Summer's onset brings that familiar buzz of the bug we all love to hate: the mosquito. The itch, the swelling, the unsightly bumps on the skin---not to mention the scratching---are the annoying price we pay for outdoor fun.
Like sunscreen, you don't want to be outside without the mosquito repellent. Those annoying insects carry more than just a nasty bite---these days, they may carry West Nile virus, too.
West Nile virus is a seasonal epidemic, lasting from summer through fall. About one in five people infected by a bite become ill. The Centers for Disease Control (CDC) says that the risk of severe illness and death is highest for people over 50 years old, although people of all ages can become ill.
CDC's records report that 3,630 cases of West Nile meningitis or encephalitis (neuroinvasive disease) were reported in 2007. Of these cases, 1217 (34%) were reported as West Nile meningitis, 2350 (65%) were reported as West Nile fever (milder disease), and 63 (2%) were clinically unspecified.
West Nile encephalitis and West Nile meningitis are forms of disease that affect the nervous system. Encephalitis refers to an inflammation of the brain; meningitis is an inflammation of the membrane around the brain and the spinal cord. West Nile fever refers to typically less severe cases that show no evidence of neural invasion.
Transmission of West Nile Virus
CDC says that mosquitoes become infected when they feed on birds infected with the virus. Infected mosquitoes then transmit the virus to humans when biting to take blood. During the feeding, the virus may be injected into a human, where it can multiply, with a chance for causing illness.
Although WNV is most often transmitted by the bite of infected mosquitoes, the virus can also be transmitted through contact with infected animals, their blood, or other tissues. Laboratory, field, and clinical workers who handle tissues or fluids infected with WNV or who perform necropsies are at risk of WNV exposure.
The virus has already been circulating in some states, with human cases reported in Mississippi, Texas, Arizona and Tennessee.
West Nile Virus and Blood
What association does this virus have with the blood supply?
First of all, it is not possible to contract the virus by donating blood, so do not stop volunteering as a blood donor.
But if an infected person donates blood or tissue to a collection agency, that product can contain potentially infectious components.
"During the 2002 epidemic of West Nile virus (WNV) in the United States, a total of 23 persons were reported to have acquired WNV infection after receipt of blood components from 16 WNV-viremic blood donors, and an estimated 500 viremic donations might have been collected. Because of the possibility of recurrent WNV epidemics in the United States, blood collection agencies (BCAs) have implemented WNV nucleic acid--amplification tests (NATs) to screen all donations and quarantine and retrieve potentially infectious blood components," the CDC states.
There is currently no vaccine available for humans, although researchers are working toward a solution.
West Nile Virus and Critical Path Initiative
The Critical Path Initiative (CPI) is FDA's ongoing effort to stimulate and facilitate a national effort to modernize the scientific process through which a potential human drug, biological product, or medical device is transformed from a discovery or "proof of concept" into a medical product.
CPI was in its infancy in 2002 when major outbreaks of WNV occurred in several parts of the United States. In August of 2002, the Centers for Disease Control (CDC) confirmed that West Nile Virus could be transmitted through donated blood. That year, West Nile Virus caused 283 deaths and 2942 cases of neuroinvasive disease (meningitis, encephalitis, or meningoencephalitis ) -- and there were no tests to screen the blood supply.
In November 2002, FDA organized members of the American Association of Blood Banks (AABB), potential product sponsors, the CDC, the Health Resources and Services Administration, the Department of Defense, and the National Institutes of Health (NIH) to initiate the joint development of WNV blood screening tests. During the ensuing months, members of these groups worked together in the race to develop an initial test before the next summer's peak mosquito season arrived. The shared goal was to have one or more WNV blood tests ready for use during the 2003 season.
In May 2003 -- less than six months after the effort had begun -- the FDA gave interim approval to Gen-Probe and Roche to market new WNV blood screening tests. By July 14, 2003, every civilian and military blood bank in the United States was using one of these tests to screen blood donations. Thus protecting the blood supply from WNV became one of CPI's early success stories.
Since then, the FDA has announced approval of a second test for the detection of WNV in blood and organs. The cobas TaqScreen WNV test is an automated test that's able to detect the genetic material of the virus itself early in the infection. Such nucleic acid testing improves blood and organ safety, detecting whether donated blood and organs have been infected even before the donor's body has begun to produce antibodies against the virus.
Persecute the Pests!
While it's reassuring to know that the blood supply is being inspected, an ounce of prevention ensures peace of mind. So this summer, what's the best course of action?
Defanging the Virus
University of Queensland researchers are developing a vaccine for the virus. Associate Professor Alex Khromykh, from UQ's School of Molecular & Microbial Sciences and his associates discovered a method to generate immune response levels comparable to a live virus vaccine. They hope to move to pre-clinical and clinical trials soon.
Robyn Barnes is a marketing communication specialist at MasterControl Inc., a global provider of GxP process and document management software solutions for life science companies (www.mastercontrol.com).
Read more about West Nile virus and the blood supply:
West Nile Virus http://www.fda.gov/oc/opacom/hottopics/westnile.html
"West Nile Vaccine Breakthrough." ScienceDaily. Retrieved June 10, 2008, from http://www.sciencedaily.com/releases/2008/05/080519120154.htm