1. Medical & Veterinary Entomology
from Vector Borne and Zoonotic Diseases. Stephen Higgs, ed. v. 1, No. 1.

2. Some Major Arthropod-Borne Human Disease Systems

3. protozoan, Plasmodium spp.

4. No. (%) of taxa as vectors of above diseases; Note: predominance of DIPTERA; all piercing-sucking!

5. Malaria, Disease Agent Life Cycle
Most important human disease (now matched by AIDS in some countries.)
Mosquitoes do not cause it; they are only the vectors (Anopheles spp.).
Disease organism = Plasmodium spp., sporozoites.
Taxonomic and geographical range of potential vectors is increasing with increased human mobility & climate change.
Resistance to treatments increasing in parasite; search for a vaccine continues.
Disease system can be analyzed and models constructed to predict epidemics.
Important Points
Malaria, Disease Agent Life Cycle
from Gullen & Cranston 2000

6. Arthropod Vector Aspects
Malaria System
Ecology Distribution Abundance
Population Biology
Growth Rate
Survival Rate
Behavior Feeding Rate
Anthropophily
Physiology Vector Competence
Anopheles mosquitoes are mostly tropical but ranges are expanding with warming climates.
Generally, epidemics follow sharp increases in vector numbers following rains &/or warm weather.
Anopheles populations can increase 100X in 14 days!
A small percentage of long-lived, multiple-biting females can comprise a large proportion of the infective vector population. The ability to bite more than once is of paramount importance in disease transmission.
Some species of Anopheles prefer to bite humans; many breed in urban environments.
Anopheles mosquitoes are resistant to the effects of the parasite, and parasite can reproduce in the vector.

7. Some Important Points About Arbo Diseases
In most systems, there must be a “reservoir” host where the disease agent survives and multiplies when not inside humans or vector. (In malaria there is no such 3rd host!)
The infective agent must be able to survive and multiply inside the vector’s body. (This is vector “competence”.)
The vector in it’s human-biting stage must be present in large numbers so the probability of an infectious bite is large.
The vector must have a tendency to bite reservoir host + humans or humans multiple times (malaria).
The vector must reach the human host and, as it feeds, inadvertently inject or provide entry for the disease organism.
Any of these relationships may be used as life cycle pressure points at which spread of the disease can be interrupted.

8. West Nile Virus
Early history: known only from Africa and a few minor outbreaks in Europe.
Discovered in New York in 1999.
Vectors: many mosquito species.
Intermediate host (& frequently dead-end) = birds, especially corvids.
Has now spread to most states.
by 2002: over 200 deaths.
Pattern of spread is irregular in many respects; no one knows exactly why.
See WA DOH slide show on Biol. 454 web site. (dated but still informative)

10. Bubonic Plague System Reservoir Phase
Disease organism: Yrsinia pestis, a bacterium.
Reservoir organisms: rodents, especially rats and ground squirrels.
Up to 120 flea species may transmit the bacterium.
Fleas get sick, digestive tract blocked, unable to feed normally.
Starving fleas may leave host, attempt to feed from other nearby animals, including pets & humans.
Tend to regurgitate when feeding, injecting bacterium into blood of host.

11. Bacterium transmitted by accidental flea bite.
Human Phase
Bacterium transmitted by accidental flea bite.
Contracted initially through flea saliva.
May be communicated aerially from patients with advanced, pneumonic form.
Survivable if treated in first few days, otherwise may be fatal.
Endemic in many parts of the world, incl. N. America.
Ecology: increasing human presence in wild areas (reservoir habitat) brings people and domestic animals into frequent contact with rodents.

12. Plagues Through the Ages: Fleas have changed the course of human history!
AD 541, Mediterranean countries, up to 10,000 deaths per day
AD 1347, Sicily (origin in europe) “Black Death:, throughout Europe, 25 million deaths, ~ 1/3 of population.
AD 1665, “Great Plague”
late 1800’s, “Third Pandemic”, last world-wide outbreak.
Recent, cases still regularly reported from many populous countries, including U.S.A., India.
Plague is easily treated with conventional antibiotics if detected in the early stages of infection.

13. Plague influenced religion & art.

14. Deaths due to outbreaks of plague in a European Renaissance town
Deaths due to outbreaks of plague in a European Renaissance town. Recurring local epidemics characterized the middle period of plague. Reliable records either do not survive or were not kept before this period.

15. The Bite about Spiders …an arachnologists viewpoint
Spider bites are over-diagnosed.
If your doctor says you’ve received a “spider bite” it may actually be due to something else.
Unless the spider culprit can be found and positively associated with the “bite”, you can not be sure.
There are many causes of “spider-bite”-like irritations.
Most doctors are not trained to recognize real spider bites.
Spiders rarely bite!
Of those that do, very few are dangerously venomous.
Spiders are difficult to identify to species.
Visit Rod Crawford’s “Spider Myths” web site.

16. Spider Bites black widow Laterodectus mactans
Range Native to Western N. America. Common in E.WA; not normally found in W. WA.
Habitat Dry rock piles, ledges, tree hollows, etc. Outbuildings, cellars.
Ecology Preyed upon by mud dauber wasps and other insects.
Bite Pain, swelling, nausea, rarely serious.

17. Bown Recluse (“Violin”) Spider
Loxosceles reclusa
Range Native to central states, epicenter = MO; highly unusual in WA.
Habitat Barns, uncleanly houses, etc.
Bite Can cause serious illness, tissue decay; worst cases: amputation.

18. Aggressive house (“hobo”) spider, Tegenaria agrestis
Range European, exotic in Pac. NW. infrequently encountered in W. WA.
Habitat mostly outdoors.
Ecology Preyed upon by more common T. gigantea, which is also exotic, larger, and common indoors, but not dangerous.
Bite similar to brown recluse.
Difficult to identify! Also common and not dangerous: T. domesticus.
male
Tegenaria gigantea

19. Human Bot Fly
Dermitobia hominis (Gasterophilidae: DIPTERA) Range tropical America Vector mosquitoes Hosts humans, prob. other primates (other mammals?)
from Evans, 1984
Phoretic eggs laid on mosquito; how the fly does it is still a mystery!
from Evans, 1984
larva burrowing in skin
surgical bot removal

20. Screwworm Fly, a native insect controlled by genetic manipulation
Cochliomyia hominivorax (Calliphoridae: DIPTERA)

21. Development of the Problem
Origin: Mexico and Central America
Native Hosts: native large mammals
Biology: myiasis-causing fly, larva lives on live decaying tissue; related to species used in wound-cleaning; infestations not usually lethal, hosts dispersed.
Ecological disruption: growth of cattle industry in late 1800’s, especially in N. Mexico & SW U.S.A.; proliferation of potiential hosts
Response: host -switching, population explosion on domestic cattle.
Economic Consequences: many herds decimated; millions of dollars lost.

25. Sterile Male Technique
Basic Method
Sublethal dose of irradiation to pupating flies.
Males sterilized but still able to mate.
Native population swamped with sterile males.
Wild females mated with sterile males lay no eggs.
Population crashes.
Assumptions
All males successfully sterilized.
Mating ability of males not compromised.
Wild females mate only once.
Wild females can not detect &/or preferentially avoid sterilized males.

26. Screw worm rearing facility; larvae fed beef by-products.

27. Screw worm fly larvae.

28. Loading screw worm “bombs” on a program aircraft.

29. Aircraft drop of screw worm fly cannisters.

30. Monitoring: demonstrating sampling kit in the field.

32. Also, screwworm fly successfully eradicated in Libya, 1980s.
Epitaph
Screwworm suppressed over
most of original range but not (yet?) eradicated.
Flare-ups increasingly common; may be caused by changes in wild fly response to sterile males especially ability of females to mate more than once and/or discriminate.
Costa Rica, 2000

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