The West Nile Virus Essay, Research Paper

The West Nile Virus

BACKGROUND AND DISTRIBUTION

A West Nile ( WN ) virus was foremost isolated in 1937 from the peripheral blood of a adult female in the West Nile state of Uganda in Central Africa. Since so, WN viruses have been reported from North Africa ( Egypt, Israel ) , East, Central, and South Africa, Asia ( India, Pakistan ) , Borneo, Europe ( Cyprus, France, Romania ) and, most late, the northeasterly USA. Trials for antibody to WN suggest it has besides been present in Thailand, the Philippines, Malaysia, Turkey, and Albania.

West Nile viruses are members of the virus household Flaviviridae and are closely related to Nipponese phrenitis viruses from the Old World and St. Louis phrenitis ( SLE ) viruses from the New World. In add-on, WN cross-reacts in a assortment of serological trials, including the plaque decrease neutralisation trial, with Murray Valley phrenitis ( MVE ) , Usutu, Kunjin, Kokobera, Stratford, and Alfuy viruses. It was this transverse responsiveness of the New York City ( NYC ) WN with SLE serologic reagents that ab initio confused this virus with SLE. Additional trials that used direct scrutiny of the cistron sequence of the NYC virus identified it as a WN-like virus, non SLE.

West Nile is represented by at least 2 distinguishable antigenic groups. One, the African-Middle Eastern group, contains WN isolates from the Congo, Egypt, Israel, Uganda, South Africa, Pakistan, France, and Eastern Europe. The 2nd antigenic group contains WN isolates from India and South Africa.

History

The earliest reported epidemics caused by WN were in Israel. The first involved more than 500 clinical instances in 1950. Extra epidemics were reported from Israel in 1951, 1952, 1953, and 1957. The 1950 and 1957 epidemics were reported from a site 40 stat mis north of Tel Aviv, while the 1951 epidemic occurred at a site 15 stat mis south-east of Tel Aviv. In 1952, 1953, and 1954, instances were reported from both countries, indicting the ability of this virus to be highly focal in its epidemic transmittal forms.

Epidemics of WN occurred in the Rhone delta part of France in 1962, 1963, and 1964. The largest epidemic of WN, affecting 1000s of clinical instances, was reported in South Africa in 1974. Epidemic activity was once more reported in South Africa in 1983 and 1984. Human instances were reported in sou’-east Romania in 1996 and 1997. Most late, WN virus ( Es ) was seemingly introduced into the northeasterly part of the borough of Queens in NYC during the summer of 1999.

West Nile is more nomadic than other closely related viruses like the SLE viruses in North America and MVE viruses in Australia. West Nile viruses have spread from Africa to Western Europe, the Middle East, Eastern Europe, and now North America. To day of the month, close relations of WN like SLE and MVE have remained confined to their place parts.

THE DISEASE

In worlds, infection with WN can do clinical or subclincal symptoms. Clinical symptoms vary from impermanent febrility to serious phrenitis. The disease can be terrible in the aged, but is normally mild in healthy grownups and kids. The incubation period for WN is 3-6 yearss. Onset of disease symptoms is normally sudden, get downing with a sustained, elevated febrility. Clinical infection can include terrible concern ; a roseola, normally on the bole ; and swollen lymph nodes. Symptoms of WN infection can besides include oculus, muscular and back strivings, and GI jobs. In terrible instances, there are frequently symptoms of phrenitis with eventual neurological engagement and sometimes decease. Humans see a low-level viraemia that lasts approximately 6 yearss. Mortality rates in worlds range from 5 to 13 % .

In domestic animate beings, clinical marks of WN infection have merely been observed in Equus caballuss, even though most Equus caballus infections are symptomless. However, in the WN epidemic in France during 1962-64, Equus caballuss experienced 25 % mortality. As with Equus caballuss, cowss, sheep, and camels can besides be infected with WN, but clinical symptoms and viraemia capable of infecting arthropod vectors have non been reported from these hosts. Birds, nevertheless, do see viraemia capable of infecting arthropod vectors.

Transmission BY ARTHROPODS

Mosquitos and ticks serve as natural vectors of WN. Most virus isolates have been from mosquitoes, proposing that they serve as primary vectors. Culex univittatus appears to be the major WN vector in Africa. Culex pipiens is a secondary vector in South Africa and may be the primary vector in Israel. Members of the Cx. vishnui composite are the primary vectors in India and Pakistan. West Nile infected ticks in the genera Argas, Hyalomma, and Ornithodoros have been collected in northern Africa and eastern Europe. The vector ( s ) responsible for the 1999 NYC eruption have non yet been identified. The most likely campaigners, nevertheless, are members of the Cx. pipiens species complex. Members of this complex have been implicated in West Nile eruptions elsewhere in the universe, and they are among the most common mosquitoes in NYC during the summer.

Vertebrate HOSTS

As with other mosquito-borne viruses, many craniate species show grounds of natural infection with WN. Wild and domestic birds, nevertheless, show the most consistent grounds of infection. Hooded Crows and House Sparrows in Egypt showed high antibody prevalence, and WN has been isolated from of course infected Hooded Crows. West Nile was besides isolated from Equus caballuss demoing marks of clinical phrenitis infection during the 1962-64 eruption in France and from camels in Sudan. A WN virus was isolated from a tick collected on a camel in Central Kara-Kum in Eastern Europe. West Nile has been isolated from pigeons in Egypt, turtledoves in Turkey and wild bird species in Borneo, Cyprus, and Nigeria. Crows experimentially infected with WN showed high mortality. In nature, some crows must last infection since antibody-positive persons are frequently captured. A domestic pigeon infected with WN and demoing clinical marks of unwellness was captured in Egypt. Domestic pigeons are abundant in urban scenes and may turn out to be peculiarly of import in epidemics such as that observed in NYC during the summer of 1999.

WN viruses have been isolated from the peripheral blood of septic worlds, particularly during the first few yearss of clinical unwellness. Surveies were done in Israel where back-to-back day-to-day blood samples were collected and analyzed for virus. West Nile virus isolation rates were 77 % for the first twenty-four hours of infection, 27 % for twenty-four hours 2, 18 % for twenty-four hours 3, and 6 % for twenty-four hours 4. Twenty-three strains of WN virus were isolated from feverish kids in Egypt during the early 1950s.

WEST NILE VIRUS IN NEW YORK CITY

The mechanism ( s ) by which WN was introduced into NYC is likely to be a subject of spirited argument. Several debut mechanisms are possible. First, it is possible that WN has been maintained in low-level transmittal rhythms in the northeasterly USA for many old ages and merely became apparent during the summer and early fall of 1999. This rush of epidemic activity may hold been due to environmental conditions that pre-disposed the NYC country to the epidemic transmittal of a flavivirus like WN. Urban epidemics of SLE in North America have typically occurred during highly dry summers, conditions such as those that existed in NYC during the summer of 1999.

Recent debut of WN to the NYC country is besides possible. A freshly infected homo may hold traveled from Africa, Eastern Europe or some other location with a active WN transmittal, geting in NYC merely as their viraemia ( the sum of virus in their peripheral blood ) peaked. If an person & # 8217 ; s viraemia is high plenty to infect vector mosquitoes ( Cx. pipiens in NYC ) , some of the mosquitoes that feed on the infected blood will go morbific. Newly infected mosquitoes necessitate a temperature-dependent extrinsic incubation period ( EIP ) , normally enduring at least 2 hebdomads, before they become morbific. Virus replicates in mosquito tissue during the EIP, finally infecting most of the internal variety meats including the salivary secretory organs. Once the salivary secretory organs are infected, the mosquito is normally able to convey the virus to extra hosts during blood eating. In NYC, these hosts may hold included local wild birds: crows, pigeons, sparrows, chumps or as yet unidentified elaboration hosts. This would therefore set up an elaboration and transmittal rhythm capable of traveling virus out of the original transmittal focal point. The 1999 New York City focal point was probably the Whitestone, Auburndale, and Blushing subdivisions in the borough of Queens.

Another possibility is that a bird infected with WN virus may hold been imported into the metropolis either lawfully or illicitly. Legally imported birds are quarantined for at least 30 yearss. This should guarantee that septic birds do non come into contact with arthropod vectors. Illegally imported birds are non quarantined and may hold been a beginning of virus capable of infecting local mosquitoes. Finally, septic ticks or infected mosquitoes may hold hitched a drive on an international air flight and exited at Kennedy International. Infected nymphs or grownup ticks could besides hold hitched a drive while attached to a human traveller or a wild or domestic animate being. These ticks might so hold dropped off and subsequently fed on a New York animate being susceptible to WN virus, therefore originating a NYC transmittal rhythm.

Finally, the virus may hold been released by chance from a legitimate scientific experiment or on intent as an act of bio-terrorism. The inadvertent or purposeful release of any mosquito-borne pathogen would necessitate timing that coincides with environmental conditions that favor virus elaboration in vertebrate elaboration hosts and transmittal by suited vectors, prior to any possible wide-spread transmittal of the virus to worlds.

West Nile viruses possess distinguishable RNA profiles which can be characterized to spot different familial signifiers. These profiles are sometimes rather specific and dependent on the original geographic location of the virus. Several recent surveies have characterized the RNA profiles of WN viruses including several isolates from the NYC eruption. The consequences show that all the NYC WN virus isolates were about indistinguishable to one another. All the NYC WN isolates portion really near affinity with a 1998 WN virus isolated from a spell

ose in Israel. This determination that there is merely a individual familial strain of WN in North America would surely suit the possibility that the virus was late introduced and it had non resided in North America long plenty to diverge into extra strains.

THE FUTURE OF WEST NILE VIRUS IN NORTH AMERICA.

Regardless of its beginning, WN virus is likely here to remain in North America. If and when it spreads from the NYC metropolitan country remains to be seen. Of importance, has been the inquiry of whether this virus will prevail through the winter, either in a craniate reservoir, or possibly in an overwintering mosquito. Current observations indicate that both liklihoods for continuity have so occurred. Three pools of Culex species collected during January and February 2000 at Fort Totten, New York City ( northeasterly Queens ) yielded WN virus RNA utilizing a really sensitive check called contrary RNA polymerase polymerase concatenation reaction ( RT-PCR ) . On subsequent analysis utilizing a Vero cell civilization, one of the three RT-PCR positive pools was found to incorporate unrecorded WN virus. This was so confirmed utilizing a WN-specific monoclonal antibody staining of septic cells and by virus cistron sequencing.

In mid-February 2000 WN virus was isolated from a Red-tailed Hawk found moribund near Bronxville, New York ( North of NYC and E of Yonkers, NY ) . These informations indicate that, as of mid-winter 2000, live WN virus was still extant in the NYC metropolitan country.

Factors that may ease dispersion of WN include the motion of septic worlds, infected vectors ( ticks and mosquitoes ) , and septic elaboration hosts ( domestic birds, wild occupant birds, and wild migratory birds ) . It is non hard to visualize ways in which this virus may rapidly travel around the state. Many metropoliss have big populations of vector mosquitoes capable of conveying this virus. These include Cx. pipiens in the northern half of the state, its close comparative Cx. quinquefasciatus in the South, Cx. tarsalis in the West, and Cx. nigripalpus in the deep South. These species of mosquitoes are surely among the most likely North American campaigners to convey WN to birds and worlds. There are likely many other mosquito and tick species that could play a function in maintaining WN go arounding within a part. If WN is introduced into another part of the USA, it will, in clip be observed in domestic avian populations. Nation-wide watchfulness for WN is indispensable.

WHAT CAN Be DONE?

An of import inquiry refering WN motion and transmittal throughout North America is: ? What can be done to supervise the motion and debut of WN in new metropoliss and vicinities throughout North America? ? The reply is simple: surveillance, surveillance, surveillance, and more surveillance. Vector surveillance, elaboration host surveillance, meteoric surveillance, and virus surveillance.

Mosquito and vector control plans throughout the USA already have considerable experience monitoring WN & # 8217 ; s near comparative, SLE ( see the page on SLE ) . St. Louis phrenitis has been a go oning job peculiarly in the upper mid West, Florida, Louisiana, Texas, and California where there have been many terrible eruptions. A comprehensive incorporate arboviral surveillance plan for SLE in Florida has been proposed and implemented ( see Day and Lewis 1992 ) . Programs similar to this should be considered for countries that are at hazard for arboviral transmittal, particularly WN, SLE, and dandy fever viruses. The dandy fever viruses present another possible job for worlds, particularly in the southern USA.

It is merely through argus-eyed surveillance that epidemics can be recognized before local, province, and federal wellness functionaries are blind-sided by the unexpected visual aspect of big Numberss of septic worlds in topographic points like NYC. Accurate hazard appraisal of a vector borne epidemic will give all public wellness governments clip to establish control schemes and public consciousness runs that will cut down the impact of an epidemic.

A 2nd of import inquiry is: ? What can be done to minimise the impact of WN, or other vector borne pathogens, when they do go established in a region. ? It is indispensable that the most efficient and effectual control or hazard direction schemes be applied. Authorities will do their determinations about what schemes to utilize based on scientific information about the pathogen and vectors involved, and local or regional environmental conditions. It is by and large accepted that it would be tremendously dearly-won and really hard to immunize big human populations to forestall a vector borne epidemic, even were vaccinums for these viruses available. Vaccines are non presently available for the huge bulk of arthropod-borne pathogens including WN and SLE.

Personal protection against seize with teething arthropods, peculiarly when they are infected with unsafe pathogens, remains one of the most of import ways to avoid disease. Avoid mosquitoes. Make certain screens are in good fix to forestall mosquitoes from come ining houses. If you must come in countries where there is a menace of meeting septic mosquitoes, wear protective vesture. Finally, use a personal insect repellant that provides a sensible Complete Protection Time ( CPT ) . The CPT is the entire clip following rebarbative application that the treated person will stay bite free. For illustration, under normal conditions the CPT for a 5 % preparation of DEET ( diethyl toluamide, soon the most effectual insect repellant ) is about 2 hours. The CPT for a 24 % DEET preparation is more than 4 hours.

Fortunately, the USA has some of the best mosquito and arthropod control plans in the universe. Vector control and personal protection against vectors and the diseases they carry are the best manner to avoid infection with vector-borne pathogens. For illustration, schemes that might be effectual against WN in NYC include: the beginning decrease of mosquito genteelness sites ; focal applications of insect powders directed against grownup and immature mosquitoes ; public service proclamations to educated occupants about the vector, the disease, and disease turning away ; tips to assist forestall home-invasion by septic vectors ; and information about the most effectual agencies of personal protection. Recent SLE epidemics and eruptions in Florida have proved that one of the most effectual agencies of cut downing human infection is to widely circulate accurate information through the media in an attempt to educate the populace. An single & # 8217 ; s first line of defence during a vector-borne disease exigency is cognition and personal protection.

The U. S. centres for Disease Control and Prevention ( CDC ) has initiated the National WN Virus Surveillance System for 2000 as a consequence of the WN virus debut to North America. The aims of this surveillance system are:

& # 183 ; To supervise the possible geographic and temporal spread of WN virus over the eastern and southern U. S.

& # 183 ; To further develop national public wellness schemes for WN virus surveillance.

& # 183 ; To develop a more complete regional image of the geographic distribution and incidence of the other clinically of import arborviruss in the eastern and southern U. S.

& # 183 ; To supply national and regional information to public wellness functionaries every bit good as the populace.

& # 183 ; To measure the usage of concerted understanding financess and the demand for extra resources.

ADDITIONAL Reading

ANDERSON, J. F. , et Al. 1999. Isolation of West Nile Virus from mosquitoes, crows, and a Cooper & # 8217 ; s Hawk in Connecticut. Science 286:2331-2333.

BIGLER, W. J. , E. LASSING, E. BUFF, et Al. 1975. Arbovirus surveillance in Florida: Wild craniate surveies, 1965-1974. Journal of Wildlife Diseases 11:348-356.

BIGLER, W. J. , E. LASSING, E. BUFF et Al. 1976. Endemic eastern equid encephalomyelitis in Florida: A twenty-year analysis, 1955-1974. American Journal of Tropical Medicine and Hygiene 25:884-890.

CHAMBERLAIN, R. W. 1980. History of St. Louis phrenitis, In St. Louis phrenitis, T. P. Monath ( ed. ) . American Public Health Association, Washington D.C. , pp. 3-61.

CDC UPDATE. 2000. Surveillance for West Nile virus in overwintering mosquitoes, New York, 2000. MMWR 49:178-179.

DAY, J. F. AND G. A. CURTIS. 1993. Annual outgrowth forms of Culex nigripalpus females before, during and after a widespread St. Louis phrenitis epidemic in south Florida. Journal of the American Mosquito Control Association. 9: 249-255.

DAY, J. F. AND G. A. CURTIS. 1994. When it rains they soar-and that makes Culex nigripalpus a unsafe mosquito. American Entomologist 40: 162-167.

DAY, J. F. AND G. A. CURTIS. 1999. Blood eating and oviposition by Culex nigripalpus ( Diptera: Culicidae ) before, during, and after a widespread St. Louis phrenitis virus epidemic in Florida. Journal of Medical Entomology 36: 176-181.

DAY, J. F. AND L. M. STARK. 1999. Avian serology in a St. Louis phrenitis epicentre before, during, and after a widespread epidemic in South Florida, USA. Journal of Medical Entomology 36: 614-624.

DAY, J. F. AND A. L. LEWIS. 1992. An incorporate attack to St. Louis phrenitis surveillance in Indian River County, Florida. Florida Journal of Public Health 4:12-16.

HUBALEK, Z. AND J. HALOUZAK. 1999. West Nile Fever-a reemerging mosquito-borne viral disease in Europe. Emerging Infectious Diseases 5:643-650.

KRAUSE, R. M. ( erectile dysfunction ) . 1998. Emerging Infections. Academic Press, New York, New York.

LANCIOTTI, R. S. , et Al. 1999. Beginning of the West Nile Virus responsible for an eruption of phrenitis in the Northeastern United States. Science 286:2333-2337.

TABACHNICK, W. J. 1998. Arthropod-borne pathogens: Issues for understanding emerging infective diseases. In R. M. Krause ( ed. ) , Emerging Infections. Academic Press, New York, New York, pp. 411-430.

Bibliography

The 1999 Introduction of the West Nile Virus to North America

Year:1999.

Writers: Jonathan F. Day and Walter J. Tabachnick

Unit of measurement: Florida Medical Entomology Laboratory.

Citation: Florida Medical Entomology On-line Publications PH1004.

University of Florida, IFAS.

hypertext transfer protocol: //www.ifas.ufl.edu/~veroweb/online/WNile/WNilemain3.htm.