Essentials of vector-borne disease control

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.