Avian malaria prevalence and mosquito abundance in the Western Cape, South Africa

Abstract

BackgroundThe close relationship between vector-borne diseases and their environment is well documented, especially for diseases with water-dependent vectors such as avian malaria. Mosquitoes are the primary vectors of avian malaria and also the definitive hosts in the disease life cycle. Factors pertinent to mosquito ecology are likely to be influential to observed infection patterns; such factors include rainfall, season, temperature, and water quality.MethodsThe influence of mosquito abundance and occurrence on the prevalence of Plasmodium spp. in the Ploceidae family (weavers) was examined, taking into account factors with an indirect influence upon mosquito ecology. Mosquitoes and weaver blood samples were simultaneously collected in the Western Cape, South Africa over a two-year period, and patterns of vector abundance and infection prevalence were compared. Dissolved oxygen, pH, temperature and salinity measurements were taken at 20 permanent waterbodies. Rainfall during this period was also quantified using remotely sensed data from up to 6 months prior to sampling months.ResultsSixteen wetlands had weavers infected with avian malaria. More than half of the mosquitoes caught were trapped at one site; when this site was excluded, the number of mosquitoes trapped did not vary significantly between sites. The majority of mosquitoes collected belonged to the predominant vector species group for avian malaria (Culex culex species complex). Seasonal variation occurred in infection and mosquito prevalence, water pH and water temperature, with greater variability observed in summer than in winter. There was a significant correlation of infection prevalence with rainfall two months prior to sampling months. Mosquito prevalence patterns across the landscape also showed a close relationship to patterns of rainfall. Contrary to predictions, a pattern of asynchronous co-variation occurred between mosquito prevalence and infection prevalence.ConclusionOverall, salinity, rainfall, and mosquito prevalence and season were the most influential vector-related factors on infection prevalence. After comparison with related studies, the tentative conclusion drawn was that patterns of asynchronous variation between malaria prevalence and mosquito abundance were concurrent with those reported in lag response patterns.

Prevalence of malaria parasites in indigenous chickens and ducks in selected districts of Bangladesh

“…This finding was almost similar to Okanga et al (2013) who detected higher prevalence in weaver birds of South Africa during late summer (16.0%) than winter (10.0%) season with significant seasonal difference. In India Gupta et al (2011) recorded highest infectivity of pigeon malaria during the summer season (82.9%) followed by spring season (59.4%) and least in the winter season (42.3%).…”

“…Ishtiaq et al(2007) recorded 28.0% prevalence in wild birds of India, but in Myanmar the prevalence rate was 60.0%. In addition, Dranzoa et al (1999) and Okanga et al (2013) recorded 29.4% and 27.0% infection rate with Plasmodium parasites in rock pigeons and weavers in Uganda and South Africa, respectively. The lower prevalence is reported by Elahi et al(2014), Borji et al(2011), Permin et al(2002 and Forrester et al(2001) in wetlands of Bangladesh (0.6%), Eastern Iran (2%), Zimbabwe (3%) and Florida (9.2%) in wetland birds, pigeons, chickens and ring-necked ducks, respectively.…”

Host species, and not environment, predicts variation in blood parasite prevalence, distribution, and diversity along a humidity gradient in northern South America

“…One limitation of this study in relation to water availability and infection patterns is the lack of information on vector ecology. Because we did not characterize the seasonal distribution, abundance, or diversity of dipteran vectors across our sampling locations, we cannot evaluate whether the precipitation gradient affected vector assemblages (Hijmans et al., ; Wilson & Jetz, ; Zomer et al., ), nor whether changes in vector assemblages affect parasite prevalence patterns (Glad & Crampton, ; Loaiza & Miller, ; Okanga et al., ; Svensson & Ricklefs, ). We found, however, that the proportion of individuals infected was similar between wet and dry seasons, suggesting little influence of seasonality on prevalence patterns.…”

“…Environmental factors are known to play a fundamental role in bird-haemosporidian interactions (Loiseau et al, 2010;Sehgal, 2015). In particular, water availability is likely a key determinant of infection patterns in haemosporidians because it is critical for the development of vector larvae (Krama et al, 2015;Loaiza & Miller, 2013;Okanga, Cumming, & Hockey, 2013;Padilla, Illera, Gonzalez-Quevedo, Villalba, & Richardson, 2017). Accordingly, the geographic distribution, transmission, and prevalence of haemosporidians are often predicted by variation in water availability over time (Cornuault et al, 2013; Hernández-Lara, González-García, & Santiago-Alarcon, 2017) and space (Coon & Martin, 2013;Gonzalez-Quevedo, Davies, & Richardson, 2014;Svensson & Ricklefs, 2009;Wood et al, 2007).…”

Conservation implications of avian malaria exposure for African penguins during rehabilitation

“…The climate along the South African west and south coasts exhibits variable temperatures and rainfall conditions (Supplementary table 1) that in turn can influence vector and parasite abundance and host exposure. 44 November 2002 experienced a higher than normal rainfall which could have caused a hatch delay with an increase in mosquito populations in subsequent months, 45 (Table 3).…”