Advances and challenges in predicting the impact of lymphatic filariasis elimination programmes by mathematical modelling

Table 1 Quantification of several key biological parameters in the EPIFIL and LYMFASIM model variants for Pondicherry, where Wuchereria bancrofti is transmitted by Culex quinquefasciatus. Values in bold-face were estimated indirectly by fitting the model outcomes to observed epidemiological data; other values were quantified directly from literature, theory, and analysis of local data

Parameter	EPIFIL	LYMFASIM
		Anti-L3 immunity	Anti-fecundity immunity
Parasite lifecycle
Average adult worm life span in years	8 ^a	10.2 ^b	11.8 ^b
Average mf life span in months	10 ^a	10 ^c	10 ^c
Premature period in months	-	8	8
Exposure variation by age
Exposure at age zero as fraction of maximum exposure	0	0.26	0.40
Age in years at which maximum exposure is achieved	9	19.1	21.3
Density dependence in mosquitoes
Maximum number of L3 larvae that can develop in mosquitoes at high mf intensities	6 ^d	6.6 ^e	6.6 ^e
Acquired immunity
Duration of acquired immunity in years	lifelong	9.6 ^f	11.2 ^f
Other parameters
Monthly biting rate	5760	2200	2200
Proportion of L3 larvae in mosquitoes that enters the human host when a mosquito bites	0.414*0.32 = 0.13	0.1	0.1
Proportion of inoculated L3 larvae that develops successfully into adult worms (x10^-3)	0.113	1.03 ^g	0.42
Mf production per worm	2	0.61 ^h	4.03 ^{h, i}

- Not considered in the model; mf, microfilaria.
^a Assuming an exponential distribution.
^b Assuming a Weibull distribution with shape parameter α = 2.
^c Assuming an exponential distribution, approximated with discrete time steps.
^d Exponential saturating function with initial increase from zero = 0.047.
^e Hyperbolic saturating function with initial increase from zero = 0.09.
^f Period in which the strength of the immune response is halved in the absence of boosting.
^g In the absence of anti-L3 immunity.
^h In the presence of at least 1 male worm, scaled to the number of mf per 20 μl peripheral blood.
ⁱ In the absence of anti-fecundity immunity.