This fact sheet includes the latest information on West Nile Virus (WNV) and provides recommendations for the affected Harvard community to minimize the potential for WNV. April has now arrived and the concerns over WNV that went into hibernation for the winter season are now coming back onto our radar in advance of the early mosquito-breeding season. Unlike the previous few years, WNV last year become a national phenomenon and is now clearly an endemic mosquito-borne virus effecting the entire North American continent. Last year's experience was unprecedented, with the detection of new routes of transmission.
Though many residents across the country have now been infected with the virus (3,852 people nationally as of December 31, 2002), people in the Northeast have been spared from the greatest impact. Of the 25 confirmed human cases in Massachusetts 2 were probably acquired out-of-state, placing this state in the middle of the pack with regard to human WNV cases. The 25 human cases in Massachusetts pales in comparison to some western states which had human case totals in the hundreds (Illinois, 778; Michigan, 558; Ohio, 431). Obviously, it is difficult to predict the number or locations of WNV in New England this year.
In 2002, Cambridge had 32 out of 112 dead birds sent to the State Lab test positive for WNV. (In 2000 and 2001 there were more than 280 total birds that tested positive.) There have been no human WNV cases reported from Cambridge.
How is WNV transmitted?
Mosquitoes that hatch in the spring are a larger contributor to WNV activity than those born in the summer. Mosquitoes born in the spring, survive through the summer, and have a greater chance of acquiring and transmitting the virus than those that hatch later in the year. Also, and more importantly, adult mosquitoes that hatch and acquire WNV early in the season are capable of infecting their eggs throughout the summer resulting in many more infected mosquitoes.
In Massachusetts, WNV has been most closely associated with the Culex pipiens mosquito. This mosquitoes species, commonly referred to as the "northern house mosquito" because of its tendency to breed in standing water found around houses, will generally only bite birds but will bite humans and other mammals if they are found in abundance. The Culex species will remain active as long as the weather permits, but when the temperature falls below 60 degrees they become lethargic and at temperatures below 50 degrees they become inactive. A very small number of mosquitoes may remain active into November.
Prevention - What you can do to minimize the risks.
These measures are based upon the West Nile Virus Task Force report from the Harvard School of Public Health. See http://www.uos.harvard.edu/ehs/pes_wes.shtml. These mosquitoes will breed in any puddle or standing water that is stagnant for more than a week. Standing water can be found in area storm or roof drains, lawn furniture, pots, discarded containers, dumpster areas, tire swings, etc. Included below is a facility inspection checklist to be used early in the season to eliminate these areas and reduce these breeding grounds for mosquitoes. Eliminating areas of standing water and encouraging neighbors and others to do the same will reduce the number of mosquitoes that breed in your neighborhood. You can also protect yourself from mosquitoes by ensuring that all window and door screens are intact and that there are no openings large enough for a mosquito to enter your home.
It is important to remember that the threat of WNV exists whenever mosquitoes are active and Harvard University residents should protect themselves by wearing loose long sleeve shirts and loose pants when outside. Residents should apply an insect repellant that contains DEET to exposed skin (less than 30% for adults, 10% - 15% for children and not for use on infants). Always follow the manufacturer instructions when applying DEET.
Report Dead Crows
Moribund crows and other birds will be collected from Harvard campuses and tested for West Nile Virus at the State Labs. If you spot a dead crow - please notify the University Operations Center (617-495-5560)
Control
The West Nile Virus Task Force will evaluate the potential for outbreaks and will formulate appropriate intervention measures. In response to this emerging disease, Harvard University authorized the application of chemicals to storm drains to control mosquito larvae and coordinated efforts by public health agencies to spray for adult mosquitoes in the summer of 2000. In 2001 and 2002, storm drains were again treated for control of mosquito larvae but spraying for mosquito adults did not occur in Boston or Cambridge. In 2002 an increased effort to locate and remove standing water on campus was implemented. For 2003, Landscape Services and outside vendors will be responsible for the application of larvicides to storm drains, etc. for larval mosquito control.
The new early breeding season for mosquitoes is now weeks away and Harvard University will join the rest of the U.S. in preparing our 2003 response. No major changes in implementation will occur this year as we continue to follow the West Nile Virus Plan (2001) produced by the Harvard West Nile Virus Task Force.