Seasonality, Parasite Diversity, and Local Extinctions in Plasmodium falciparum Malaria

Abstract

We incorporate stochastic, density-dependent seasonal recruitment in adult Anopheles mosquito populations in a discrete-event model of Plasmodium falciparum malaria transmission and find the probabilities of parasite extinction higher than with perennial transmission. Seasonal fluctuations in vector populations act to synchronize the dynamics of infection and immunity in host populations, leading to fluctuations in parasite prevalence greater than expected solely on the basis of high-and low-season vector densities. This synchronization also biases frequencies of infection with multiple parasite phenotypes or genotypes.

On the Delayed Ross–Macdonald Model for Malaria Transmission

“…Recently, various models of malaria transmission have been developed to improve our understanding of the likely impact of climate change on malaria transmission (Craig et al, 1999;Martens et al, 1995;Rogers and Randolph, 2000;Hoshen and Morse, 2004). The sporogonic incubation of the parasite can strongly influence transmission intensity and can vary seasonally (Burkot et al, 1990;McKenzie et al, 2001) or with longer term climate cycles (Craig et al, 1999). Warming temperatures tend to decrease the duration of the extrinsic incubation period, which will increase the basic reproduction number R 0 .…”

A biologic basis for integrated malaria control.

“…Here we set K at a high-season value (5,000, a 10:1 ratio with the human population) for 0, 30, 60, 90, 180, 270, 300, 330, or 360 days, and at a low-season value (500, a 1:1 ratio) for the remainder of each 360-day year. 9 Note that a high-season length of 0 days implies a mosquito population size perennially 10% of that at a 360-day (i.e., perennial) high season. For perennial-transmission conditions, we have derived an epidemiologic power-law relationship over a wide range of mosquito:human ratios.…”

“…These extinctions occurred only with extremely low mosquito densities or when the parameter describing the duration of human infection-blocking immunity was at its maximum value, and, simultaneously, those describing vector survivorship and the duration of human infectivity were at their minimum values. 8,9 Here we model seasonal fluctuation in Anopheles populations ( Figure 2) and meiotic recombination among P. falciparum genotypes (Figure 3), and in that context examine how rates of human population turnover and the frequency with which new parasite genotypes are introduced might affect the local persistence of malaria. We approximate the introduction of a vaccine by setting infection-blocking immunity at levels that would eliminate the parasite, and examine the influence of vector survivorship, duration of human infectivity, seasonality of transmission, and parasite cross-reactivity on its success.…”

Outbreak properties of epidemic models: The roles of temporal forcing and stochasticity on pathogen invasion dynamics

“…Present climatedriven transmission models for these diseases do not explicitly take account of the impact of the factors investigated here. Our results indicate that improving understanding of the impact of climate change on disease invasion dynamics will require a more realistic analysis of these factors, especially as increasing variability in climatic components has been linked to changes in malaria infection dynamics (McKenzie et al, 2001;Zhou et al, 2004). Zhou, G. et al, 2004.…”