Tsetse AR

Question 1

Tsetse fly info?

Answer 1

Inhabit mid-continental Africa between Sahara and Kalahari deserts
Vectors of trypanosomes (protozoans)
Associated disease killed 9,000 people in 2010 down from 34,000 in 1990
Estimated deaths are higher due to unreported cases
Fossil specimens date back at least 30 million years

Question 2

Extra info Tsetse background

Answer 2

• Live 90-100 days - in lab conditions can produce 10 offspring in a lifetime - Thought that the huge abundance of tsetse fly in some are prevented humans hunting a number of big animals to extinction

Question 3

Study into tsetse reproduction

Answer 3

Langley, 1977 After single mating, viable sperm is stored in the spermathecae for the rest of the females adult life

Question 4

Study into burrow location

Answer 4

Solano et al., 2010 - Females use aggregation pheromones to detect suitable sites - larvae burrow 1-5cm into the ground to pupate - takes ~30 days for pupae to develop and emerge

Question 5

Study into trypanosomes defence mechanism

Answer 5

Zambrano-Villa et al., 2002 - Immune response to Trypanosomes is antibody dependent - Parasite counters this through continually changing glycoproteins (Variable Surface Glycoproteins, VSGs)

Question 6

Study into SIT Zanzibar

Answer 6

Vreyson et al., 1998 - Areawide integrated tsetse eradication project initiated in 1994 to eradicate the tsetse fly (Glossina austeni) from the island of Unguja, Zanzibar - Sterile male flies were mass produced at the Tsetse and Trypanosomiasis Research Institute (TTRI) in Tanzania

Question 7

Suppression of tsetse on Unguja

Answer 7

Vreyson et al., 1998 - Suppression was initiated in 1988 by applying residual pyrethroids as a pour-on formulation on livestock and by deployment of insecticide impregnated screens on forested areas - This was then followed by release of Gamma sterilised male flies by light aircraft

Question 8

Dispersal of sterile males

Answer 8

Vreyson et al., 1998 - Dispersed twice a week in carton release containers along specific flight lines - Max total release time was 2 hours where 600-1000km/squared could be covered - More than 8.5million sterile males were released by air from August 1994 to December 1997 - Released at different dispersal rates dependent on the stability of the habitat and the abundance of the indigenous tsetse population i.e. <30 sterile males per km/squared in mid-northern part if the island compared to >500 in the primary habitat of the Jozani Forest

Question 9

Ratio statistics Zanzibar

Answer 9

Vreyson et al., 1998 - Sterile to indigenous male ratio of 50:1 was obtained in mid-1995 increasing to 100:1 by the end of 1995 - Effect on female population: proportion of sampled females with egg in vitro in embryonic arrest or uterus empty due to expulsion of dead embryo rose from 25% first quarter to >70% in the last quarter of 1995 - Additionally age distortion skewed in favour of older females (>4 ovulations) by the end of 1995

Question 10

Population crash Zanzibar

Answer 10

Vreyson et al., 1998 - Last nulliparous female captured in week 5 of 1996 - Population crashed in the beginning of 1996 - Last indigenous male and female trapped in weeks 32 and 36 respectively - 6 fly generations elapsed between the last catch of indigenous flies and the end of sterile male release in December 1997

Question 11

Study into SIT in other African countries

Answer 11

Meyer et al., 2016

• Pan-African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC) was initiated in 2000 with the aim of eradicating the tsetse fly from Africa
• Planned to use SIT on a large scale in three countries (Burkino Faso, Ethiopia and Uganda)
• Only Deme Valley, Ethiopia being treated so far
• SIT is hugely expensive to carry out
• As well as this there is 2 main reasons for the delays in these countries
  i) No insect rearing facility currently in a position to produce the weekly amount of sterilised males neccessary to implement SIT on such a large scale
  ii) SIT should be applied on a previously suppressed and naturally or artificially isolated tsetse population which it has not been in these areas

Question 12

Study into alternate methods of tsetse control

Answer 12

Tirados et al., 2015

• Odour baited traps

o trialled in Uganda at a density of ~6 traps/km squared

o found to reduce tsetse population density by >90% in 3 months

o relatively inexpensive method of control

• Insecticide treated cattle

o Cheapest method

o requires large amount of cattle, large enough to be an important part of the tsetse diet

Question 13

Study into sleeping sickness

Answer 13

Checchi, 2008 - Diagnostic tools too complex to integrate into primary healthcare - As a result haemolymphatic stage usually already progressed to neurological stage before detection - Untreated patients have an almost 100% risk of dying within 1-4 years

Question 14

Treatments for HAT and AAT?

Answer 14

HAT
first stage - intravenous or intramuscular pentamidine for T.b. gambiense or intravenous suramin for T.b. rhodesiense
Second stage - eflornithine or nifurtimox
AAT
Drugs most important control method in Africa
- 35 million doses are given every year to animals
- includes diminazene
- resistance has developed as result of overuse

Question 15

Study into the main medication for HAT

Answer 15

Burri and Brun, 2003 - Efloronithine used to treat HAT but has numerous side effects - Similar to cytotoxic drugs used for treatment of cancer - Side effects include convulsions, nausea, vomiting, diarrhoea and bone marrow toxicity

Question 16

Study into trypanosome resistance

Answer 16

Dagnachew et al., 2015

• Resistance to diminazene aceturate (DA) and isometamidium chloride documented in trypanosomes in Ethiopia against the recommended doses of both trypanocidal drugs