海南岛两个虫媒病毒分离物的初步鉴定

本文报告,1985年夏从海南岛采集的6种蚊子中,分离到4株乙型脑炎病毒和38株非乙脑病毒,其中两株(HN8和HN99)为甲组虫媒病毒。二者抗原性非常相近,对乳小白鼠脑内、腹腔和皮下接种部有较强的致病力,能在多种组织培养细胞上增殖并产生病变,能在鸡胚纤维母细胞上形成空斑,能凝集多种动物红细胞,血凝pH范围为5.75～6.4,最适pH为5.75或6.0,血凝素在4～37℃均较稳定,血凝素对福尔马林敏感。病毒呈球形,有包膜,直径60～65nm,属RNA病毒,对热、酸、乙醚和紫外线均敏感。血清学鉴定表明这两株病毒只与甲组虫媒病毒抗体有反应,尤其与MAY病毒抗原性关系较密切。同年从当地人、畜血清中检查了HN99病毒抗体,其阳性率为:健康人14％,猪23％,山羊35％。另外还与北京的M4株病毒作了初步比较,并对新毒株及我国其它有关毒株的分类学地位提出了初步看法。     

Bioinsecticide and leaf litter combination increases oviposition and reduces adult recruitment to create an effective ovitrap for Culex mosquitoes

Mosquito egg traps, aquatic habitats baited with oviposition attractant and insecticide, are important tools for surveillance and control efforts in integrated vector management programs. The bioinsecticide Bacillus thuringiensis subsp. israelensis (Bti) is increasingly used as an environmentally friendly alternative to chemical insecticides and the combination of Bti with a simple oviposition attractant like leaf litter to create an effective egg trap seems appealing. However, previous research suggests that Bti may itself alter oviposition, and that leaf litter may dramatically reduce Bti toxicity. Here we present results from field experiment designed to link the effects of litter and Bti on mosquito oviposition habitat selection and post‐colonization survival to production of adult mosquitoes. Tripling litter increased Culex spp. oviposition nearly nine‐fold, while Bti had no effect on oviposition. Neither factor altered egg survival, thus larval abundance reflected the effects of litter on oviposition. Both Bti and litter reduced larval survival by ～60%. We found no evidence that increased litter reduced Bti toxicity. Adult production was dependent upon both litter and Bti. In the absence of Bti, effects of litter on oviposition translated into three‐fold more adults. However, in the presence of Bti, initial increases in oviposition were erased by the combined negative effects of Bti and litter on post‐colonization survival. Thus, our study provides field evidence that combined litter and Bti application creates an effective ovitrap. This combined treatment had the highest oviposition and the lowest survival, and thus removed the greatest number of mosquitoes from the landscape.     

Culicoides biting midges (Diptera,Ceratopogonidae) in various climatic zones of Russia and adjacent lands

Culicoides biting midges play an important role in the epidemiology of many vector‐borne infections, including bluetongue virus, an internationally important virus of ruminants. The territory of the Russian Federation includes regions with diverse climatic conditions and a wide range of habitats suitable for Culicoides. This review summarizes available data on Culicoides studied in the Russian Federation covering geographically different regions, as well as findings from adjacent countries. Previous literature on species composition, ranges of dominant species, breeding sites, and host preferences is reviewed and suggestions made for future studies to elucidate vector‐virus relationships.     

Vector competence of northern and southern European Culex pipiens pipiens mosquitoes for West Nile virus across a gradient of temperatures

In Europe, West Nile virus (WNV) outbreaks have been limited to southern and central European countries. However, competent mosquito vectors and susceptible bird hosts are present in northern Europe. Differences in temperature and vector competence of mosquito populations may explain the absence of WNV outbreaks in northern Europe. The aim of the present study was to directly compare vector competence of northern and southern European Culex pipiens (Cx. p.) pipiens mosquitoes for WNV across a gradient of temperatures. WNV infection and transmission rates were determined for two Cx. p. pipiens populations originating from The Netherlands and Italy, respectively. Mosquitoes were orally exposed by providing an infectious bloodmeal, or by injecting WNV (lineage 2) in the thorax, followed by 14‐day incubation at 18, 23, or 28 °C. No differences in infection or transmission rates were found between the Cx. p. pipiens populations with both infection methods, but WNV transmission rates were significantly higher at temperatures above 18 °C. The absence of WNV outbreaks in northern Europe cannot be explained by differences in vector competence between Cx. p. pipiens populations originating from northern and southern Europe. This study suggests that low temperature is a key limiting factor for WNV transmission.     

Health evaluation of translocated free-ranging primates in French Guiana

Among over 40 mammal species threatened by the filling of a hydroelectric dam reservoir in French Guiana, three species of primates have been translocated, comprising 124 red howler monkeys, six white-faced sakis, and 95 golden-handed tamarins. Health status of the animals was evaluated by direct physical examination and by hematological, biochemical, virological, and parasitological surveys of collected blood. The physical condition of the howlers was slightly worse toward the end of the capture period, but that of sakis and tamarins remained satisfactory. Several ectoparasites (ticks, larvae of dipterous insects, fleas, and lice) were collected, and various wounds, apparently nondebilitating, were recorded in howlers. Hematological and biochemical profiles determined for the three species revealed a slight anemia in howlers. Entamoeba, Strongyloides, and Trypanoxyurus were common in fecal samples of howlers. A survey of blood smears from the three species revealed infection by several types of microfilaria, Trypanosoma rangeli-like and Plasmodium brasilianum in all three, and Trypanosoma cruzi-like in howlers. These infections had no significant impact on the health status or the hematological profiles. Serologic investigations revealed occasional reactions against Toxoplasma gondii, a strong anti-Plasmodium response in the two Cebidae species, and a weaker one in tamarins. Attempts to isolate arbovirus failed, but antibody responses to Mayaro and yellow fever viruses were strong, especially in the howlers. A strong correlation between age and serological status led to a better understanding of the epidemic cycles. Our survey indicates French Guianan primates are reservoirs for several anthropozoonoses, including malaria, Chagas disease, and arboviruses.     

The 2000 epidemic of Rift Valley fever in Saudi Arabia: mosquito vector studies

In mid-September 2000, Rift Valley fever (RVF) virus was diagnosed as the cause of infection in humans and livestock in Jizan Region, Saudi Arabia. This is the first time that this arbovirus has been found outside Africa and Madagascar. Collections of mosquitoes (Diptera: Culicidae) were therefore undertaken (from 25 September to 10 October) at eight sites during the epidemic to obtain mosquitoes for attempted RVF virus isolation. Among 23 699 mosquito females tested, six isolations of RVF virus were made from 15 428 Culex (Culex) tritaeniorhynchus Giles and seven from 8091 Aedes (Aedimorphus) vexans arabiensis Patton [corrected]. Minimum mosquito infection rates per 1000 at sites with infected mosquitoes were 0.3-13.8 Cx. tritaeniorhynchus and 1.94-9.03 Ae. v. arabiensis. Viral activity moved northwards as collecting was in progress and collectors 'caught up' with the virus at the two most northerly sites on the last two trapping evenings. Other species occurred in small numbers and were identified but not tested. Both Cx. tritaeniorhynchus and Ae. v. arabiensis were susceptible to RVF virus and transmitted between hamsters, and an additional quantitative test with Cx. tritaeniorhynchus showed that 71-73% of mosquitoes became infected after ingesting 6.9-7.9 log10 FFU/mL of virus; transmission rates were 10% (post-infection day 14) and 26% (post-infection day 20). It was concluded that both species were vectors on grounds of abundance, distribution, preference for humans and sheep, the virus isolations and vector competence tests.     

Parity and gonotrophic discordance of females of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in the city of São Paulo,SP, Brazil

The objective of this study was to assess the parity, presence of blood in the stomach, and the gonotrophic discordance of females of Aedes aegypti and Aedes albopictus captured in two areas of the city of São Paulo. The captures were undertaken monthly, by aspiration, in the period from January, 2015 to August, 2017. All the females of the two species had their midguts and ovaries dissected to determine the presence of blood and the parity/stage of maturation. With regard to parity, 27% and 34% of the females of Ae. aegypti and Ae. albopictus, respectively, were parous or were in advanced stages of the development of their ovaries (33% and 27%, respectively). The larger part of the females of Ae. aegypti and Ae. albopictus contained blood in their stomachs (77% and 60%, respectively), beyond which 36% and 27% of the females of Ae. aegypti and Ae. albopictus, respectively, were in gonotrophic discordance. Our results indicate favorable conditions in the study areas because of the presence of parous females. Moreover, this frequent and multiple contact of Ae. aegypti and Ae. albopictus females with vertebrate hosts, such as humans, increases the possibility of transmitting the viruses they may be carrying.     

Molecular approaches to mosquito parasite interactions

The success of vector borne disease transmission depends on the interplay between mosquito and pathogen. Understanding the genetic and molecular basis of refractoriness of mosquito may lead to novel disease control mechanisms. To complete the life cycle within the vector mosquito, a pathogen needs to overcome several physical barriers, such as the peritrophic matrix, midgut epithelium, or salivary glands. The immune response of the mosquito has to be neutralized or avoided. Genomic approaches are being employed to identify the genetic and molecular differences between selected strains of refractory and susceptible mosquitoes. Detailed molecular genetic maps based on restriction fragment length polymorphism (RFLP) and microsatellite (or simple sequence repeat) markers have been developed for two important vectors, Aedes aegypti and Anopheles gambiae, respectively. Recent success in genetic localization of quantitative trait loci controlling refractoriness/susceptibility of mosquitoes for Plasmodium and Brugian microfilariae provides a framework for further molecular characterization. Libraries of large genomic DNA inserts in bacterial or yeast artificial chromosomes (BACs and YACs) will facilitate physical mapping of the genetic loci controlling refractoriness. Identification of candidate refractory genes, and the cloning of other molecular markers for the mosquito immunity, provides tools for fruitful analysis of mosquito-parasite interactions. © 1997 Wiley-Liss, Inc.