Etiology of interepidemic periods of mosquito-borne disease

Abstract

Dengue viruses and malaria protozoa are of increasing global concern in public health. The diseases caused by these pathogens often show regular seasonal patterns in incidence because of the sensitivity of their mosquito vectors to climate. Between years in endemic areas, however, there can be further significant variation in case numbers for which public health systems are generally unprepared. There is an acute need for reliable predictions of within-year and between-year epidemic events. The prerequisite for developing any system of early warning is a detailed understanding of the factors involved in epidemic genesis. In this report we discuss the potential causes of the interepidemic periods in dengue hemorrhagic fever in Bangkok and of Plasmodium falciparum malaria in a highland area of western Kenya. The alternative causes are distinguished by a retrospective analysis of two unique and contemporaneous 33-year time series of epidemiological and associated meteorological data recorded at these two sites. We conclude that intrinsic population dynamics offer the most parsimonious explanation for the observed interepidemic periods of disease in these locations.

Potential impact of a presumed increase in the biting activity of dengue-virus-infected Aedes aegypti (Diptera: Culicidae) females on virus transmission dynamics

“…This pattern of biennial epidemics more closely resembles the observed multi-annual cycle of dengue epidemics in endemic countries, including the pattern observed in Brazil (Nogueira et al 2007, Nogueira & Eppinghaus 2011. In agreement, other studies have shown the importance of the parameters related to the vector-host interaction, including the biting rate, in determining the seasonal and multi-annual cycle of dengue (Hay et al 2000, Bartley et al 2002. A more severe biennial epidemic implies that the virus, during the epidemic, is circulating among a greater proportion of the population, thus causing the number of secondary infections to increase.…”

Climate change and mosquito-borne disease.

“…Whatever the cause, the history of multiple epidemics in the earlier part of the century, including many at higher altitudes, makes it unnecessary to infer climate change as a contributory factor. Moreover, a set of wellmaintained meteorologic records shows no significant change in temperature over recent decades (103,128), and a retrospective study of 33 years of monthly incidence data from the Brookebond tea-growing estates did not reveal any relationship between climate variables and the timing or duration of interepidemic periods (130). Indeed, in a detailed report to WHO (131), a group of malaria specialists based in Nairobi dismissed those who claim a global warming link as "scientific Nostradamuses.…”

“…Immunologic history, expressed as the herd immunity, is presumably the dominant factor. Moreover, a retrospective analysis of 33 years of monthly data on DHF incidence in Bangkok, Thailand, did not reveal any relationship between climate variables and the timing of epidemics (130).…”

Shifting patterns: malaria dynamics and rainfall variability in an African highland

“…For this reason, a second malaria time series at an adjacent plantation was also considered (this has already been the subject of previous studies, e.g. Hay et al 2000), as a basis for comparison and discussion (figure S5 in the electronic supplementary material). We refer to this time series as BBK, for Brooke Bond Farms.…”