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■Bio-mathematics, Statistics and Nano-Technologies: Mosquito Control Strategies

have rebound effects, especially in endemic areas [113], [102], [55], [57]. An illustration

was captured in individual-based model simulations in [102] which indicated that protec-

tion against new infections reduces the acquisition of asexual blood-stage immunity. This

causes accumulated immune memory to wane, such that a compensatory rise in clinical in-

cidence may result when protection measures are not available (see also [113], [194]). The

same case is postulated for the use of bednets, as it may only shift the age of the incidence

of severe disease without considerably reducing the overall disease burden.

In the individual-based model of malaria transmission developed in [72], a short-lived

effect of the intervention program was noticed which could be due to a rebound after im-

munity has waned in the population [113], [116], [102]. On the contrary, no rebound effect

was noticed with administering a hypothesized vaccine which was assumed to not only

provide an immediate boost in immune response, but also brings about the early matura-

tion of the immune response, normally associated with aging. This suggests that the use of

intervention should be effective and long-lived [154], [153] (see the diagrammatic illustra-

tion in [154]). On the other hand, reduction in the use of short-lived intervention measures

will reduce drug pressure and the emergence of parasite variants resistant to the widely

used anti-malaria drug treatment [17], [18], [108], [106], [149]. This is because immunity

acts especially by reducing the frequency and severity of clinical attacks, and thus the drug

pressure. The same case is applicable to chemicals used in treating insecticidal-net. The

negative effect of having small number of immune individuals in low transmission areas,

can be counterbalanced by the sustained implementation of very effective transmission-

reducing interventions for an indefinite period [154], [54]. This can also be augmented by

a transmission blocking vaccine which enhances and artificially induces immunity.

5.2.9.2

Climatic driving effect on immunity acquisition

Although climate is the dominant driver of seasonal outbreaks of malaria, it has been

demonstrated that NAI can buffer its effects [103], [26]. To clarify the differences in the

impact of NAI among high and low-transmission settings, Laneri et al. [103] developed

a stochastic human–mosquito model to fit the data from two unique adjacent cohorts

in settings with mesoendemic (Table 5.2) seasonal and holoendemic (Table 5.2) peren-

nial malaria transmission in Senegal, which were followed up for two decades, recording

their daily malaria cases. Thus, for the cohort in which epidemic transmission is limited

by mosquito density and rainfall, the highly dynamic pattern of cases is climate-driven

whereas the impact of climate on incidence was largely buffered by clinical immunity in

the endemic village where mosquitos are present year-round. This is consistent with the

field observations in [147], suggesting that places with dry season transmission are as-

sociated with stable hotspots of largely asymptomatic parasitaemia and robust immunity

acquired early in life.

Yamana et al. [26], [27], [28] developed a coupled hydrology and agent-based ento-

mological model that uses environmental data (such as temperature, rainfall and topogra-

phy) which typically regulates mosquito population dynamics, to simulate the mosquito

biting rates and subsequently the malaria prevalence alongside the level of NAI in the hu-