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Arthropod-borne virus encephalitis
Published in Avindra Nath, Joseph R. Berger, Clinical Neurovirology, 2020
While humans and horses represent dead-end hosts, mounting an insufficient viremia to sustain a cycle of infection, the Culex tarsalis mosquito and passerine birds are the principal components of the normal cycle of virus replication and transmission. Both older people and infants are at increased risk of infection with a wide range of the inapparent to apparent infection ratios by age group.
Mosquitoes
Published in Gail Miriam Moraru, Jerome Goddard, The Goddard Guide to Arthropods of Medical Importance, Seventh Edition, 2019
Gail Miriam Moraru, Jerome Goddard
Western Equine Encephalitis. Western equine encephalitis (WEE), occurring in the western and central United States, parts of Canada, and parts of South America, has occurred in several large outbreaks (Figure 25.25). There were large epidemics in the northcentral United States in 1941 and in the central valley of California in 1952. The 1941 outbreak involved 3000 cases. From 1964 to 1997, 639 human WEE cases were reported to the U.S. Centers for Disease Control and Prevention (CDC), for a national average of 19 cases per year.65 WEE is generally less severe than EEE and SLE, with a mortality rate of only 2–5%. Cases appear in early to midsummer and are primarily due to bites by infected Culex tarsalis mosquitoes. The incidence of WEE has declined significantly over the past few decades.
St. Louis Encephalitis
Published in Sunit K. Singh, Daniel Růžek, Neuroviral Infections, 2013
Luis Adrian Diaz, Lorena I. Spinsanti, Marta S. Contigiani
In the eastern and western regions of the US, SLEV transmission networks are separated by epidemiological differences based on the virus transmission’s ecological determinants (Reisen 2003). In the eastern states, main vectors belong to the Culex pipiens complex (Culex pipiens pipiens and Culex pipiens quinquefasciatus) and its main hosts are house sparrows (Passer domesticus). These peridomestic mosquitoes vectors develop frequently in rich organic material water such as sewers and peridomestic water reservoirs. These mosquitoes are spread in urban and suburban ambient densely populated, especially where sanitary conditions are deficient. In the western regions of the USA, the main vector mosquito is Culex tarsalis. This specie reproduces in flooded and irrigated soils, and in industrial or urban residual water (Mitchell 1980). Humans are frequently exposed in rural areas, often determined by recreational and working activities. Periurban and wild birds act as hosts, mainly those abundant in agricultural areas close to water sources such as house sparrows (Passer domesticus) and house finches (Carpodacus mexicanus) (McLean and Bowen 1980).
Wolbachia-Virus interactions and arbovirus control through population replacement in mosquitoes
Published in Pathogens and Global Health, 2023
Thomas H Ant, Maria Vittoria Mancini, Cameron J McNamara, Stephanie M Rainey, Steven P Sinkins
The first published study describing Wolbachia-mediated enhancement of a (+)RNA virus is from Dodson et al [76], and describes an increased infection rate of West Nile virus (WNV) Culex tarsalis mosquitoes transiently infected with the wAlbB Wolbachia strain. Following challenge with WNV, Cx. tarsalis transiently infected with wAlbB showed a significantly higher WNV infection rate compared to non-Wolbachia controls at 7-days post infection – although there was no effect of the Wolbachia infection on rates of viral dissemination to mosquito legs or transmission in salivary secretions at this time point. A second time point (14-days post infection) found no significant differences in rates of infection, dissemination or transmission between Wolbachia-positive and Wolbachia-free controls.
Current development of Zika virus vaccines with special emphasis on virus-like particle technology
Published in Expert Review of Vaccines, 2021
Velasco Cimica, Jose M Galarza, Sujatha Rashid, Timothy T. Stedman
An indirect immunization approach against ZIKV and other arboviruses such as DENV, YFV, and CHIKV is represented by the AGS-v (NIAID) (Table 1), a subunit peptide vaccine (NIAID) that targets the mosquito salivary proteins [126]. This novel approach resulted from the observation that co-deposition of mosquito saliva with an arbovirus allows the pathogen to enter the host and replicate more efficiently. Mouse studies revealed that intradermal inoculation of West Nile virus (WNV) with Culex tarsalis saliva resulted in higher viral loads and faster onset of neuro-invasive disease compared to mice who were inoculated intradermally with the virus alone [127]. AGS-v was administered by prime-boost immunization in healthy adults with and without an adjuvant during a phase I clinical trial. The results of the trial demonstrated that the vaccine was relatively safe in all immunization groups, and it was immunogenic only when formulated with an adjuvant (Montanide ISA 51) [128]. The AGS-v immunization strategy, however, has some caveats. There is a lack of evidence that mosquito salivary proteins are involved in arbovirus infection in humans, and the approach lacks protection for non-mosquito routes of Zika transmission such as sexual, intrauterine, or blood transfusion.
The knowns and unknowns of West Nile virus in Europe: what did we learn from the 2018 outbreak?
Published in Expert Review of Anti-infective Therapy, 2020
Jeremy V Camp, Norbert Nowotny
One potential hypothesis in explaining the dramatic increase in WNV cases in Europe in 2018 is that a genetic change in the virus resulted in increased replication efficiency, transmission efficiency, and/or pathogenicity. For example, the introduction of WNV to New York in 1999 and the spread across the US was marked by an abrupt change in the virus genome in 2002. Viruses with this genetic change (the ‘WN02’ genotype, signified by a positively selected valine to alanine substitution at residue 159 of the envelope protein) rapidly replaced the previously circulating genotype (‘NY99’) [34, 35]. It was demonstrated that WN02 was associated with increased rate of replication and dissemination in laboratory experiments with Culex pipiens [36], but not in similar experiments with Culex salinarius nor in Culex tarsalis [37, 38]. Another viral variant (a proline at position 249 in the NS3 protein) has been associated with increased viremia in American crows experimentally infected with lineage 1 WNV, and viruses with this same substitution (a histidine to proline) were found in lineage 2 WNV during the 2010–2013 outbreak in Greece [29, 39]. However, experimental data suggested that this residue (a proline at NS3-249) is not associated with increased virulence or replication of lineage 2 WNV in native European birds [40, 41], and this variant seems to be restricted to the southern Balkan region [28]. Similar to the mosquito competence studies, the interaction between the virus and avian hosts is likely species specific. More research should be done to understand host competency for European bird species, and whether specific European strains have differential virulence in native birds, as has been done with North American species [13].