Surveillance of mosquito populations and animal welfare provides vital information which helps guide efficient control of vectors and vector-borne diseases in Sacramento and Yolo Counties. The District closely monitors mosquito activity, climate change, and virus activity by constantly testing mosquitoes, sentinel chickens, and wild birds for the presence of a virus.

The District uses four types of traps: American light traps, mosquito magnet traps, red boxes and gravid traps which we set out in representative sites of all habitats in Sacramento and Yolo Counties. Our interactive map displays the general locations of our weekly traps and how many female mosquitoes were collected during the most recent cycle.

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American Light Trap	Magnet Trap
Red box	Gravid Trap

All traps are operated year round and the data is analyzed by District staff. Samples are collected weekly from all traps and transported to the District's main laboratory located at the Elk Grove facility.

The District surveillance system is designed to assess mosquitoes in urban and rural locations. Traps are strategically located throughout Sacramento and Yolo Counties.

Mosquito Magnet Trap
This trap was developed by American Biophysics in 1998. This device collects host seeking mosquitoes (adult mosquitoes looking for a blood meal from a preferred host). This trap is powered by liquid propane and is very portable. It emits carbon dioxide, water vapor, and heat that attract female mosquitoes to the trap. Once a host seeking female mosquito locates the trap it approaches the CO2 outlet and hovers. A fan draws the mosquito into a collection net inside the trap. MMTs are located in either urban or suburban sites. In addition to the surveillance traps, five MMTs are strategically located in the District rice culture regions from May until October to determine if ULV criterion is achieved. This unit operates around the clock.

Gravid Trap
This trap was developed by Reiter in 1983 and updated in 1987. This device collects gravid mosquitoes that are seeking a location to lay eggs. A special mixture of ground meals is added to the trap once a week to replenish the trap's attractiveness. When a gravid adult mosquito approaches this trap a fan positioned over the water pulls the mosquito up into a one way collection container. This trap is very attractive to Cx. pipiens, a potential vector of WNV. A photocell operates the trap from dusk to dawn.

American Light Trap
This trap was developed by Mulheren in 1934. This device collects phototactic (mosquitoes attracted to light) species. A 5 watt compact florescent light is used to attract adult mosquitoes to the trap. Once near the trap the mosquitoes are pulled inside by a small fan and down to a collection jar. A photocell operates the trap from dusk to dawn.

Red Boxes
Red boxes were developed to standardize collections spatially. Different researchers have used red boxes of varying dimensions. Largest catches are made in semi permanent walk-in red boxes which measure 4’ x 4’ x 6’ (Meyer 1985). Smaller 1’ x 1’ x 1’ foot boxes typically collect fewer specimens, but are readily portable. The entrance of the walk-in red box should be left open, draped with canvas, or closed with a plywood door. The canvas or plywood door should have a 1 or 2 ft gap at the bottom to allow entry of mosquitoes, while affording some protection from the wind and decreasing the light intensity within the box. The box entrance should not face eastward into the morning sun or into the predominant wind direction.

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Encephalitis Virus Surveillance

Mosquitoes are trapped and collected from the field. The collected females are then pooled together by species. Each pool contains a minimum of one to a maximum of 50 mosquitoes per pool. Each sample is tested for the presence of St. Louis Encephalitis, Western Equine Encephalomyelitis and West Nile virus by TaqMan real-time polymerase chain reaction (PCR).

Sentinel Chickens

By strategically placing sentinel flocks of chickens at unique locations within Sacramento and Yolo Counties the District is able to monitor and track virus activity. Within a few days after having been bitten by a mosquito infected with one of these viruses the chickens develop specific antibodies to that virus. They do not become ill or die. Blood samples from the chickens are routinely taken by laboratory staff and tested for the presence of these antibodies. Typically, the chickens are sampled every other week during the mosquito season (May until October) and once a month during November until April.

If the presence of these antibodies is confirmed by the California Department of Health Services laboratory there is an increased potential risk that these viruses could be transmitted to wildlife, equines or humans.

Dead Bird Surveillance

In collaboration with the California Department of Health Services (DHS), the District implements a dead bird collection program to enable arbovirus detection in Sacramento and Yolo Counties. District staff are trained to safely collect and identify dead birds that are found by the public and reported to DHS. Dead bird samples are transported to the California Animal Health and Food Safety laboratory at the University of California, Davis campus where necropsies are performed on acceptable bird samples. All tissue samples are tested for West Nile virus at the University of California, Davis Vector-Borne Disease Research laboratory.

Wild Bird Arbovirus Surveillance

The purpose of this surveillance program is to monitor the relative encephalitis virus infection in avian reservoir hosts and to identify local enzootic virus transmission to help predict the threat of transmission to people. The District started the wild bird encephalitis surveillance program in the spring of 1996. During the last nine years, the team has sampled more than 16,000 birds from 132 species to test for infection with arboviruses. Birds are captured using mist nets, crow traps, and ground traps. Each captured bird is aged, sexed, weighed, measured, and banded, and a small blood sample is collected. After processing, each bird is released. The District's overall recapture rate is just over 25 percent.

Malaria Surveillance

Malaria is a mosquito-borne disease, caused by a protozoan parasite that attacks red blood cells and destroys the cell during asexual reproduction. Malaria is transmitted to humans primarily by Anopheline mosquitoes. In Sacramento and Yolo Counties, there are two species of mosquitoes that can transmit the malaria parasite: Anopheles freeborni (the Western Malaria Mosquito) and Anopheles punctipennis (the Woodland Malaria Mosquito). Malaria cases are routinely reported to the District by the Sacramento and Yolo County Health and Human Services Departments.

The District laboratory responds to the reports by trapping mosquitoes for 24 hours in the area surrounding the malaria case. The mosquitoes are returned to the laboratory for identification, and all female Anopheline mosquitoes are tested for malaria parasites.

Lyme Disease Surveillance

The bacterium that causes Lyme disease is called Borrelia burgdorferi. The primary vector for Lyme disease in Sacramento and Yolo Counties is Ixodes pacificus, also known as the western black-legged tick.

Tick specimens are collected by dragging a flannel sheet along the side of a trail, a technique called flagging. The ticks are pooled and tested by indirect immunofluorescence assay (IFA). A sample is considered positive by IFA if one or more fluorescently stained spiral-shaped bacteria are present. Some positive samples have been confirmed using a polymerase chain reaction assay and by culture in liquid media.

Pesticide Management and Calibration

Pesticide resistance is of great concern in control programs. Pesticide resistance occurs when the same compound is used routinely and mosquito populations develop resistance to the specific compound. It is ideal to rotate treatment compounds used so that mosquito populations do not become resistant. When resistance develops in a mosquito population, previous treatments which had controlled the mosquitoes are no longer effective. Therefore, it is critical to monitor local mosquito populations to be sure we are effectively controlling the mosquitoes. To monitor this, the District performs numerous bioassay tests using both larvae and adults.

Research and Special Projects

Upon request the District provides wild-caught and colonized Cx. tarsalis adult mosquitoes to researchers at University of California, Davis and the Arbovirus Field Station for ongoing mosquito research. The District continues to collaborate with Dr. William Reisen on the ecology of West Nile virus in California.

Laboratory staff calibrates and performs droplet size analysis on all Ultra Low Volume foggers to assure that appropriate amounts of control compounds are applied when the equipment is used in the field.

Surveillance for Unmaintained Swimming Pools

The District works in cooperation with county agencies, municipalities, real estate associations, and the Foreclosure.com "Housing Outreach Partner Effort" to locate foreclosed, vacant homes with unmaintained swimming pools.