Showing papers by "Jefferson A. Vaughan published in 1994"
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TL;DR: This approach provides a framework for identifying mechanisms of susceptibility and evaluating Plasmodium sporogonic development in naturally occurring vector species in nature and indicates that gene frequencies determining susceptibility fluctuated with time in all species, except A. freeborni where susceptibility remained homogenous throughout the study.
Abstract: Sporogonic development of cultured Plasmodium falciparum was compared in six species of Anopheles mosquitoes. A reference species, A. gambiae, was selected as the standard for comparison. Estimates of absolute densities were determined for each lifestage. From these data, four aspects of parasite population dynamics were analyzed quantitatively: 1) successive losses in abundance as parasites developed from gametocyte to ookinete to oocyst stages, 2) oocyst production of sporozoites, 3) correlation between various lifestage parameters, and 4) parasite distribution. Parasite populations in A. gambiae incurred a 316-fold loss in abundance during the transition from macrogametocyte to ookinete stage, a 100-fold loss from ookinete to oocyst stage, yielding a total loss of approximately 31,600-fold (i.e., losses are multiplicative). Comparative susceptibilities in order were A. freeborni >> A. gambiae, A. arabiensis, A. dirus > A. stephensi, A. albimanus. The key transition(s) determining overall susceptibility differed among species. Despite species differences in oocyst densities and infection rates, salivary gland sporozoite production per oocyst (approximately 640) was the same among species. The most consistent association among lifestage parameters was a positive correlation between densities and infection rates of homologous lifestages. A curvilinear relationship between ookinete and oocyst densities in A. gambiae indicated a threshold density was required for ookinete conversion to oocysts (approximately 30 ookinetes per mosquito). The same relationship in A. freeborni was linear, with no distinct threshold. Ookinete and oocyst populations were negative binomially distributed in all species. Indices of heterogeneity in mosquito susceptibility to infection indicated that gene frequencies determining susceptibility fluctuated with time in all species, except A. freeborni where susceptibility remained homogenous throughout the study. This approach provides a framework for identifying mechanisms of susceptibility and evaluating Plasmodium sporogonic development in naturally occurring vector species in nature.
85 citations
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TL;DR: Parasite populations were not normally distributed in any mosquito species but were adequately described by a negative binomial type of distribution.
Abstract: Sporogonic development of Plasmodium yoelii yoelii 17XNL was examined in 5 species of Anopheles mosquitoes; A. albimanus, A. dirus, A. freeborni, A. gambiae, and A. stephensi. The kinetics of ookinete formation differed among species. In A. freeborni, A. gambiae, and A. stephensi, mature ookinetes formed synchronously at 8 hr, then quickly subsided. In A. albimanus and A. dirus, ookinete formation was more protracted, and ookinete densities peaked from 12 to 24 hr. Losses in parasite abundance during the conversion of ookinetes to oocysts were similar between A. dirus and A. gambiae (55- and 41-fold losses, respectively) but were an order of magnitude less in A. stephensi (1.3-fold loss). Ookinete conversion to oocysts in A. albimanus was nil. Melanotic encapsulation of oocysts occurred in 25-30% of infected A. gambiae and A. dirus. Melanized parasites in A. gambiae at days 7-10 were small (10 microns diameter) and retort-shaped, whereas melanized parasites in A. dirus were generally as large as normal oocysts (60 microns) and many were incompletely melanized. Melanotic encapsulation did not occur in A. stephensi, A. freeborni, or A. albimanus. On day 16, sporozoites were present in the salivary glands of A. freeborni, A. gambiae, and A. stephensi, but only half of mosquitoes were mature oocysts also had gland infections. When present in the glands, sporozoites were successfully transmitted to mice via mosquito bite. Parasite populations were not normally distributed in any mosquito species but were adequately described by a negative binomial type of distribution.
66 citations
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TL;DR: If a reliable parasite isolate or clone is used, there is no need to measure other characteristics of in vitro gametocyte populations because these will not significantly improve one's ability to predict oocyst infection rates.
25 citations
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TL;DR: Prior blood feeding accelerated digestion of the infective blood meals and subtly altered susceptibility to infection with P. falciparum made all experimental groups equally susceptible to infection, however, when gametocyte fertility was low, accelerated digestion had a detrimental effect on the transition of ookinetes to oocysts.
Abstract: We examined the relative susceptibilities of Anopheles gambiae Giles of different physiological ages to infection with cultured Plasmodium falciparum (Welch). Cohorts of mosquitoes were divided into three groups; one was fed uninfected blood on day 3 after emergence (i.e., one prior blood meal); another on days 3 and 7 after emergence (i.e., two prior blood meals); and a control group was maintained on sucrose. On days 10 to 12 after emergence, mosquitoes were fed human blood containing P. falciparum gametocytes. Prior blood feeding accelerated digestion of the infective blood meals and subtly altered susceptibility to infection with P. falciparum . When gametocyte cultures were highly fertile, all experimental groups were equally susceptible to infection. However, when gametocyte fertility was low, accelerated digestion had a detrimental effect on the transition of ookinetes to oocysts. Accelerated digestion may raise the threshold density of ookinetes required for the successful conversion of ookinetes to oocysts.
13 citations