Seasonal changes in the Plasmodium falciparum population in individuals and their relationship to clinical malaria: a longitudinal study in a Sudanese village

Abstract

Residents of Daraweesh village in Sudan were monitored for Plasmodium falciparum infection and malaria morbidity in 3 malaria seasons from 1993 to 1996. Malaria parasites were detected microscopically and by polymerase chain reaction (PCR) in a series of cross-sectional surveys. PCR revealed submicroscopical infections during the dry season, particularly among individuals who had recovered from a malaria episode following successful drug treatment. Clinical and subclinical infections were contrasted by assaying for allelic polymorphism at 2 gene loci, MSP-1 and GLURP and 2 hypotheses examined with reference to these data: that clinical malaria is associated with infection with novel parasite genotypes not previously detected in that host, or alternatively, that clinical malaria episodes are associated with an increased number of clones in an infection. We detected more mixed infections among clinical isolates, but people carrying parasites during the dry season were not found to have an increased risk of disease in the following malaria season. There was a clear association of disease with the appearance of novel parasite genotypes.

Similarities and seasonal variations in bacterial communities from the blood of rodents and from their flea vectors

“…Finally, we show that, whereas the structure of communities in both the rodent blood and the fleas is largely independent of host characteristics, both these communities are prone to seasonal variations. These findings are consistent with data on other vector-borne microbes (Philip et al, 1976;Pumpuni et al, 1993;Kirstein et al, 1997;Noda et al, 1997;Roper et al, 1998;Aksoy, 2000;Cox, 2001;Macaluso et al, 2002;Gonzalez-Ceron et al, 2003;Sutherst, 2004;Scarborough et al, 2005;Clay et al, 2006;Steiner et al, 2006;Wielinga et al, 2006;Ostfeld, 2009;Jones et al, 2010;Telfer et al, 2010;Cirimotich et al, 2011;Lalzar et al, 2012). Collectively, they highlight the following candidate factors as affecting the overall abundance of a specific vector-borne microbe: (1) the abundance of microbial endosymbionts of vectors, (2) the abundance of other vector-borne microbes that co-occur in the vector and in the blood of its host and (3) seasonal variation in the host environment.…”

“…To determine whether the observed spring-to-summer variations in fleaborne bacteria reflect a more general temporal pattern, one should sample microbes in additional timeframes and in multiple years and vector species. Reports of climatic influences on microbial abundance and composition in flies, mosquitoes and ticks support a general role of seasonality (Kirstein et al, 1997;Roper et al, 1998;Sutherst, 2004;Wielinga et al, 2006;Ostfeld, 2009;Lalzar et al, 2012). If seasonal variability in microbial community structure Vector-borne bacterial communities C Cohen et al indeed plays an important role in determining the overall abundance of vector-borne bacteria, then future investigations of the specific causes of seasonal variability are encouraged.…”

A prospective study of Plasmodium falciparum multiplicity of infection and morbidity in Tanzanian children

“…A study in São Tomé found that the apparent protection extended also to nonmalaria fever episodes (Muller et al, 2001). Other studies, such as those of infants in Idete Smith et al, 1999a), of children aged less than three years in western Kenya (Branch et al, 2001), of children in Ghana (Ofosu-Okyere et al, 2001), and of individuals in relatively low transmission settings in the Sudan (Roper et al, 1998) and Mozambique (Mayor et al, 2003) have found that multiple infections were a risk factor for clinical malaria attacks.…”

Epidemiology and Seasonal Pattern of Malaria in an Irrigated Area of Eastern Sudan

“…However, the presence of malaria during April-July may be inevitable in extent of the underlying parasite reservoir in the human host, to maintain the low level of malaria transmission at the beginning of the rainy season. In fact, low submicroscopic malaria has been detected throughout the year including the dry season in eastern Sudan [9,10,11,13,19] . The study showed a seasonal pattern of malaria with two peaks during the rainy and irrigation seasons.…”

“…Malaria causes nearly 7.5-10 million cases and 35,000 deaths every year in Sudan [8] . Although the epidemiology of malaria has been subject to extensive studies in other parts of the Sudan [9][10][11][12][13][14] , probably no proper published data exists concerning the epidemiology of malaria in the study area. Recently, high levels of annual vector densities and antimalrial drugs resistance have been reported in New Halfa, an irrigated area in eastern Sudan [15,16] .…”