Lecture 2 - Vector Control Flashcards
When can targeting larvae in vector control (i.e. breeding sites) be effective?
It can be effective if breeding sites are easily identified and small in number.
Name four ways of targeting larvae.
- Environmental modification
- Removal or coverage of breeding sites
- Desert ploughing
- Larviciding
A form of environmental management and modification is the preventing of mosquitoes from laying eggs. How is this accomplished?
- Piped water
- Clean-up campaigns (disposing of waste, removing containers)
- Emptying domestic water storage containers on weekly basis
- Covering water storage containers with ‘insecticide treated nets’
What is usually the issue in environmental management and modification e.g. clean-up campaigns?
Community involvement is necessary. There’s no need to apply strategies if your neighbours don’t.
Explain the objective of emergency control in epidemics e.g. Zika, Dengue.
The objective is to kill as many adults as possible as quickly as possible to bring epidemic under control.
How can ‘emergency control’ be achieved in epidemics?
Name also a disadvantage of this control.
ULV (ultra-low volume) ‘space’ spraying of insecticides:
- Early morning, evening spraying for maximal effectiveness
- Vehicles or light aircrafts
But…
- Expensive
- Damaging to environment
Why can indoor residual spraying be successful (IRS)?
It targets insects resting, before or after blood feeding.
IRS is the spraying of insecticide on interior walls and has been successful for endophilic anthropophilic vectors, which is important in malaria control. What is a disadvantage about IRS?
Logistically challenging: person needs to be well trained to know right dosage (against resistance), etc. Pyrethroids are usually used.
Describe what insecticide treated nets (ITNs) are.
ITNs are bednets impregnated with insecticide. It provides personal and community protection.
What are some important requirements for ITNs?
- It requires community participation.
- It requires long lasting, low toxicity, fast acting chemicals (important for malaria control)
What are consequences of ITNs in mosquito behaviour?
What is something to keep in mind regarding to human behaviour?
Mosquitos are adapting to their environment (so they’re biting at an earlier time). People used nets as fishing nets, so they got holes in them, which makes the net not very effective.
What are the four ways of vector control?
- Emergency control
- Odour bated traps and targets
- Indoor residual spraying (IRS)
- Insecticide treated nets (ITNs)
What are problems of insecticide resistance?
- It can occur very rapidly
- There are very few insecticides available
- Increase in vector diseases
- Cross-resistance
Explain the two mechanisms of insecticide resistance.
Genetic: alterations in the target site, reducing insecticide binding.
Metabolic: increase in rate of insecticide breakdown through amplification or modification of enzymes.
Name 4 resistance management strategies.
- Rotations (IRS)
- Combinations (IRS plus LLIN)
- Mosaics (IRS)
- Mixtures (not yet available)
… Nog extra info zoeken…
How does bio-insecticide work, in which bacteria produce Cry and Cyt pore-forming toxins?
- Lyses larval midgut epithelial cells.
- Kills larvae.
Name two disadvantages of bio-insecticides.
- Efficacy declines steadily over a few months.
- Logistically difficult: frequent applications needed.
Biological control can be obtained by using predators: name the example of Vietnam used in the lecture.
Copepods to attack Ae. aegypti in large water storage containers.
What are characteristics of intracellular bacterium Wolbachia (from the ‘eliminate dengue program’)?
- Manipulates reproduction,
- Invades populations,
- Protects the host against viruses.
wMel strain (of Wolbachia) is injected in Aedes via sterile insect technique (SIT). Why?
wMel strain inhibits dengue virus from inhabiting in Aedes.
It’s a way of protection against dengue.
Name a few advantages of using wMel strain.
- wMel strain inhibits DENV
- Lower fitness costs
- Can invade populations.
Another form of dengue vector control is RIDL. Explain this concept.
RIDL = Release of male Insect carrying Dominant Lethal gene: Female descendants die as a result of inheriting female dominant lethal gene. –> Population reduction by reduced reproductive potential.
RIDL versus SIT:
Lower … than from irradiation
Reliable … (fluorescence)
May include genetic … prior to release (easy and …)
Reduced … hazard
… lethality (added benefit of competition with … larvae)
Lower fitness costs than from irradiation
Reliable genetic markers (fluorescence)
May include genetic sexing prior to release (easy and efficient)
Reduced escape hazard
Late acting lethality (added benefit of competition with indigenous larvae)
Bisex late-acting lethal line OX513A:
OX513A is a … DNA that acts in both … cell death in larvae and contains … gene.
Genetically modified male Aedes … have … strain. These flies pass on a self-limiting gene preventing the next generation from … .
OX513A is a recombinant DNA that acts in both late-acting cell death in larvae and contains fluorescent marker gene.
Genetically modified male Aedes aegypti have OX513A strain. These flies pass on a self-limiting gene preventing the next generation from surviving to functional adulthood.
Why is female flightless line OX3604C used?
It makes it easier to obtain the males: actin4 gene only expressed in female flight muscles.
Name three ways of vector control via the male sex.
- Natural bacteria that block/reduce malaria transmission
- X-shredder genes (all male offspring)
- Malaria refractory genes
Fill in:
Vector transgenesis has the goal to transform vectors with a gene whose … impair pathogen …, making them incapable of functioning as vectors of pathogen.
Vector transgenesis has the goal to transform vectors with a gene whose protein impair pathogen development, making them incapable of functioning as vectors of pathogen.
Explain paratransgenesis in one sentence.
Paratransgenesis aims at reducing vector competence by genetically manipulating symbionts (e.g. gut bacteria).
What’s another name for X-shredders?
X-shredders target and cut genes on X chromosome in male meiosis, so that offspring will be all male.
HEGs = Homing Endonuclease Genes driving Y chromosome.
