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

(a)

(b)

Figure 5.2: (a) Age prevalence and (b) immune curve simulated using the Aron model [44]

for different forces of infection with r = 0.9/yr, q = 0.25/yr andτ = 5yrs.

exposure, have the least acquired immunity to infections and are also at highest risk of nu-

tritional problems [115]. However, with frequent re-exposure, the vulnerability to severe

clinical attacks is reduced by NAI as they age. Parasite infection prevalence begins to rise

only at about 20 weeks of age, since infants are peculiarly resistant to high parasitemia

and severe disease [205], [57]. This kind of protection is known to be either linked with

the presence of maternal immunoglobulin antibodies such as secretory IgA and/or para-

site growth-inhibitory factors such as lactoferrin found in breast milk and in the sera of

mother-infant pair [74], [162]. Some models however, for simplicity, ignore this protec-

tive maternal immunoglobulin antibodies and assume that all individual lack immunity at

initial stage [6], [109], [62]. Nevertheless, maternal protection has been incoporated in a

stochastic model by [76] in a biologically reasonable way. The host’s age was modelled to

be inversely related to the amount of maternally gained protection. The extent of maternal

protection is treated as independent of maternal exposure. This was based on the argu-

ment that if transmission is low, only few infants will be exposed in their first few months