Gouagna L C, Mulder B, Noubissi E, Tchuinkam T, Verhave J P, Boudin C
Malaria Department, OCEAC, Yaoundé, Cameroun.
Trop Med Int Health. 1998 Jan;3(1):21-8. doi: 10.1046/j.1365-3156.1998.00156.x.
This study investigated the successive losses in the parasite densities of Plasmodium falciparum stages during the early sporogony in laboratory-reared Anopheles gambiae infected by membrane feeding with blood from naturally infected gametocyte carriers (>50 gametocytes/mm3). The developmental stages of P. falciparum in the mosquito were studied from zygote to oocyst, by immunofluorescent method using monoclonal antibodies against the Pfs25 protein present on the surface of newly formed gametes. This method allows for assessment of the various sporogonic stages before, during and after passage of the midgut wall. Parasite densities were determined within the entire blood meal at 3 h (zygotes and macrogametes) and 24 h (ookinetes) post-infection. At 48 h after the mosquito blood meal, midguts were checked for the presence of early oocysts. For the mid-size oocysts count, classic microscopy examination was used at day 7 postinfection. The parasite efficacy was estimated by following successive losses in parasite densities between different early stages of the sporogonic cycle in A. gambiae. Thirty-seven experimental infections were realized with high gametocyte densities, ranging from 64 to 2392 gametocytes/mm3. All gametocyte carriers showed infection with round forms 100%; ookinetes were found in 91.9%. The prevalences of infections with oocysts were 48.6% at day 2 (young oocyst) and 37.8% at day 7 (mid-size oocyst). The mean densities per mosquito for each parasite stage were 12.6 round forms, 5.5 ookinetes, 1.8 young oocyst and 2 mid-size oocysts. Significant correlations were found between two consecutive parasite stages (round forms/ookinetes, ookinetes/young oocysts, young oocysts/mid-size oocysts) and between round forms and mid-size oocysts. The mean parasite density significantly decreased between round forms and ookinetes (yield Y1 = 41.6%) and between ookinetes and young oocysts (Y2 = 61.4%). By contrast, no significant decrease was observed between young oocysts and mid-size oocysts (Y3 = 91.2%). The overall yield of the early sporogonic cycle (from round form to oocyst at day 7) was equal to 25.7%, indicating that almost 3/4 of the total parasites were lost during the early step of the sporogonic cycle, from 3 h post-infection to day 7.
本研究调查了实验室饲养的冈比亚按蚊在通过膜饲法吸食来自自然感染配子体携带者（配子体密度>50个/立方毫米）的血液后，恶性疟原虫各阶段在早期孢子生殖过程中寄生虫密度的连续损失情况。利用针对新形成配子表面存在的Pfs25蛋白的单克隆抗体，通过免疫荧光法研究了疟原虫在蚊子体内从合子到卵囊的发育阶段。该方法可用于评估中肠壁通过之前、期间和之后的各个孢子生殖阶段。在感染后3小时（合子和大配子）和24小时（动合子）测定整个血餐中的寄生虫密度。在蚊子吸食血餐48小时后，检查中肠是否存在早期卵囊。对于中等大小卵囊计数，在感染后第7天采用经典显微镜检查。通过追踪冈比亚按蚊孢子生殖周期不同早期阶段之间寄生虫密度的连续损失来估计寄生虫效力。用高配子体密度（范围为64至2392个/立方毫米）进行了37次实验感染。所有配子体携带者100%显示有圆形体感染；发现动合子的比例为91.9%。感染卵囊的发生率在第2天（年轻卵囊）为48.6%，在第7天（中等大小卵囊）为37.8%。每个寄生虫阶段每只蚊子的平均密度为12.6个圆形体、5.5个动合子、1.8个年轻卵囊和2个中等大小卵囊。在两个连续的寄生虫阶段（圆形体/动合子、动合子/年轻卵囊、年轻卵囊/中等大小卵囊）之间以及圆形体和中等大小卵囊之间发现了显著相关性。圆形体和动合子之间以及动合子和年轻卵囊之间的平均寄生虫密度显著降低（产量Y1 = 41.6%），以及动合子和年轻卵囊之间（Y2 = 61.4%）。相比之下，年轻卵囊和中等大小卵囊之间未观察到显著降低（Y3 = 91.2%）。早期孢子生殖周期（从圆形体到第7天的卵囊）的总体产量等于25.7%，表明在孢子生殖周期的早期步骤（从感染后3小时到第7天）中，几乎3/4的寄生虫损失了。
