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West Nile Virus (WNV) is this month's fear phrase. This virus is killing a lot of crows and some horses, but few humans. To compare WNV with things such as the plague is far fetched. Since its discovery in 1937, there has been little interest in creating a human vaccine. Viruses are almost invisible specks of genetic material with protein coats, much smaller and simpler than bacteria, which survive by manipulating the reproductive machinery in the cells of the invaded host. Ideally, the host is not affected. Any virus which routinely kills its host runs the potential of extinction. We humans have survived eons side by side with viruses. We have acquired many natural anti-viral mechanisms over the years. Our skin is a wondrous barrier, while saliva and gut acids form another line of protection. Our natural immune system is perhaps the most dramatic with the constant auto-pilot capability to seek and destroy particles deemed foreign. The goal of a vaccine is to teach the immune system how to recognize and destroy WNV.
WNV is an arbovirus which is spread to humans by some species of mosquitoes and ticks. This strategy bypasses the skin, and is used by the Flaviviridae cousins of West Nile such as Dengue and Yellow Fever, and also other viruses like Malaria, Q Fever and Lyme Disease. Not long ago even HIV was falsely thought to be transmitted this way. Foreign mosquitoes laden with WNV most likely arrived here accidentally by hitching rides on one of the thousands of planes traveling the globe daily. WNV was recognized in North America in 1999, and spread rapidly. WNV can also be spread between humans directly through blood similar to Hepatitis C and HIV. Now, medicine is far from being an exact science. One disease state that WNV is capable of producing is called West Nile Fever (WNF). The symptoms overlap with numerous flu-like diseases and cannot be diagnosed without a specific blood test. Most people who develop WNF do fine. Retrospectively, this may explain the rash of "summer colds" that have been cropping up. Blood testing for WNV was non-existent in Ontario last year. The response has been rapid, and this year there is a blood test available to detect IgM antibodies to WNV for acute infections. Treatment is aimed at improving symptoms with some success in using anti-viral drugs and interferon.
Current data suggest the following. Eighty percent (80%) of people who are challenged with WNV show no symptoms. The other 20% get the flu like state (WNF) within a few days. Less than 1% will develop a severe neurological state called West Nile Encephalitis (WNE). It is this rare side effect that generates our fears and has pushed for the development of a vaccine. This group is severely affected since the virus attempts to take up residence in the nervous system. Nerve cells do not function well when viruses are borrowing their cellular machinery. WNV seems to have a slight preference for nerve cells. Advanced age is the only risk factor predisposed to WNE. We see seizures, malaise, muscle weakness, loss of consciousness, visual and mental problems. Most of the individuals in this group require ICU care and even ventilation. Most survive, but recovery seems to be long, complicated and drawn out. I had the dubious distinction of investigating the first West Nile death in Canada. This person was a retired but active gentleman who developed WNE and deteriorated despite dogged determination on the part of his doctors to diagnose and aggressively treat him. His death marked the first of 10 people to succumb to the complications produced by WNV infection in Ontario last year. This represents a death rate of roughly 1 in 1000 people infected with WNV. This experience showed that a heavily overburdened medical system still has some ability to respond to new challenges presented by our environment.
I work in Peel but enjoy the deep woods of Haliburton for solitude. I calculate that in the last four years, I have probably sustained over 100 mosquito bites. One of those female critters (only females need my blood) might have been from the right family to introduce me to WNV among other things. Playing with the above numbers, it suggests that I and several thousand other Ontarians may already have immunity! There is just no practical way to determine this yet on a mass scale. There lies the problem of vaccine production. A vaccine for horses is already being administered with success. At least two types of human vaccine trials are in progress, and a viable product will probably be available in the next few months. The question for manufacturers who invest millions in vaccine research is one of need. The WNV is spreading quickly and has the potential to produce huge numbers of natural immunity. This shrinks any potential market, and makes it a tough sell. In the meantime, measures to reduce the number of those pesky mosquitoes are fine with me. For the time being, immunization will have to be sprayed on!
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