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Essentials of vector-borne disease control

Essentials of vector-borne disease control. David M. Claborn, DrPH CDR MSC USN Assistant Professor Uniformed Services University of Health Sciences. Arthropod vectors in order of importance. Mosquitoes Ticks (order after this can be challenged ) Sand flies Fleas Lice

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Essentials of vector-borne disease control

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  1. Essentials of vector-borne disease control David M. Claborn, DrPH CDR MSC USN Assistant Professor Uniformed Services University of Health Sciences

  2. Arthropod vectors in order of importance • Mosquitoes • Ticks (order after this can be challenged) • Sand flies • Fleas • Lice • Cone-nosed bugs and tsetse flies • Filth flies and cockroaches

  3. Vector: def. • An arthropod that picks up a disease agent from one source and transmits it to a susceptible host. • Biological vector – pathogen undergoes some kind of change in the body of the vector • Mechanical vector-pathogen is just a hitchhiker

  4. Insecticide application techniques • Residual (inc. interior residual sprays) • Space spray (inc. aerial spray) • Thermal fog • ULV • Larval control • Insecticides • Bti, IGR (altocid) • Barriers and repellents

  5. Diseases spread by mosquitoes Malaria Arboviruses West Nile EEE, WEE, VEE, Dengue, Yellow fever, Japanese encephalitis Filarid worms

  6. Essentials of Mosquito Biology • Four life stages: egg, larva, pupa, adult • Require water during larval and pupal stages • Female takes blood meals for egg production; males feed on plant juices. • Different aqueous habitats harbor different mosquitoes.

  7. Anopheles Night biters Only vector of human malaria Larvae in clean water, often with vegetation Characteristics of a good malaria vector Long lived Takes multiple blood meals Anthropophagic Endophilic Those with only a few of these characteristics are less efficient, often secondary, vectors. Gross generalizations of mosquito biology: useful but dangerous

  8. Gross generalizations of mosquito biology: useful but dangerous (con’t) • Dengue and yellow fever spread by Aedes aegypti (yellow fever mosquito) • Day biter • Larval habitat in artificial containers • Move only a few hundred yards from original containers

  9. Gross generalizations of mosquito biology: useful but dangerous (con’t) • West Nile imported into the U.S. in late 1990’s. • Most widely spread arbovirus in the world. • Man is incidental host; birds are primary. • Bird deaths very useful in monitoring virus distribution and “activity” • Variety of possible vectors.

  10. Gross generalizations of mosquito biology: useful but dangerous (con’t) • Filarid worms spread by common house mosquito (Culex spp.) (others also) • Larvae are highly tolerant of polluted water. • Urban disease transmission increasing. • Gross pathology of elephantiasis usually associated with long-term exposure.

  11. Malaria Most efficient is interior residual spray (IRS) for many vectors. Insecticide-treated bed nets (ITN’s) Space spray for emergencies ULV Thermal fog Larval control (igr/bacterial) Dengue Removal of artificial containers Flower pots Tires Rubbish Interior space sprays Exterior space sprays Aerial Truck-mounted Ulv Thermal fog Control of insect borne disease through vector control

  12. Control of insect borne disease through vector control (con’t) • Control of Culex mosquitoes • Larviciding • Physical disruption of water surface • Polystyrene beads • Monomolecular oils • Aerial spray *Note that interior residual sprays may not be appropriate for some diseases and vectors. Why not???

  13. Ticks • Very slow feeders • High reproduction rate; high mortality • 1 host vs. 2 host vs. 3 host ticks • Saliva may cause tick paralysis in absence of pathogen. • Soft ticks (argasids) vs. hard ticks (ixodids)

  14. Tick-borne diseases • Bacterial • Lyme disease • Tularemia • Rickettsial • Rocky Mountain Spotted Fever • Viral • Congo Crimean Hemorrhagic Fever • Tick-borne encephalitis • Protozoan • Babesiosis (rodent-deer-tick-human)

  15. Disease prevention through tick control Treatment of hosts 4-poster for deer treated cotton for mice pet collars Residual insecticides in yards/animal trails Controlled burns Natural enemies (cure may be worse than the disease)

  16. Sand Flies • Small delicate flies of little importance in U.S. except: • Outbreak of leishmaniasis in Texas • Leishmaniasis in fox hounds in Virginia • Common vectors in areas of military deployment • Diseases • Leishmaniasis • Sand fly fever • Control similar to that of mosquitoes except larvae do not need water; grow in moist organic matter (animal waste)

  17. Fleas • Well known to veterinarians • Vectors of plague, murine typhus, intermediate host of tapeworms, etc. • Treatment of host and environment is key to control. • Insect growth regulators combined with other adulticide are method of choice. • For plague: fleas 1st; rodents 2nd.

  18. Lice • Body louse, head louse, pubic louse. • Only body louse is a vector of human disease, but very important. Morphologically similar to head louse. • Presence of lice is disease in itself (pediculosis) • Mass delousing for body lice not feasible anymore; clean clothing and baths usually sufficient; problem among refugees, prisoners and homeless. • Individual treatments for pubic and head lice.

  19. Cone-nosed bugs • Vectors of American trypanosomiasis in Central and South America • Often associated with native housing (thatched roofs and mud walls) • Control with residual sprays or “bug bombs” • Transmission of trypanosomes is through “posterior station” or fecal contamination of wound. • In Africa, trypanosomiasis is spread by the tsetse fly.

  20. Filth flies and cockroaches • Mechanical vectors of various pathogens. • Pathogens do not depend on insects for dispersal; mechanical. • Sanitation is the key to insect and disease control • Human waste and garbage management. • Proper food storage and refrigeration • Trapping and insecticides may be useful; baits for cockroaches.

  21. Bed bugs • Resurgent due to reduced use of residual insecticides in housing. • Although have characteristics of being good vectors (long-lived, multiple meals, anthropophilic, endophagic), they have not been proven to be vectors of disease. • Most likely pathogen would be Hepiatitis C, but little evidence. • Residual insecticides useful, but heavy infestations difficult to eliminate.

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