Temporal changes in mosquito abundance (Culex pipiens), avian malaria prevalence and lineage composition

Abstract

Background: Knowledge on the temporal dynamics of host/vector/parasite interactions is a pre-requisite to further address relevant questions in the fields of epidemiology and evolutionary ecology of infectious diseases. In studies of avian malaria, the natural history of Plasmodium parasites with their natural mosquito vectors, however, is mostly unknown.

Methods: Using artificial water containers placed in the field, we monitored the relative abundance of parous females of Culex pipiens mosquitoes during two years (2010-2011), in a population in western Switzerland. Additionally, we used molecular tools to examine changes in avian malaria prevalence and Plasmodium lineage composition in female C. pipiens caught throughout one field season (April-August) in 2011.

Results: C. pipiens relative abundance varied both between years and months, and was associated with temperature fluctuations. Total Plasmodium prevalence was high and increased from spring to summer months (13.1-20.3%). The Plasmodium community was composed of seven different lineages including P. relictum (SGS1, GRW11 and PADOM02 lineages), P. vaughani (lineage SYAT05) and other Plasmodium spp. (AFTRU5, PADOM1, COLL1). The most prevalent lineages, P. vaughani (lineage SYAT05) and P. relictum (lineage SGS1), were consistently found between years, although they had antagonistic dominance patterns during the season survey.

Conclusions: Our results suggest that the time window of analysis is critical in evaluating changes in the community of avian malaria lineages infecting mosquitoes. The potential determinants of the observed changes as well as their implications for future prospects on avian malaria are discussed.

Figure 1

Seasonal changes in the density of Culex pipiens egg rafts and in the rainfall, at Dorigny (Switzerland). Egg raft density was determined as the mean of monthly collected egg rafts per container and per trap date. Error bars are the standard errors of the means. Values between parentheses indicate mean monthly temperature. Egg raft density was significantly different between months not connected by the same letters (Tukey’s HSD test, P < 0.05).

Figure 2

Relationship between cumulated densities of Culex pipiens egg rafts and degree-days accumulation. Densities of C. pipiens egg rafts (collected egg rafts per container and per collection date) were cumulated throughout collection dates. Cumulated values are presented on a log scale (log(n +1)). Degree-days accumulation (log scale) started with the 1^st January as biofix date. The regression line (full line) has the following equation y = 1.97× -5.15, R² = 0.95. N= 137 days sampled across seasons (April-September) in 2010 (grey circles) and in 2011 (empty circles).

Figure 3

Changes in avian Plasmodium community structure throughout the season (April-August) 2011. Grey bars (Plasmodium relictum), black bars (P. vaughani) and white bars (Plasmodium spp.). The total number of infected female C. pipiens (N) is given for each month.