The following notes are provided to provide an overview of the field of medical entomology. You are responsible for sections I (humans as food), II (insects and disease - the big picture), III (entomphobia and delusory parasitosis), IV (envenomization), V (dermatosis), VII (arthropods and allergies), and VIII (arthropods as vectors). You are not responsible for VI (myiasis). Do not panic about the material in VIII - read the notes and the book material (Ch. 7), and you'll do fine on the few questions I'll have on your final over this material. If you have any questions, please let me know.

Ch. 7: Blood-sucking and flesh-eating insects (and arachnids) and disease.

I. Humans as food - insects just want a hot meal

--> protein rich, carbohydrate poor
--> we're nutritionally incomplete!

A. skin: keratin

Flesh eaters:

· scabies mites: live entire life cycle in burrows in skin
· chiggers: pierce skin, inject saliva that dissolves skin, suck up mix
· screw worms: fly maggots invade wounds, eat necrotic tissues, then move into healthy skin and muscle
· bots and warbles (flies): maggots enter body by mouth or skin, burrow through tissues, develop in "boils" with air opening in skin
--> blow flies, flesh flies: maggot therapy --> eat only dead flesh
--> secrete allantoin --> antibiotic

Goo eaters: mucus is a protein solution

· eye gnats: feed on sweat, goo from body openings
--> gnat line (fall line)
· follicle mites: live entire life cycle within hair follicles
dogs and other animals: mange

B. body cavities:

Intestines: --> compete for partially digested food

· cheese skippers (flies): ingested with contaminated meat
· soldier flies, blow flies: ingested with rotting food
· dung beetles: crawl into rectum (canthariasis) (not myiasis)

Mucus, mucus membranes of nasopharynx, eyes, genitalia:

· blow flies, flesh flies: eggs laid at opening, maggots feed on
protein-rich mucus and tissues

C. blood:

--> insects (or arachnids) suck or lap blood or lymph

· mosquitoes: 2500+ spp.
· ticks: 800+ spp.
· black flies
· fleas: cat flea, rodent fleas, human flea
· sucking lice: head lice, body lice, crab lice
· sand gnats (no see 'ums, punkies, "sand flies")
· horse and deer flies
· kissing bugs (blood-sucking conenoses); bed bugs
· sand flies
· tsetse
· stable flies
· Congo floor maggots
· "buffalo" moth (vampire moths)

II. Insects and disease: THE BIG PICTURE

--> medical and veterinary entomology and acarology

--> medical and veterinary importance of arthropods

A. Arthropods as DIRECT agents of disease or discomfort

1. Entomophobia and delusory parasitosis
· arachnophobia
--> mild (random bug squishing) to severe psychosis

2. Annoyance ("fly worry") and blood loss from bites
· desanguination and exsanguination

3. Accidental injury to sense organs
· spines/fluids in eyes, etc.; cockroaches in ear

4. Envenomization
· stings: bees, ants, wasps, scorpions
· bites (venom): spiders, centipedes
· bites (saliva): ticks, true bugs
· urticating hairs

5. Dermatosis: living in the skin
· scabies mites, itch mites (baker's itch, straw itch, etc.)
· mange in domestic animals
· demodectic mange
· sarcoptic mange

6. Myiasis: fly maggots infesting living tissue
· dermal myiasis (furuncular myiasis)
· nasooropharyngeal myiasis
· intestinal myiasis

7. Allergies and related conditions (asthma, etc.)
· allergies to venoms, saliva
· allergies to insect waste (bodies, secretions, feces)

B. Arthropods as vectors

· vector: organism that carries infectious agent from one host to
another

1. Mechanical carriers: mechanical transmission
--> viruses, bacteria
· transmission an "accidental" result
· contamination of mouthparts, feet --> transmission
· examples:
· equine infectious anemia by horse flies
· tularemia by deer flies
· polio, etc. by house flies
· plant viruses by planthoppers, aphids

2. Obligatory vectors: biological transmission

--> viruses, bacteria, protozoa, nematodes
--> intimate assoc. between vector and microbe

· propagative transmission: viruses, bacteria

VIRAL:
· yellow fever (mosquitoes)
· dengue (mosquitoes)
· equine encephalitis viruses (mosquitoes)

MOSQUITOES DO NOT TRANSMIT AIDS

BACTERIAL:
· Lyme disease (deer ticks)
· Rocky Mountain spotted fever (dog ticks)
· the plague (fleas) ***
· epidemic typhus (lice) ***

· cyclopropagative transmission: protozoa
· malaria (mosquitoes) ***
· leishmaniasis (sand flies)
· sleeping sickness (tsetse)
· Chagas disease (kissing bugs)

· cyclic transmission: nematodes
· river blindness (black flies)
· human filariasis [elephantiasis] (mosquitoes)
· canine filariasis [dog heartworm] (mosquitoes)

· propagative: increase in numbers in the vector (reproduce asexually) [viruses, bacteria]
· cyclopropagative: increase in numbers (asexually) AND
metamorphose into infectious state [protozoa]
· cyclic: metamorphose in vector (develop) [nematodes]

3. Arthropods as intermediate hosts:

· dog flea and dog tapeworm

--> adult tapeworm lives in intestinal tract
--> reproductive packets [proglottids with eggs] shed in feces
"rice grains"
--> crawl off feces, dry up in area
--> flea larvae consume eggs, become infected with tapeworm
larva
--> flea grows up, tapeworm larva persists
--> flea gets on dog, dog eats flea, flea digested, tapeworm
released

4. Phoretic carriers of other offending arthropods
· human bot fly egg on mosquito!!

C. Arthropods as control agents of medically important arthropods

1. Competitors
· dung beetles in Australia controlled bush fly

2. Parasites or predators
· predaceous mosquito larvae
· mites for fly control in poultry houses


III. Entomophobia and delusory parasitosis: (Ch. 9: pp. 300-305)

A. entomophobia and arachnophobia

· insect fear · spider fear

· dislike of arthropods:
· 1/3 dislike them outside
· 4/5 dislike them inside
· 1/100 like them inside

· phobias: irrational fear of a thing or situation

· phase 1: anxiety, sense of doom, fear of loss of control
· phase 2: panic attack - rapid heart rate, shaking, cold sweat, etc.
· phase 3: motor responses - running away or freezing

· inherent (genetically determined) behavior?
--> genuine respect for the damaging potential of insects is a
wise thing
--> people who avoided insects gave birth to children who
avoided insects

· conditioned behavior: from direct experience OR from repeated
cautions (from parents/guardians)

· most cases: children 2-7 (most cleared by age 12)
· boys and girls equally afraid
· moderately rare in adults (< 3%)
· 2-9 X more common in females

· neurotic phobias can be paralyzing
--> insects are virutally everywhere!
--> attempts to rid homes of (mostly) harmless insects and
spiders using potent pesticides causes more damage
than the targets EVER would

· spiders feared the most
· bees & wasps second

B. delusory parasitosis

· delusion that insects, mites, "bugs" are living in or on the skin

· neurosis --> psychosis (but sometimes it's not delusional!)

· itching/scratching -->
scrubbing body with wire brush/treating body with excess
insecticides

· delusional person usually thinks bugs have set up homes in
their skin

· can "see" them crawling around; others can't see them

· will often contact physician; medical entomologist
--> provide skin scrapings/secretion samples

· careful exam of samples finds skin, hair, goo BUT no bugs

· typical presenters:

· member or members of group of middle-aged women who work
in tedious job with central air/no windows
--> one person will claim to being bitten, etc.; others follow

· drug abusers:
· "heebie jeebies" during alcohol withdrawls
· "crawling skin" during heroin, cocaine, barbiturate
withdrawls

IV. Envenomization (Ch. 7)

· most likely health effect of arthropods in SE Georgia

· probably most important direct effect of arthropods on humans in
North America in terms of fatalities

BUT

· numbers of deaths are LOW!

· total deaths by venom (all causes) = < 100 per year in US

· snakes: 30%
· bees (ants and wasps): 50%
· spiders: 10-15%
· scorpions: <2%
· centipedes: 0% in US
· miscellaneous: <3%

· effects of venoms: proteins that cause cellular changes

· neurotoxicity: paralyzes neurons
e.g., black widow spider venom, scorpion venom

· cytotoxicity: kills cells --> causes tissue death (necrosis)
e.g., brown recluse spider venom

· pain:
· pressure on neurons from vasodilation
· edema:
· swelling from leaky blood vessels
· redness:
· combination of leaky blood vessels and vasodilation near
skin surface

· anaphylaxis (anaphylactic shock):
· ~ 0.5% of people
· hyper sensitized to proteins in venom
· subsequent exposure --> systemic immune response
· venom induces release of histamines
· histamines cause swelling of tissues, mucus production
--> hives, difficulty breathing, coma, death
· injectable adrenaline (epinephrine) used for emergency
treatment

· causes of envenomization in this area (in order of likelihood):

1. · fire ants! (Hand out)
· Solenopsis invicta : the red imported fire ant
· individual stings (not bites!) are minor, but large numbers
often occur
· DO NOT "pop" vesicular lesion ("pimple") that forms
---> secondary bacterial infection
· most ants do NOT sting, e.g., carpenter ants
(bullet ant of central america)

2. · yellow jackets:

· nest in ground or in ball like structures on
structures or trees, up to 30,000 individuals/nest
· aggressively defend nest, actively forage around parks,
picnic grounds, yards --> attracted to sugar solutions
· second most common stinging insect on campus
· will not sting when foraging unless provoked
· sting is painful, lasts for 1-3 days, often causes swelling,
numbness

3. · paper wasps:

· build hanging nests, often on building eaves,
in garages/sheds
· aggressively defend nest, often enter houses
· sting painful, but much less so than yellow jacket, usually
gone within an hour

4. · honey bees, bumblebees:

· barbed stinger of honey bee needs to be carefully removed
to avoid emptying venom sac
· bumblebees nest in ground --> watch where you step!
--> bees are relatively uncommon around Statesboro

5. · velvet ants: wingless wasps

· "cow killer" - solitary, very painful sting, easily
recognized terrestrial wasp

6. · spider wasps: solitary large black wasps that flick wings in
characteristic way, very painful sting, feed on spiders

7. · cicada killer wasp: largest stinging insect in US, scary but
reluctant to sting, not especially painful

8. · urticating caterpillars:
· saddleback caterpillar, puss moth larva,
flannel moth larva, etc.
· poison spines or setae
· cause direct envenomization by contact:
· burning sensation followed by redness/rash
· cause indirect envenomization when inhaled:
· irritation of lungs --> coughing, burning, etc.

9. · brown recluse spider:
· Loxosceles reclusa
· common in Statesboro, but rarely encountered
· only bites if seriously compromised
· bites result in hemolytic and necrotic lesions
· may require surgery to prevent gangrene

10. · black widow:
· Latrodectus mactans
· very common in Statesboro

11. · scorpions:
· local scorpion about 1 1/2 - 2 in., sting is mild

V. Dermatosis: infestation of the skin (usually with mites)

A. demodex mites

· Demodex follicularum : the follicle mite, in hair follicles
· Demodex brevis : in sebaceous glands

· found in hair follicles/glands of 20-90% of people
· most common in eyelids, nose, other facial areas
· commensal organisms that usually do no harm
· blepharitis --> loss of eyelashes

· Demodex canis in dogs

· demodectic mange (red mange)
· may be serious or fatal!
· most dogs have the mite + staphylococcus bacterium
· some (immune-compromised) develop mange
· hair loss around muzzle, eyes, forefeet
--> severe hair loss, scabbing

B. sarcoptic mites

· Sarcoptes scabei (itch mite, scabies mite)

· found worldwide in humans
· more frequent in crowded, unsanitary conditions
· up to 75% infested in some groups
· up to 5% infested in developed countries during
outbreaks
· common within:
· families
· dormitories
· mental instituitions
· elder care facilities, child nurseries
· transmitted by intimate physical contact,
--> usually by sleeping with an infested person
· no transmission by bed linen

· infestation:

· mated female (about 0.4 mm) crawls onto skin

· burrows into skin in about 3 min.

· continues burrowing for about 2 months
· burrow reaches 3-4 inches long
· lays eggs at intervals along
· eggs hatch in a few days
· immatures crawl to skin and develop
· males mate with females

· more burrows made, esp. in:
· skin between fingers
· back of knees, elbows
· scrotum, penis
· breasts
· shoulder blades
· buttocks

· at ~ 1 month, itching becomes INTENSE
· immune response to:
· mite exoskeletons, saliva, feces

· treatment: proper use of insecticidal soap
· note: typical infestation is < 20 mites

C. chiggers (velvet mite larvae)

· about 1200 spp. worldwide; approx. 20 spp. feed on humans
(but normally feed on birds, rodents, reptiles etc.)

· most important in SE US:
· Eutrombicula alfreddugesi and E. splendens

· found in second-growth cutover areas
· wild blackberry patches
· forest edges, bottom lands

· chigger dermatitis:

· larval stage of mite climbs onto body
· inserts mouthparts into skin, attaches firmly
· reaction with skin forms "feeding tube"
· releases digestive fluid
· ingests cell fragments, contents
· site of bite itches after several hours
· digestive fluid causes itch
· at about same time, mite is working loose its mouthparts

­p;­p;> topical anesthetic (e.g., benadryl) lessens itching
---> insect repellent (with deet) prevents chiggers from
climbing on

VI. Myiasis: infestation of the body with fly maggots

· accidental myiasis:

· flies that can develop in other materials
· infestations of the digestive tract, nasal passages

· obligatory myiasis:

· life cycle of the fly requires that it consume fresh flesh
· treatment requires surgical removal

· screwworms (Cochliomyia hominivorax )

· blow fly with larvae that eats living instead of dead flesh!
· named for fatal case of nasal myiasis in 1883
(hominivorax = "human eater")
· major pest of livestock and humans in the South until the
1950s
· Texas (1935):
· 1.2 million livestock cases
· ~150 human cases
· eggs (~200) laid around almost any wounds or sores
· after hatching, larvae burrow head down into wound
· enlarge and deepen wound
· attracts more flies!

· eradication program in 1950s used sterile-male technique:
--> female only mates once
--> mass releases of radiation-sterilized male flies
--> females would mate with sterilized males
--> eggs wouldn't hatch
· still present in Mexico, points south
· regular reintroductions occur along border

· bots ("maggot") and warbles ("boil" or "wart"):

· found in rodents, ungulates, humans
· common in rodents, cattle, sheep, deer, horses
· rare in humans but seriously icky!

· adult flies resemble honeybees or bumblebees
· do NOT have a mouth!

· larvae cause dermal (mostly) or intestinal myiasis

· attempts to lay eggs by flies on animals causes "gadding"
· panic behavior in attempt to flee fly
· may run off cliffs, etc. to avoid flies
· may induce abortions in cattle!
· "gadflies"

· rodent bots: eggs laid around nests, larvae invade skin,
rarely found in humans

· human bot fly: Dermatobia hominis
· mainly a pest of cattle in C. America
· eggs laid on mosquitoes or other flies!
· when these land on a human (or cow), egg hatches,
larva burrows into skin
· lives in skin for ~ 1 month

· cattle grubs: eggs laid on hairs, larva migrates through
body, settles in skin on back
· cattle grubs can develop in humans, usually make
warbles on upper body (back, neck, chest, head)

· horse bot: lays eggs around mouth, larva crawls into mouth,
burrows into tongue, travels through body to reach
intestine
· in humans, larva can't finish development, wanders in
skin

· sheep bot: lays eggs around nose, larva crawls into nasal
passages
· in humans, larva can't finish development
· most human cases involve infestation of the eye

VII. Arthropods and Allergies:

Allergy:
· hyperimmune response to insect-associated allergens
· excess production and release of histamines

· mild: itchy runny eyes, runny nose, sneezing
to
· severe: hives, eczema, asthma, anaphylaxis

· response determined by:

1. individual susceptibility
2. previous exposure (frequency and amount)
3. method of exposure:
· skin (mostly venoms and saliva)
· inhalation
· arthropod feces with digestive proteins
· arthropod bodies and parts

· Two most common insect associated allergies:

1. house dust mite allergy:

· Dermatophagoides farinae (American house dust mite)
· D. pteronyssinus (European house dust mite)
· ~ 1/100 in. (0.25 mm) long

· present in EVERY home
· live on skin particles, fungus that grows on skin, pollen, food
crumbs
· typical bedroom may have 5000+ mites
· esp. common on rugs, upholstery, bedding, cracks in floors
· vacuum regularly (frequently!) to keep numbers low

2. cockroach allergy:

· cockroaches leave behind:
saliva, feces, egg shells, exoskeletons, "skin oils"
· cause inhalation allergies, food allergies (e.g., chocolate!!)
· German cockroach (Blatella germanica ) worst in US

VIII. Arthropods as vectors (pp. 202-237)

· BLOOD SUCKERS THAT TRANSMITS MICROBES
--> fleas, lice, mosquitoes, ticks, etc.

A. Fleas and the plague:

· "Ring around the rosies,
A pocketful of posies,
Ashes, ashes,
We all fall DOWN!"

· Fleas (Order Siphonaptera):

· blood-sucking ectoparasites of nest-dwellers (~1900 spp.)
· male and female fleas feed on blood

· not particularly picky feeders
--> most common flea (Ctenocephalides felis ) the cat flea,
is the most common flea biting people, dogs, cats

· most flea populations in the South are resistant to most
common pesticides
· extremely difficult to control, esp. in houses with rugs and dogs

· fleas hop on (up to 180X their height per hop!)
· take a quick blood meal
· hop off
· lay eggs in "nest"
· larvae (grub like) feed on:
· debris, pre-digested blood
· pupate and lay in wait (up to a year or more)
· vibrations make adults emerge from pupae
· the cycle starts anew

· THE PLAGUE:

· Yersinia pestis , the plague bacillus
· naturally found in rodents (rats, ground squirrels)
· transmitted rat-to-rat by flea bite

· in US, enzootic in ground squirrel populations
· human cases occur in high desert settings (Utah, Arizona,
New Mexico, Colorado, etc.)

· epidemics occur when rats and rat fleas become infected in
urban areas (Africa, Asia, [Europe])

· great plagues (pandemics):

500-600: 25% of population of S. Europe
Fall of the Roman Empire!

1300-1700: Great plagues of Europe
THE BLACK DEATH
Peasant revolts!
Wanton behavior!
Loss of church power!
All sorts of silly superstitions!
Death of about 1/8 of world's population!

1890-1910: The Asian Plague:

China --> India (6 million dead), etc.
China --> Honolulu (~ 10 dead BUT 4000 homes)
destroyed!
China --> S. America --> San Francisco (122 dead)

B. Lice and typhus

· sucking lice: Order Anoplura
· essentially permanent ectoparasites of warm-blooded vertebrates
· adapted to holding onto hairs of host
· males and females feed on blood as nymphs and adults

· three major species on humans

1. crab louse, Pthirus pubis

· sexually transmitted --> embarrassing itching!
· lives around pubic hairs

2. head louse, Pediculus humanus capititis

· common in school children, transmitted by combs, bedding
· permanent resident of head hair

3. body louse, Pediculus humanus humanus

· common in crowded unsanitary conditions, transmitted
by close contact, infested clothing
· identical in appearance to head louse but distinguished by
location
· not found on head, crawls onto body, feeds, then crawls
back onto clothes

· body lice also called "cooties" and "seam squirrels"

· only body louse associated with transmission of microbes

· epidemic typhus: infected louse or louse feces crushed into
break in skin --> bacterium enters blood

· outbreaks occur during periods crowding war
---> most important factor in defeat of Napoleon's army?

· campaign in Italy: outbreak in Naples --> DDT introduced


C. Mosquitoes: malaria, arboviruses, and filarial worms

· Mosquito diversity:

· Order Diptera: the true flies
· easily distinguished:
· proboscis for biting
· scales on wings, body
· 2500+ spp. worldwide: found anywhere there's fresh water
· arctic tundra
· ALL woodlands (rainforest, hardwood forests, pine forests)
· coastal marshes, swamps, ponds, deserts, mountains
· urban settings
· ~ 50 spp. in Georgia; ~ 10 are important pests
· Asian tiger mosquito (Aedes albopictus )
· introduced to Georgia in 1986
· now present in ALL counties
· bites during day --> common on campus

· Mosquito importance:

· annoying pest of humans and domestic animals

· transmitter of blood-borne pathogens:

· viruses: > 200 kinds

· worldwide importance:
· dengue (Caribbean, Latin America, Asia)
· yellow fever (Latin America, Africa)
· US importance:
· LaCrosse encephalitis (E. US, Appalachians)
· Eastern, Western equine encephalitis
(thoughout US)
· West Nile Virus

· mosquitoes DO NOT transmit HIV (AIDS virus)

· why think so?

· mosquitoes transmit viruses
· cultural biases against gay men, IV drug users
· fear of government intrigue

· why DON'T mosquitoes transmit HIV?

· no biological transmission:
· virus digested with blood
· no growth in mosquito when injected
· no mechanical transmission:
· blood on mosquito mouthparts miniscule
· < 1 millionth of required amount
· mosquitoes aren't flying syringes:
· blood pumped in food canal (ONE WAY)
· saliva pumped out salivary canal
· it simply doesn't happen: Belle Glade, FL study

· blood-borne worms (filarial worms)

· human filariasis (elephantiasis)
(L. Am., Africa, Asia)

· canine heartworm (throughout US)
--> if your dog isn't protected it WILL get it

· malaria parasites
(L. Am. Africa, Middle East, Asia)

· 1 million + deaths/year; 250 million new infections/year
· major cause of misery and poverty in the world
· cyclic disease makes regular work difficult

· Mosquito borne diseases and history:

· development of South delayed by yellow fever, malaria
· yellow fever affected Southern port cities every summer
· malaria endemic in lowlands

· yellow fever and malaria major impediment to Panama Canal

· malaria:
· Sir Ronald Ross in India (1890s) --> Anopheles mosquitoes
· mosquito control
· anti-malarial drugs (quinine, etc.)
· DDT --> malaria eradication program
· worked in US, Europe; failed elsewhere

· yellow fever:
· Walter Reed and Carlos Finlay (1890s)
· Aedes aegypti in urban settings
· control of container breeders

· Mosquito breeding habitats:

· containers (treeholes, old tires, trash, cemetery urns!)
· woodland pools
· snowpools, puddles, marshlands
· ponds, streams
· plants: pitcher plants, bromeliads
· waste water: sewage, manure lagoons

Mosquito life cycle:

· female feeds on blood to make eggs; male feeds on nectar
· female lays eggs:
· on water (floating eggs that hatch quickly)
· on damp stuff (sticky eggs that hatch "later")
· eggs hatch --> tiny swimming larvae emerge
· larvae [wrigglers] (most) feed on microbes, detritus in water
· some feed on other mosquito larvae!
· most develop in about a week
· active pupae in water [tumblers]
· come to surface, emerge, fly up and away
· males emerge first --> wait in swarm for females
· females rest in day (in shelters or on vegetation)
· attempt to suck blood at night (especially dusk and dawn)
· attracted to CO2, lactic acid, stinky bodies!
· everybody differs in attractiveness
· feed on: mammals, birds, reptiles, amphibians, fish!

Mosquito control:

· screens!
· behavioral modification (watch TV instead of sunsets!)
· repellents (with DEET)

· organized control: mosquito abatement districts
· control of breeding:
· eliminate container breeding (tire dumps, etc.)
· ditching of marshlands (BAD idea!)
· control of pondside vegetation
· control of water levels (reservoirs)
· use of mosquito-specific control agents:
· BTI · insect growth regulators
· control of adults:
· emergency only: if disease outbreak may occur
· sprays of insecticides from foggers, planes, etc.

· things that DO NOT work:
· zappers (electric bug shockers)
· ultrasonic devices
· garlic and eucalyptus
· B vitamins
· citronella
· Skin-so-Soft

D. Ticks and Lyme disease

· arachnids that feed on blood for each life cycle stage
(larvae [tiny], nymph, adult)

· > 800 spp. worldwide; over 15 spp. in Georgia

· most important:

· deer tick (black-legged tick): Ixodes scapularis
· transmits Lyme disease bacterium: bulls-eye rash,
joint pain, "flu"
· disease rare in Georgia:
· tick and bacterium found in coastal areas
· very common from Maryland north
· >10,000 cases since 1975
· Lyme disease also occurs in midwest, west coast

· American dog tick: Dermacentor variabilis
· usually most common tick on dogs
· transmits bacterium that causes Rocky Mountain spotted fever
· most common in NC, VA, SC, TN; present in GA

· Lone star tick (human ehrlichiosis)

· gopher tortoise tick (biggest tick in US)