The resurgence in cases of neurologic disease caused by West Nile virus (WNV) in the United States in 2012 came as a surprise to the general public and to many non-arbovirus researchers. Following the introduction of WNV into the US in 1999, the number of human infections rose dramatically, peaking in 2002-03. However, cases declined from 2008-11, and it was unclear if the virus would continue to have a low-level endemic transmission pattern with occasional outbreaks, like the related flavivirus, Saint Louis encephalitis virus, or a more active pattern with annual outbreaks, including occasional years with large epidemics, like Japanese encephalitis virus. The large epidemic in 2012 suggests that the United States can expect periodic outbreaks of West Nile fever and neurologic disease in the coming years. In this paper, we consider the causes of the upsurge in WNV infections during the past year and their implications for future research and disease control measures.

Tick-borne viruses are causative agents of several important human diseases. Tick-borne encephalitis virus (TBEV) is the most prominent representative considered medically to be the most important arbovirus (arthropod-borne virus) in Europe and northern Asia. Tick-borne virus transmission cycles are determined by the interactions between viruses, vectors, and their vertebrate hosts. Several mechanisms of tick-borne virus circulation in nature are currently considered to include transovarial transmission via the eggs from an infected female tick to its offspring, "viraemic" transmission between host and tick via feeding on a viraemic, infectious vertebrate hosts, and the virus transmission between co-feeding ticks, termed non-viraemic transmission (NVT). For NVT, the local skin site where ticks aggregately feed is an important focus of viral replication where migratory immune cells provide a vehicle for virus transmission from infected to uninfected co-feeding ticks. For TBEV at least, NVT is an important mechanism of virus maintenance in nature and offers explanations for some specific aspects of tick-borne virus ecology such as focal virus distribution and vector competency of particular tick species. Keywords: routes of transmission; non-viraemic transmission; arbovirus; tick-borne viruses; co-feeding; tick-borne encephalitis virus.

Increases in vector-host contact rates can enhance arbovirus transmission intensity. We investigated weekly fluctuations in contact rates between mosquitoes and nesting birds using the recently described Nest Mosquito Trap (NMT). The number of mosquitoes per nestling increased from < 1 mosquito per trap night to 36.2 in the final 2 wk of the nesting season. Our evidence suggests the coincidence of the end of the avian nesting season and increasing mosquito abundances may have caused a "host funnel," concentrating host-seeking mosquitoes to the few remaining nestlings. The relative abundance of mosquitoes collected by the NMT suggests that significantly more Aedes albopictus (Skuse) and Culex pipiens (L.) /restuans (Theobald) sought nesting bird bloodmeals than were predicted by their relative abundances in CO2-baited Centers for Disease Control and Prevention light and gravid traps. Culex salinarius (Coquillett) and Culex erraticus Dyar and Knab were collected in NMTs in proportion to their relative abundances in the generic traps. Temporal host funnels and nesting bird host specificity may enhance arbovirus amplification and explain observed West Nile virus and St. Louis encephalitis virus amplification periods.

Culex (Diptera: Culicidae) mosquitoes, the primary summer vectors of West Nile virus (family Flaviviridae, genus Flavivirus, WNV), also may serve as overwintering reservoir hosts. Detection of WN viral RNA from larvae hatched from eggs deposited by infected females during late summer and fall may provide evidence for the vertical passage of WNV to overwintering cohorts. To determine whether vertical transmission to the overwintering generation occurs in populations of Culex mosquitoes throughout California, larvae from naturally infected females were tested by family for WN viral RNA by real-time quantitative reverse transcription-polymerase chain reaction during August through October 2011. Viral RNA was detected in 34 of 934 Culex tarsalis Coquillett and Cx. pipiens complex females that laid viable egg rafts. From these egg rafts, first-instar larvae from nine families tested positive, yielding an overall field vertical transmission rate of 26% (n = 34). To determine whether the WNV may be lost transtadially during development to the adult stage, first-instar larvae and adult progeny from experimentally infected Cx. pipiens complex females were assessed for the presence and quantity of WN viral RNA. Most (approximately 75%) WNV infections were lost from positive families during larval development to the adult stage. In field and laboratory studies, only infected mothers with mean cycle threshold scores < or = 20 vertically transmitted WNV to larval progeny, adult progeny, or both. In summary, vertical transmission of WNV was detected repeatedly in naturally infected Culex mosquitoes collected throughout California during late summer and fall, with females having high titered infections capable of passing WNV onto their progeny destined for overwintering.

China has experienced noticeable changes in climate over the past 100 years and the potential impact climate change has on transmission of mosquito-borne infectious diseases poses a risk to Chinese populations. The aims of this paper are to summarize what is known about the impact of climate change on the incidence and prevalence of malaria, dengue fever and Japanese encephalitis in China and to provide important information and direction for adaptation policy making. Fifty-five papers met the inclusion criteria for this study. Examination of these studies indicates that variability in temperature, precipitation, wind, and extreme weather events is linked to transmission of mosquito-borne diseases in some regions of China. However, study findings are inconsistent across geographical locations and this requires strengthening current evidence for timely development of adaptive options. After synthesis of available information we make several key adaptation recommendations including: improving current surveillance and monitoring systems; concentrating adaptation strategies and policies on vulnerable communities; strengthening adaptive capacity of public health systems; developing multidisciplinary approaches sustained by an new mechanism of inter-sectional coordination; and increasing awareness and mobilization of the general public.

St Louis encephalitis virus (SLEV) is a re-emerging human pathogen widely distributed in the American continent. Although it is not fully understood, the SLEV transmission network may involve Culex quinquefasciatus mosquitoes as vectors and Columbidae species as hosts.To calculate infection rates, we inoculated Cx. quinquefasciatus mosquitoes from Córdoba, Argentina by feeding them on viremic chicks.We observed differences in infection rate among the viral strains, the highest rate (78/87 mosquitoes, 90.8%) being seen in strain 78V-6507. After re-feeding on susceptible chicks, mosquitoes were able to transmit the virus.Our findings suggest that Cx. quinquefasciatus populations are susceptible to and able to transmit different SLEV strains.

In 1999 and 2006, two viral diseases emerged massively and unexpectedly in the United States (West Nile disease) and northern Europe (bluetongue disease). Control of infectious diseases transmitted by insect vectors is based on a variety of approaches (including sanitary measures), but primarily on vaccination. Vaccination is more efficient and less expensive than monitoring of insect vectors. The dynamics and epidemiology of two arboviral diseases (West Nile and bluetongue) are described, together with the different vaccines and vaccination methods.

Infections of the central nervous system (CNS) with cytopathic viruses require efficient T cell responses to promote viral clearance, limit immunopathology, and enhance survival. We found that IL-1R1 is critical for effector T cell reactivation and limits inflammation within the CNS during murine West Nile virus (WNV) encephalitis. WNV-infected IL-1R1(-/-) mice display intact adaptive immunity in the periphery but succumb to WNV infection caused by loss of virologic control in the CNS with depressed local Th1 cytokine responses, despite parenchymal entry of virus-specific CD8(+) T cells. Ex vivo analysis of CD4(+) T cells from WNV-infected CNS of IL-1R1(-/-) mice revealed impaired effector responses, whereas CD8(+) T cells revealed no cell intrinsic defects in response to WNV antigen. WNV-infected, IL-1R1(-/-) mice also exhibited decreased activation of CNS CD11c(+)CD11b(-)CD103(+) and CD11c(+)CD11b(-)CD8α(+)Dec-205(+) cells with reduced up-regulation of the co-stimulatory molecules CD80, CD86, and CD68. Adoptive transfer of wild-type CD11c-EYFP(+) cells from WNV-infected CNS into WNV-infected IL-1R1(-/-) mice trafficked into the CNS restored T cell functions and improved survival from otherwise lethal infection. These data indicate that IL-1R1 signaling promotes virologic control during WNV infection specifically within the CNS via modulation of CD11c(+) cell-mediated T cell reactivation at this site.

A seroprevalence study for anti-West Nile virus-specific antibodies was carried out in healthy blood donors resident in the metropolitan area of Milan in two different years, 2009 and 2011. In 2009 no positive sera were found, whereas 5 positive sera were found in 2011, revealing viral circulation in this naive area. The seroprevalence rate identified in 2011 was 0.57%, suggesting that the area of WNV circulation in Italy is larger than that previously identified.