Tsetse Flies, Oestrids

1. Tsetse Flies, Oestrids Announcements Speaking Today: Lauren Torbett, Micah Pepper Speaking Next Thursday: Christie Lee Scott Reading: Chapter 19 About today’s lecture …

2. 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”

3. 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

4. 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

5. 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.

6. 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

7. 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

8. Myiasis • Invasion of body tissue by fly larvae – not other fly stages, not other insects. • Three kinds: • 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.

9. 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: • 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.

11. 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]

12. 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.

13. Urogenital Myiasis • Usually involve blow flies & flesh flies • Typically facultative, often following trauma • Also associated with urogenital infection.

14. 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

15. Nasopharyngeal Myiasis • Very similar to opthalomyiasis • A particularly dangerous form as larvae can migrate to brain tissue

16. 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”

17. Cutaneous Myiasis • The most common form in humans • In South/Central America, mostly caused by the human bot fly, Dermatobia hominis

18. 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

19. 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).

20. Lotus seed pod

21. 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

22. 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.

24. 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).

25. 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

26. Tiny antennae, no mouths Human bot fly, Dermatobia hominis