Testimony Committee on Environment and Public Works
United States Senate
Fairfield University, Fairfield, CT
November 18, 1999
Dr. Theodore G. Andreadis, Chief Medical Entomologist
The Connecticut Agricultural Experiment Station
123 Huntington Street
New Haven, CT 06505

I am here today to report you the research and surveillance activities that occurred in the State of Connecticut during the recent West Nile Virus (WNV) crisis. I will focus my comments on specific work that was done to isolate, identify and determine the distribution of the virus in birds and mosquitoes in the state. Let me begin by stating that since 1997, the State of Connecticut has had a comprehensive Mosquito Management Program to monitor mosquito populations and mosquito-borne viruses known to cause human disease, most notably eastern equine encephalitis (EEE). This program is a cooperative effort that involves three state agencies. The Connecticut Agricultural Experiment Station (CAES), which is responsible for trapping and testing mosquitoes; the Department of Environmental Protection (DEP) which is responsible for implementing all mosquito control measures; and the Department of Public Health (DPH) which is responsible for communicating health risks and protective measures to the public. Mosquito trapping is conducted daily from June through October at 37 permanent locations (principally in freshwater swamps) throughout the state. Since 1997, we have trapped and tested over 150,000 mosquitoes and detected the EEE virus on 9 occasions from 6 different locations.

Because we had this surveillance system in place we at the CAES were able to respond immediately to the WNV crisis. On September 4th, the New York City Health Department and the Centers for Disease Control (CDC) announced the death of an elderly resident of Queens from what was initially thought to be St. Louis Encephalitis, a mosquito transmitted virus. The following day (September 5) we placed mosquito traps in the town of Greenwich and began a supplementary mosquito-trapping program that was eventually extended to 15 towns throughout lower Fairfield and New Haven Counties. This was in addition to the normal trapping in other areas of the state. The purpose of this trapping was to determine the types of mosquitoes in the region, assess their relative abundance and to determine if these mosquitoes were carrying the potentially deadly virus and if they were did this represent a public health threat. Mosquito trapping was conducted over an 8 week period through the end of October during which 261 traps were placed in 80 different locations throughout the region and over 3,500 mosquitoes were trapped and tested in our laboratories.

Shortly after we initiated our mosquito surveillance program, we began to receive reports of an "extraordinary" number of crow deaths throughout lower Fairfield County. Similar crow die-offs were being observed in New York City, Long Island and New Jersey as well, and suspicion was rising that perhaps these crows were dying from the virus. However, this would be highly unusual, since St. Louis encephalitis does not typically kill birds. A plan was put into place to systematically collect and test dead crows. This was coordinated by the DPH with assistance from local health departments and wildlife personnel within the DEP. Birds were sent to the Department of Pathobiology at the University of Connecticut where necropsies were performed by veterinary pathologists. Brains and other tissues from crows that had diagnostic symptoms consistent with a viral encephalitis were them submitted to the CAES for testing. Over 300 birds were assessed from 38 towns through October 12 and 40 were tested in our laboratory for WNV.

On September 21 we obtained our first isolations of this virus from 2 different species of mosquitoes (Aedes vexans and Culex pipiens) that were trapped on the evening of September 14 at the Innis-Arden County Club in Old Greenwich, and from the brain of a dead crow collected in the town of Westport on September 13. This announcement was made by Governor Rowland who subsequently directed the DEP to initiate limited ground spraying of insecticides against adult mosquitoes in the affected areas.

The isolation of this virus from adult mosquitoes and the brain of a wild domestic crow, was a critical step in the eventual identification of the virus. Despite the increasing number of human cases that were being reported in NYC, the CDC had yet to obtain an actual isolation of the living virus from a human. We believe our isolations were the first from mosquitoes and a wild domestic crow. Following our announcement, we were immediately contacted by CDC who requested that we submit our isolations to them. We complied on September 23rd. The following day the CDC announced that the virus was not St. Louis encephalitis but was a "West Nile-like". Two days later they informed us that the viruses that we isolated from the mosquitoes and crow were the same.

We then proceeded to obtain specific reagents to test for WNV and initiated molecular studies to sequence a portion of the genome (RNA) of the virus with the intent of definitively identifying the virus, determining its possible origin and assessing its virulence for birds and humans. Early information which appeared in the British journal Lancet on October 9 from studies conducted at the University of California at Irvine had indicated that this virus was Kungin/WN-like virus which occurs in Australia. However, their analysis was incomplete and our genetic analysis showed a much closer relationship to WNV that had been isolated from mosquitoes and humans during a recent outbreak in 1996 in Romania thus suggesting a common origin. The results of our investigations are due to be published in the journal Science later this week.

Bird testing continued through mid-October and of the 40 birds that we tested, 29 were found to be positive for WNV. These included 28 American crows and one Cooper's Hawk that were collected from 18 towns in lower Fairfield and New Haven Counties along a 62-mile corridor from Greenwich to Madison, CT. No virus isolations were made from 3 crows and a Canadian goose collected from Hartford County.

Our isolations of West Nile virus from birds and mosquitoes conclusively documented the presence of this virus in Connecticut during September and October 1999 and virus activity appeared to be limited to lower Fairfield and New Haven Counties. All of the work that I have described was accomplished in State with no assistance from the CDC or any other Federal Agency. Our timely coordinated response in trapping and testing mosquitoes and birds provided indispensable data that was effectively used to inform and protect the public and fortunately, no human cases were reported in Connecticut.

The high mortality in crows and other bird species in the region suggest a recent introduction of WNV into a na‹ve wildlife population that has never been exposed to the virus. The isolation of WNV from a variety of native birds, which are likely capable of circulating this virus at relatively high titers over a broad geographic region, further suggests that this exotic virus is likely to become established in the avian fauna of the United States. How the virus will behave is unknown but if established in North America, WNV likely will continue to have severe effects on human health, horses, and on avian populations, such as American crows and raptors. The environmental, social and economic implications of permanent establishment of this exotic virus are considerable.

While many important questions need to be investigated, among the most urgent include: Will the virus persist in the region? How widespread will it become? What impact will the virus have on native bird and horse populations? How will the virus affect humans? How will the virus over winter? How will we monitor virus activity to protect the public? What birds will serve as natural reservoir hosts? What mosquito species will serve as competent vectors?

Additional resources and funding are urgently needed to address these and other research questions. This will lead to a better understanding of the natural ecology and epidemiology of this new exotic virus in North America. This information will provide critical fundamental knowledge that is presently unknown. This will be an essential component for developing effective virus surveillance, disease management and mosquito control strategies throughout the region. The information obtained in these studies will further aid in assessing the relative risk of WNV to human health and help to determine its impact on wildlife and domestic animals. We would further anticipate that increasing our knowledge in the aforementioned areas will reduce the need for application of toxic chemical insecticides to the environment.

We are at a very critical juncture and we stand ready to act. We have the expertise and laboratory facilities to undertake these investigations. We have initiated studies on overwintering mosquitoes and wild bird populations and with additional funding we can increase our mosquito surveillance program, continue our basic research on bird populations and continue our molecular studies to develop a rapid procedure for identification of the WNV.