对约氏疟原虫不同易感性的大劣按蚊和斯氏按蚊基因组RAPD序列比较

目的分析对约氏疟原虫不易感的大劣按蚊和易感的斯氏按蚊基因组RAPD谱带并测序，探讨媒介按蚊基因型与疟原虫基因型间的相互关系。方法用已筛选的一条随机引物，随机扩增大劣按蚊和斯氏按蚊成蚊的基因组DNA，扩增产物经琼脂糖凝胶电泳后，对相同迁移率的DNA条带克隆、测序，并采用相关在线程序及软件进行序列比较分析。结果大劣按蚊和斯氏按蚊RAPD谱带具有明显的种间差异，但有4对相同迁移率的条带。序列分析显示4对DNA条带在序列长度和组成上呈现多态性，序列的GC含量和简单重复序列存在差异，序列相似性介于48％～52％之间。结论大劣按蚊和斯氏按蚊之间存在不同的遗传背景，其基因多态性可能与产生对约氏疟原虫的易感性不同有关，为进一步研究按蚊与疟原虫之间的相互作用奠定了基础。     

Molecular strategies for interrupting arthropod-borne virus transmission by mosquitoes

Arthropod-borne virus (arbovirus) infections cause a number of emerging and resurgent human and veterinary infectious diseases. Traditional means of controlling arbovirus diseases include vaccination of susceptible vertebrates and mosquito control, but in many cases these have been unavailable or ineffective, and so novel strategies for disease control are needed. One possibility is genetic manipulation of mosquito vectors to render them unable to transmit arboviruses. This review describes recent work to test the concept of pathogen-derived resistance in arthropods by expression of viral genes in mosquito cell cultures and mosquitoes. Sense and antisense genome sequences from La Crosse virus (LAC) (a member of the Bunyaviridae) and dengue viruses serotypes 1 to 4 (DEN-1 to DEN-4) (members of the Flaviviridae) were expressed in mosquito cells from double-subgenomic and replicon vectors based on Sindbis virus (a member of the Togaviridae). The cells were then challenged with homologous or related viruses. For LAC, expression of antisense sequences from the small (S) genome segment, particularly full-length antisense S RNA, effectively interfered with replication of challenge virus, whereas expression of either antisense or sense RNA from the medium (M) segment was completely ineffective in LAC inhibition. Expression of sense and antisense RNA derived from certain regions of the DEN genome also blocked homologous virus replication more effectively than did RNA from other regions. Other parameters of RNA-mediated interference have been defined, such as the time when replication is blocked and the minimum size of effector RNA. The mechanism of RNA inhibition has not been determined, although it resembles double-stranded RNA interference in other nonvertebrate systems. Prospects for application of molecular strategies to control arbovirus diseases are briefly reviewed.     

California encephalitis virus transmission by arctic and domestic mosquitoes

Summary A zero passage arctic mosquito isolate of California encephalitis (CE) virus (showshoe hare subtype) was transmitted by wild-caughtAedes communis mosquitoes after 13 days incubation at 13° and 23° C, after 20 days incubation at 13° C, when mosquitoes imbibed 1 mouse LD₅₀ in a blood meal. Transmission occurred after 20 days incubation at 13° and 23° C when mosquitoes were injected intrathoracically with 1 or 0.1 mouse LD₅₀. Virus was also transmitted byA. aegypti 13 days after infection with 100 mouse LD₅₀ by feeding or intrathoracic injection, and incubation at 13° C. Virus antigen was detected in salivary glands of 42 per cent virus-positiveA. communis mosquitoes by direct immunofluorescence, and in 50 per cent or less ofA. aegypti mosquitoes by immunoperoxidase and immunofluorescence, with somewhat greater regularity by the indirect than the direct technique.This work was supported by Operating Grant MT-2811, Medical Research Council, Canada.     

Ultrastructural studies on the interaction of Plasmodium falciparum ookinetes with the midgut epithelium of Anopheles stephensi mosquitoes

The interaction of Plasmodium falciparum ookinetes with the midgut epithelium of Anopheles stephensi is described by electron microscopy. Plasmodium falciparum ookinetes have been traced during the early stages of invasion and localization beneath the basal lamina of the midgut. It is generally assumed that ookinetes break through two membranes to reach the basal lamina of the midgut epithelium by an intracellular route. In the present study evidence is presented that the ookinete takes an intercellular route in traversing the epithelial layer. Compared to the mode of penetration and intracellular development of sporozoites and merozoites, an intercellular route for penetration of the ookinete is not inconsistent with its further extracellular development.     

Leukocytes in a Plasmodium falciparum-infected blood meal reduce transmission of malaria to Anopheles mosquitoes.

Mosquitoes are infected with Plasmodium falciparum by taking a blood meal from a gametocyte carrier. Since a mosquito takes a volume of 1 to 2 microl, a blood meal may contain 1 x 10(4) to 3 x 10(4) leukocytes (WBC). The majority of WBC are composed of neutrophils which may phagocytose and kill developing gametes inside the mosquito midgut. Phagocytosis was measured in vitro by a luminol-dependent chemiluminescence (CL) assay. In the presence of P. falciparum gametes, sera from areas of endemicity had an increased CL response compared to controls. In mosquito membrane feeding experiments some such sera showed a transmission reduction which was related to the presence of viable WBC. The results of this study suggest that phagocytosis of opsonized gametes inside the mosquito midgut occurs and can contribute to a reduction in the transmission of P. falciparum parasites.     

Blood vessel location time by Anopheles stephensi (Diptera: Culicidae).

Probing behavior of Anopheles stephensi Liston is characterized by the following: the first probe is longer than subsequent ones, the probability of blood location rises initially and then falls, and blood vessel location is deterministic. The overall probing behavior of An. stephensi, therefore, is similar to that of Aedes aegypti (L.); i.e., differences between them were quantitative and may be accounted for by different levels of salivary apyrase and different experimental vertebrate hosts.     

The Chikungunya virus

Chikungunya virus (CHIKV), a member of the Alphavirus genus, represents a real public health problem in tropical regions of the Southeast Asia and Africa. It is transmitted to the man by Aedes mosquitoes and the illness, known as Chikungunya, is characterized by fever, eruptions and invalidating arthralgia. An increased surveillance in tropical and subtropical areas is necessary, as far as we have noticed recently the emergence of this new disease in regions where it had never existed before. The epidemic context is of a high importance for diagnosis. It is very important to know the clinical characteristics of the infection, to detect forms rarely or never described previously. Permanence of a highly technical core in specialized laboratories will allow, fast, specific and differential diagnosis. The knowledge of the epidemiological chain of transmission from reservoir, still unknown, to the host aims to protect populations by limiting the risks of exposure when it is possible. The only prevention measures available are individual protection against mosquitoes and antivectorial fight, in the absence of specific antiviral treatment and vaccine.     

Rubidium marking of Anopheles stephensi (Diptera: Culicidae)

Immature Anopheles stephensi Liston were reared in untreated water and water containing eight 2-fold dilutions of rubidium (Rb) from 1,000 to 7.8 ppm to determine the concentration that allowed reliable detection and produced the least toxic effects as measured by adult emergence, weight, and survival. The amount of Rb detected in mosquitoes increased positively with increasing concentrations in the rearing water. Concentrations > or = 31.2 ppm Rb in the rearing water provided high and consistent detection levels of > or = 3,500 ppm Rb/mg of adult mosquito. There were no adverse effects of Rb on the weights of mosquitoes. However, increased Rb concentrations in the rearing water were associated with decreased emergence and survival. After 8 d, percentage emergence from Rb concentrations of 0-31.2 ppm was > or = 50%. At day 21, Rb concentrations of 0-31.2 ppm showed < or = 29% reduction of female survival compared with controls. The recommended concentration for reliable Rb detection with minimal toxic effects in An. stephensi was 32 ppm.     

Antennal sensory receptors of the male mosquito,Anopheles stephensi

Summary It was shown by electron microscopy that antennae of maleAnopheles stephensi have the same types of sensory receptors as the females, with sunken pegs (sensilla ampullacea and sensilla coeloconica), surface pegs (sensilla basiconica), hairs (sensilla trichodea), bristles and fibrillae (sensilla chaetica), and scolopidia in the Johnston's organ. Compared with the female, the male mosquito has fewer than half of the sensory cells in the flagellum, but many more in the Johnston's organ. The smaller number of flagellar sensory neurons in the male was due mainly to fewer sensory receptors of possibly olfactory types. Sensory cells of mechano- and thermoreceptors were present in almost identical numbers in both sexes, as only about 15% of the long fibrillae, abundant as whorls in the male mosquito, are innervated by a single neuron.     

The effect of Plasmodium yoelii nigeriensis infection on ovarian protein accumulation by Anopheles stephensi

Both anopheline and culicine mosquitoes have been shown to incur a reduction in reproductive fitness when infected with malaria parasites. The agent of rodent malaria, Plasmodium yoelii nigeriensis, was used as a laboratory model to investigate changes in the accumulation of protein in the ovaries of Anopheles stephensi when infected with oocysts or when feeding on mice with heavy asexual parasitaemia but no mature gametocytes. Herein we report that during the early phases of the gonotrophic cycle the ovarian protein content increased normally; however, after 16 h post-blood-feeding there was a significant reduction in the total protein content in ovaries from infected mosquitoes. The development of ovaries from mosquitoes undergoing a second gonotrophic cycle and containing maturing oocysts was similarly affected. Ovarian protein profiles produced by sodi- um dodecyl sulfate-polyacrylamide gel electrophoresis showed a depletion of the yolk protein vitellin. Ovaries from mosquitoes feeding on a mouse with 31 % parasitaemia, no detectable gametocytes and a low haematocrit (29 % packed cell volume) also exhibited a reduction in protein content, although this did not occur until much later in the gonotrophic cycle. The role of blood-meal quality and malaria infection in the reduction in egg production is discussed. Received: 18 October 1996 / Accepted: 15 November 1996     

Rates of infection in, and transmission of, African horse-sickness virus by Aedes aegypti mosquitoes.

Very low infection rates (less than 3%) were obtained when Aedes aegypti mosquitoes ingested blood contained 5.8--6.5 log10 MLD50/0.02 ml African horse sickness virus (AHSV). When A. aegypti mosquitoes were inoculated intrathoracically with virus, however, high infection rates were achieved. Mosquitoes infected by inoculum failed to transmit virus to embryonated hens eggs by bite, and virus could not be detected in membrane or blood when inoculated mosquitoes were allowed to engorge on uninfected blood through a chick skin membrane. It was concluded that the mosquito A. aegypti is unlikely to be an effective vector of AHSV.