The population dynamics of cultured Plasmodium falciparum parasites was examined during their sporogonic development in Anopheles gambiae mosquitoes. Estimates of absolute densities were determined for each life stage, and life tables were constructed for each of 38 experimental infections. Macrogametocyte and ookinete mortalities contributed equally to the overall mortality. On average, there was a 40-fold decrease in parasite numbers in the transition from the macrogametocyte to the ookinete stage, a 69-fold decrease in the transition from ookinete to oocyst stages, and a total net decrease in parasite numbers from macrogametocyte to oocyst stage of 2,754-fold (i.e., multiplicative). There was no relationship between macrogametocyte and ookinete densities due to the inherent variability in fertility among different gametocyte cultures. There was a curvilinear relationship (r2 = 0.66) between ookinete and oocyst densities. Above a threshold of about 30 ookinetes/mosquito, the oocyst yield per ookinete became increasingly greater with increasing ookinete density. There was a linear relationship (r2 = 0.73) between oocyst and sporozoite densities, with an average of 663 salivary gland sporozoites produced per oocyst. Sporozoite production per oocyst was not affected by oocyst density and virtually all oocyst infections resulted in sporozoite infections of the salivery glands. This quantitative study indicates that the sporogony of cultured P. falciparum in laboratory-infected A. gambiae is an inefficient process and that the ookinete is the key transitional stage affecting the probability of vector infectivity.
Objective: The main objective of this study was to compare the performance of nested PCR with expert microscopy as a means of detecting Plasmodium parasites during active malaria surveillance in western Thailand.
Methods:The study was performed from May 2000 to April 2002 in the village of Kong Mong Tha, located in western Thailand. Plasmodium vivax (PV) and Plasmodium falciparum (PF) are the predominant parasite species in this village, followed by Plasmodium malariae (PM) and Plasmodium ovale (PO). Each month, fingerprick blood samples were taken from each participating individual and used to prepare thick and thin blood films and for PCR analysis.Results: PCR was sensitive (96%) and specific (98%) for malaria at parasite densities ≥ 500/µl; however, only 18% (47/269) of P. falciparum-and 5% (20/390) of P. vivax-positive films had parasite densities this high. Performance of PCR decreased markedly at parasite densities <500/µl, with sensitivity of only 20% for P. falciparum and 24% for P. vivax at densities <100 parasites/µl.
Conclusion:Although PCR performance appeared poor when compared to microscopy, data indicated that the discrepancy between the two methods resulted from poor performance of microscopy at low parasite densities rather than poor performance of PCR. These data are not unusual when the diagnostic method being evaluated is more sensitive than the reference method. PCR appears to be a useful method for detecting Plasmodium parasites during active malaria surveillance in Thailand.
Data regarding the mosquito-to-human transmission efficiency (b).Columns: country: country where the study was undertaken; place: location of the study site; long: longitude of the study site (-999.00: position is either unknown or was not seeked out); lat: latitude of the study site (-99.00: position is either unknown or was not seeked out); M1: month, when the study started; YYY1: year of the start of the study; M2: month, when the study ended; YYY2: year of the end of the study; b ave : average mosquito-to-human transmission efficiency; b min : as b ave , but for the minimum; b max : as b ave , but for the maximum; species: involved mosquito species; notes: notes; ref:reference. The '-8' denotes data that were not available in the literature and that could not be checked due to limited access, respectively. Note that
Aim: Macroecological analyses provide valuable insights into factors that influence how parasites are distributed across space and among hosts. Amid large uncertainties that arise when generalizing from local and regional findings, hierarchical approaches applied to global datasets are required to determine whether drivers of parasite infection patterns vary across scales. We assessed global patterns of haemosporidian infections across a broad diversity of avian host clades and zoogeographical realms to depict hotspots of prevalence and to identify possible underlying drivers.
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