How Do People and Animals Get West Nile Virus?
WN virus is transmitted to people and animals by infected mosquitoes.  Only certain species of mosquitoes carry the virus and very few mosquitoes are actually infected.  A mosquito first acquires the infection by feeding on a bird with virus in its blood.  The virus lives in the mosquito and is transmitted to a new host in the mosquito’s saliva when the insect bites a person or animal.

Humans and horses are incidental hosts for WN virus.  New evidence suggests there is a possibility of acquiring WNV through blood transfusion or organ transplants from an infected donor.  It has also been found in breast milk of affected mothers but these findings do not suggest a change in breastfeeding recommendations.

There is no documented evidence of bird or animal-to-person transmission.   However, it is still a good idea to avoid barehanded contact with any dead birds or animals and to use gloves, a shovel, or double plastic bags to dispose of or transport a carcass.  

The virus is most prevalent from May to October when mosquitoes are more abundant.

TRANSMISSION CYCLE OF WEST NILE VIRUS

	Bird to Insect
Reservoir Host: Birds		Insect Vector: Mosquitoes
	Insect to Bird			“Dead End” or Incidental Hosts: People and Animals

What Are The Symptoms of West Nile Virus?
Most people who are infected with WN virus have no symptoms whatsoever.  However, of those who become ill, symptoms can include fever, headache, nausea, body aches, mild skin rash, or swollen lymph nodes.  In a few cases, the disease will progress to encephalitis (inflammation of the brain) marked by headache, high fever, neck stiffness, disorientation, coma, seizures, muscle weakness, paralysis and rarely death.  The time between a mosquito bite and the onset of illness, known as the incubation period, ranges from 3-14 days in humans.  It is estimated that 1 in 150 people who are infected with WN virus will require hospitalization.  The elderly are particularly susceptible to clinical illness caused by WN virus.  There is no known specific treatment for infection with WN virus although supportive care is important.

WEST NILE VIRUS AND WILD GAME HUNTERS 
The extent to which West Nile Virus may be present in wild game is unknown.  Hunters should apply insect repellant to clothing and exposed skin according to label instructions to prevent mosquito bites.  

Gloves should be worn when handling and cleaning animals to prevent exposure to bare hands and meat should be cooked thoroughly. 

Which Animals Get West Nile Virus?
An infected mosquito can bite any animal, but not all animals will become infected.  The disease most often affects birds, but occasionally causes disease in other animals as well. 

Birds
Wild birds are the animals from which the mosquito vector primarily acquires the virus. Infection has been reported in more than 100 bird species.  Although many birds that are infected with WN virus will not appear ill, WN virus infection can cause serious illness and death in some birds.  The most severe illnesses are seen among the corvid birds, which include crows, jays, ravens, and magpies.  American crows constitute the majority of birds reported dead due to WN virus.

Horses
Horses are susceptible to WN virus.  The disease does not seem to be specific to a particular breed or age of horse.  Clinical signs of disease consist of central nervous system abnormalities similar to those caused by infection with eastern equine encephalitis (EEE) and western equine encephalitis (WEE).  EEE and WEE vaccines are available for horses and are recommended for use in the spring.  An equine WN virus vaccine is available for horses and is recommended.

West Nile Virus Prevention and Control

To decrease exposure to mosquitoes and the infections they carry:

• Avoid outside activity at dawn, dusk and early evening during the mosquito season (May to October).  This is especially important for the elderly and young children.
• Wear protective clothing (long pants and long sleeves).
• Apply insect repellent containing DEET according to instructions when outside.  Other products known to provide effective repellant protection for you may be used.
• Place mosquito netting over infant carriers when outdoors.
• Make sure that doors and windows have tight fitting screens.  Repair or replace screens that have tears or holes in them.

What is the Deschutes County West Nile Surveillance Program?

• Mosquito Testing
  Mosquitoes from selected sites in Deschutes County are sampled for the presence of WN, WEE, and SLE (St. Louis Encephalitis).  Our local mosquito vector control agency also monitors the abundance and type of mosquitoes.
• Mosquito Control
  Control of mosquitoes can focus on either larvae (immature) or adults.   Deschutes County concentrates on the aquatic (larvae) stage because the products available are less expensive, biological in nature, and very specific to mosquitoes.  An adult mosquito insecticide is also used when the numbers reach a point that warrants it.  The products used are either natural pyrethrin or synthetic pyrethroid that are approved by the EPA.
• Dead Bird Surveillance
  Oregon State University Diagnostic Laboratory has been funded to test corvids (crows, jays, and magpies) submitted through the Health Department for West Nile Encephalitis (WNE).  Birds must have been dead for less than 24 hours.  Birds killed on the road, in parking lots, or deaths related to possible pesticide spraying or injury will not be tested.

What Do I Do If I See A Dead Bird?
American crows are found throughout most or Central Oregon.  They have entirely black plumage, black beak, and black feet.  Adult size is 17-21 inches from tip of tail to beak.

If you find a dead corvid (crow, jay, magpie) between the months of April and October, please call the number below for instructions to determine is testing for WN virus is appropriate.  Do not touch the bird with bare hands.

MOSQUITO LIFE CYCLE

Egg Stage

Breeding site “source reduction”:
Drain standing water or fill puddles.  Clean up garbage.  Eliminate or empty “artificial water collecting containers”.  Drill holes in tires or store dry and under cover.  Store small boats upside down or covered.  Remove decaying vegetation and floating debris from ponds and treatment plant lagoons.  Change water weekly in birdbaths, stock tanks, animal water bowls or other containers.

 

Life cycle disruption:
Eggs, larvae, & pupae live in standing water.   Keep rain gutters, roadside ditches, etc. free of debris so water can flow.  Aerate “lily ponds” and swimming pools.

 

Mosquito predation:
Encourage natural aquatic ecosystems.  Introduce permitted fish that eat mosquito larvae in closed water bodies.  Clear decaying vegetation from shallow water edges and construct ponds to facilitate predation.

LARVAL STAGE
Source reduction & habitat modification (see 'egg stage').

Larvicide:
If elimination or modifications of breeding sites is not possible, consider applying larvicide to water bodies containing larvae.  Products permitted for use by the "lay person" are sold in garden supply stores, etc.  Certified pesticide applicators have several 'reduced risk' options including bacterial toxins specific to mosquitoes, monomolecular films that coat water bodies, methoprene insect growth regulator (IGR).

PUPAL STAGE
Source reduction and habitat modification (see 'egg stage').

ADULT STAGE

• Reduce exposure to biting mosquitoes.

• Apply mosquito repellents.  Read label instructions and precautions prior to use.  Pay attention to the type & concentration of 'active ingredients' in the product.

• Use yellow yard lights.  Insects don't see the light but people do.

Pesticides:
Consider applying mosquito adulticides (pesticides that kill mosquito adults) only when disease is detected or suspected in human population in the area.