Tabanids:%20Horse%20Flies%20and%20Deer%20Flies

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Tabanids Horse Flies and Deer Flies

• Announcements
• Reading Chaps 15, 18, 19.
• Speaking Today Mark Goodman, Charity Selbrede
• Speaking Next Tuesday Lauren Torbett, Micah
  Pepper

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Quiz Review

• Question 1. Any 2 out of 3.
• a. Black Fly Pupae (Fig. 13.2, p.190)
• b. Adult Fly
• c. Habitat Fast/Free flowing water Location
  Anywhere (Except Arctic/Ant)
• Question 2, 3, 4, 5 A, A, B, D
• Question 6. Grading 3 out of 4.
• a. Sporozoans
• b. Malaria
• c. Anopheles spp. mosquitoes
• d. P. falciparum most dangerous, different time
  intervals were the most common answers.

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Class Scores on Quiz 2
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Tabanids

• 4300 spp in 133 genera
• 3 subfamilies (one of which is not common)
• Tabaninae Horse Flies, livestock pests but do
  not often bite humans
• Chrysopinae Deer Flies, livestock AND people
  biters

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Blood Feeding

• Only females take blood
• Anautogenous species usually need a single large
  blood meal
• Anautogenous need a blood meal to make eggs
• Autogenous can make eggs without a blood meal
  using reserves left over from larval stage
• Facultatively Autogenous can make eggs without
  a blood meal but, with a blood meal, typically
  make more eggs with higher viability
• Attracted to host by a variety of visual,
  chemical, and thermal cues

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Tabanids are Classic Telmophages

• Mouthparts use a scissor action to cut skin
• Saliva produces anticoagulant vasodialator
• Lap up the pool of blood
• Wound often continues to bleed after the fly has
  fed (attracting other insects)
• Painful bite means that the flies are often
  selective on the body part that they target.

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Medical/Veterinary Significance

• Nuisance
• Allergy from saliva
• Secondary Infections
• Transmit a variety of pathogens to livestock and
  deer
• Most of the serious problems are in the tropics
  of Africa and S. America
• Two significant human diseases

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Tularemia

• AKA deer fly fever or rabbit fever
• Etiological agent is the bacterium, Francisella
  tularensis
• Ticks are more important vectors (of this and a
  couple of other diseases)
• Can also be contracted by contact with blood of
  infected rabbits
• Causes a distinctive septicemic ulcer requiring
  antibiotics.

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Especially bad in Arkansas and Missouri
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Tularemia in humans has declined

• Decline in wild rabbit hunting,
• Greater use of insect repellents
• Greater public awareness
• Note many anecdotal reports of increasing
  rabbit populations in US suburbs.

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Loiasis

• Most important tabanid-transmitted disease in
  humans
• Etiological agent are filarial nematodes in the
  genus Loa, esp. L. loa.
• Transmitted by deer flies in the genus Chrysops
  in Western Central Africa.
• In some areas gt 90 of people are infected.

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Transmission Cycle

• Humans are definitive hosts
• Flies ingest microfilarae
• Microfilarae penetrate fly gut wall, migrate to
  fat tissue, grow to 3rd instar
• Third instars migrate to fly head/mouthparts
• When fly feeds, larvae exit burrow into human.
• Live beneath skin, esp. in the thorax and scalp
  particularly in eyes.
• For this reason, human loiasis also called eye
  worms

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Eye Worms

• Loa loa extraction from human eye
• Another extraction

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Interaction with Ivermectin Onchocerciasis

• Patients treated with ivermectin for
  onchocerciasis who also have loa loa sometimes
  develop encephalopathy (generic brain disorder)
• Mostly men from Cameroon
• Most Serious Adverse Effect (SAE) of Ivermectin
  treatment
• Includes an unknown but suspected involvement
  with malaria
• Involves filarae migrating from subcutaneous
  tissue to brain tissue.
• Recent mass treatment of 800,000 people resulted
  in 65 of these SAEs

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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

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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

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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

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West African Sleeping Sickness

• Initially a skin lesion with swelling
• Winterbottoms sign swelling of cervical lymph
  nodes
• Eventually parasite enters CNS
• CNS involvement often results in wasting
  condition.
• Untreated patients lapse into stupor,
  convulsions, death.

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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

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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