Genetic control of vectors Flashcards
what is population suppression
elimination of reduction of a wild vector population - introduce sterile males or introduce a selfish genetic drive element that destroys essential genes in the vector
what is population replacement
replace a pathogen susceptible vector population with pathogen resistant o
describe SIT
-mass reared sterile males are released which do not produce viable offspring
what is needed to conduct SIT
- ability to mass rear insects
- sexing: physical or genetic, to make male only population
- sterility method-radiation
- method to release the like trucks
- ability to measure dispersal and mating competitiveness e.g. mark release recapture
- knowledge of chosen insect
what methods of sexing are there?
- physical separation based on pupal size difference between sexes(poor efficiency and labour intensive)
- y linked translocation of an insecticide resistance allele - females die in presence of insecticide
describe RIDL
Release of Insects carrying a Dominant Lethal
- Stock colony given repressor (tetracycline) and both sexes survive
- release males, in wild no repressor, so males mate with wt females and produce only viable male progeny
advantage of RIDL SIT over normal SIT
introduce a sexing mechanisms and sterility mechanism
therefore get faster reduction in population of females
limitations of SIT approaches
scale and cost of rearing
insects need to be transported to release site
fitness of SIT insects
immigration from non-treated areas- therefore only good for urban areas (aedes)
why would SIT not work well for anopheles
they live predominantly in rural areas, distributed across large areas, big risk of reinvasion and also the areas of resource poor
what is a gene drive and why is it important when transforming a whole population?
Any genetic element that is able to bias its own inheritance among offspring and spread in a population, conferring on it some desirable trait. It can spread genes that suppress or modify a mosqutio population.
Without a gene drive most genetic modifications would remain at a low freq in the population and be lost due to selection or drift.
name some natural examples of gene drives
transposable elements
sex distorters (changes % of sexes in popn)
Homing endonuclease genes
wolbachia
describe homing endonuclease genes
they are selfish genetic elements found in bacteria.
they target the dna seq, cut, and repair using intact chromsome as template.
repairs either by HDR (leads to homing) or NHEJ (indels)
differences in homing based gene drive in suppression and modification
suppression: disrupt an essential gene (female fertility gene, recssive lethal, mosq receptor for parasite)
modification: carry an effector gene as cargo- anti parasite immune gene or single chain Ab
what are the possible concerns with gene drive
- variants with resistance to endonuclease cleavage
- ecological and biodiversity effects (goal is malaria suppression no mosq extinction)
- stability concerns-losing the load(losing the effector) leads to spread of empty construct
what are the differences in selection pressures between suppression and modification
S: target of selection for resistance is vector
M: pathogen
What is Wolbachia pipientis?
Obligate intracellular symbiont that infects range of insects (females benefit)
Vertically transmitted (mother to baby)
blocks pathogens
manipulates reproduction of its host
How can wolbachia manipulate the reproduction of its host
- male killing
- parthenogenesis (asexual reproduction)
- feminization (males become females)
- cytoplasmic incompatibility
why does wolbachia infect so many species?
- it can jump between species (co-feeding, predation…)- jump into medically rel species
- manipulates reproduction of its host to spread into popns- release few individuals and spreads
- it can protect host from pathogens therefore preventing pathogen transmission
do all vectors with wolbachia exhibit the same wolbachia phenotype?
No- it is host dependent. wolbachia infection if native hosts shows little pathogen suppression. A threshold must be reached for it to spread.
describe wolbachia control in aedes
what are the pitfalls
- release wolbachia infected males (aegypti if trying to do dengue suprression)
- cytoplasmic incompatibility results in non-viable offspring-suppress population
pitfalls: logistics and continuous releases needed
describe wolbachia control in anopheles
- Embryonic or adult microinjection of wolbachia (does it have it naturally??)
- it reduces sporozoite rates in salivary gland
variable effects on parasite, not sure if good
compare wolbachia for use in suppression and replacement
suppression
Release males only
Reduce mosq population
need big release rates and reapplication needed
replacement
release m+f and can replace populations with non-transmitting individuals, they have wolbachia so cant transmit parasite
