all over the surrounding area. So for us, we focus mainly on the treatment of it - but we do want to protect the other patients, as well as our resident population.