Fecundity

Effects on fecundity of bloodmeal source and insecticide

New combination long-lasting insecticidal nets are being developed that are treated with a pyrethroid and pyriproxyfen, an insect growth regulator that disrupts the maturation of oocytes in mosquitoes exposed to the net. Resistant mosquitoes don't die but take a blood meal, yet have a reduced number of viable eggs. This can be modeled, assuming that the effect lasts only for the duration of the present gonotrophic cycle, by introducing PFi, the probability of eggs being fertile after biting host i. Then Pdff = Sum(PAiPBiPCiPDiPEiPFi) is the Probability of finding a host and surviving the feeding cycle and producing fertile eggs. (Analogous to Pdf= Sum(PAiPBiPCiPDi*PEi)).

This has effect only with the simple dynamic model option active (described in [ https://github.com/SwissTPH/OpenMalaria/wiki/ModelMosqPopDynamics ] and in [ https://github.com/SwissTPH/openmalaria/wiki/docs/MosquitoLifeCycleSimplePer.pdf ]), where equation 2b y(t) = bPdfx(t-tau); would be modified into y(t) = bPdffx(t-tau).

From Schema 38 onward, it is possible to simulate fecundity-reducing effects of insect growth regulators (e.g. pyriproxyfen) applied on bed nets (module: ITN) and as used in IRS (module: Generalized Vector Intervention (GVI)) and module: IRS. For ITNs, this can be done both via the classic specification, and via the logit specification. In Schema 38, a single insecticide is simulated in IRS and ITNs, and it is not (yet) possible to specify differential decay curves of e.g. pyriproxyfen and a pyrethroid, and the lethal effect of insecticide has to be scaled to the concentration of growth regulator, or vice versa.

ITN, classic specification

The element fecundityReduction models the effect of an (insecticide treated) net on fertility of mosquitoes who survive feeding on a protected human, relative to an unprotected human, via the classic ITN model. Fertility (number of eggs laid) is multiplied by (1-K) / (1-B), similar to killing effects. This is not allowed to be greater than 1.

K is an infertility inducing effect, for protected humans, and B is an infertility inducing effect of unprotected humans (Typically = 0).

The element fecundityReduction has the following attributes: baseFactor: Mosquito infertility without intervention (typically = 0) insecticideFactor: Coefficient for insecticide. Value expected to be at least 0. Negative values are not necessarily invalid, but allow nets to increase fertility. insecticideScalingFactor: holeFactor: Value expected to be at least 0. Negative values are not necessarily invalid, but allow nets to increase transmission. holeScalingFactor: interactionFactor: holeFactor + insecticideFactor + interactionFactor must not be greater than 1, and is expected to be at least 0. A negative value is not necessarily invalid, but allows nets to increase transmission.

Schema documentation: https://swisstph.github.io/openmalaria/schema-latest.html#elt-fecundityReduction → scenario → interventions → human → component → ITN → anophelesParams → fecundityReduction

ITN, logit specification

The element fecundityReductionLogit models the effect of an (insecticide treated) net on fertility of mosquitoes who survive feeding on a protected human, relative to an unprotected human, via a logit model. Fertility (number of eggs laid) is multiplied by (1-K) / (1-K0), similar to killing effects. This is not allowed to be greater than 1.

The element fecundityReductionLogit has attributes baseFactor, insecticideFactor, holeFactor and interactionFactor. baseFactor: Logit of the probability (e.g. of death, of entry, of attacking) without intervention. insecticideFactor: Coefficient of log(insecticide content+1) in a generalized linear model with logit link function. holeFactor: Coefficient of log(total holed surface area (in cm2) +1) in a generalized linear model with logit link function. interactionFactor: Coefficient of the interaction term of log(total holed surface area (in cm2) +1) with log(insecticide content+1) in a generalized linear model with logit link function.

Schema documentation: https://swisstph.github.io/openmalaria/schema-latest.html#elt-fecundityReductionLogit → scenario → interventions → human → component → ITN → anophelesParams → fecundityReductionLogit

IRS

The IRS element fecundityReduction models the effect of IRS on fertility mosquitoes after successfully feeding on a human host, relative to an unproteced human. Parameterisations should take into account that mosquitoes do not always bite indoors. First, we calculate K = B + P×p where B is the base (without protection) probability of death, and P is the insecticide factor, p=1−exp(-insecticideContent×insecticideScalingFactor). Fecundity is multiplied by (1−K) / (1−B). It is not allowed to be greater than 1. To keep this in the range [0,1], we require that B+P ≤ 1 and P ≥ 0. Attributes are baseFactor: Probability of mosquito death without intervention insecticideFactor: Value expected to be at least 0. Negative values are not necessarily invalid, but allow IRS to increase transmission. insecticideScalingFactor:

Schema documentation: https://swisstph.github.io/openmalaria/schema-latest.html#elt-fecundityReduction-2 → scenario → interventions → human → component → IRS → anophelesParams → fecundityReduction

GVI

fecundityReduction Effect of intervention on fertility mosquitoes after successfully feeding on a human host, relative to an unproteced human. Parameterisations should take into account that mosquitoes do not always bite indoors. Fertility is multiplied by 1 - (fecundityReduction * decay).

Schema documentation: https://swisstph.github.io/openmalaria/schema-latest.html#elt-fecundityReduction-3 → scenario → interventions → human → component → GVI → anophelesParams → fecundityReduction

Blood source effect on fecundity

This functionality also allows the modeling of reduced fecundity after biting hosts with less suitable blood (see e.g. : http://scialert.net/fulltext/?doi=je.2011.459.467&org=10). From Schema 38 onward, it is possible to simulate such differential fecundity of mosquitoes depending on the blood-host. This can be specified for each non-human host with the element 'hostFecundityFactor', which is a multiplicative factor for the number of fertile eggs laid by a mosquito after biting this type of host, relative to an unprotected human.

Schema documentation: https://swisstph.github.io/openmalaria/schema-latest.html#elt-hostFecundityFactor → scenario → entomology → vector → anopheles → nonHumanHosts → hostFecundityFactor