Mosquito Surveillance

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Mosquito-borne encephalitis viruses affect the well-being of Fort Bend county residents and represent a continuing public health threat. Although most attention is given to these infectious diseases when explosive outbreaks occur, scattered cases are reported each year. Fort Bend County Health & Human Services and Road and Bridge Departments have undertaken a mosquito surveillance in a coordinated effort. Mosquitoes are collected and submitted for testing by staff at the Road and Bridge Department. The laboratory tests results are received and reviewed by Health & Human Services staff. Targeted investigation and spraying follows any report that indicates a disease-causing mosquito may be in a specific area of the County. The immediate purposes of the Fort Bend County Mosquito Surveillance program are:
  1. Collection of vector mosquitoes to be shipped to the laboratory for identification and arboviral isolation studies, and
  2. Determination of vector mosquito breeding sites

Please note that although the treatment of the nuisance mosquitoes and surveillance for disease causing species are not the same, they are closely related. We must work closely with nuisance abatement programs if we are to adequately determine whether disease-causing mosquitoes exist.

Mosquito Characteristics and Lifecycle


Mosquitoes are the Culicidae family in the order Diptera, the true flies. There are around 3,000 species of mosquitoes worldwide over 50 of which are found in Fort Bend and Harris Counties. Mosquitoes have small slender bodies with six long legs and one pair of membranous wings. The main characteristic that distinguishes the mosquito from other true flies is its long, slender proboscis.


Mosquitoes make use of almost all types of standing water whether it is a permanent body of water or a temporarily created one from rain, tide or human use of water. The most important species to Fort Bend County Mosquito Surveillance is Culex quinquefasciatus because it is the vector of St. Louis Encephalitis. All Culex species lay eggs on standing water, but this one prefers very foul water such as cesspools, wastewater from any source, heavy oak leaf infusion in natural pools or artificial containers.


Mosquitoes go through complete metamorphosis. The lifecycle of the mosquito is categorized into four distinct developmental stages: egg, larva or "wiggler", pupa or "tumbler", and adult. The entire process usually takes between one to two weeks.

Biting Habits

Most mosquitoes bite after the sun has gone down; although there are kinds that will bite during the day as well. A variety of reasons attract mosquitoes to human beings: the carbon dioxide they emit, the color clothing they wear, as well as, perfumes and aftershaves.

Disease Transmission

In addition to being a nuisance, mosquitoes are known to transmit several kinds of disease. These diseases are Encephalitis, Dog Heartworm, Dengue Fever, Malaria and Yellow Fever. For Fort Bend county resident, St. Louis Encephalitis is the primary concern for the human population.

Role of Mosquitoes in Disease Transmission

Mosquitoes are pests and a part of life for Southeast Texans. Although, no one likes to be bitten, the more important issue is that mosquitoes can also transmit diseases to humans. The great majority of people bitten by infected mosquitoes only experience a slight illness commonly thought to be a case of the flu. It is only a small percentage that contracts a more serious case. People at greatest risk for more serious disease include the elderly (biologic risk factor), those living in low socioeconomic areas (environmental risk factor) and those with outdoor occupations (environmental risk factor). Symptoms of the disease include fever, headache, nausea, vomiting, stiff neck, trembling and changes in mental function such as sleepiness or disorientation. Symptoms usually occur five to 10 days after an infected mosquito bites the person.

West Nile Virus

In 1999, the West Nile Virus emerged as a new mosquito-borne disease in the United States. The arrival of the virus to Southeast Texas came in June of 2002, when birds in Harris County tested positive for the disease. In the summer of 2012, West Nile illness cases began to rise, specifically in the Dallas/Fort Worth Area. For specific information about West Nile Virus in Fort Bend County, please refer to our West Nile Virus page and the Centers for Disease Control and Prevention website.

For specific information regarding Fort Bend County Mosquito Surveillance, please contact Mr. Weldon Sheard at 281-342-0508 or email us at

St. Louis Encephalitis

Encephalitis is the most common mosquito-borne disease in the United States. Encephalitis means "inflammation or infection" of the outer lining of the brain.  St. Louis Encephalitis (SLE) is the primary concern in Fort Bend and Harris Counties. The Harris County Mosquito Control District was voted into existence after an outbreak of SLE in 1964. Individuals thought to have SLE should contact a physician immediately. A blood test is needed for confirmation, and most patients fully recover under the care of a physician. There is no cure. More information about SLE is available on the Centers for Disease Control and Prevention website.