Tsetse Fly Flashcards
Tsetse fly info?
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
Genus of tsetse fly
how many spp.?
Species and sub-species of trypanosome
Glossina
31 spp.
Trypanosoma brucei
rhodesiense + gambiense
Describe the 2 sub species of T.brucei
rhodesiense - transmitted by G. morsitans and g. pallidipes in Eastern and Southern Africa
- fewer reported cases but high mortality rate, likely hugely under-reported
- causes acute disease
gambiense - transmitted by palpalis and fuscipes in Central and West Africa
- 95% reported cases
- often not fatal but causes chronic disease
What do trypanosomes cause?
Human or Animal African Trypanosomisis (HAT) (AAT)
AAT is the biggest threat to livestock production in Africa with losses running 1-4 billion US dollars annually
Native ruminants are largely unaffected
How do trypanosomes reproduce?
Undergoes a cycle of development in the insect mid-gut and salivary glands where reproduction and multiplication is via binary fission
Name human epidemics
1896 - Uganda and Congo
1920 - Various countries
1970 - last major outbreak in Africa
2005 - 70,000 cases in Africa
2009 - 30,000 cases
2010 - Congo, Chad, Sudan and Uganda only countries with major problems
2012 - 80% of new cases of the most serious problems with the disease occur in Congo
What other organism can Tsetse flies act as vectors of?
Filarial roundworm (Wuchereria bancrofti)
- causes elephantiasis
- Affects 120 million worldwide in both Africa and South America
- Debilitating chronic condition
What do tsetse flies prevent and why is this important?
Prevent the integration of crop and livestock farming
Crucial to the development of sustainable agricultural production and food security for resource poor farmers
What is the 38 tsetse infested countries correlated with?
Most heavily indebted countries in Africa
Flies are therefore a major cause of hunger and poverty in many African countries
Describe the tsetse fly reproductive cycle
Low reproductive rate (K-strategists) - one egg at a time
- eggs develop and hatch in females after mating and go through at least 2 instarts (2-3 days) before third stage larvae emerge and burrow into the soil for pupation (Adenotrophic viviparity)
Pupation lasts 30 days within the soil
Describe the motility of tsetse flies
Don’t move much, largely driven by feeding
Utilise both olfactory cues and visual cues to detect hosts for feeding
What are the main control methods?
Treatment of humans (drugs) Treatment of animals (drugs) Use of trypanotolerant cattle Suppression/eradication of the fly using insecticides Sterile insect technique
Describe the human symptoms of trypanosomiasis
Haemolymphatic phase - Initially experience joint aches, headaches (1-3 weeks after bite)
Neurological phase- Advanced stages can penetrate the CNS and cause behavioural changes (weeks-months)
- once crossed the blood brain barrier usually results in death
- patients fall into coma and die
Which drugs can be used for the treatment of HAT and AAT
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
Why are trypanotolerant cattle not widely used?
Useful in areas with moderate to low populations
Not widely used however because the cattle tend to be smaller and produce less milk
