Tsetse Flies, Oestrids

AnnouncementsSpeaking Today: Lauren Torbett, Micah PepperSpeaking Next Thursday: Christie Lee ScottReading: Chapter 19About 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. Accidental (pseudomyiasis) – unusual situation results in a

non-parasitic fly inside a vertebrate.2. 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. Temporary Obligatory Myiasis – Larvae spend most of their

time off of the host, come to host only to feed.2. 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 non-human 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