Chapter 3. Mosquitoes as Vectors of Diseases 1. Discuss the importance of mosquitoes besides their pure nuisance activity. Mosquitoes are not only a nuisance; they are a serious health threat to people and their pets and livestock. With just one bite, mosquitoes can transmit West Nile Virus and other viruses that cause encephalitis. They can also transmit heartworm disease to dogs and cats.
2. Name the major diseases the mosquitoes typically transmit in Georgia.
Most Common Arboviral Diseases in Georgia
West Nile Virus
Eastern Equine Encephalitis
Internationally acquired Dengue
Diseases Carried by Mosquitoes* Eastern equine encephalitis Heartworm Japanese encephalitis Chikungunya La Crosse encephalitis Barmah Forest virus St. Louis encephalitis Kunjin virus West Nile virus Ross River fever Western equine encephalitis O'Nyong-nyong fever Dengue Fever/DHF Yellow Fever Malaria Murray Valley encephalitis virus Rift Valley Fever Venezuelan equine encephalitis Elephantiasis/Filariasis *a partial list
Encephalitis with meningitis is known as meningoencephalitis.
Symptoms include headache, fever, confusion, drowsiness, and fatigue.
More advanced and serious symptoms include seizures or convulsions, tremors, hallucinations, and memory problems.
Encephalitis is most often caused by a viral infection.
3. Recognize and understand the importance of the term encephalitis.
West Nile Virus Most human cases occur in late summer and in autumn 1 ◦ Vector – Culex quinquefasciatus Highest Risk – the elderly Case Fatality Rate ~3 to 15% Yearly Occurrence (so far) West Nile virus was first isolated from a febrile adult woman in the West Nile District of Uganda in 1937. WNV first appeared in North America in 1999 in New York City. WNV was first detected in Georgia in 2001. other possible vectors : Culex spp Aedes albopictus Ochlerotatus spp 4. Describe the recent history of WNV in the US. 5. Describe the typical transmission cycle of WNV. 6. Name the primary vector of WNV in Georgia.
WNV is not the only mosquito-borne disease found in Georgia. We also have: LaCrosse Encephalitis (LAC) – small mammals Most human cases occur in July, Aug, & Sept Vector - Oc triseriatus , the treehole mosquito Highest Risk – children under 15 Case Fatality Rate ~1% St Louis Encephalitis (SLE) – birds Most human cases occur in late summer and in autumn Vector – Culex spp Highest Risk – the elderly Case Fatality Rate ~10% Eastern Equine Encephalitis (EEE) - birds Most human cases occur in late summer and in autumn Vector – Culiseta melanura ; a variety of bridge vectors Highest Risk – young children and the elderly Case Fatality Rate >50% Horse Fatality Rate 90-95% Sporadic Occurrence
Eastern Equine Encephalitis Eastern equine encephalitis virus (EEEV) is maintained in a cycle between Culiseta melanura mosquitoes and avian hosts in freshwater hardwood swamps. Cs. melanura is not considered to be an important vector of EEEV to humans because it feeds almost exclusively on birds. Transmission to humans requires mosquito species capable of creating a "bridge" between infected birds and uninfected mammals such as some Aedes , Coquillettidia , and Culex species 7. Understand the importance of EEE to mosquito control operators. 8. Describe the EEE transmission cycle.
Malaria 9. Name the most important disease transmitted by mosquitoes world-wide .
Malaria affected 30 percent of the population in the region when the TVA was incorporated in 1933. The Public Health Service played a vital role in the research and control operations and by 1947, the disease was essentially eliminated. The U.S. Tennessee Valley Authority (TVA) - The Integration of Malaria Control with Economic Development (1933) Mosquito breeding sites were reduced by controlling water levels and insecticide applications.
Dengue is a viral disease, commonly called "breakbone fever." Dengue epidemics were common in the 1800s and early 1900s in the U.S. The last major epidemic of dengue in the continental US occurred in Louisiana in 1945 with 62 confirmed cases, but authorities estimated that there were probably several hundred unapparent and/or unreported cases. In 1980, Texas recorded 23 locally acquired cases of dengue, and new cases occurred sporadically until 1999, when 18 cases were reported. Although dengue is not endemic now in most of the US, potential vectors are present in the southern US, and the virus is commonly reported in people entering the country from endemic areas of the tropics.
What is Yellow Fever? Initial symptoms include fever, headache, vomiting and backache. As the disease progresses, the pulse slows and weakens, and bleeding of the gums and bloody urine occur. Jaundice may also occur. Rural cycle Urban cycle Sylvatic cycle
11. Recognize the economic importance of dog heartworm in Georgia .
Mosquito Biological Data SPECIES LARVAL HABITAT HOST PREFERENCE OVER-WINTER BITING TIME FLIGHT RANGE Aedes albopictus AC, TH Humans, Large Mammals Egg D 100 to 300 yards Aedes vexans FW, GP, IP Humans, Large Mammals Egg C, N 1 to 15 miles Anopheles quadrimaculatus FW, GP, LM, RP Large Mammals Adults C 1/2 to 1 mile Coquillettidia perturbans FS, RE, LM, DD Humans, Mammals, Birds Larvae C 1 to 5 miles Culex nigripalpus GP, FW, DD Humans, Large Mammals Adults C 1/2 to 1 mile Culex quinquefasciatus AC, SCB, GRP Birds, Humans, Mammals Adults C, N 1/4 to 1/2 mile Culex restuans WP, GRP, DD Birds, Humans, Mammals Adults C, N 1 to 2 miles Culex salinarius AC, GP, LM, FS Birds, Humans, Mammals Adults C, N 1/4 to 5 miles Culiseta melanura FS, WP Birds Larvae C, N 1/2 to 2 miles Ochlerotatus canadensis WP, DD, FS Small Mammals, birds, reptiles Egg C, D 0 to 1/4 mile Ochlerotatus japonicus AC Humans, Mammals, Birds Egg, Larvae D Ochlerotatus sollicitans SM Humans, Birds Egg C, D 5 to 100 miles Ochlerotatus taeniorhynchus SM Humans, Birds, Mammals Egg C, N, D 2 to 40 miles Ochlerotatus triseriatus TH, AC, Red Maple Humans, Mammals, Squirrels Egg C 1/2 to 1 mile
Mosquito Myths Can AIDS be transmitted by mosquitoes? There is no scientific evidence to suggest that this is possible. Is it impossible? It is safe to say that the involvement of blood-feeding insects and arthropods is biologically insignificant if it occurs at all. 12. Recognize that AIDS is not transmitted by mosquitoes.
2. Discuss the importance of sanitation in controlling container breeding mosquitoes around homes . Most Mosquito Problems Start at Home: Home Owner Checklist
Cover or properly dispose of any water-holding containers.
Fill in or drain low places in yard.
Keep ditches, drains, gutters, and culverts free of weeds and trash.
Cover trash containers to keep out rain water.
Repair leaky pipes
and outdoor faucets.
Empty wading pools
weekly and store
indoors when not
Take proper care
of the backyard
Fill in tree holes
and hollow stumps.
Change water in
bird baths weekly.
Keep grass cut and shrubs trimmed to eliminate adult mosquito
3. Describe the proper technique for using insect repellents. The 5 D’s of DISEASE PREVENTION: Dusk Avoid being outdoors when Dawn mosquitoes are most active. Dress Cover your skin with protective clothing DEET Protect bare skin with mosquito repellent. Drain Empty containers holding stagnant water in which mosquitoes breed. Credit: J.Rutherford, Monroe CHD
7. Explain why source reduction is the best way to control mosquitoes. Source reduction ranges from the simple overturning of a discarded bucket or disposing of waste tires to complex water‑level manipulations in marshes. The removal or reduction of mosquito breeding habitat is often the most effective and economical long‑term method of mosquito control.
Prevention of breeding can be accomplished by removing surface waters from productive sites to reduce oviposition, manipulating shoreline water levels or flooding areas in which mosquitoes oviposit in the soil.
open marsh water management
8. List 3 modes of action for commonly used larvicides. Reduction of breeding sites is the most effective intervention for controlling mosquito populations. Because many sites cannot be controlled by source reduction, the next most effective intervention is mosquito larviciding.
Several materials in various formulations are labeled for mosquito larviciding, including:
biological control agents (Diptera‑specific bacterial based products),
insect growth regulators (IGR),
non-petroleum oils, and
monomolecular film agents.
Larvicide Modes of Action The timing of larvicide application is dependent on the nature of the control agent.
IGRs – Insect Growth Regulators
mimic an essential insect hormone
upsets the physiological molting process and kills mosquitoes in the subsequent pupal stage
reduce the water surface tension
the larvae are unable to attach to the water surface
the larva is not able to obtain air
must be ingested by the larvae
toxins are released by the mosquito gut pH
toxins damage the larval gut
9. Name the most common type of adulticide application conducted today. Treatment of adult mosquitoes (adulticiding) is the most visible practice exercised by mosquito control operations. This option is usually reserved for managing mosquito populations that have reached the adult stage in spite of efforts to intervene in the larval stage or when such treatments have not, or cannot, be conducted. Adulticides are often applied as ultra‑low‑volume (ULV) sprays in which small amounts (3 fluid ounces or less per acre) of insecticide are dispersed either by truck-mounted equipment or from fixed‑wing or rotary aircraft.
ULV droplets must drift through the habitat and impinge on flying mosquitoes in order to provide optimal control benefits
These applications are typically programmed to occur between dusk and shortly after dawn, when most beneficial insects are resting
These tiny droplets are unlikely to impinge on objects larger than mosquitoes because those larger objects' physical characteristics and size cause the droplets to drift around rather than deposit on them
The use of the fine ULV droplets means that there are literally millions more droplets to impinge on mosquitoes than there would be if larger droplets were used
10. Explain why the calibration of adulticide machines is so critical. Using the proper size range for the droplets makes it possible to increase control efficiency and decrease the risk of adverse impact to the environment and public health.
The primary reason a piece of equipment must be calibrated is to make sure it is operating in an effective manner and discharging insecticide in the correct amounts according to label recommendations of the particular insecticide.
11. Discuss the importance of insecticide resistance to a mosquito control operator.
Individual differences in susceptibility exist within each species.
Individuals who are substantially less susceptible may be present,
generally at low frequencies, in at least some insect populations.
In the presence of a insecticide, it is these substantially less susceptible
individuals that survive and reproduce.
Hence the development of a portion of a population of insects that are
increasingly tolerant to a specific type of insecticide.
Insect populations exposed to insecticides that have a similar mode of
action for extended periods can be expected to develop resistance.
How to prevent this resistance is an important aspect of mosquito control today.
Insecticide resistance is defined by differences in susceptibility that arise among populations of the same species exposed to insecticides.
The risk of developing insecticide resistance in insect populations can be minimized by the use of Integrated Mosquito Management techniques. These practices try to reduce the need for insecticide applications. In addition, it is prudent to rotate the type of insecticide, active ingredient and corresponding mode of action of the insecticides used against an insect population. While this may necessitate the use of a more expensive product for some applications, the long term benefits of preserving susceptibility far outweigh any short term costs. There are a limited number of insecticides registered for mosquito control.
12. List 3 larvicides and 3 adulticides. http://www.epa.gov/opp00001/health/mosquitoes/control.htm
Larvicides kill mosquito larvae. Larvicides include biological insecticides, such as the microbial larvicides Bacillus sphaericus and Bacillus thuringiensis israelensi s . Larvicides include other pesticides, such as temephos, methoprene, oils, and monomolecular films. Larvicide treatment of breeding habitats help reduce the adult mosquito population in nearby areas. Spinosad Methoprene - IGR Temephos - OP Monomolecular Films Oils
Mosquito adulticides are applied as ultra-low volume (ULV) sprays. ULV sprayers dispense very fine aerosol droplets that stay aloft and kill flying mosquitoes on contact. ULV applications involve small quantities of pesticide active ingredient in relation to the size of the area treated, typically less than 3 ounces per acre, which minimizes exposure and risks to people and the environment.