Horizontal and Vertical Transmission of West Nile Virus by Aedes vexans (Diptera: Culicidae).

West Nile virus (family Flaviviridae, genus Flavivirus) first caused human and veterinary disease, and was isolated from Culex pipiens pipiens L. and Aedes vexans (Meigen) (Diptera: Culicidae) in the United States in 1999. We report that a Connecticut strain of Ae. vexans was competent to transmit West Nile virus both horizontally to suckling mice and vertically to its progeny in the laboratory. Horizontal transmission was first observed on day 6 post-exposure (pe). Daily horizontal transmission rates generally increased with the day post-virus exposure with highest rates of 67-100% recorded on days 28-30 pe. One female vertically transmitted West Nile virus on day 21 pe, but only after it had taken its third bloodmeal. Horizontal and vertical transmission may contribute to West Nile virus infection rates in Ae. vexans in summer, and vertical transmission provides a means of survival of West Nile virus during winter.

Spatial-temporal analysis of Cache Valley virus (Bunyaviridae: Orthobunyavirus) infection in anopheline and culicine mosquitoes (Diptera: Culicidae) in the northeastern United States, 1997-2012.

Cache Valley virus (CVV) is a mosquito-borne bunyavirus (family Bunyaviridae, genus Orthobunyavirus) that is enzootic throughout much of North and Central America. White-tailed deer (Odocoileus virginianus) have been incriminated as important reservoir and amplification hosts. CVV has been found in a diverse array of mosquito species, but the principal vectors are unknown. A 16-year study was undertaken to identify the primary mosquito vectors in Connecticut, quantify seasonal prevalence rates of infection, and define the spatial geographic distribution of CVV in the state as a function of land use and white-tailed deer populations, which have increased substantially over this period. CVV was isolated from 16 mosquito species in seven genera, almost all of which were multivoltine and mammalophilic. Anopheles (An.) punctipennis was incriminated as the most consistent and likely vector in this region on the basis of yearly isolation frequencies and the spatial geographic distribution of infected mosquitoes. Other species exhibiting frequent temporal and moderate spatial geographic patterns of virus isolation within the state included Ochlerotatus (Oc.) trivittatus, Oc. canadensis, Aedes (Ae.) vexans, and Ae. cinereus. New isolation records for CVV were established for An. walkeri, Culiseta melanura, and Oc. cantator. Other species from which CVV was isolated included An. quadrimaculatus, Coquillettidia perturbans, Culex salinarius, Oc. japonicus, Oc. sollicitans, Oc. taeniorhynchus, Oc. triseriatus, and Psorophora ferox. Mosquitoes infected with CVV were equally distributed throughout urban, suburban, and rural locales, and infection rates were not directly associated with the localized abundance of white-tailed deer, possibly due to their saturation throughout the region. Virus activity in mosquitoes was episodic with no consistent pattern from year-to-year, and fluctuations in yearly seasonal infection rates did not appear to be directly impacted by overall mosquito abundance. Virus infection in mosquitoes occurred late in the season that mostly extended from mid-August through September, when adult mosquito populations were visibly declining and were comparatively low. Findings argue for a limited role for vertical transmission for the perpetuation of CVV as occurs with other related bunyaviruses.

Control of mosquitoes in catch basins in Connecticut with Bacillus thuringiensis israelensis, Bacillus sphaericus, [corrected] and spinosad.

Catch basins are a major source of Culex pipiens pipiens, Cx. restuans, and Aedes japonicus in northeastern USA. VectoBac CG (Bacillus thuringiensis israelensis [Bti]), VectoLex CG (Bacillus sphaericus [Bs]), and VectoBac 12AS (Bti), each applied at maximum label rate of 1.8 g, 1.8 g, and 0.193 ml per catch basin, respectively, significantly reduced the numbers of larvae for 1 wk. The dosages on the labels for treatment of mosquito larvae in catch basins, where mosquito breeding is continuous, are not adequate for providing long-term control in the northeastern USA without the need for frequent retreatment. When applied at 3 times the maximum label rate, VectoLex CG, VectoBac 12AS, and VectoBac CG significantly reduced the numbers of larvae for 5, 4, and 2 wk, respectively. A single application of VectoMax WSP (Bti + Bs) (1 pouch containing 10 g) per catch basin significantly reduced the numbers of 3rd and 4th instars and healthy pupae in catch basins in 2008, but numbers of 3rd and 4th instars in treated catch basins at 21 days after treatment had increased to 40% of the numbers in untreated catch basins. A 2nd treatment of 1 pouch per catch basin reduced the numbers of 3rd and 4th instars and healthy pupae to near zero for the next 4 wk, into the middle of September 2008. In 2009, VectoMax applied as 1 pouch per catch basin on July 1 and again on August 18 significantly reduced the numbers of healthy pupae throughout the summer until the end of September. A 2nd application of VectoMax to catch basins is likely needed during summer, when rainfall averages 13.7 in. (approximately 34.25 cm) during June through September, to keep the numbers of Culex and Ae. japonicus significantly reduced to lower risk of human exposure to West Nile virus. The application of 1 Natular XRT tablet, each weighing approximately 40.5 g (6.25% spinosad), to individual catch basins in 2009 significantly reduced the total numbers of larvae for 5 wk.

Isolations of Jamestown Canyon virus (Bunyaviridae: Orthobunyavirus) from field-collected mosquitoes (Diptera: Culicidae) in Connecticut, USA: a ten-year analysis, 1997-2006.

Jamestown Canyon virus (JCV) (Bunyaviridae: Orthobunyavirus) is a mosquito-borne zoonosis belonging to the California serogroup. It has a wide geographic distribution, occurring throughout much of temperate North America. White-tailed deer, Odocoileus virginianus are the principal amplification hosts, and boreal Aedes and Ochlerotatus mosquitoes are the primary vectors. A 10-year study was undertaken to identify potential mosquito vectors in Connecticut, quantify seasonal prevalence rates of infection, and define the geographic distribution of JCV in the state as a function of land use and white-tailed deer populations, which have increased substantially over this period. Jamestown Canyon virus was isolated from 22 mosquito species. Five of them, Ochlerotatus canadensis, Oc. cantator, Anopheles punctipennis, Coquillettidia perturbans, and Oc. abserratus were incriminated as the most likely vectors, based on yearly isolation frequencies and the spatial geographic distribution of infected mosquitoes. Jamestown Canyon virus was isolated from Oc. canadensis more consistently and from a greater range of collection sites than any other species. Frequent virus isolations were also made from Aedes cinereus, Aedes vexans, and Oc. sticticus, and new North American isolation records were established for Anopheles walkeri, Culex restuans, Culiseta morsitans, Oc. sticticus, Oc. taeniorhynchus, and Psorophora ferox. Other species from which JCV was isolated included C. melanura, Oc. aurifer, Oc. communis, Oc. excrucians, Oc. provocans, Oc. sollicitans, Oc. stimulans, Oc. triseriatus, and Oc. trivittatus. Jamestown Canyon virus was widely distributed throughout Connecticut and found to consistently circulate in a diverse array of mosquito vectors. Infected mosquitoes were collected from June through September, and peak infection rates paralleled mosquito abundance from mid-June through mid-July. Infection rates in mosquitoes were consistent from year to year, and overall virus activity was directly related to local mosquito abundance. Infected mosquitoes were equally distributed throughout the state, irrespective of land use, and infection rates were not directly associated with the abundance of white-tailed deer, possibly because of their saturation throughout the region.

Bionomics of phlebotomine sandflies at a peacekeeping duty site in the north of Sinai, Egypt.

A longitudinal entomological survey for sandflies was conducted from 1989 to 1991 at a focus of enzootic cutaneous leishmaniasis in Northeast Sinai, Egypt, within the border region monitored by multinational peacekeepers. Standardized sampling with CDC light traps, oiled paper "sticky traps", and human landing collection was employed to determine monthly trends in species composition, density, sex ratio, and reproductive status of vector sandflies. Each collection method independently defined sandfly seasonality as the period May-November in 1990, and March-October in 1991. Plebotomus papatasi was the only anthropophagic species found and comprised more than 94% of the sandfly population. Two population peaks (May, July) were observed for this species in both survey years. Density of P. papatasi in underground bunkers was higher than outside but inflated by a greater proportion of male flies. During 1990, the proportion of gravid P. papatasi increased progressively during the 5 months period from May to September and averaged 29.5% and 29.7% for interior and exterior collections, respectively. Density of P. papatasi was greater during 1991, but proportions of gravid flies were significantly lower in each survey month and averaged 14.9% and 12.3% for interior and exterior collections, respectively. Seasonal rates of Leishmania-infected P. papatasi averaged 0.8% and 0.9% in 1989 and 1990, but fell to zero in 1991, suggesting an unstable focus of Leishmania major transmission. Proportions of gravid flies may be a valid indicator of the physiological age and epidemiologic importance of the vector sandfly population at this focus. The strong correlation of sticky trap indices to human-landing/biting rates shows that this is an accurate, inexpensive, and no-risk alternative to human bait collections.

Isolations of Potosi virus from mosquitoes (Diptera: Culicidae) collected in Connecticut.

Potosi virus (POTV) (Bunyaviridae: Orthobunyavirus) was first isolated from Aedes albopictus (Skuse) collected in Potosi, MO, in 1989, and subsequent isolations were reported from Illinois, Michigan, Ohio, and the Carolinas. To determine whether the distribution of this virus extends into the northeastern United States, we analyzed arboviruses acquired from mosquitoes collected in Connecticut from 1998 to 2004. In 2001, a bunyavirus was isolated from Aedes vexans (Meigen) that was different from other arboviruses known to occur in Connecticut by cross-neutralization and reverse transcription-polymerase chain reaction (RT-PCR) assays. Nucleotide and encoded amino acid sequences of a portion of the G2 envelope gene were 99 and 100% similar to POTV, respectively, yet distinct from indigenous strains of Jamestown Canyon (JCV), Cache Valley (CVV), and Trivittatus virus (TVTV). Viral isolates obtained from the statewide surveillance program were retested by RT-PCR coupled with restriction enzyme analysis to distinguish POTV from other bunyaviruses. POTV isolates, previously typed by neutralization, were correctly identified by RT-PCR; however, many isolates classified as JCV or CVV by enzyme-linked immunosorbent assay proved to be POTV by molecular assays. In total, 92 strains of POTV were isolated from 12 mosquito species in 2000, 2001, and 2003, whereas POTV was not detected in mosquitoes sampled during 1998, 1999, 2002, and 2004. Viral isolation rates were highest for Anopheles punctipennis (Say) (3.2-11.3 infection rate per 1,000 mosquitoes), whereas the greatest number of isolates came from Ochlerotatus trivittatus (Coquillett) (8-16 isolates). This finding represents the first detection of POTV in the northeastern United States where it infects a diverse array of mosquito species.

Epidemiology of West Nile virus in Connecticut: a five-year analysis of mosquito data 1999-2003.

Two hundred and ten isolations of West Nile virus (WNV) were obtained from 17 mosquito species in six genera in statewide surveillance conducted in Connecticut from June through October, 1999-2003. Culex pipiens (86), Culex salinarius (32), Culex restuans (26), Culiseta melanura (32), and Aedes vexans (12) were implicated as the most likely vectors of WNV in the region based on virus isolation data. Culex pipiens was abundant from July through September and is likely involved in early season enzootic transmission and late season epizootic amplification of the virus in wild bird populations. Epidemic transmission of WNV to humans in urban locales is probable. The abundance of Cx. restuans in June and July and isolations of WNV in early July suggest that this species may play an important role as an enzootic vector involved in early amplification of WNV virus among wild birds. Its involvement as a bridge vector to humans is unlikely. Culex salinarius was the most frequently captured Culex species and was abundant in August and September when virus activity was at its height. Frequent isolations of WNV from this species in September when the majority of human cases were reported in union with its abundance at this time of the year, demonstrated vector competence, and broad feeding habits, make Cx. salinarius a likely bridge vector to humans, horses and other mammals. Multiple isolations WNV from Cs. melanura collected in more rural locales in late August and September, provide supportive evidence to suggest that this predominant avian feeder may play a significant role in epizootic amplification of the virus among wild bird populations in these environs. Aedes vexans was the only species of Aedes or Ochlerotatus from which multiple isolations of WNV were made in more than one year and was among the most frequently trapped and abundant species throughout the season. Since Ae. vexans predominately feeds on mammals it is unlikely to play a significant role in epizootic amplification of WNV, however, because of its abundance and aggressive mammalian and human biting behavior it must receive strong consideration as a bridge vector to humans and horses. The occasional virus isolations obtained from Aedes cinereus (4), Uranotaenia sapphirina (3), Ochlerotatus canadensis (2), Ochlerotatus trivittatus (2), Ochlerotatus sollicitans (2), Ochlerotatus sticticus (2), Psorophora ferox (2), Anopheles punctipennis, Anopheles walkeri, Ochlerotatus cantator, Ochlerotatus taeniorhynchus, and Ochlerotatus triseriatus in conjunction with their inefficient vector competency and host feeding preferences indicate that these species likely play a very minor role in either the enzootic maintenance or epizootic transmission of WNV in this region. The principal foci of WNV activity in Connecticut were identified as densely populated (>3,000 people/mi2) residential communities in coastal Fairfield and New Haven Counties, and in the case of 2002, similar locales in proximity of the city of Hartford in central Hartford County. In almost all instances we observed a correlation both temporally and spatially between the isolation of WNV from field-collected mosquitoes and subsequent human cases in these locales. In most years the incidence of human cases closely paralleled the number of virus isolations made from mosquitoes with both peaks falling in early September. We conclude that the isolation of WNV from field-collected mosquitoes is a sensitive indicator of virus activity that is associated with the risk of human infection that habitually extends from early August through the end of October in Connecticut.

Transstadial transfer of West Nile virus by three species of ixodid ticks (Acari: Ixodidae).

Larvae and/or nymphs of four species of ixodid ticks, Ixodes scapularis Say, Amblyomma americanum (L.), Dermacentor andersoni Stiles, and Dermacentor variabilis Say, were fed to completion on laboratory hamsters or mice which had been inoculated with a West Nile (WN) virus isolate from Culex pipiens L. captured in Connecticut USA. Maximum titers in mice and hamsters were approximately 5 and two logs, respectively, lower than recorded (10 logs) in a naturally infected American crow, Corvus brachyrhynchos Brehm. WN virus was isolated in Vero cell culture from ticks and detected by TaqMan RT-polymerase chain reaction (PCR) in ticks that had completed their feeding as larvae or nymphs, and in I. scapularis, D. andersoni, and D. variabilis that had molted into the next stage of development. Naive hosts, fed upon by nymphs that as larvae had fed on viremic hosts, did not become infected. WN virus was isolated in Vero cell culture from one female I. scapularis and was detected by TaqMan RT-PCR in 24 adult I. scapularis, one D. andersoni, and two D. variabilis adults that had fed to completion as larvae on viremic hosts and as nymphs on naive mice or hamsters. Three species of ixodid ticks acquired WN virus from viremic hosts and transstadially passed the virus, but vector competency was not demonstrated.