Vector & Vector-Borne Disease

The Surveillance Department performs weekly mosquito surveillance ranging from Desert Hot Springs all the way to the North and West shores of the Salton Sea. Surveillance of adult populations of mosquitoes provides quality control on larval abatement and directs operational intensity, modifications to methodologies, and the initiation of adult suppression. Control failures cause increase in adult mosquito population and spatially indicate areas of potential health risk due to associated amplification of arboviruses. Overall, the District uses 82 traps (62 CDC and 17 GT) for mosquito surveillance. Carbon Dioxide Traps

(CDC – CO2 baited traps)

This trap is used to selectively sample host seeking females and provides an efficient and productive means of collecting mosquitoes, both in numbers and in diversity of species captured. The carbon dioxide trap works by placing 1-3 lbs of dry ice in a Styrofoam container. Mosquitoes flying around the trap are drawn in by a 3” fan inside a PVC cylinder, run on an ac/dc motor and a 6-volt battery.

Gravid Trap (GT)

This trap attracts females by means of an oviposition medium (rabbit pellet/brewers yeast infused water) contained in a pan below the trap. This trap collects mostly the southern house mosquito, Culex quinquefasciatus that are ready to lay their eggs. Attracted by the oviposition medium, female mosquitoes attempt to land on the water surface to lay their eggs but are drawn into the collection chamber and trapped unharmed.

Mosquitoes collected from both types of traps are brought back to the Surveillance lab where they are sorted and identified to species. Two mosquito species found in the valley, Culex tarsalis (Western Encephalitis Mosquito) and Culex quinquefasciatus (Southern House Mosquito) are isolated from the collections and used for arbovirus testing for West Nile virus (WNv), St. Louis encephalitis (SLE), and western equine encephalomyelitis (WEE).

Arbovirus Surveillance

As part of it’s disease surveillance program, the Surveillance Department regularly collects mosquito samples from the environment to test for the presence of mosquito transmitted diseases (arboviruses) such as West Nile virus (WNv), Saint Louis encephalitis (SLE), and western equine encephalitis (WEE). These samples of mosquitoes are tested by the Center for Vectorborne Diseases (CVEC, UC Davis) to determine the prevalence of disease in the Coachella Valley. Testing results enable the District Operations Department to maximize and focus their larval and, if necessary, adult mosquito control efforts to the highest benefit of the Valley residents.

To further enhance and expedite the District’s ability to act upon infected mosquitoes with viruses, the Surveillance Department staff performs in-house testing (RAMP) on select mosquito samples for WNv. This test detects the presence of WNv antigens in the mosquito sample within hours of sample collection. These samples are also sent to CVEC for conformation.

Sentinel chicken flocks are stationed throughout the Coachella Valley for detection of WNV, SLE, and WEE. Biweekly chicken samples of blood collected on a filter paper are tested in house by ELISA (Enzyme-Linked Immunosorbant Assay). The ELISA test is an antigen capture assay that is able to detect the presence of antibodies produced by infected organisms and sent to California Department of Public Health (CDPH) for conformation.

Fly populations benefit from both urban development and agricultural activities in the Coachella Valley. The District’s goal is to prevent massive fly breeding, to suppress fly populations in certain areas to tolerable levels, and reduce the risk of fly role in mechanical transmitting certain diseases.

The Surveillance Department utilizes 25 baited fly traps throughout the valley to monitor seasonal changes in filth fly abundance. This information is then used by the Operations Department and the District Community Education Coordinator to promote education on fly prevention, sanitation, and control measures.

Eye Gnat Surveillance

Eye Gnats (Hippelates spp.) are very small nuisance flies that frequently congregate around the eyes and can transmit bacteria that cause conjunctivitis (pink eye). Eye gnats may be present all year if the weather is mild but are most numerous from March to November.

The Surveillance staff sets 22 eye gnat traps on a weekly basis. Traps are located through out the Valley at sites such as golf courses, date groves, residences and schools. Eye gnats are drawn to the trap by odors given off by egg bait at the bottom of the trap and are collected in a jar located above the egg bait. Trap jars are collected and the number of eye gnats is counted per trap. This information is then used by Operations Department staff to focus deployment of bottle bait traps to reduce and control the Valley eye gnat population.