Mosquito Surveillance
The Merced County Mosquito Abatement District conducts mosquito surveillance to monitor mosquito populations and detect disease activity early. Our laboratory team plays a critical role in protecting public health by collecting, identifying, and testing mosquitoes across the county.
How Our Surveillance Program Works
Our trained laboratory staff set and collect mosquito traps daily throughout Merced County. These traps help us understand what species are present, how populations are changing, and whether disease is circulating.
Encephalitis Virus Surveillance (EVS) Traps
EVS traps are used to monitor mosquitoes capable of transmitting West Nile virus.
- Traps are placed in strategic locations throughout the county
- Collected daily by our surveillance team
- Mosquitoes are brought back to the lab for processing
In the laboratory:
- Mosquitoes are sorted by species and sex
- Female mosquitoes of species capable of transmitting disease are separated
- These mosquitoes are grouped into samples
- Samples are sent to the DART Laboratory in Sacramento for testing
The results of this testing allow us to:
- Detect West Nile virus activity early
- Identify specific areas of increased risk
- Focus mosquito control treatments where they are needed most
Invasive Aedes Mosquito Traps
Invasive Aedes mosquitoes, such as Aedes aegypti, are aggressive day-biters that can spread diseases like dengue.
To monitor these mosquitoes:
- Traps are placed at residential properties with permission
- Traps are collected and checked daily
- Mosquito counts help us determine the extent of an infestation
This data allows us to:
- Identify neighborhoods with invasive mosquito activity
- Track how populations change over time
- Apply targeted treatments to reduce mosquito numbers
In the event of a travel-related dengue case:
- Additional trapping is conducted around the resident’s home
- Mosquitoes may be tested to assess local transmission risk
- Rapid response measures are implemented to prevent spread
Dead Bird Testing for West Nile Virus
Dead Bird Testing for West Nile Virus
Dead birds can help us identify where West Nile virus (WNV) may be circulating in our community.
Certain birds, especially crows, ravens, jays, and magpies, can become infected with WNV and may die from the virus. Reporting these birds helps the Merced County Mosquito Abatement District identify areas where WNV may be active and helps guide our mosquito surveillance and control efforts.
Can the Bird Be Tested?
Not every dead bird can be tested. For a bird to be eligible for WNV testing, it must:
- Have died within the past 24 hours
- Have shiny, non-sunken eyes
- Be free of insects and decay
- Be free of obvious trauma or injury
- Be a corvid, such as a crow, raven, jay, or magpie
If the bird meets these conditions, report it to the California Dead Bird Hotline:
Online: westnile.ca.gov/report
Phone: 1-877-968-2473 (1-877-WNV-BIRD)
What Happens After You Report a Bird?
The California Dead Bird Hotline will determine whether the bird qualifies for testing. If it does, the hotline will notify our laboratory staff to pick up the bird and collect a swab for West Nile virus testing.
If the bird qualifies for testing and you have reported it, please:
- Use a shovel or other tool to place the bird in a sealed plastic bag. Avoid handling the bird with your bare hands.
- Place the sealed bag near your front door or porch for pickup.
- Our laboratory staff will pick up the bird for testing.
Why Do We Test Dead Birds?
Birds play an important role in the West Nile virus disease cycle. Culex mosquitoes become infected when they bite a bird carrying the virus. Once infected, mosquitoes can spread WNV to people and other animals when they bite.
Corvids can become sick and die from West Nile virus. Finding and testing recently deceased birds can provide an early warning that the virus is circulating in an area.
If you find a recently deceased crow, raven, jay, or magpie that meets the testing criteria, please report it to the California Dead Bird Hotline.