The Virus
West Nile Virus is a mosquito-borne virus, particularly of the Culex species of arthropod, with birds being the principle host. Of the family of viruses known as Flaviviridae, West Nile Virus is closely related to St. Louis encephalitis and Japanese Encephalitis but had not been found in the United States prior to an outbreak in 1999. West Nile can also be misdiagnosed with Dengue Fever – an increasingly problematic mosquito-borne disease in the Americas as well. Birds, such as crows, grackles, and blue jays act as amplifying hosts for WNV. (Center for Disease Control and Prevention) . Within 10-14 days of an infected mosquito’s bite, a bird can transmit the disease to a human or other mammal (Guharoy, Gilroy, Noviasky, & Ference, 2004) . An initial infection may not kill a bird but subsequent bites by infected mosquitoes will cause the virus to multiply and eventually sicken and/or kill the bird. In humans, usually a dead-end host, the virus is very often asymptomatic. Less than 3 percent of the affected population will acquire an active infection. In some instances however, the human can become sick with a quick onset fever, headache, muscle aches, and general malaise. Acute onset of fever can happen within 2-14 days after inoculation by an infected mosquito. The aggressiveness of the disease appears to be a direct correlation between the numbers and feeding behavior of infected mosquitoes as well as ecological factors determining human exposure to infected mosquitoes. Residents in the New York outbreak were found to reside in areas near wetlands where mosquitoes were more prevalent and had greater access to human hosts. (Hayes & Gubler, 2006) . The West Nile Fever can last a few days to as long as a few months and has been reported to be quite debilitating. While 80% of WNV infections are asymptomatic, 20% result in West Nile Fever and less than 1% result in nueroinvasive disease – presenting as encephalitis, meningitis, or flaccid paralysis (Hayes & Gubler, 2006) . Humans, horses, and other mammals are susceptible to the virus but not all become sick (Rappole, Derrickson, & Hubalek, 2000) . Before the New York City Outbreak, West Nile Virus was endemic to Africa, West Asia, and had been reported in Israel (Guharoy, Gilroy, Noviasky, & Ference, 2004) .
The disease can be passed down from female mosquitoes to their offspring after a winter of hibernation. It has been suspected that WNV made it to the American via migratory birds; however that would explain north-south migration of the disease but not the east-west progression evidenced across the United States. Peak activity for WNV is July – October (Hayes & Gubler, 2006)
The disease can be transmitted among humans by blood transfusions and organ transplants, trans-placentally, and perhaps through breast feeding (Hayes & Gubler, 2006) . The cases of West Nile Nueroinvasive Disease (WNND) and death occurs at a slightly higher rate among males (53%), the elderly, and those immunosuppressed individuals who have had organ transplants (Hayes & Gubler, 2006)
The New York City Outbreak of 1999 - Timeline
At the end of June, 1999, residents of the neighborhoods in northern Queens, New York City, started to notice and report an usual number of diseased and dead crows. By July, a local veterinarian began to note that some of the diseased birds walked with an uneven gait, possibly denoting a neurological disease (Eidson, et al., 2001) .
On August 12 a sixty-year old man presented to a New York City hospital with complaints of a fever, nausea, and weakness. He was admitted. On August 15th an eighty-year old man was admitted with complaints of fever, headache, weakness and diarrhea. He developed flaccid paralysis and subsequently died. Between the dates of August 18th and September 6th six more patients were admitted with similar symptoms (Petersen & Hayes, 2008) . It wasn’t until August 23rd that a New York City infectious disease physician contacted the New York City Department of Health (NYCDOH) to report an encephalitis-like illness in two of his patients, both New York City residents. An investigation by the NYCDOH identified a cluster of six other area patients with encephalitis. Of the earliest case patients, eight lived within a two by two mile area of northern Queens. (Center for Disease Control and Prevention, 1999) . At the same time residents were coming down with the mysterious illness zookeepers at the nearby Bronx Zoo were noticing an increase in bird deaths also (Rappole, Derrickson, & Hubalek, 2000) . On August 30th the NYCDOH initiated an active surveillance (Center for Disease Control and Prevention, 1999) . By the 3rd of September specimens were testing positive for antibodies common in arboviruses and the Center for Disease Control and Prevention (CDC) determined an initial diagnosis of St. Louis encephalitis. An immediate vector control program was initiated on the 3rd, with areal and ground applications of mosquito pesticides in northern Queens and the south Bronx areas of the city. Emergency hotlines were set up to help field questions by the public and ease panic. (Center for Disease Control and Prevention, 1999)
During the days of September 7 – 9 officials at the Bronx Zoo noted the deaths of two Chilean Flamingos, a Cormorant, and an Asian Pheasant. Necropsies on the birds revealed cases of meningo-encephalitis and severe myocarditis. By the 10th of September tissue specimens from the zoo birds and one crow were sent by zoo officials to the United States Department of Agriculture’s National Veterinary Service Laboratory (NVSL) for further testing. Common avian pathogens and equine encephalitis tests all turned up negative. The NVSL then isolated tissue from the birds and sent them on to the CDC on September 20 for further identification. By September 23rd testing at the CDC indicated the disease was closely related to West Nile Virus, previously not found in the Americas. Eidson reports that initial evaluations were made by the New York State Department of Environmental Conservation’s Wildlife Pathology Unit and the Wildlife Conservation Society and the CDC confirmed West Nile Virus on September 25th (Eidson, et al., 2001) . Meanwhile, specimens of brain tissue collected from three human encephalitis cases, sent from the NYCDOH to the University of California, Irvine, were genetically analysed and found to be positive for a West Nile-like virus (Center for Disease Control and Prevention, 1999) . In response to these test results, local health departments were requested to complete active surveillance for disease and deceased birds, collect the birds and send them to the New York and Connecticut State Health Departments.
The 1999 Outbreak is estimated to have caused 8200 human infections in which 1700 resulted in West Nile Fever (Petersen & Hayes, 2008) . The disparity in numbers estimated and numbers confirmed is due to the fact that asymptomatic people certainly did not seek medical care and those who came down with WNF may have weathered the disease without seeking healthcare as many people tend to pass things off as “the flu” and suffer at home until symptoms ease. By September 28, 1999, there were 17 confirmed cases, 20 probable cases, and 4 deaths in New York City and surrounding counties. It was determined that onset dates ranged from August 5 – September 16 but after mosquito control measures were expanded to include the entire city no more cases were reported for that year (Center for Disease Control and Prevention, 1999) .
Despite the evidence that an encephalitic disease was causing nueroinvasive disease and in some cases death in humans, information was not published by the Center for Disease Control until its October 1, 1999 Morbidity and Mortality Weekly Report.
In 2011 the CDC has reported, as of November 15, a total of 429 cases of WNND (68%) and non-nueroinvasive disease manifestation of the disease as 198 total cases (32%) for the year of 2011 alone. ArboNET, the surveillance system set up to monitor West Nile, reported 627 cases with 36 of these resulting in death. 117 individuals who were asymptomatic at the time of donating blood tested positive. The bias lies in the fact that serious cases are more likely reported than mild cases, as noted before, and that syndromic surveillance systems cannot detect asymptomatic cases (Center for Disease Control and Prevention)
Lessons Learned
While it is commendable that surveillance systems were set up after the reporting of diseased and deceased birds in the New York City neighborhood of Queens and around the Bronx Zoo, it took nearly a full month before vector control measures were put into place. It was also reported that when vector control measures were begun, emergency hotlines were set up for individuals in the New York City area who might have concerns. No mention is made about media coverage and if the media caused any kind of suspicion in the public that something worse was besetting the city. It seems odd that Morbidity and Mortality Weekly published its first report on October 1st if hotlines were already in place September 3rd. This suggests that the media was in some respect reporting the unusual deaths of birds and sickness in humans. If this is the case, the Center for Disease Control should have been more pro-active in alerting the healthcare community AND the public as to their initial findings and on-going testing.
It is obvious from this outbreak that animal specialists, such as zookeepers, conservationists, avid bird watchers, veterinarians, and organizations dedicated to the health and welfare of wildlife should continually communicate with human health care specialists when special circumstances affect the animal world. In this way, novel zoonotic diseases can be identified early through testing of both animal and human specimens. The wider movement of migratory animals and the changing climate add to animals moving into areas they have not previously inhabited. This increases the introduction of diseases not endemic to these areas. Humans will be vulnerable to many of these “new” zoonotic viruses. Therefore, surveillance systems need to be kept up to date and programs like ArboNET kept in active status. In the 1999 West Nile Virus outbreak public health officials made good use of the information they had at the time. Though not documented in the readings, the CDC has put clear instruction on their website dedicated to West Nile Virus information on how individuals can protect themselves from mosquito bites by using personal protective gear (long sleeves, long pants, socks, hats, etc) and the pesticides that are safe to use on skin and clothing. Steps to remove favorable mosquito breeding habitat is also described (removing areas of stagnate water such as accumulates in old tires and bird baths). It is through personal responsibility in protecting oneself from being bitten and city-wide efforts to enforce vector control that will help minimize the arboviruses that continue to cause disease. West Nile Virus spread from New York City in 1999 to now be found, in 2011, in nearly every state, as well as Canada. It isn’t going to go away as quickly as it came.
Works Cited
Center for Disease Control and Prevention. (1999, October 1). Morbidity and Mortality Weekly Report. Retrieved November 15, 2011, from Center for Disase Control and Prevention: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm4838a1.htm
Center for Disease Control and Prevention. (n.d.). West Nile Virus. Retrieved November 15, 2011, from Center for Disease Control and Prevention: http://www.cdc.gov/ncidod/dvbid/westnile/index.htm
Eidson, M., Komar, N., Sorhage, F., Nelson, R., Talbot, T., Mostashari, F., et al. ( 2001). Crow Deaths as a Sentinel Surveillance System for West Nile Virus in the Northeastern United States, 1999. Emerging Infectious Diseases , 7 (4).
Guharoy, R., Gilroy, S., Noviasky, J., & Ference, J. (2004). West Nile Virus Infection. American Journal of Health-System Pharmacy , 61, 1235-1241.
Hayes, E., & Gubler, D. (2006). West Nile Virus: Epidemiology and Clinical Feature of an Emerging Epidemic in the United States. Annual Review of Medicine , 57, 181-194.
Petersen, L., & Hayes, E. (2008). West Nile Virus in the Americas. Medical Clinics of North America (92), 1307-1322.
Rappole, J., Derrickson, S., & Hubalek, Z. (2000). Migratory Birds and Spread of West Nile Virus in the Western Hemisphere. Emerging Infectious Diseases , 6 (4).
