Plasmodium prevalence

Gonz, Merit, alez-Olvera, Hernandez-Colina, Arturo, Himmel, Tanja, Eckley, Lindsay, Lopez, Javier, Chantrey, Julian, Baylis, Matthew & Jackson, Andrew P., 2022, Molecular and epidemiological surveillance of Plasmodium spp. during a mortality event affecting Humboldt penguins (Spheniscus humboldti) at a zoo in the UK, International Journal for Parasitology: Parasites and Wildlife 19, pp. 26-37 : 31

3.5. Plasmodium prevalence in mosquitoes

In total, 753 mosquitoes tested positive by PCR out of 6459 analysed (11.7%). The number of mosquitoes infected with Plasmodium spp. increased as the year progressed from zero at the beginning of May to a peak of 147/496 (29.6%) mosquitoes trapped during mid-July ( Fig. 3 ). Parasite prevalence in mosquitoes remained high into early August (77/ 323; 23.8%) as mosquito abundance gradually fell, before declining sharply to 6.3% (9/142) in early September. Infected mosquitoes were then not observed, apart from a minor recrudescence in November when 3/23 (13%) and 2/6 (33.3%) mosquitoes were PCR-positive.

From the seven species of mosquitoes identified at Chester Zoo during 2017, Plasmodium DNA was only detected in Culex pipiens and Culiseta annulata . In total, 11.4% (619) of Cx. pipiens and 10.3% (25) of Cs. annulata mosquitoes were positive respectively; a difference in prevalence that is non-significant (χ 2 = 0.18, df = 1, P = 0.67). There were also PCR mosquito positives that could not be fully identified, including 96 Culex spp. , one Culiseta spp. and 37 as Culicinae.

Parasite prevalence was higher in July and August, but not significantly different (Table D in S1 File). There was a difference in Plasmodium prevalence by trapping site, with A2 having a significantly higher prevalence (18%) than the other areas (Table E in S1 File) ( Fig. 1 ).

Figures

Fig. 3. Temporal distribution of mosquito and Plasmodium spp. prevalence at Chester Zoo between May and November 2017. Continuous top line: total number of mosquitoes collected on a weekly basis; Continuous bottom line: total number of Plasmodium infections; Dashed line: parasite prevalence estimated as a proportion of infected mosquitoes of the total captured on a weekly basis.

Fig. 1. Mosquito abundance and Plasmodium prevalence compared at ten sampling sites across Chester Zoo. The Chester Zoo site (zoo perimeter is outlined) overlaid with a heat map of total mosquito numbers trapped at 10 sampling sites. Locations of traps are indicated by numbers 1–7, 10–12 inclusive. The location of the penguin exhibit in 2017 is indicated by a penguin symbol. a. Mosquito abundance. b. Plasmodium prevalence in trapped mosquitoes. Heat maps were generated using Heatmapper with a Gaussian radius multiplier of 1.