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West Nile Virus Updates  

September 23, 2005

Although the number of Culex mosquito numbers are low in most of Mesa County and the West Nile season will soon be over, residents need to be aware that there is still risk of West Nile infection and should continue to use personal protective measures well into October.

Culex mosquito numbers have declined in most of Mesa County with the exception of DeBeque which is still seeing elevated activity. So far this season, sixteen of the 620 mosquito pools tested were positive for West Nile virus. This week two mosquito pools were reported as positive after two weeks of no positives.

Colorado currently reports 68 cases of West Nile virus for the 2005 season. Nine of those cases have been in Mesa County residents. In addition, two blood donors were reported positive for West Nile virus this week.

Following is a summary of the nine cases reported to the Mesa County Health Department:

  • Age distribution is from 38 to 89 years
  • Of the 9 cases, 8 are fever, and 1 meningitis
  • Four individuals were hospitalized
  • Two females and 7 males
  • Six cases are from Grand Junction, one from DeBeque, one from Loma, one from Palisade

In 2004, Mesa County experienced its peak season of West Nile activity with 127 confirmed cases and four deaths.

September 1, 2005

The Mesa County Health Department urges residents to take personal protective measures against West Nile virus. These precautions are critical with Labor Day weekend approaching and the associated increase in outdoor activity.

An additional human case of West Nile illness is also being reported. A Mesa County man is currently hospitalized with West Nile fever illness. A total of four human cases have been reported in Mesa County this year.

To date, thirteen mosquito samples have tested positive for West Nile virus. These samples were collected from combined and individual traps located throughout Mesa County. Most of the positive mosquito activity is being reported in the western part of the valley (please see attached map for locations).

Dr. Aduddell, Director of the Mesa County Health Department, continues to stress the importance of personal protective measures to prevent West Nile virus infection. Individuals can reduce their risk of mosquito-borne diseases by taking these precautions:

  • Avoid spending time outside when mosquitoes are most active, especially at dawn and the first two hours after sunset.
  • When outdoors, wear long pants and long-sleeved shirts.
  • Apply insect repellent containing DEET, oil of lemon eucalyptus, or Picaridin, according to label instructions.
  • Make sure that doors and windows have tight-fitting screens. Repair or replace screens that have tears or holes.
  • Eliminate all sources of standing water on your property that can support mosquito breeding.
  • If water cannot be removed, treat it with a mosquito larvicide.

August 29, 2005

At this time, the risk of West Nile infection is moderate. Mesa County has had a total of 10 mosquito pools test positive for the virus. It is important for individuals to take personal precautions now. These precautions include:

  • Use insect repellent containing DEET, picaridin, or oil of lemon eucalyptus
  • Avoid being outdoors at dusk and dawn when mosquitoes are most active
  • Drain or treat standing water on your property
  • Dress in long sleeves and pants when in areas with heavy mosquito activity

Mesa County has reported a total of three human cases of West Nile illness so far this season. Last year, the county reported 127 cases and 4 deaths.

August 17, 2005

The Mesa County Health Department is announcing that four additional mosquito pools have tested positive for West Nile virus. This brings the total number of positive pools in Mesa County to five.

These results come less than one week after the first positive mosquito pool was reported near Rosevale Road. To date, there have been three human cases of West Nile illness and one positive horse in Mesa County. However, the level of West Nile activity that Mesa County is experiencing this year is approximately six weeks later compared to last summer.

At this time, risk of West Nile infection is considered moderate. Residents are strongly encouraged to take preventive action. Increased outdoor activity can lead to increased exposure to mosquito bites; the best way to avoid getting West Nile is to avoid being bitten by mosquitoes. This can be done by using an insect repellant that contains DEET, Picaridin, or oil of lemon eucalyptus. It is also important to treat standing water located on personal property. Free mosquito larvicide dunks are still available at several locations throughout the county.

August 12, 2005

The Mesa County Health Department received notification from the Colorado Department of Public Health and Environment that a mosquito pool and a horse have tested positive for West Nile virus in Mesa County . Mesa County has also reported a total of three human cases of West Nile illness so far this season. At this time last year, 104 mosquito pools were positive and 78 human cases had been reported.

The positive mosquito pool was collected on August 3 rd in the vicinity of Grand Junction near Rosevale Road . This area has produced the first positive mosquito pool for the last three years. A total of 326 pools have been tested so far in 2005 with 325 testing negative and one testing positive. The first positive mosquito pool from 2004 was collected on June 16th, approximately 2 months earlier than in 2005.

The positive horse was tested on August 1 st and is from the Mack area. This animal was not vaccinated against the virus. Last year, 1 horse tested positive for the virus in Mesa County.

At this time, the risk of West Nile infection is low to moderate. Health officials reported a significant increase in the Culex mosquito populations during the high temperatures in mid-July. The Culex populations appear to have reached their peak and are declining.

August 4, 2005

The Mesa County Health Department is announcing two additional human cases of West Nile virus. Both individuals are in their 60’s and were diagnosed with West Nile virus fever illness. One of these individuals believes that he was infected in California .

This brings the total number of West Nile cases in Mesa County to three.

  • 2 cases from Grand Junction , 1 from Palisade
  • Of the 2 Grand Junction cases, 1 is from Orchard Mesa

Last year at this time Mesa County had 103 positive mosquito pools and 27 positive birds. The Mesa County Health Department has tested 285 mosquito pools and four corvids so far this season. All have tested negative.

At this time, the risk of West Nile infection is low to moderate. Health officials reported a significant increase in the Culex mosquito populations during the high temperatures a couple of weeks ago. The Culex populations appear to have reached their peak and are declining.

Residents can reduce their chances of infection with West Nile virus by using insect repellant and can help reduce the number of mosquitoes by reducing standing water on their property. The Mesa County Health Department has free mosquito dunks available to homeowners at several sites across the County.

July 25, 2005

At this time, the risk of West Nile infection in Mesa County is low to moderate. One human case of West Nile has been reported, but over 175 mosquito pools have been tested for West Nile and all have been negative. In addition, there have been no positive corvids this year.

Last year, at a public hearing on July 24th, 2004 the Mesa County Health Department requested emergency funding from the County Commissioners. The funding was used for aerial spraying of adulticide for mosquito control. Ten human cases of West Nile illness were reported at this time last year. In addition 27 corvids and 55 mosquito pools had also tested positive for the virus. The risk of human infection resulted in a declaration of a public health emergency.

Surveillance throughout the Grand Valley indicates that there has been a significant increase in the Culex mosquito population. This is the type of mosquito that is the most common vector of West Nile so it is important for people to take personal protective measures. Those attending the Mesa County Fair this week should remember to take insect repellent with them when attending 2/28/07 your risk of being infected, please take the following precautions:

  • Use insect repellent containing DEET, picaridin, or oil of lemon eucalyptus
  • Avoid being outdoors at dusk and dawn when mosquitoes are most active
  • Drain or treat standing water on your property
  • Dress in long sleeves and pants when in areas with heavy mosquito activity

Last year, at a public hearing on July 24th, 2004 the Mesa County Health Department requested emergency funding from the County Commissioners. The funding was used for aerial spraying of adulticide for mosquito control. Ten human cases of West Nile illness were reported at this time last year. In addition 27 corvids and 55 mosquito pools had also tested positive for the virus. The risk of human infection resulted in a declaration of a public health emergency.

July 20, 2005

The Mesa County Health Department is announcing that a 76-year-old Grand Junction man has been diagnosed with West Nile fever. This is one of ten cases from nine counties which have been reported in Colorado so far in 2005. All cases were classified as West Nile fever. In 2004, Colorado reported 292 cases with 127 of those from Mesa County. There were four deaths from West Nile virus in 2004, all from Mesa County.

Dr. Aduddell says, “Risk is present in Mesa County, but at the current time is low.” Last year at this time Mesa County had 49 positive mosquito pools and three positive birds. The Mesa County Health Department has tested 136 mosquito pools and three corvids so far this season. All have tested negative.

Residents can reduce their chances of infection with West Nile virus by reducing standing water on their property. The Mesa County Health Department has mosquito dunks available to homeowners at several sites across the County.

July 11, 2005

Currently there has been no positive West Nile virus activity reported in Mesa County. Mesa County Health Department staff has been conducting surveillance to determine if and when the virus is present. To date, 86 mosquito pools have been tested for West Nile and all are negative. Three birds have also been tested with no positive results.

At this time last year, Mesa County was reporting 25 positive mosquito pools and eight positive dead birds. The first human case of West Nile virus was reported on July 13th.

Although West Nile activity has not been confirmed in Mesa County at this time, five cases have been reported in the state of Colorado. It is important to take preventive measures including using insect repellent, draining or treating standing water, avoiding being outdoors at dusk and dawn, and wearing light weight long sleeves and pants in areas with mosquito activity.

Please remember that free samples of mosquito larvicide are still available. Larvicide can be used to treat standing water that cannot be drained. Click here for more information.  


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