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Mosquitoes & West Nile Virus
Mosquito Fact Sheet
West Nile virus is carried long distances by infected birds and then spread locally by mosquitoes that bite these birds. The mosquitoes can then pass the virus; primarily to birds, but also to humans and animals, particularly horses. There is a vaccine for horses, but none for humans. House pets do not spread the illness. Health departments across the state are closely monitoring human and horse illnesses and tracking the virus by testing dead birds and trapping mosquitoes. Mosquito season in Colorado starts in the Spring and ends in mid-September.
West Nile Virus Fact Sheet
West Nile Virus Fact Sheet (Spanish)
Fewer than 1% of mosquitoes carry this virus and fewer than 1% of people infected with the virus will develop severe illness. Symptoms generally appear 3 to 14 days after exposure. All residents of areas where West Nile virus activity has been confirmed are at risk, but people over age 50 seem to be especially vulnerable to the severe forms of disease. In rare cases, it can be fatal.
West Nile virus can cause encephalitis (inflammation of the brain) and/or meningitis (inflammation of the brain's lining). However, most infections are mild and symptoms include fever, headache, body aches, and occasionally include skin rashes and swollen lymph nodes. More severe infections may include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, muscle weakness or convulsions. Persons with these symptoms need to seek medical attention immediately.
Mosquitoes lay up to 250 eggs in still water, which hatch in 7 to 14 days. If standing water is eliminated weekly, many mosquitoes will be kept from breeding in the first place. This also reduces the number of mosquitoes around the home.
Home and Garden Checklist
Check for items that might hold water including wheelbarrows, tires, hubcaps, toys, garden equipment, pool covers, tarps, plastic sheeting, pipes, drains, boats, canoes and trash. Remove standing water in ponds, ditches, rain gutters, flower pots, plant saucers, puddles, buckets and cans.
West Nile virus is a disease that can be transmitted to humans by mosquitoes. It has been common in Africa, West Asia and the Middle East for decades. It first appeared in the U.S. in 1999 in New York. It has since traveled westward across the U.S. and now is in Colorado.
It is not common to get a severe case of this illness, and most infected people will not get sick or will have only mild symptoms. However, West Nile virus can be fatal. We want you to have the facts in order to ease your fears, and so that you can take appropriate prevention
How West Nile Virus is Spread
West Nile virus is carried long distances by infected birds and then spread locally by mosquitoes that bite these birds. The mosquitoes can then pass the virus; primarily to birds, but also to humans and animals, particularly horses. There is a vaccine for horses, but none for humans. House pets do not spread the illness. Health departments across the state are closely monitoring human and horse illnesses and tracking the virus by testing dead birds and trapping mosquitoes. Mosquito season in Colorado starts in the Spring and ends in mid-September.
West Nile Virus Fact Sheet
West Nile Virus Fact Sheet (Spanish)
Risks & Symptoms
Fewer than 1% of mosquitoes carry this virus and fewer than 1% of people infected with the virus will develop severe illness. Symptoms generally appear 3 to 14 days after exposure. All residents of areas where West Nile virus activity has been confirmed are at risk, but people over age 50 seem to be especially vulnerable to the severe forms of disease. In rare cases, it can be fatal.
West Nile virus can cause encephalitis (inflammation of the brain) and/or meningitis (inflammation of the brain's lining). However, most infections are mild and symptoms include fever, headache, body aches, and occasionally include skin rashes and swollen lymph nodes. More severe infections may include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, muscle weakness or convulsions. Persons with these symptoms need to seek medical attention immediately.
Prevention - What You Can Do
Mosquitoes lay up to 250 eggs in still water, which hatch in 7 to 14 days. If standing water is eliminated weekly, many mosquitoes will be kept from breeding in the first place. This also reduces the number of mosquitoes around the home.
Home and Garden Checklist
Check for items that might hold water including wheelbarrows, tires, hubcaps, toys, garden equipment, pool covers, tarps, plastic sheeting, pipes, drains, boats, canoes and trash. Remove standing water in ponds, ditches, rain gutters, flower pots, plant saucers, puddles, buckets and cans.
- Drill drainage holes in tire swings.
- Completely change water in birdbaths and wading pools weekly.
- Stock ponds and fountains with fish that eat mosquito larvae.
Personal Protection
- Avoid mosquitoes at dawn and dusk when they are most active.
- Wear long-sleeved shirts and long pants while outdoors.
- Apply insect repellent that contains DEET. Follow directions carefully. (CDC)
- Install or repair window and door screens to keep mosquitoes out.
- Personal Protection Checklist