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

Okanga S, Cumming GS, Hockey PA - Malar. J. (2013)

Bottom Line: 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.There was a significant correlation of infection prevalence with rainfall two months prior to sampling months.Overall, salinity, rainfall, and mosquito prevalence and season were the most influential vector-related factors on infection prevalence.

View Article: PubMed Central - HTML - PubMed

Affiliation: Percy FitzPatrick Institute, DST/NRF Centre of Excellence, University of Cape Town, Rondebosch, Cape Town 7701, South Africa. sokanga@gmail.com.

ABSTRACT

Background: The 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.

Methods: The 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.

Results: Sixteen 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.

Conclusion: Overall, 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.

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Seasonal variation in the mean number of mosquitoes caught per site (n = 524; p = 0.04).
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Figure 5: Seasonal variation in the mean number of mosquitoes caught per site (n = 524; p = 0.04).

Mentions: Mosquito abundance varied significantly between seasons (Figure 5): 490 individuals (between 1–260 specimens per site) were caught in the summer from 14 sites, whereas only 34 (1 – 8 specimens per site) were caught in winter from eight sites (t = 2.131, 38; p = 0.04). Overall, Plasmodium infection per site showed little correlation with vector abundance (r2 = - 0.29; p = 0.21). Mosquito seasonal prevalence and Plasmodium infection were not significantly correlated (r2 = - 0.28; p = 0.08), although this association strengthened notably after the exclusion of STR mosquitoes (r2 = - 0.33; p = 0.04).


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

Okanga S, Cumming GS, Hockey PA - Malar. J. (2013)

Seasonal variation in the mean number of mosquitoes caught per site (n = 524; p = 0.04).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4016263&req=5

Figure 5: Seasonal variation in the mean number of mosquitoes caught per site (n = 524; p = 0.04).
Mentions: Mosquito abundance varied significantly between seasons (Figure 5): 490 individuals (between 1–260 specimens per site) were caught in the summer from 14 sites, whereas only 34 (1 – 8 specimens per site) were caught in winter from eight sites (t = 2.131, 38; p = 0.04). Overall, Plasmodium infection per site showed little correlation with vector abundance (r2 = - 0.29; p = 0.21). Mosquito seasonal prevalence and Plasmodium infection were not significantly correlated (r2 = - 0.28; p = 0.08), although this association strengthened notably after the exclusion of STR mosquitoes (r2 = - 0.33; p = 0.04).

Bottom Line: 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.There was a significant correlation of infection prevalence with rainfall two months prior to sampling months.Overall, salinity, rainfall, and mosquito prevalence and season were the most influential vector-related factors on infection prevalence.

View Article: PubMed Central - HTML - PubMed

Affiliation: Percy FitzPatrick Institute, DST/NRF Centre of Excellence, University of Cape Town, Rondebosch, Cape Town 7701, South Africa. sokanga@gmail.com.

ABSTRACT

Background: The 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.

Methods: The 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.

Results: Sixteen 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.

Conclusion: Overall, 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.

Show MeSH
Related in: MedlinePlus