Some definitions: a. host: organism in which pathogen survives or reproduces b.

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Transcript Some definitions: a. host: organism in which pathogen survives or reproduces b.

Some definitions:
a. host: organism in which pathogen survives or reproduces
b. vector: organism that transmits (carries) microbes from
one host to another
insects vector many pathogens: viruses, bacteria, rickettsia,
protozoa, and nematodes
c. intermediate host: host that is utilized by non-sexually
reproducing stages (asexual repro common in microbes)
e.g., humans are the intermediate host for malaria
d. definitive host: host in which sexual reproduction of parasite
occurs, e.g., in malaria mosquito is the definitive host
e. reservoir: normal organism where disease persists
- often less virulent or non-lethal in reservoir species
e.g., monkeys are the reservoir for yellow fever in tropics
(1) bed bugs
* no diseases transmitted
* bite painless when feeding; often rather uncomfortable later
(swelling and itching)
* hide in crevices, feed at night
- very difficult to control; more common in run-down motels
(2) Chagas Disease from kissing bug (Triatoma),
a blood-feeding reduviid
* feed at night, often at night on lips, hence kissing bug
* feces defecated near feeding wound (later scratched in...bite area
is itchy)
* trypanosome (Protozoa): 10 million cases in South America
Psocodea (Suborder Troctomorpha)
Chewing or biting lice
* mostly on birds, few on mammals
* do not feed on blood no diseases
Sucking lice (Anoplura)...these are the bad bugs
* vector important human diseases
* "sucking" is a tip off (insects with sucking
mouthparts often involved in disease
Human body lice
a. head louse or body louse (Pediculus humanus)
* disease vector
* common in some public school systems
* without disease here in CT...mostly just a
nuisance and embarrassment
* in the past they have been of enormous
* epidemic typhus (a rickettsia) [also known as
trench fever] often resulting in high mortality
* relapsing fever
b. pubic louse or crab louse (Pthirus pubis)
* embarrassment and humiliation but no diseases
lice probably account for most preening behavior
in vertebrates
a. blood-feeders (vectoring diseases)
b. myiases: fly larvae living in or on their host
c. mechanically (externally on tarsi or mouthparts), carry diseases
e.g., house fly: typhoid and diarrhea
d. nuisance or annoyance
little acalyptrate flies (e.g., chloropids) that feed on lacrymal
Many families
Psychodidae (Phlebotomidae)
Muscidae (Glossininae)
Learn four of these diseases for the final
From Evans (1984) The Biology of Insects
A. Psychodidae (moth flies)
* subfamily Phlebotominae
* sand flies
* Central and South America
* vector leishmaniasis
- protozoan (Leishmania)
- cartilage disintegrates
- dermal lesions not so bad
- very dangerous form attacks abdominal tissue
- often fatal by the time it is diagnosed
* other species feed on eye secretions
* in tropics can cause River Blindness
B. Simuliidae (black flies)
* rasping mouthparts (leave circular
feeding wound)
* anticoagulants cause wound to bleed,
often after fly has departed
* often get a sizeable, itchy welt
* do not vector diseases in US
* transmit onchocerciasis (River
Blindness) in Africa
C. Culicidae (mosquitoes)
* most important family of medically
important Diptera
* ?kill more people every year than all
other put together
* vector many important diseases
* control measures of many insectborne diseases focused on vectors,
but such is especially true of
mosquito-vectored diseases
Asian tiger mosquito courtesy CDC
Yellow Fever
* virus
* reservoir: monkeys and humans
* yellow fever: destroyed Napoleon’s army in Cuba and Hispanola
before troops could arrive in Louisiana
* France sent 33,000 men; 29,000 died before making it to New
* bargain price on Louisiana
Purchase made possible by
Yellow Fever
* Panama Canal--French never completed it. Yellow fever and
malaria killed 50,000 Frenchmen
* Walter Reed discovered that mosquitoes vectored yellow fever
* Americans took on campaign to eliminate yellow fever in 1904
* William Crawford Gorgas, Walter Reed et al. began program to
eliminate mosquitoes: trenching (for fish), draining of marsh lands,
sulfur in all living quarters, screening in some domiciles, and oiled
aquatic habitats
* By 1906 (18 months later) cases of yellow fever were rare in the
Canal Zone
Filariasis (Elephantiasis)
* causal organism, a nematode,
* plugs up lymphatic system
* 300 to 400 million people infected
- 5% get some really gross
humankind's most prevalent infectious disease
> 250 million people infected each year
1+ million people die each year (up to 3 million)
control directed at vector, i.e., Anopheles mosquitoes
- for awhile malarial control (of mosquitoes) the glory of DDT
- DDT introduced during WWII in Europe
- dusted troops in trenches, no more typhus
- for awhile malaria was really knocked back
- non-target impacts were serious
Malaria from Wikipedia
Five species of the Plasmodium parasite can infect humans:
* Plasmodium falciparum most serious (often fatal)
* malaria caused by Plasmodium vivax, Plasmodium ovale and Plasmodium
malariae causes milder disease in humans that is not generally fatal.
* transmitted by the bite of a female Anopheles mosquito. When a mosquito
bites an infected person, a small amount of blood is taken, which contains
malaria parasites. These develop within the mosquito, and about one week
later, when the mosquito takes its next blood meal, the parasites are injected
with the mosquito's saliva into the person being bitten.
* after a period of between two weeks and several months (occasionally
years) spent in the liver, the malaria parasites start to multiply within red
blood cells, causing symptoms that include fever, and headache.
* in severe cases the disease worsens leading to hallucinations, coma, and
Other Blood Feeding (Biting) Flies
4. Tabanidae (horse and deer flies)
- anthrax (mostly in livestock)
- tulaeremia (Pasteurella)(bacterial)
Green-headed fly[email protected]/34503250
5. Muscidae (including Glossinidae)
- Glossina: African Sleeping Sickness
(Tsetse Fly)
6. Ceratopogidae (no-see-ums)
- salt marshes (Hammonasett) can be
unbearable nuisance
7. Rhagionidae (snipe flies)
8. Hippoboscidae (keds)
Dipteran Larval Myiases
* live maggots feeding on living organism
- i.e., where larva feeds on host (vertebrate tissue) adult is free-living
* some calliphorids in (genus Phaenicia) feed on dead tissue
and bacteria in wound
- defecate allatonin: an antiboitic substances which kills and
bacteria and sterilizes area around larva
* Napoleon's surgeon Larrey noted enhanced healing in wounds with
calliphorid activity
* important in Civil War in this country and later in Europe in World
War I in trenches
* larvae referred to as "surgical maggots”
* but most myiases are bad, e.g.,
- screw worms (calliphorids) in cattle tunnel through skin/hide,
resulting in agony and death
Larval Myiases
Oestridae: Bot and gad flies
Gastrophilinae: bot flies
e.g. horse bot fly
* mother lays egg on coat and horse licks fur and gets eggs on tongue
* first instar burrows into tongue
* second instar emerges from tongue and ends up in stomach, intestine
or rectum (right)
- larvae have hemoglobin for dealing with low oxygen tensions of gut
Larval Myiases
Oestridae: Bot and gad flies
Oestrinae: gadflies
* borrow in/live in skin for four months; form pustule at surface
* mature over three-month period then drop to ground
* rodents, especially around head and scrotum
* a number of species get into the nose and sinus cavities (very specific)
Human Bot Fly: (Dermatobia hominis)
* another Oestridae
* female captures mosquito (other flies
and lays egg on it
* larva crawls off when female mosquito
taps into host for blood (sense heat of host)
* swelling and itching
* somewhat painful by last instar
esp. when they twirl around;
* minor spontaneous bleeding of pustule
* take 5 to 10 weeks to develop…[email protected]/34503250
Hurd, P. 1954. Science 119: 814-815
* adults blood-feeding
* larvae detritivores in vertebrate nests
* in homes larvae may live in crevices
* larvae of some species require iron
- often get by feeding on feces of blood-feeding adults
- incentive to keep your couches and floors well vacuumed
Siphonaptera: Bubonic plague
* the black death
* bacterial disease: Yersinia pestis
* reservoir: rodents, not lethal in many rodent species
* vector: rodent fleas, esp. rat flea
- in rat (a non-host) bacteria plugs proventriculus
- fleas begin to starve and start biting indiscriminately
* symptoms: high fevers, swellings in lymph nodes (buboes),
black spots on skin (black plague), surrounded by
bright red ring
* other symptoms: unquenchable thirst, insanity…
Bubonic Plague
* 80% of infected people die in 5 days
* plagues: biblical accounts, Athens
* Europe 1348: 25 million people died
(25% of the population in Europe)
* England 1664: 50% of all people in
* can spread to lungs at which time
coughs and sneezes can transmit disease
* still present in western US: best not to
handle or dawdle around dead and dying rodents
Learn four of these diseases for the final
From Evans (1984) The Biology of Insects