West Nile Virus - End Of Year
Summary And Update
From Patricia A. Doyle, PhD

By Lois Levitan, PhD
Program Leader - Environmental Risk Analysis Program
Center for the Environment - Cornell University
The 2002 WNV epidemic in the US 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. Other information is incorporated into pertinent sections of ERAP's WNV summary pages.
An infant born in November to a woman who contracted WNV while pregnant is hospitalized in Syracuse, New York (Onondaga County Health Dept, PR Dec 18, 2002). "WNV has not previously been associated with intrauterine infection or adverse birth outcomes" in the formal record, although at least one other human case of transplacental transmission has been described anecdotally. Details are described in the CDC MMWR Dec 20, 2002 and were also covered in the Dec 19 CDC press conference. CDC recommends that "pregnant women should take precautions to reduce their risk for WNV or other arboviral infection and should undergo diagnostic testing when clinically appropriate." [For additional information and background, see WestNileVirus-l listserv postings from Oct 13, 15, and 17 and Dec 20].
At least 2 US lab workers became infected with WNV in 2002 when their skin was cut while handling infected animals. These cases of "percutaneous inoculation" are described in the Dec 20 MMWR, which recommends precautions that should be taken by labs -- e.g., avoiding contact with fluids, tissues and aerosols -- and presumably also heeded by hunters and others who might come in contact with infected animals.
In 2002 WNV has been 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 has not been detected are Alaska, Arizona (several cases imported from elsewhere), Hawaii (case in infected tourist from Minn), Nevada, Oregon (it has been found in a human case contracted elsewhere and in a horse in a border county in Idaho) and Utah. In many states WNV has been detected in all, or nearly all, counties, including several on the Mexican border [Dec 7, 2002 range map]. The 2002 range compares with 359 counties in 27 states and Washington DC in 2001. Despite this large increase, CDC believes that the ArboNET data reported in their Dec 20 MMWR likely underestimate 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 are not yet reported; and (c) there is not a nationwide surveillance case definition for WNME and WNF.
As of Dec 19, 2002 CDC reports 3,852 human cases (232 fatalities) from 39 states and Washington DC (as compared with 149 human cases accounted by CDC 1999-2001). This is an increase of a little more than 100 cases in the 3 weeks since Nov 26 (3,737 cases, 201 fatalities). Illinois (778), Michigan (553), and Ohio (431) have the highest case loads.
Of 3,389 cases reported in the Dec 20 MMWR, 69% were persons with WN meningoencephalitis (199 fatalities among 2,354 cases, = 9% fatalities), 21% with what is being referred to as WN fever (2 of 704 cases fatal, = 0.3%, both persons over 80), and 10% with unspecified illness. The epidemic peak was during the week ending August 24 (317 cases in northern states), a week later than the peak in the southern states (88 cases in southern states week ending Aug 17) [Case load graph]. Among all reported human cases median age=55 (range 1 months-99 yrs, 54% male); for persons with WNME median age=59, same range; for persons with WNF median age=48 (range 1-93 yr). Median age of 201 decedents=78 (range 24-99); 60% deaths male.
The Health Ministry ann Oct 16 that there have been 26 human cases of WNV in Israel in 2002 (2 fatalities), which is comparable to the case load in 2001 and about 5% the number of human cases in 2000. WNV-positive mosquitoes were detected as early as May this year, as compared with first detections in Aug in previous years.
The University of Minnesota's Raptor Center had reported increasing numbers of raptors picked up sick or dead earlier this fall, and thought to be infected with WNV. Dr. Emi Kate Saito, WNV Surveillance Coordinator with the National Wildlife Health Service updated this information as of Dec 18, 2002: "The National Wildlife Health Center (NWHC) has tested some of the raptor cases admitted to raptor rehabilitation centers. These cases underwent full diagnostic evaluation to determine whether the deaths were due to WNV or to other causes. The NWHC WNV testing protocol consists of isolating virus from organ tissues (such as kidneys, spleen, brain, etc.) and then performing RT-PCR on the virus isolates to confirm WNV. Other tests include looking for other infectious causes (bacterial, fungal or other viral) and toxin exposure. As of December 18, 2002, the NWHC had received 73 raptor carcasses from several states. Diagnostic evaluation has been completed for 30 cases : 9 died due to WNV, 6 were infected with WNV but did not show any or sufficient brain damage to explain symptoms, 4 were WNV-negative but had sufficient brain damage suggestive of viral encephalitis, and 11 died from other causes. In sum, NWHC has diagnosed 9 confirmed and 10 possible cases of WNV. Further confirmatory testing is planned for the 10 possible cases." [For additional information see WestNileVirus-l listserv postings from Sept 13, 15, 18, 23 and December 19, as well as ERAP's Summary on WNV and birds.]
As of Dec 1, 2002, USDA APHIS reports 14,358 equine cases of WNV-illness either confirmed at USDA's National Veterinary Services Laboratories (NVSL) or reported by state officials in 2002. This is an increase of 313 cases since the previous report on Nov 20. Case numbers had been increasing at a rate of 400-500 per week since Oct 20, when 11,526 cases were reported. llinois, Iowa, Nebraska, and Texas each have more than 1000 equine cases. Minnesota, Missouri and Oklahoma have nearly as many. In Texas the 1377 cases represent about 0.15% of the million horses in the state. CDC reports many fewer cases in the current MMWR (9,038 equines, 3 canines, and 10 other species). [More about Horses]. WNV has now been associated with illness and death in several other mammal species including reindeer, mountain goats, squirrels, etc. [More]. The Nov 29, 2002 CDC MMWR also reports WNV infection from 42 states and Washington DC in thousands of dead birds (7,715 dead crows and 6,275 other dead birds).
This summary is slightly revised from the "Latest News" posted on ERAP's West Nile Virus
webpages. Weblinks are "live," while links in this email are not
Lois Levitan, PhD Program Leader
Environmental Risk Analysis Program
Center for the Environment
213 Rice Hall, Cornell University
Ithaca, New York USA 14853-5601
Phone (607) 255-4765 Fax: (607) 255-0238
Program Email:
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