Industrial Hygiene & Environmental Health Office
West Nile Virus (WNV) Background
West Nile Virus (WNV) was first isolated from an adult woman in the West Nile District of Uganda in 1937 and the ecology characterized in Egypt in the 1950s. Then, during an outbreak in Israel in 1957, the virus became recognized as a cause of severe human meningitis or encephalitis (inflammation of the spinal cord and brain) in elderly patients. Soon after, in the early 1960's, equine disease was first noted in Egypt and France. Then, in 1999, WNV appeared in North America, with encephalitis reported in humans and horses. The subsequent spread in the U.S. is an important milestone in the evolving history of this virus.
When the disease was first detected in the U.S. in 1999, only four states (New York, Connecticut, New Jersey, and Maryland) had reports of WNV in animals, birds, and/or mosquitoes. By the end of 2005, WNV had been reported throughout the continental U.S. and Puerto Rico (WNV has not yet been reported in Hawaii or Alaska).
In 2002, 4 novel routes of WNV transmission to humans were documented for the first time: 1) blood transfusion, 2) organ transplantation, 3) transplacental transfer, and 4) breastfeeding. In 2004, a spokesperson for the CDC stated that more than 1,000 blood donors had tested positive for WNV in the U.S., making [it] one of the most common illnesses that can be acquired through transfusions.
The height of the WNV outbreak in the U.S. occurred during 2002 and 2003. In 2002, WNV infected 4,156 people nationwide and claimed 284 lives, making that year one of the deadliest mosquito-borne illness years in recent U.S. history. In 2003, there were 9,862 cases of WNV reported with 264 deaths.
While Fort Detrick was able to dodge WNV in 2001 by successfully locating and eliminating potential mosquito breeding areas, the spread of the virus overwhelmed the entire northeast region, finally landing at Fort Detrick in July 2002, with the discovery of the first WNV infected bird. Later, during August 2002, WNV infected mosquitoes were found at Fort Detrick.
The result of finding WNV infected birds and mosquitoes at Fort Detrick was stepped-up efforts to minimize or eliminate mosquito breeding areas, including coordinated efforts between Industrial Hygiene/Environmental Health (IH/EH) Office, Environmental Management Office, and Directorate of Installation Services (DIS) staffs to inspect and clean out storm drains and stock ponds with mosquito-eating fish. An environmentally safe larvicide, Altosid®, was also obtained and applied to areas with standing, stagnant water. During 2005, the number of human and animal illnesses reported to the CDC declined significantly (3,000 cases reported with 119 deaths), however, according to Lyle Petersen, Director of CDC's Division of Vector-Borne Infectious Diseases, "Nearly the entire US population now lives in areas endemic for the WNV. For the third consecutive year, WNV was, by far, the most common vector-borne infection in North America, indicating that it will remain a significant public health problem for the foreseeable future."
While there has been a decline in reported WNV in mosquitoes, birds and animals during the last several years, it does not mean the disease has gone away. Once recognized as an endemic disease, sampling and reporting activities tapered off throughout the U.S. Routine sampling at Fort Detrick also ended after the 2005 mosquito season; however, surveillance and mitigation of mosquito breeding areas begins in early Spring and continues through late Fall.
When viewing WNV statistics , it is important to consider the rate of progression of a previously non-endemic arboviral virus within the U.S. Again, while reported positive WNV findings in mosquitoes, birds, and animals has declined since 2006 due to reduced or absent sampling activities, WNV in humans remains a reportable disease to the CDC.
West Nile Virus FAQ's
The following "Frequently Asked Questions" and responses are provided for both residents and personnel living and working at Fort Detrick, and relate simple steps which may reduce or avoid the chances of acquiring WNV while at work or play:
What is the connection between birds, mosquitoes, and West Nile Virus?
WNV is usually a disease of birds spread by mosquitoes. The mosquitoes become infected when they feed on WNV-infected birds, and after an incubation period of 3 days to 2 weeks, these infected mosquitoes can transmit the virus to humans and animals when biting to take blood (noting that only female mosquitoes take blood and transmit the virus).
Will I get sick if a mosquito bites me?
Probably not. Even when bitten by a WNV-infected mosquito, most people do not get sick.
What are the symptoms of WNV?
Symptoms of WNV in humans are usually mild and may include flu-like symptoms (fever, headache, swollen glands, and/or rash). More severe reactions include high fever, stupor, disorientation, coma, tremors, and muscle weakness. Deaths linked to the disease have occurred but are rare.
Is it true that WNV can be transmitted from donated blood?
According to the CDC, additional routes of infection became apparent during the 2002 West Nile epidemic (it is important to note that these other methods of transmission represent a very small proportion of cases).
Studies now confirm WNV transmission through transplanted organs and investigations are ongoing of patients who developed WNV infection within several weeks of receiving blood products or organs to determine whether WNV was transmitted by transfusion or transplantation in any of these cases. In the meantime, the U.S. Food and Drug Administration reports the risk of acquiring the disease through blood transmission is low. Further, once these findings were confirmed, the Army voluntarily joined a nationwide effort to pull blood products in hopes of curtailing the spread of WNV.
Individuals are encouraged to talk with their healthcare professionals regarding concern about blood products or mosquito-borne illness/disease.
What is being done at Fort Detrick?
IH/EH and DIS personnel are continuing efforts to detect and control mosquito breeding areas by surveying and eliminating potential or current breeding areas and applying larvicide to areas with standing, stagnant water.
Prior to the start of the 2006 season, Army officials announced that there would be no routine collection and sampling of mosquitoes for WNV. Also, the U.S. Geological Survey's National Wildlife Health Center announced it will no longer accept dead birds from DoD sources for routine WNV testing. Local and Army Preventive Medicine officials will be monitoring the national mosquito-borne disease situation and if any unusual occurrences are detected, program requirements will be adjusted accordingly.
What can I do to prevent WNV and other mosquito-borne illnesses?
- Take corrective measures if you see areas or objects around buildings or homes that could collect and hold water (clean and/or store upside-down any water collecting containers such as buckets, flowerpots, and cigarette ash/butt containers).
- Maintain wading pools, birdbaths, and pet dishes to ensure stagnate water does not collect in them. Small wading pools should be emptied after each use and ornamental ponds should be aerated and/or stocked with fish.
- Ensure covers on outdoor furniture, play sets, lawn tools, and other equipment do not collect pockets of water.
- Ensure gutters are cleaned and maintained so that they drain properly and ensure water does not collect at the bottom of drain spouts.
How do I avoid being bitten by mosquitoes?
- Avoid or minimize mosquito bites by reducing time spent outdoors when mosquitoes are most active (dawn and dusk).
- Wear pants, long sleeves, shoes, and socks if you are outdoors when mosquitoes are active.
- Use a mosquito repellent that contains DEET on exposed skin (read label precautions carefully to ensure proper use for children and pregnant women). Effective repellents contain 20-35% DEET, noting that products with high concentrations of DEET (greater than 35%) should be avoided, especially for children.
- Ensure screens on doors and windows are in good condition and fit tightly.
- Do not rely on ineffective measures to avoid mosquito bites (Vitamin B, 'ultrasonic' devices, and bug zappers).
What if I find dead birds or see mosquito-breeding sites?
- Do not attempt to collect any birds or mosquitoes yourself.
- If you spot an actual or potential mosquito breeding site, contact the IH/EH Office at 301-619-7471.
- If you find a dead bird or any other dead animal, contact the Work Order Desk at 301-619-2726.
Fort Detrick Press Releases 2005
- West Nile Virus still a threat, mosquitoes not gone just yet
- Detrick continues winning battle against West Nile Virus
Fort Detrick Press Releases 2004
Fort Detrick Press Releases 2003
- Fort Detrick Prepares to Combat West Nile Virus
- Mosquito Traps on Post Safe - No Cause for Alarm
- Two Crows Positive for West Nile
Fort Detrick Press Releases 2002
- West Nile Virus Monitoring at Detrick Begins
- West Nile Virus Update and Tips
- Birds Test Positive for Wes Nile Virus
- West Nile Found on Post
Fort Detrick Press Releases 2001
- West Nile Monitoring Continues at Detrick
- USAMRIID Support West Nile Virus Investigations
- West Nile Virus: Symptoms, Prevention, Local Actions