Genetic control of vectors

Question 1

what is population suppression

Answer 1

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

Question 2

what is population replacement

Answer 2

replace a pathogen susceptible vector population with pathogen resistant o

Question 3

describe SIT

Answer 3

-mass reared sterile males are released which do not produce viable offspring

Question 4

what is needed to conduct SIT

Answer 4

• 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

Question 5

what methods of sexing are there?

Answer 5

1. physical separation based on pupal size difference between sexes(poor efficiency and labour intensive)
2. y linked translocation of an insecticide resistance allele - females die in presence of insecticide

Question 6

describe RIDL

Answer 6

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

Question 7

advantage of RIDL SIT over normal SIT

Answer 7

introduce a sexing mechanisms and sterility mechanism

therefore get faster reduction in population of females

Question 8

limitations of SIT approaches

Answer 8

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)

Question 9

why would SIT not work well for anopheles

Answer 9

they live predominantly in rural areas, distributed across large areas, big risk of reinvasion and also the areas of resource poor

Question 10

what is a gene drive and why is it important when transforming a whole population?

Answer 10

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.

Question 11

name some natural examples of gene drives

Answer 11

transposable elements
sex distorters (changes % of sexes in popn)
Homing endonuclease genes
wolbachia

Question 12

describe homing endonuclease genes

Answer 12

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)

Question 13

differences in homing based gene drive in suppression and modification

Answer 13

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

Question 14

what are the possible concerns with gene drive

Answer 14

1. variants with resistance to endonuclease cleavage
2. ecological and biodiversity effects (goal is malaria suppression no mosq extinction)
3. stability concerns-losing the load(losing the effector) leads to spread of empty construct

Question 15

what are the differences in selection pressures between suppression and modification

Answer 15

S: target of selection for resistance is vector

M: pathogen

Question 16

What is Wolbachia pipientis?

Answer 16

Obligate intracellular symbiont that infects range of insects (females benefit)
Vertically transmitted (mother to baby)
blocks pathogens
manipulates reproduction of its host

Question 17

How can wolbachia manipulate the reproduction of its host

Answer 17

1. male killing
2. parthenogenesis (asexual reproduction)
3. feminization (males become females)
4. cytoplasmic incompatibility

Question 18

why does wolbachia infect so many species?

Answer 18

1. it can jump between species (co-feeding, predation…)- jump into medically rel species
2. manipulates reproduction of its host to spread into popns- release few individuals and spreads
3. it can protect host from pathogens therefore preventing pathogen transmission

Question 19

do all vectors with wolbachia exhibit the same wolbachia phenotype?

Answer 19

No- it is host dependent. wolbachia infection if native hosts shows little pathogen suppression. A threshold must be reached for it to spread.

Question 20

describe wolbachia control in aedes

what are the pitfalls

Answer 20

1. release wolbachia infected males (aegypti if trying to do dengue suprression)
2. cytoplasmic incompatibility results in non-viable offspring-suppress population

pitfalls: logistics and continuous releases needed

Question 21

describe wolbachia control in anopheles

Answer 21

1. Embryonic or adult microinjection of wolbachia (does it have it naturally??)
2. it reduces sporozoite rates in salivary gland

variable effects on parasite, not sure if good

Question 22

compare wolbachia for use in suppression and replacement

Answer 22

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