Historical Summary
Human Cases & History of the West Nile
Virus
West Nile Virus has been detected in the United States every year since its initial outbreak in1999, and its range has extended.
Range Map of the West Nile Virus 1999 - 2002
Source: Dr. Henry Huang, Washington U. School of Medicine
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| [Larger Map] | [Larger Map] |
| Source: CDC NIOSH | Source: CDC Division of Vector-Borne Infectious Diseases |
In 2002 there were 4156 human cases of West Nile Virus reported to the CDC, with 284 fatalities. This was "the largest arboviral meningoencephalitis epidemic documented in the western hemisphere and the largest reported WNME epidemic. Epizootic and epidemic activity was most intense in the central US, especially in the Great Lakes region, and extended to the west coast... [indicating] complete transcontinental movement of WNV within 3 years." These are some of the key points made in the Dec 20 MMWR (Morbidity and Mortality Weekly Report) from the Centers for Disease Control (CDC) in summarizing information reported through Nov 30 2002 via ArboNET, a web-based data network through which 54 state and local public health departments report results of surveillance activities.
In 2002 WNV was detected in 44 states (2,289 counties) across the US and 5 provinces in Canada, from Saskatchewan to Nova Scotia. In the US the only states where it had not been detected were Alaska, Arizona (several cases imported from elsewhere), Hawaii (case in infected tourist from Minn), Nevada, Oregon (it was found in a human case contracted elsewhere and in a horse in a border county in Idaho) and Utah. In many states WNV was detected in all, or nearly all, counties, including several on the Mexican border. The 2002 range compares with 359 counties in 27 states and Washington DC in 2001. Despite this large increase, CDC believed that the ArboNET data reported in their Dec 20 MMWR likely underestimated the actual geographic range and intensity of WNV transmission in the US because (a) only 27% of birds reported in 2002 were tested as compared with 50% in 2001; (b) some data were not yet reported; and (c) there was not a nationwide surveillance case definition for WNME and WNF.
| Weekly Cases Counts | Cumulative Case Counts |
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Case numbers were far higher than the prediction reported in newspapers across the country in August 2002 that there would be 1000 human cases, a prediction based solely on extrapolating from dates-of-onset data from previous years [More]. More accurate predictive models would require far better understanding about the factors leading WNV outbreaks in certain areas.
According to the Nov 13 MMWR, among the 3,226 patients for whom data were available, the median age = 56 years (range: 1.5 mn - 99 years); 1,719 (54%) male; illness onset June 10-Oct 21; median age of 196 decedents = 78 years (range: 24-99 years); 119 (61%) deaths were among men. These statistics have not varied considerably during this season (age range has expanded) and can be compared with those from other WNV outbreaks during the past decade (Weinberger et al. 2000).
| Reported deaths in West Nile virus outbreaks during the last decade | ||||
|---|---|---|---|---|
| Year | Location | # of Cases Studied | Deaths (%) | Reference |
| 1994 | Algeria | 13 | 13.3 | Le Guenno et al. 1996 |
| 1996 | South Romainia | 393 | 4.3 | Tsai et al. 1998 |
| 1999 | New York | 61 | 11.5 | CDC 1999 , CDC 2000 |
| 1999 | South Russia | 1000 | 4.0 | Lvov et al. 2000 |
| 2000 | New York, New Jersey | 19 | 10.5 | Marfin et al. 2000 |
| 2000 | Israel | 417 | 8.4 | Weinberger et al. 2001 |
| Source: Weinberger et al. 2001. West Nile Fever Outbreak, Israel, 2000: Epidemiologic Aspects. EID 7(4): 686-691. | ||||
A number of human cases reported this season were contracted while traveling in another state, and therefore tallies of human cases by state of residence are not completely consistent with those tallied by the location of the illness. For example, a visitor to Washington State contracted WNV while in Louisiana, a 22-year-old Maryland resident contracted WNV while working in Illinois (not reported as a Maryland case), a 38-year-old Massachusetts woman became ill in Missouri (reported as a Massachusetts case), a Florida resident likely contracted the disease in Louisiana [More], a Texas resident is suspected of having WNV in Arkansas, several residents of Alabama and Florida have been hospitalized in the other state, a WNV-infected Michigan woman was hospitalized in Oregon, a 47-year-old Idaho resident and a 23-year-old Montana woman are thought to have contracted WNV while travelling in Ohio (both ann Sept 6), 2 persons in the Los Angeles area are known to have acquired the virus out-of-state, and a Mexican man became infected in Texas. [More information and Maps of locations where WNV has been reported].
Prior to 2002, 19 people with WNV infection died in the US (7 fatalities in 1 state in 1999, 2 in 2000 and 10 in 2001), although several of the deaths were attributed to other causes. About 150 persons had become seriously ill (62 in 1999, 20 in 2000 and 64 in 2001). The numbers of infected persons with lesser or no symptoms is much larger, but not known. CDC epidemiologists estimate that 150 people may be infected with WNV for every person who is hospitalized with serious WNV-associated illness, 30 of whom show some flu-like symptoms.
Prior to 2002, 835 horses are known to have shown WNV symptoms (9 in Long Island, New York the first year, 88 in 2000 and 738 in 2001). These cumulative numbers are far surpassed by the 2002 caseload.
2002:
As of Nov 13, 2002, WNV-infection was confirmed in 7,522 dead crows and 5,730 other dead birds from 42 states and Washington DC; WNV seroconversions were reported in 366 sentinel chicken flocks (Florida, Iowa, Nebraska, North Carolina, Pennsylvania, Texas, and New York City); 8,312 WNV infections in horses and/or other mammals (8,299 equines, three canines, and 10 other species) had been reported from 37 states (note that USDA APHIS reports much higher numbers of infected horses--13,577 horses in 39 states as of Nov 12); and 4,906 WNV-positive mosquito pools had been reported from 27 states.
In mid-November Idaho became the 44th state to announce presence of WNV in 2002, joining (date of first findings or reports in 2002 are in parenthesis): Florida (ann Feb 18), Louisiana (ann Mar 21), Pennsylvania (found Apr 29), Virginia (found Apr 8), New Jersey (found Apr 16), Washington DC (found May 1), Illinois (found May 2), New York (reported May 16), Connecticut (found May 16), Massachusetts (found May 21), Georgia (reported May 24), Michigan (found May 23), Ohio (reported May 30), Indiana (reported Jun 6), Tennessee (reported Jun 7), Rhode Island (found Jun 16-22), Maryland (ann Jun 17), Texas (ann Jun 19), Alabama (ann Jun 20), Arkansas (found Jun 22) North Carolina (ann Jun 23), Kentucky (ann Jun 25), Wisconsin (found Jun 25), Nebraska (found Jun 28), North Dakota (found Jun 30), Missouri (found Jul 8), Minnesota (found Jul 9), Delaware (found Jul 9), West Virginia (found Jul 12), Iowa (found Jul 15), Oklahoma (ann Jul 18), Mississippi (ann Jul 18), South Dakota (found Jul 22), New Hampshire (found Jul 26), Maine (tested Jul 30), Kansas (ann Aug 8), Vermont (confirmed Aug 6) and South Carolina (ann Aug 13), Colorado (ann Aug 16), Wyoming (ann Aug 16), New Mexico (ann Aug 22), Montana (ann Aug 22), California (ann Sept 6), Washington (ann Oct 2) and Idaho (ann mid-Nov). WNV has also been detected this year in Manitoba, Ontario, Quebec, Saskatchewan and Nova Scotia provinces in Canada (as well as in an "imported" human case in Alberta); and in people and mosquitoes in Israel. Imported human cases have been confirmed in Mexico, with possible detections in birds in the Yucatan. WNV antibodies have been detected in birds in the UK (ann Oct 28).
Prior to the human case reported from coastal Los Angeles County CA on Sept 6, the range of WNV had extended past the 108th meridian on its trek west, detected as far west as Yellowstone County, Montana. Its range has expanded in each of the 4 years since the initial North American outbreak in 1999, and has expanded considerably in 2002; in the Continental US only 5 westernmost states have not reported WNV detections.
In addition to the significant expansion in range, in a number of areas WNV was detected much earlier this season than in previous years. For example, WNV was detected for the first time in Louisiana on Labor Day Weekend 2001, whereas in 2002 the first case (a cardinal) was announced in March. Other examples: WNV-positive birds were not found in Massachusetts until mid-July 2001, 7 weeks later than in 2002; and were not found in Canada until August 2001, as compared with late May 2002. In previous years WNV-positive mosquitoes were not detected in Israel until mid-summer, whereas in 2002 they were detected in early May. This year, the first human case was diagnosed in Louisiana July 8, with exposure to infection likely two weeks earlier, in late June. Last year, in 2001 onset of symptoms in the first case was about July 15 in Florida; in 2000 it was on July 20 in Staten Island, NY; in 1999 onset of the first case was in the latter part of August, in Queens, NY [More].
WNV's appearance in New York City in Summer of 1999 caught scientists and government agencies by surprise because this arbovirus (a virus spread by mosquitoes and other arthropods) had never before been detected in the Americas. The 1999 outbreak was centered in Queens, NYC, but also detected in other locations within a 75-mile radius of New York City (in NY, NJ and Connecticut). The only case outside the NYC metropolitan area was in a single crow in Maryland. Sixty-two people were hospitalized with infection of the central nervous system (CNS), of whom 7 died. Nine horses on Long Island, in SE NYS also died, as well as large numbers of birds.
Year 2000 saw recurrence and spread of the virus, in 12 states and Washington DC, from New Hampshire to North Carolina (CT, DE, MD, MA, NH, NJ, NY, NC, PA, RI, VT, VA), but with considerably less human illness despite a much larger range of WNV activity (+/- 20 people were hospitalized with central nervous system (CNS) infection from WNV, of whom 2 died).
In 2001, its third year in the US, WNV spread into the Midwest and deeper
into the Southeast [CDC Map].
It was detected in 27 states in the US and Washington DC
(
AL,
AR,
CT,
DE,
FL,
GA,
IL,
IN,
IA,
KY,
LA,
ME,
MD,
MA,
MI,
MS,
MO,
NH,
NJ,
NY,
NC,
OH,
PA,
RI,
TN,
VA,
DC,
WI), as well as elsewhere in the Americas, in Ontario,
Canada and the Cayman Islands in the
Caribbean.
WNV had its largest impact on human health in 2001, seriously affecting at
least 64* people from 10 states in the US. However, this impact was spread
over a much wider geographic area than in 1999, when a similar number of people
were affected.
*Note: CDC ArboNET reports 66 confirmed cases for 2001, but two of the NYC cases were reported as mild, outpatient cases. Thus we report 64 serious cases.
Although older/elderly persons had been considered the highest risk group, in 2001 at least 12 of the severe cases reported in 2001 were persons in their thirties, forties and early fifties (cases from Connecticut, Florida, New Jersey and New York). A case reported late in 2001 involved a 19-year-old. The human cases were in Alabama (2), Connecticut (6), Florida (12), Georgia (6), Louisiana (1), Maryland (6), Massachusetts (3), New Jersey (12), New York (15*), and Pennsylvania (3). The first human case of 2001 was in Florida, a 73-year old man who became ill July 13, a few days earlier than the first human onset in 2000 and more than a month earlier than the first human onset in 1999. Descriptive statistics for 2001: 65% males; median age 68 years (range 19--90 years); 9 deaths (14%); and dates of onset July 13-December 7 [CDC Graph]. Descriptive statistics from several outbreaks around the world have been compiled by Weinberger et al. (2001) for comparison [Table].
At least 10 persons in the US infected with WNV in 2001 have died, although the primary cause of several of these cases is attributed to underlying severe health problems. The 10 fatalities confirmed by CDC are:
1) 71-year-old woman from Atlanta, Georgia (Aug 17)
2) 63-year-old woman from Eastpoint, Maryland infected with WNV died from other causes (early Sept)
3) 70-year-old woman from Baltimore, Maryland infected with WNV succumbed to an underlying illness (late Sept)
4) 45-year-old man from Carteret, New Jersey (Oct 4)
5) 70-year-old from Woburn, Massachusetts (mid-Oct)
6) woman in her nineties from New Haven, Connecticut (mid-Oct)
7) 44-year-old man in Alabama (Oct 30)
8) 71-year-old woman from East Meadow in Nassau County, NY (Oct 26)
9) 77-year-old man from the same community in Nassau County (Nov 22)
10) 73-year-old man from West Baltimore, Maryland (ann Aug 22, 2001, died May 25, 2002, 9 months after contracting WNV).
In 2001 WNV was found in at least 80 species of birds (though most noticeable in Corvids, which include crows and blue jays) and 8 mammal species (horses appear to be the most susceptible mammals). There had been questions about how well WNV could survive northern winters but by 2002 it had survived three northern winters. There is an additional concern that it may more easily become permanently established in the milder sections of the country, particularly in the Gulf Coast States.
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ERAP's West Nile Virus education program has been supported by Smith-Lever funds from the USDA Cooperative State Research, Education and Extension Service (CSREES), through a grant from Cornell Cooperative Extension, and by a grant from the National Oceanic & Atmospheric Administration's Office of Global Programs (NOAA-OGP) for the project "Climate Effects, West Nile Virus Vector Development, and Transmission Risk" (Sept 1, 2004-Aug 31, 2007).
