Transcript Tsetse Flies, Oestrids

Tsetse Flies, Oestrids
Announcements
Speaking Today: Lauren Torbett, Micah
Pepper
Speaking Next Thursday: Christie Lee
Scott
Reading: Chapter 19
About today’s lecture …
Tse Tse Flies
• Family Glossinidae
• One genus, Glossina, with
23 spp.
• All in subsaharan Africa
• Species are grouped by
generic habitat
– palpalis group of 5 riverine
spp.
– fusca group of 5 forest spp.
– morsitans group of 5
savanna spp.
• Vector of African
trypanosomiasis, “Sleeping
Sickness”
Tse Tse Fly Biology
• Both sexes blood feed
• Strong host preferences by species
– Humans are not preferred hosts of any
species
• Female usually only mates one time.
• Populations are often scattered at low
densities over wide areas.
• Flies congregate near hosts as a way of
mate location
Biggest Med/Vet Issue is
Trypanosmiasis
• Trypanosoma.
– 6 spp. cause sleeping sickness in
wild/domesitic animals.
– One of these, T. brucei, also infects humans
– It has two subspecies, each causing a
different disease
• T. b. gambiense – West African Sleeping Sickness
• T. b. rhodesiense – East African Sleeping Sickness
West African Sleeping Sickness
• Initially a skin lesion with
swelling
• Winterbottom’s sign – swelling
of cervical lymph nodes
• Eventually parasite enters CNS
• CNS involvement often results
in wasting condition.
• Untreated patients lapse into
stupor, convulsions, death.
East African Sleeping Sickness
• Acute onset of fever, headache dizzyness
• Instead of lymphatic disease, this is a circulatory
disease
• Early heart problems (tachycardia [rapid beating]
& arrythmia [abnormal heart rate])
• Biochemical interaction between immune
response and trypanosomes kill blood cells,
damage brain tissue (other organs too)
• Trypanosomes migrate to the CNS
• From there, similar to WASS but faster
Like most arthropod borne
pathogens, vector control is important
• Flies are sparse in most of their range, location
of hotspots is known.
• Eradication technology is available but not the
resources.
• Instead, main plan is to:
– reduce fly populations via insecticides, habitat
manipulation, etc.
– reduce trypanosome burden via trypanotolerant
livestock
– reduce human impact pharmacologically
Myiasis
•
•
Invasion of body tissue by fly larvae – not other fly
stages, not other insects.
Three kinds:
1.
2.
Accidental (pseudomyiasis) – unusual situation results in a
non-parasitic fly inside a vertebrate.
Facultative – opportunistic fly species, e.g. open wounds
invaded by carion flies
•
•
•
•
Primary – A species initiates myiasis
Secondary – A follow-on species continues myiasis after a
primary species
Tertiary – Occurs when there is Primary + Secondary + Imminent
host death. Host is nearly indistinguishable from a corpse.
Facultative species are “borderline parasites” attacking a
weakened host and continuing after host death as carion feeders.
3. Obligatory Myiasis
•
•
•
Fly larvae are always parasitic, parasitism is required
to complete life cycle
Usually very host specific, fly larvae have developed
mechanisms for dealing with healthy host defenses
(unlike previous 2 forms)
Related subtypes:
1.
2.
Temporary Obligatory Myiasis – Larvae spend most of their
time off of the host, come to host only to feed.
Incidental Obligatory Myiasis – Myiasis of an atypical host by
an obligate species. Eg. Sheep bot in a human.
Myiasis is also classified by the
affected host tissue
• Gastrointestinal – Digestive system, “Enteric”
refers to intestinal tract. Includes anus.
• Urogenital – urogenital openings to the outside.
• Ocular – eyes, esp. subconjunctival myiasis
• Nasopharyngeal – nasal & sinus passages
• Auricular – ear, inner & outer
• Cutaneous – generic skin
• Oral - mouth
• Furuncular – “boil-like” [Note not in text]
Gastrointestinal Myiasis
• Most human cases are
accidental (esp. from
eating uncooked fruit)
• Most veterinary cases are
from obligatory species
• cf. Table 18.1
• Most common in our area
are the horse bots,
Gasterophilus spp. (G.
intestinalis is most
common).
• Lay eggs on hair, horse
ingests eggs when they
groom themselves.
Urogenital Myiasis
• Usually involve blow
flies & flesh flies
• Typically facultative,
often following trauma
• Also associated with
urogenital infection.
Ocular Myiasis
• Most human cases are
incidental infestation from nonhuman bot flies
• Also called “Opthalomyiasis”
• Sheep bot is most common
agent and can cause
epidemics
– 1977 - Benghazi, Libya, had 80
human cases.
– Usually a combination of poor
sheep AND human health in
close proximity.
Can superficially resemble Romaña’s sign
Nasopharyngeal Myiasis
• Very similar to
opthalomyiasis
• A particularly
dangerous form as
larvae can migrate
to brain tissue
Auricular Myiasis
• Typically incidental or
accidental.
• Most human cases are
with the Old World
Screwworm
• Lay their eggs in
batches, larvae stay
together
Chrysomya bezziana larvae “en pabellón”
Cutaneous Myiasis
• The most common
form in humans
• In South/Central
America, mostly
caused by the
human bot fly,
Dermatobia
hominis
Oral Myiasis
• Fairly rare pathology
in humans
• Associated with poor
oral hygiene,
alcoholism, senility,
trauma with lesions,
severe halitosis and
others conditions.
• Caused by a wide
variety of species
African Furuncular Myiasis
• Also called “Tumbu Dermal
Myiasis”
• “Furuncular” means boil-like or
“pustule-like”
• Caused by the Tumbu fly,
Cordylobia anthrophaga
• Common in eastern Africa,
Humans are incidental hosts
• Form of cutaneous myiasis but
prevalence is rapidly increasing
• Fly lays eggs on damp clothes
on clotheslines. Can be
controlled by ironing clothes
(including bras).
Lotus seed pod
About the Flies:Calliphorid &
Sarcophagids
• Calliphoridae (Carrion & blow flies) &
Sarcophagidae (flesh flies)
– Most myiasis spp are necrophagous
– Only a few are obligate myiasis spp.
– Calliphorids include temporary myiasis spp. (Congo
floor maggot, nest blow fly).
– Tumbu flies are Calliphorids
– Most economically important spp are the
Screwworms, major livestock pests.
• Old World Screwworm Chrysoma bezziana
• New World Screwworm, Cochliomyia hominivorax
New World Screwworm
• Mostly a livestock pest
• Untreated myiasis results
in animal death
• Invasion produces more
flies that lead to more
infestation.
• Wounds become infected,
large number leads to
septicemia.
• Presence of flies leads to
gadding (stampedes).
Does not happen with bot
flies that use egg porters.
• Eradication has proven
possible with this species.
About the Flies: Oestrids (Bot Flies)
• Four Suborders
– New World Skin Bots, Cuterebrinae.
• Most are parasites of rodents & rabbits.
• Tórsalo, Human bot fly, Dermatobia hominis. S.
Mexico to Argentina
– Old World Skin Bots, Hypodermatinae
• Mostly parasitic on larger mammals.
• Most important species are the cattle grubs
(northern & southern).
About the Flies: Oestrids (Bot Flies)
• Four Suborders
– Nose Bots, Oestrinae.
• Sheep bot is the most common.
Can also infest human with very bad
results.
– Stomach Bots, Gasterophilinae
• Horse bots previously mentioned
Tiny antennae, no mouths
Human bot fly, Dermatobia hominis