Evidence of Efficient Transovarial Transmission of Culex Flavivirus by Culex pipiens (Diptera: Culicidae)

This study determined the transovarial transmission (TOT) potential and tissue tropisms of Culex flavivirus (CxFV), an insect-specific flavivirus, in Culex pipiens (L.). Several hundred mosquito egg rafts were collected in the field, transferred to the insectaries, reared to the fourth larval instar, and identified using morphological characteristics. Cx. pipiens were reared to adults, allowed to oviposit in individual containers, and tested for CxFV RNA by reverse transcription-polymerase chain reaction (RT-PCR) and nucleotide sequencing. Eighteen CxFV RNA-positive females were identified from 26 females that oviposited viable egg rafts. Thirty F1 adults from each positive female were individually tested by RT-PCR for CxFV RNA. Viral RNA was detected in 526 of 540 progeny, and thus, the filial infection rate was 97.4%. Because all 18 positive females produced infected offspring, the TOT prevalence was 100%. These data indicated that efficient TOT of CxFV occurs in nature. To define the tissue tropisms of CxFV, different tissues (salivary glands, ovaries, testes, head, fat bodies, and midguts) were removed from the remainder of the F1 and tested by RT-PCR for CxFV RNA. Viral RNA was detected in all tissues. Additionally, uninfected laboratory-colonized Cx. pipiens were infected with CxFV by needle inoculation, and ovaries were collected at 4, 6, 8, and 12 d postinoculation and tested for CxFV RNA by RT-PCR. Viral RNA was detected at all time points, demonstrating that CxFV infects the ovaries as early as 4 d postinoculation. Surprisingly, however, we were unable to demonstrate transovarial transmission despite the presence of viral RNA in the ovaries. Nevertheless, the experiments performed with field-infected Cx. pipiens demonstrate that TOT is an efficient mechanism by which CxFV is maintained in mosquitoes in nature

Transmission dynamics of an insect-specific flavivirus in a naturally infected Culex pipiens laboratory colony and effects of co-infection on vector competence for West Nile virus

AbstractWe established a laboratory colony of Culex pipiens mosquitoes from eggs collected in Colorado and discovered that mosquitoes in the colony are naturally infected with Culex flavivirus (CxFV), an insect-specific flavivirus. In this study we examined transmission dynamics of CxFV and effects of persistent CxFV infection on vector competence for West Nile virus (WNV). We found that vertical transmission is the primary mechanism for persistence of CxFV in Cx. pipiens, with venereal transmission potentially playing a minor role. Vector competence experiments indicated possible early suppression of WNV replication by persistent CxFV infection in Cx. pipiens. This is the first description of insect-specific flavivirus transmission dynamics in a naturally infected mosquito colony and the observation of delayed dissemination of superinfecting WNV suggests that the presence of CxFV may impact the intensity of enzootic transmission of WNV and the risk of human exposure to this important pathogen

The distribution of potential West Nile virus vectors, Culex pipiens pipiens and Culex pipiens quinquefasciatus (Diptera: Culicidae), in Mexico City

<p>Abstract</p> <p>Background</p> <p><it>Culex </it>spp. mosquitoes are considered to be the most important vectors of West Nile virus (WNV) detected in at least 34 species of mosquitoes in the United States. In North America, <it>Culex pipiens pipiens, Culex pipiens quinquefasciatus</it>, and <it>Culex tarsalis </it>are all competent vectors of WNV, which is considered to be enzootic in the United States and has also been detected in equines and birds in many states of Mexico and in humans in Nuevo Leon. There is potential for WNV to be introduced into Mexico City by various means including infected mosquitoes on airplanes, migrating birds, ground transportation and infected humans. Little is known of the geographic distribution of <it>Culex pipiens </it>complex mosquitoes and hybrids in Mexico City. <it>Culex pipiens pipiens </it>preferentially feed on avian hosts; <it>Culex pipiens quinquefasciatus </it>have historically been considered to prefer mammalian hosts; and hybrids of these two species could theoretically serve as bridge vectors to transmit WNV from avian hosts to humans and other mammalian hosts. In order to address the potential of WNV being introduced into Mexico City, we have determined the identity and spatial distribution of <it>Culex pipiens </it>complex mosquitoes and their hybrids.</p> <p>Results</p> <p>Mosquito larvae collected from 103 sites throughout Mexico City during 2004-2005 were identified as <it>Culex, Culiseta </it>or <it>Ochlerotatus </it>by morphological analysis. Within the genus <it>Culex</it>, specimens were further identified as <it>Culex tarsalis </it>or as belonging to the <it>Culex pipiens </it>complex. Members of the <it>Culex pipiens </it>complex were separated by measuring the ratio of the dorsal and ventral arms (DV/D ratio) of the male genitalia and also by using diagnostic primers designed for the <it>Ace.2 </it>gene. <it>Culex pipiens quinquefasciatus </it>was the most abundant form collected.</p> <p>Conclusions</p> <p>Important WNV vectors species, <it>Cx. p. pipiens</it>, <it>Cx. p. quinquefasciatus </it>and <it>Cx. tarsalis</it>, are all present in Mexico City. Hybrids of <it>Cx. p. pipiens </it>and <it>Cx. p. quinquefasciatus </it>were also collected and identified. The presence and abundance of these WNV competent vectors is a cause for concern. Understanding the distribution of these vectors can help improve viral surveillance activities and mosquito control efforts in Mexico City.</p

Use of Geographic Information System and Remote Sensing Technologies to Describe Mosquito Population Dynamics in the Ray Roberts Greenbelt, Denton County, Texas

A population survey was conducted from April through September 2002 on mosquito species occurring on the Ray Roberts Greenbelt, a riparian corridor used for public recreation on the Elm Fork of the Trinity River, in Denton County, Texas. ArcGIS software was used to set up a stratified random sampling design based on habitat parameters. Multivariate analyses of sampling data and climatic variables were used to describe spatial and temporal patterns of mosquito species. A total of 33 species were collected during this study belonging to the following genera: Aedes, Anopheles, Coquillettidia, Culex, Mansonia, Ochlerotatus, Orthopodomyia, Psorophora, Toxorhynchites, and Uranotaenia. Seasonal distributions of the dominant species revealed population fluctuations. Aedes vexans was the primary species collected in April and May, occurring in low numbers throughout the rest of the sampling period. Psorophora columbiae reached its highest population density in June, with a smaller peak occurring in late July. Present from May through the end of September, Culex erraticus was the most abundant species collected with major peaks in mid-June and the end of July. Abundance of Culex salinarius followed the same general trend as that for Cx. erraticus, but with smaller numbers. The specimens were tested for a variety of arboviruses by the Texas Department of Health. One pool of Cx. erraticus and Cx. salinarius, collected in August 2002, tested positive for West Nile virus. Variables that were important factors for determining dominant species abundance were temperature, wind speed, rain accumulation occurring one-week and two-weeks prior to sampling, number of day since last rain event, dew point, and average canopy coverage

Flavivirus surveillance in mosquitoes from northern Colorado, with the detection and description of two insect-specific flaviviruses

Department Head: Edward Arthur Hoover.2010 Spring.Includes bibliographical references (pages 107-121).Vector-borne diseases remain a major public health concern worldwide. The studies described here underline the importance of combining field surveillance activities with laboratory experiments to provide a comprehensive understanding of the dynamics of vector-borne disease systems. Entomological measures of West Nile virus (WNV) risk were found to be strongly associated with human WNV disease cases in northeastern Colorado. Specifically, Culex tarsalis abundance and the Vector Index for WNV-infected Cx. Tarsalis females (weekly mean per trap night x weekly proportion of WNV-infected females) were associated with weekly numbers of WNV human disease cases with lag times of 4-7 weeks and 1-2 weeks, respectively. This provides information that can be utilized for decision-making processes concerning when to initiate mosquito control activities and how to best utilize limited resources. These studies also describe the first detection of insect-specific flaviviruses in mosquitoes collected in Colorado. Culex flavivirus (CXFV), first described in Japan in 2007, and a new insect-specific flavivirus, designated Calbertado virus, were detected in Culex spp. mosquitoes. Experiments were conducted to explore the transmission dynamics of CXFV in a naturally infected Culex pipiens laboratory colony and also the potential effects of CXFV infection on vector competence for WNV. Results indicated that vertical transmission is the primary mechanism for viral persistence in the colony, with venereal transmission perhaps playing a supplemental role. Vector competence experiments suggested possible suppression of WNV replication by persistent CXFV infection. These findings are important as insect-specific flavivirus transmission dynamics have not been described yet and studies investigating putative interactions between insect-specific flaviviruses with arboviruses, like WNV, are lacking. This work provides a better understanding of local vector-borne disease systems, providing a basis for additional studies to further characterize the dynamics of co-circulating flaviviruses in vector mosquitoes

Evidence of Efficient Transovarial Transmission of Culex Flavivirus by Culex pipiens (Diptera: Culicidae)

This study determined the transovarial transmission (TOT) potential and tissue tropisms of Culex flavivirus (CxFV), an insect-specific flavivirus, in Culex pipiens (L.). Several hundred mosquito egg rafts were collected in the field, transferred to the insectaries, reared to the fourth larval instar, and identified using morphological characteristics. Cx. pipiens were reared to adults, allowed to oviposit in individual containers, and tested for CxFV RNA by reverse transcription-polymerase chain reaction (RT-PCR) and nucleotide sequencing. Eighteen CxFV RNA-positive females were identified from 26 females that oviposited viable egg rafts. Thirty F1 adults from each positive female were individually tested by RT-PCR for CxFV RNA. Viral RNA was detected in 526 of 540 progeny, and thus, the filial infection rate was 97.4%. Because all 18 positive females produced infected offspring, the TOT prevalence was 100%. These data indicated that efficient TOT of CxFV occurs in nature. To define the tissue tropisms of CxFV, different tissues (salivary glands, ovaries, testes, head, fat bodies, and midguts) were removed from the remainder of the F1 and tested by RT-PCR for CxFV RNA. Viral RNA was detected in all tissues. Additionally, uninfected laboratory-colonized Cx. pipiens were infected with CxFV by needle inoculation, and ovaries were collected at 4, 6, 8, and 12 d postinoculation and tested for CxFV RNA by RT-PCR. Viral RNA was detected at all time points, demonstrating that CxFV infects the ovaries as early as 4 d postinoculation. Surprisingly, however, we were unable to demonstrate transovarial transmission despite the presence of viral RNA in the ovaries. Nevertheless, the experiments performed with field-infected Cx. pipiens demonstrate that TOT is an efficient mechanism by which CxFV is maintained in mosquitoes in nature.This article is from Journal of Medical Entomology 48 (2011): 1031–1038, doi:10.1603/ME11043.</p

Insect-Specific Virus Discovery: Significance for the Arbovirus Community

Arthropod-borne viruses (arboviruses), especially those transmitted by mosquitoes, are a significant cause of morbidity and mortality in humans and animals worldwide. Recent discoveries indicate that mosquitoes are naturally infected with a wide range of other viruses, many within taxa occupied by arboviruses that are considered insect-specific. Over the past ten years there has been a dramatic increase in the literature describing novel insect-specific virus detection in mosquitoes, which has provided new insights about viral diversity and evolution, including that of arboviruses. It has also raised questions about what effects the mosquito virome has on arbovirus transmission. Additionally, the discovery of these new viruses has generated interest in their potential use as biological control agents as well as novel vaccine platforms. The arbovirus community will benefit from the growing database of knowledge concerning these newly described viral endosymbionts, as their impacts will likely be far reaching