West Nile Virus Encephalitis: Understanding the Risk and Public Health Implications

1. West Nile Virus EncephalitisPaul R. EarlFacultad de Ciencias BiológicasUniversidad Autónoma de Nuevo LeónSan Nicolás, NL 66451, Mexico

2. In North America since 1999, West Nile Virus (WNV) has joined the other major viruses like dengue that cause various encephalites. WNV as new is clinically little known and its role in public health (PH), epidemiology, surveilance and vector (mosquito) control is still illdefined. WNV is one more PH cost. Costs range from hospital bed time and clinical labor, loss of work hours and school time to other costs like reagents for immunological diagnosis. Birds (especially crows), horses and man are the most noteworthy in a very wide range of WNV hosts. During 1999-2002, WNV was detected in 36 mosquito species in the US.

3. WNV is a member of the family Flaviviridae which seems very close to Togaviridae. Serologically, it is a member of the Japanese encephalitis virus antigenic complex, which includes St. Louis, Japanese, Kunjin and Murray Valley encephalitis viruses. WNV was first isolated in Uganda in 1937.The 2002 WNV epidemic and epizootic resulted in reports of 4,156 reported human cases of this disease (including 2,942 meningoencephalitis cases and 284 deaths), 16,741 dead birds, 6,604 infected mosquito pools and 14,571 equine cases.

4. The central problem is morbidity and mortality by encephalites in man, domestic and wild animals caused by different mosquito-borne viruses throughout the Americas.

5. It is much more important to deal with the entire group of encephalitis viruses and dengue than it is to dwell on WNV. There SHOULD BE much better PH orientation to the geographies and seasonalities of all these viruses from local to continental levels. Medical and veterinary forces need better mutual understanding and interaction. Climate, vector control and surveillance are often neglected topics. Cyclonic winds have strong yet little known epidemiologic effects. What is the risk of infection? Of what or whom? By what !! ?What are the public sentiments ?

6. Somehow, there is a feeling of professional NEGLECT. Neglect relates to ignorance. Much of the public has been hardened by its previous disease experiences. In its turn, this relates to POLITICAL WILL. In the end or in many situations, the public must DEMAND PROTECTION in order to get it. Of course, the public best understand the RISK so that it will pay the taxes needed to reduce the risk. Where do your tax dollars go ? If you replied, “Into vector control,” that would be a reasonably good joke.

7. So we have more than WNV. We have a group of viruses with much in common that are clinically little known. Let us say that the index of suspicion is close to zero. What is it that we need to know ? The risk. Then pay taxes in PH terms to reduce the risk. This is the old erratic and encephalitic risk that WNV is increasing. People will pay willingly for mosquito control if they understand the risks to their health. The community MUST REALIZE that it MUST DUMP all standing water ! Public education for awareness of arboviruses and other agents is desired at the primary school level.

8. Encephalites of various causes and knowing the riskWhat are these virusus?They are: 1/ WNV, 2/ dengue (DEN), 3/ Venezuelan Equine Encephalitis Virus (VEEV), 4/ St Louis Encephalitis Virus (SLEV), 5/ Western Equine Encephalitis (WEEV) and 6/ Eastern Equine Encephalitis (EEEV). Yellow Fever and Powassan encephalitis/ meningitis and the California serogroup viral encephalitis/meningitis, including infections with the following viruses: La Crosse, Jamestown Canyon, Snowshoe Hare, Trivittatus, Keystone and the California encephalitis viruses

9. We have come a long way—perhaps—from WNV, because it is part of an international problem, not the problem itself. The problem involves the costs and methods of MOSQUITO CONTROL. It ACUTELY involves the public recognition of disease transmission. Many citizens do know that these diseases are insect-transmitted, but what percent of people, where, etc. is of course not known. Theydo not know the symptoms, meaning that they do not recognize the disease. Questionaires don’t seem to be used. Do we want to know WHEN the risk becomes intolerable and how to control it?

10. International surveillanceOn the surface it seems like a good idea to coordinate insect surveillance among Canada, USA & Mexico, partly because territories from the equator to northern Canada are involved. However, it’s a long way from good, because financing at all levels will raise conflicts. Is the risk great enough to demand international surveillance? Probably not. Many inland disease outbreaks are local ones. Mexico is almost singular, because it absorbs shocks from both the Eastern Pacific & Atlantic Hurricane Centers. Some of these 2 winds running over 100 km/hr mix in the Gulf of Mexico and go straight north into Texas and Louisiana.

11. Research objectivesAs given by CDC, these include: a) Current and Future Geographic Distribution of WNV, b) Bird Migration as a Mechanism of WNV Dispersal, c) Vector and Vertebrate Host Relationships and Range, d) Virus Persistence Mechanisms, e) Mosquito Biology, Behavior, Vector Competence, Surveillance, and Control, f) Development and Evaluation of Prevention Strategies, g) Laboratory Diagnosis, h) Clinical Spectrum of Disease and Longterm Prognosis in Humans, i) Risk Factor Studies, j) Detailed Clinical Descriptions and Outcome in Human Cases, k) Viral Pathogenesis, l) Genetic Relationships and Molecular Basis of Virulence,

12. WNV factsORIGINS: WNV has been found in humans, horses, birds and other animals, typically in Africa, Eastern Europe and the Middle East. In 1999, WNV was detected in the US (NY, NJ) for the first time, and since then it has spread across North America, including Mexico.

13. TRANSMISSION: WNV exists in nature through a transmission cycle involving mosquitoes, birds and horses. Mosquitoes become infected with WNV when they feed on infected birds, which may carry the virus in their blood for a few days. Infected mosquitoes can then transmit this new virus to humans and animals. when biting to take a blood meal. In rarest instances, WNW may be transmitted from human to human through organ donation or blood transfusion or from pregnant mother to fetus.

14. SYMPTOMOLOGY: Most individuals infected with WNV will not have any symptoms or signs of illness. People who do develop illness may experience mild symptoms such as fever, headache and body aches. Occasionally a skin rash and swollen lymph glands may occur. These symptoms generally appear 3-14 days following the bite of an infected mosquito. Less than 1% of persons infected with the virus will develop more severe disease with symptoms such as high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, paralysis and, most rarely, death.

15. LABORATORY FINDINGS:a) Total leukocyte counts in peripheral blood were mostly normal or elevated, with lymphocytopenia and anemia also occurring, b) Hyponatremia was sometimes present, particularly among patients with encephalitis, c) Examination of the cerebrospinal fluid (CSF) showed pleocytosis, usually with a predominance of lymphocytes, d) Protein was universally elevated, e) Glucose was normal, f) Computed tomographic scans of the brain mostly did not show evidence of acute disease, but in about 1/3 of patients, g) magnetic resonance imaging showed enhancement of the leptomeninges, the periventricular areas or both.

16. RISK REDUCTION:Reducing risk is avoiding mosquitoes. 1/ Dump all standing water to inhibit mosquitoes from breeding, 2/ Stay indoors at dawn or early in the evening, 3/ Wear long-sleeved shirts and long pants when going outdoors, 4/ Spray clothing with repellents containing permethrin or DEET (N, N-diethyl-meta-toluamide), 5/ Apply insect repellent sparingly to exposed skin and following all packageinstructions. 6/ Ensure that all window screens in your home or business are intact and do notcontain holes. Repair any damaged screens.

17. The Fort Dodge Animal Health West Nile Virus Vaccine approved by the US Department of Agriculture (USDA) is safe. Millions of vaccine doses have been used since the USDA approved its use in 2001. The Center for Veterinary Biologics within USDA's Animal and Plant Health Inspection Service maintains a tollfree telephone hotline (800-752-6255) and a mailbox on its Web site (www.aphis.usda.gov/vs/cvb) and encourages veterinarians and other vaccine consumers to report problems with vaccines.

18. Does the WNV vaccine also have DEN1-4 and VEE ?Of course not. Does it include SLEV and EEEV? Of course not. What proteins of the envelope genes of these similar viruses are used now in vaccines? What is a plasmid ?The objective would be to produce a protective vaccine against 1/ WNV, 2/ VEEV, 3/ EEEV, 4/SLEV and the 4 serotypes of dengue (DEN1-4). This is technically possible with plasmids and can solve many very expensive epidemiologic problems. Such outbreaks are EXPENSIVE to owners by animal loss.

19. One aspect of biotechnology—or industry—is that a pharmaceutical company will not do research or produce a vaccine in order to lose money. WNV vaccine is produced in the US. VEE vaccine is not produced in Mexico. This reflects the horse owners willingness and ability to pay. We want this multivaccination to go through one month before victims of a future epidemic begin to show, but—incredibly—will accept a week’s time. The organizational effort needed to stop an ongoing viral epidemic—with properly identified viruses—is likely too slow.

20. Mosquito controlStandard mosquito control measures for city populations such as one plagued by dengue may have to be vastly expanded in the countryside if the aim is to restrict an epidemic. Note that as epidemic applies to people, epizootic applies to animals, but that ‘epidemic’ is often also used for animals. Still, the point here is that huge rural areas are not like civic ones, especially when mountains are involved. Regardless, fast streams with banks unimpeded by brush may not be too difficult to control chemically over rather great distances in the hundreds of km.

21. SurveillanceAdvantages of mosquito-based surveillance include the following: 1/ The virus invader can be identified. 2/ It may provide the earliest evidence of transmission in an area. 3/ It helps establish information on potential mosquito vector species. 4/ It provides an estimate of vector species abundance. 5/ It gives quantifiable information on virus infection rates in different mosquito species. 6/ It provides quantifiable information on potential risk to humans and animals. 7/ It provides baseline data that can be used to guide emergency control operations. 8/ It allows evaluation of control methods.

22. Surveillance is a warning system that can often save both human and animal lives. An ounce of prevention is worth a pound of cure !See www.cdc.gov/epo/dphsi/casedef/ encephalitiscurrent.htm

23. Surveillance is UNPOPULAR via its costs. What are the costs with and without surveillance with or without chemical control? They are UNKNOWN and most difficult to estimate. We ASSUME that vigilance pays without even an approach to controling some future epidemic that cannot be defined. This is a typical undefined problem of preventive medicine. If the problem were profitably solved, of course, the solution would be APPLIED, but this is not the case. Finally, one is reminded of the huge populations in millions that cover these vast territories. Obviously, the magnitude of the viral encephelitis problem might result in an equivalent surveillance cost.

24. New and little knownAlthough the invasion of New York City by WNV in 1999 was a new epidemic therefore not then known, encephalitis-causing viruses are wellknown and most are worldwide. The PH steps to be taken remain irresolute, and what is taught in the classroom is unsettled. What relevent information is the 10th grader getting? The public appreciates WNV as a new threat via TV, but not its inner workings. What is still lacking is the empirical experience in epidemics, and the detailed data of epidemic progress.

25. The control of a virus outbreak is far from simple, often having local unknowns. The encephalitis virus result is often: 1/ dead or 2/ immune. At this conjuncture, the epidemic is over. For Part 2, either natural or arificial immunization serves. Of course, the difficulty is correctly attributing the cessation of the epidemic. Having too few mosquitoes (Choice 3) can—most obviously—stop the outbreak, leaving susceptibles. Choice 3 might be a larvicide campaign, reducing the number of mosquitoes. Again, we have cost and risk. It may take some deep thinking to work these things out.