Spatio-temporal analyses of West Nile virus transmission in Culex mosquitoes in northern Illinois, USA, 2004

After a severe outbreak of West Nile virus (WNV) in Cook County, Illinois, in 2002, detections of WNV in mosquitoes were frequent across the state in the following years despite small numbers of human cases. We conducted a spatio-temporal analysis of Culex (subgenus Culex) mosquitoes collected in 2004 in three mosquito abatement districts (MAD) in Cook County by calculating monthly estimates of mosquito density, prevalence of infected mosquitoes, and exposure intensity, which in turn is a product of mosquito density and infection rates. Mosquito infections were detected early at three sites in late May and were widely detected throughout the three MADs in the summer with infection rates as high as 13 per 1000 in August. Exposure intensities were higher at sites adjacent to the Des Plaines River, especially in August and September. The aggregated pattern of WNV transmission along the river might be related to the existence of substantial forest preserves and wetlands that might produce ecological conditions favorable for mosquito proliferation and interactions between mosquitoes and birds.

Seasonality and geographical occurrence of West Nile fever and distribution of Asian tiger mosquito

The importance and risk of emerging mosquito borne diseases is going to increase in the European temperate areas due to climate change. The present and upcoming climates of Transdanubia seem to be suitable for the main vector of Chikungunya virus, the Asian tiger mosquito, Aedes albopictus Skuse (syn. Stegomyia albopicta). West Nile fever is recently endemic in Hungary. We used climate envelope modeling to predict the recent and future potential distribution/occurrence areas of the vector and the disease. We found that climate can be sufficient to explain the recently observed area of A. albopictus, while in the case of West Nile fever, the migration routes of reservoir birds, the run of the floodplains, and the position of lakes are also important determinants of the observed occurrence.

Seasonal abundance and molecular identification of West Nile virus vectors, Culex pipens and Culex quinquefasciatus (diptera: culicidae) in Abeokuta, South-West, Nigeria.

Background: West Nile virus (WNV) infection, is an arbovirus infection with high morbidity and mortality, the vector responsible for both human and animal transmission is Culex pipens complex. Objective: To determine the species distribution and seasonal abundance of Culex pipens and Culex quinquefasciatus mosquitoes in Abeokuta, Nigeria. Methods: Mosquitoes belonging to the Culex pipens complex were captured in three different locations located within Abeokuta Metropolis between March 2012 and January 2013. Individual species were identified using morphometric methods. Amplification of the Ace2 gene by PCR confirmed morphormetric identification of the mosquitoes. Results: A total of 751 mosquitoes were captured. Culex quinquefaciatus recorded the highest distribution of vectors with 56.6% and Culex pipens 43.4% (P > 0.05). Idi aba community recorded the highest distribution of mosquito vectors with 42.9% (n=322) and Culex quinqueaciatus was more abundantly distributed with 183 mosquitoes. Aro community recorded 32% (n=240) of captured mosquitoes with Culex quinquefaciatus having a higher level of abundance and lastly Kemta with a distribution of 25.1% (n=189). Conclusion: Results from this study show that potential vectors of WNV abound within Abeokuta, putting residents at high risk of West Nile infection. We advocate for introduction of routine testing of WNV in Abeokuta and Nigeria. Keywords:

2016 West Nile Virus Cases

Most people get infected with West Nile virus by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread the virus to humans and other animals. In a very small number of cases, West Nile virus has been spread through blood transfusions, organ transplants, and from mother to baby during pregnancy, delivery, or breastfeeding. Recovery from severe disease may take several weeks or months. Some of the neurologic effects may be permanent. About 10 percent of people who develop neurologic infection due to West Nile virus will die.

First Record of Culex (Culex) brethesi (Dyar) (Diptera: Culicidae) in Rio Grande do Sul State, Brazil

This is the first record of Culex (Culex) brethesi (Dyar) in Rio Grande do Sul state, Brazil. The species was identified from specimens collected in a sand bar vegetation with the aid of a Nasci's trap, during an expedition for surveillance of the West Nile Virus in July of 2006, in the city of Mostardas, Rio Grande do Sul, Brazil.

Presença de culicídeos em município de porte médio do Estado de São Paulo e risco de ocorrência de febre do Nilo Ocidental e outras arboviroses

INTRODUÇÃO: O objetivo deste estudo foi mensurar a diversidade de espécies de culicídeos, descrever sua abundância e variação sazonal em áreas urbanas e matas de São José do Rio Preto, SP, e discutir o risco de ocorrência de arboviroses. MÉTODOS: Coletas de larvas e de mosquitos adultos foram realizadas mensalmente, em 2006 e 2007, em área urbana e em quatro fragmentos de mata. No perímetro urbano, coletaram-se larvas nos sítios mais prováveis de oviposição para mosquitos do gênero Culex e nas matas foi realizada a coleta de mosquitos adultos, sendo que em duas utilizaram-se armadilhas CDC à noite e, em duas, aspirador de Nasci de dia. RESULTADOS: Na área urbana identificaram-se 34 espécies de culicídeos em um total de 8.683 exemplares; destes, 80,7% corresponderam ao Culex quinquefasciatus, 9,6% ao Culex grupo Coronator, 3,2% ao Aedes albopictus (3,2%) e 1,1% ao Ochlerotatus fluviatilis. A abundância de larvas de Cx. quinquefasciatus correlacionou-se negativamente com a chuva. Nas quatro matas, foram coletados 2.268 mosquitos distribuídos entre 10 gêneros, 46 espécies ou grupos. As mais abundantes foram Aedeomyia squamipennis, Culex. coronator, Culex (Mel.) seção Melanoconion, Culex declarator, Ochlerotatus scapularis, Anopheles triannulatus, Culex bidens/interfor e Culex habilitator/pseudojhantinosoma. CONCLUSÕES: A abundância de Cx. quinquefasciatus na área urbana e a presença de outros culicídeos nas áreas urbanas e de matas apontam para a possibilidade de transmissão do vírus do Nilo Ocidental e de outras arboviroses em São José do Rio Preto e outras cidades do Brasil, sendo fundamental o estabelecimento de medidas visando à vigilância destas arboviroses.

Novos registros e potencial epidemiológico de algumas espécies de mosquitos (Diptera, Culicidae), no Estado do Rio Grande do Sul

INTRODUÇÃO: A vigilância entomológica tem se mostrado uma importante estratégia de monitoramento da fauna de culicídeos com vistas a predizer o risco de exposição a espécies vetoras de patógenos. Esse trabalho apresenta uma lista de mosquitos identificados pela primeira vez no Rio Grande do Sul e discute o potencial epidemiológico de algumas espécies ocorrentes no Município de Maquiné com registros em outras regiões do Estado. MÉTODOS: Os mosquitos foram coletados com aspirador de Nasci e armadilhas CDC, entre dezembro de 2006 e dezembro de 2008, em área silvestre, rural e urbana do Município de Maquiné. RESULTADOS: Foram verificadas 55 espécies, das quais 22 são registradas pela primeira vez no estado e 10 são potencialmente vetoras do vírus Saint Louis, Oropouche, Aura, Trocara, Ilhéus, Rocio, Una, West Nile e encefalite equina do leste. CONCLUSÕES: Esses dados demonstram a importância da Vigilância Entomológica como ferramenta de informação e ação para a Vigilância em Saúde.

Threat of Dengue to Blood Safety in Dengue-Endemic Countries

Dengue, the most common arbovirus infection globally, is transmitted by mosquito vectors. Healthcare-related transmission, including transmission by blood products, has been documented, although the frequency of these occurrences is unknown. Dengue is endemic to Singapore, a city-state in Asia. Using mathematical modeling, we estimated the risk for dengue-infected blood transfusions in Singapore in 2005 to be 1.625-6/10,000 blood transfusions, assuming a ratio of asymptomatic to symptomatic infections of 2:1 to 10:1. However, the level of viremia required to cause clinical dengue cases is person-dependent and unknown. Further studies are needed to establish the magnitude of the threat that dengue poses to blood safety in countries where it is endemic. It will then be possible to assess whether screening is feasible and to identify approaches that are most cost-effective on the basis of characteristics of local populations and seasonality of dengue.

Vector within-host feeding preference mediates transmission of a heterogeneously distributed pathogen

2. We documented the within-host distribution of two vector species that differ in transmission efficiency, the leafhoppers Draeculacephala minerva and Graphocephala atropunctata, and which are free to move throughout entirely caged alfalfa plants. The more efficient vector D. minerva fed preferentially at the base of the plant near the soil surface, whereas the less efficient G. atropunctata preferred overwhelming the top of the plant. 3. Next we documented X. fastidiosa heterogeneity in mechanically inoculated plants. Infection rates were up to 50% higher and mean bacterial population densities were 100-fold higher near the plant base than at the top or in the taproot. 4. Finally, we estimated transmission efficiency of the two leafhoppers when they were confined at either the base or top of inoculated alfalfa plants. Both vectors were inefficient when confined at the top of infected plants and were 20-60% more efficient when confined at the plant base. 5. These results show that vector transmission efficiency is determined by the interaction between leafhopper within-plant feeding behaviour and pathogen within-plant distribution. Fine-scale vector and pathogen overlap is likely to be a requirement generally for efficient transmission of vector-borne pathogens.

Cross-protective and Infection-Enhancing Immunity in Mice Vaccinated Against Flaviviruses Belonging to the Japanese Encephalitis Virus Serocomplex

The Japanese encephalitis virus serocomplex is a group of mosquito-borne flaviviruses that cause severe encephalitic disease in humans. The recent emergence of several members of this serocomplex in geographic regions where other closely related flaviviruses are endemic has raised urgent human health issues. Thus, the impact of vaccination against one of these neurotropic virus on the outcome of infection with a second, serologically related virus is unknown. We show here that immunity against Murray Valley encephalitis virus in vaccinated mice can cross-protect but also augment disease severity following challenge with Japanese encephalitis virus. Immunepotentiation of heterologous flavivirus disease was apparent in animals immunized with a 'killed' virus preparation when humoral antiviral immunty of low magnitude was elicited. (C) 2002 Elsevier Science Ltd. All rights reserved.

Polymerase chain reaction tests for the identification of Ross River, Kunjin and Murray Valley encephalitis virus infections in horses

Objective To develop and validate specific, sensitive and rapid diagnostic tests using RT-PCR for the detection of Ross River virus (RRV), Kunjin virus (KV) and Murray Valley encephalitis virus (MVEV) infections in horses. Methods Primer sets based on nucleotide sequence encoding the envelope glycoprotein E2 of RRV and on the nonstructural protein 5 (NS5) of KV and MVEV were designed and used in single round PCRs to test for the respective viruses in infected cell cultures and, in the case of RRV, in samples of horse blood and synovial fluid. Results The primer pairs designed for each of the three viruses amplified a product of expected size from prototype viruses that were grown in cell culture. The identity of each of the products was confirmed by nucleotide sequencing indicating that in the context used the RT-PCRs were specific. RRV was detected in serums from 8 horses for which there were clinical signs consistent with RRV infection such that an acute-phase serum sample was taken and submitted for RRV serology testing. The RRV RT-PCR was analytically sensitive in that it was estimated to detect as little as 50 TCID50 of RRV per mL of serum and was specific in that the primer pairs did not amplify other products from the 8 serum samples. The RRV primers also detected virus in three independent mosquito pools known to contain RRV by virus isolation in cell culture. Samples from horses suspected to be infected with KV and MVEV were not available. Conclusion Despite much anecdotal and serological evidence for infection of horses with RRV actual infection and associated clinical disease are infrequently confirmed. The availability of a specific and analytically sensitive RT-PCR for the detection of RRV provides additional opportunities to confirm the presence of this virus in clinical samples. The RTPCR primers for the diagnosis of KV and MVEV infections were shown to be specific for cell culture grown viruses but the further validation of these tests requires the availability of appropriate clinical samples from infected horses.

Vector competence of Australian mosquitoes (Diptera : Culicidae) for Japanese encephalitis virus

Australian mosquitoes were evaluated for their ability to become infected with and transmit a Torres Strait strain of Japanese encephalitis virus. Mosquitoes, which were obtained from either laboratory colonies and collected using Centers for Disease Control and Prevention light traps baited with CO2 and octenol or reared from larvae, were infected by feeding on a blood/sucrose solution containing 10(4.5+/-0.1) porcine stable-equine kidney (PS-EK) tissue culture infectious dose(50)/ mosquito of the TS3306 virus strain. After 14 d, infection and transmission rates of 100% and 81%, respectively, were obtained for a southeast Queensland strain of Culex annulirostris Skuse, and 93% and 61%, respectively, for a far north Queensland strain. After 13 or more days, infection and transmission rates of > 90% and greater than or equal to 50%, respectively, were obtained for southeast Queensland strains of Culex sitiens Wiedemann and Culex quinquefasciatus Say, and a far north Queensland strain of Culex gelidus Theobald. Although infection rates were > 55%, only 17% of Ochlerotatus vigilax (Skuse) and no Cx. quinquefasciatus, collected from far north Queensland, transmitted virus. North Queensland strains of Aedes aegypti L., Ochlerotatus kochi (Donitz), and Verrallina funerea (Theobald) were relatively refractory to infection. Vertical transmission was not detected among 673 F, progeny of Oc. vigilax. Results of the current vector competence study, coupled with high field isolation rates, host feeding patterns and widespread distribution, confirm the status of Cx. annulirostris as the major vector of Japanese encephalitis virus in northern Australia. The relative roles of other species in potential Japanese encephalitis virus transmission cycles in northern Australia are discussed.

Bionomics of Culex quinquefasciatus within urban areas of Rio de Janeiro, Southeastern Brazil

OBJECTIVE: To evaluate density, parity rates, daily survival and longevity of natural populations of Culex quinquefasciatus in three neighborhoods with distinct socio-economic and infrastructure profiles. METHODS: Mosquito collections of the Culex quinquefasciatus species were performed weekly during two four month periods, from August to November 2008 (spring) and March to June 2009 (fall), in a favela (slum), a suburban area and a middle class area of Rio de Janeiro, Southeastern Brazil. Collections were performed with backpack aspirators, in 20 randomly selected houses in each area per week, during 15-20 minutes per house. Ovaries were removed from captured females and classified as initial, intermediary or final stage. Furthermore, females were dissected for determination of parity based on the condition of the tracheal system. Mosquito survival rate and longevity were estimated on a per month basis for each neighborhood. RESULTS: We collected a total of 2,062 Culex quinquefasciatus, but monthly vector density was not correlated with temperature and rainfall. We dissected the ovaries of 625 Culex quinquefasciatus, and overall, there was a higher proportion of nulliparous females during the dryer months, while gravid females were more frequent in rainy months. In the middle class neighborhood, the parity rate reached up to 93.75% with survivorship of 0.979. Lower parity and survival rates were obtained in the suburban area (as low as 36.4% parity and 0.711 daily survival). Up to 84.7% of Culex quinquefasciatus females could survive the eight day period needed to complete West Nile Virus incubation. CONCLUSIONS: The survival rate of Culex quinquefasciatus varied significantly between the neighborhoods. This suggests that vectorial capacity and disease transmission risk may vary greatly between different urban areas, which is potentially useful information for vector control programs.