Study of combined foci of mosquito-transmitted arbovirus infections

A total of 5227 serum specimens from humans, horses and swine collected in the seasons of 1968--1976 in 15 administrative areas of the Primorskiy Kray were examined with antigens of a number of mosquito-borne arboviruses: Japanese encephalitis (JE), West Nile (WN), Getah, and Sindbis. Both independent and combined circulation of these viruses in the region was established. Sindbis virus was found to be circulating separately most frequently, West Nile virus the least frequently. According to the results of the serological analysis, the conditions for combined circulation are most closely related for JE and Getah, and JE and WN viruses. The interpretation of the results of examinations of the sera reacting simultaneously with JE and WN virus is most difficult because of close antigenic relationship of these viruses. A set of methods for serological differentiation of bivalent sera to JE and WN viruses and the criteria for the assessment of the results are recommended.     

Use of hyperimmune mouse ascitic fluids for arbovirus differentiation by indirect immunofluorescence and conventional serology

The cross-reactivity of 22 arbovirus species (alphaviruses; tick- and mosquito-borne flaviviruses; and selected bunyaviruses) was tested with monovalent immune mouse ascitic fluids by indirect immunofluorescence (IIF) in comparison with classical serological reactions (virus neutralization -- VN; haemagglutination inhibition -- HI; and complement fixation -- CF -- reactions). Known relationships within the virus groups studied were confirmed. As to the differentiation limits, the VN test was followed by IIF. Evaluation of the ratio of heterologous to homologous antibody activities showed that with the exception of antigenically closely related arboviruses (Western equine encephalomyelitis -- Sindbis; Japanese encephalitis -- Murray Valley encephalitis; dengue viruses; California -- Tahyna), most arboviruses within the antigenic complexes tested could be relatively reliably differentiated by IIF.     

Virus neutralizing antibodies to arboviruses in birds of the order Anseriformes in Czechoslovakia.

Sera from birds of the order Anseriformes in Czechoslovakia were examined for virus neutralizing (VN) antibodies to arboviruses. VN antibodies to Sindbis, Calovo and Tahyna viruses were found in 15, 5 and 6 out of 106 greylag goose (Anser anser) sera. Out of 38 ducks, 6 mallards (Anas platyrhynchos) and 1 garganey (Anas querquedula) contained VN antibodies to Sindbis virus, 6 mallards to Calovo virus, 4 mallards and 1 garganey to Tahyna virus, 2 mallards and 1 garganey to tick-borne encephalitis (TE) virus and 1 mallard to West Nile (WN) virus.     

Serological monitoring of arbovirus infections in the estuary of the Kuban River (the 2006-2007 data)

Solid-phase enzyme immunoassay, neutralization test, and the hemagglutination-inhibition test were used to study the sera from human beings (152 samples), agricultural animals (n = 77), hares (n = 3), and wild birds (n = 69), collected in 2006-2007 in the Kuban River estuary (Temryuk District, Krasnodar Territory). There were specific antibodies against viruses of West Nile (WH), tick-borne encephalitis (TBE) (Flaviviridae, Flavivirus), Sindbis (Togaviridae, Alphavirus), the antigenic complex of California, Batai (Bunyaviridae, Orthobunyavirus), Dhori (Orthomyxoviridae, Thogotovirus). The findings suggest the presence of arboviruses from 6 transmitting mosquitoes and ticks in the study area and human infection by the viruses of the antigenic complex of California (20-47%), Batai (3-15%), West Nile (3-12%), Dhori (2%). The index agricultural animals (horses, cattle) were observed to have specific antibodies to the viruses of WN (8-15%), TBE (0-2%), Sindbis (2-9%), the antigenic complex of California (27-54%). Out of the representatives of the wild fauna, virus-neutralizing antibodies to Sindbis virus were found in European hares (Lepus europaeus), California complex virus in gulls (Larus argentatus) and terns (Sterna hirundo), WN and Sindbis viruses in herons (Ardea purpurea), and WN and California complex viruses in bald-coots (Fulica atra).     

Application of enzyme immunoassay on infected cells (EIA-IC) for arboviruses

Comparative titrations of alpha-, flavi- and Bunyamwera viruses were made by EIA-IC and according to cytopathic effect (CPE). Specific enzymatic reactions appeared earlier and in higher titres than CPE. The titres of dengue type 1, Mayaro, Powassan and Langat viruses measured by EIA-IC were comparable to those measured by intracerebral inoculation of mice. The cross-reactivity testing of EIA-IC among alphaviruses (Chikungunya, Sindbis and Mayaro), flaviviruses (Japanese encephalitis, Murray valley encephalitis, Kunjin, West Nile, yellow fever and louping ill, Powassan, Langat) and Bunyamwera arboviruses using polyclonal immune ascitic fluids confirmed the high specificity of EIA-IC. Homologous reactions mostly showed higher titres than heterologous ones. No cross-reactivity was seen between alpha-, flavi- and bunyaviruses, among the three alphaviruses, between mosquito-borne and tick-borne flaviviruses, or between JE complex and YF viruses. However, a cross-reactivity to different extent was observed among the four JE complex viruses and among louping ill, Powassan and Langat viruses. The results of EIA-IC cross tests showed that this method can distinguish togavirus group- or species-specific antigens, more precisely than conventional ELISA.     

Arboviruses causing human disease in the Australasian zoogeographic region

Summary Over 65 arboviruses have been reported from countries in the Australasian zoogeographic region, but only a few have been implicated in human disease. These include the flaviviruses Murray Valley encephalitis (MVE), Kunjin (KUN), Kokobera (KOK), and dengue, particularly types 1 and 2; the alphaviruses Ross River (RR), Barmah Forest (BF), and Sindbis (SIN); and the bunyaviruses, Gan Gan and Trubanaman. In this paper recent epidemiological and clinical results pertaining to these viruses are reviewed, with major emphasis on MVE and RR viruses. The extensive early studies of Australian arboviruses have been reviewed by Doherty [49, 50], and their ecology and vectors more recently by Kay and Standfast [87]. In addition, the biology of MVE and KUN [113] and RR [87, 114] viruses have been the subjects of more detailed reviews.The Australasian zoogeographic region is defined as countries east of the Wallace and Weber lines, two hypothetical lines in the Indo-Australian archipelago where the fauna of the Australasian and Oriental regions meet. Seroepidemiological studies of human arboviral infections have suggested that the Japanese encephalitis flavivirus and the chikungunya alphavirus occur only in the Oriental region, whereas the related MVE and RR viruses, respectively, are restricted to the Australasian region [85, 148]. Serological results from Wallacea, the zone between the Wallace and Weber lines, are not so clear-cut [85]. This review is therefore restricted to countries east of Wallacea, specifically New Guinea and Australia.This Brief Review is published under the auspices of the editors of the journal and Virology Division News, the section of the journal reporting proceedings of the Virology Division of the International Union of Microbiological Societies.     

The influence of arboviral infection on the susceptibility of cultured cells to immune injury in vitro.

The susceptibility of LLC-MK2 monkey kidney cells to antivirus (antibodies versus viral antigens in the plasma membrane) and anticell (antibodies versus plasma membrane antigens) immune cytolysis in vitro was observed during the course of 100 continuous subcultures of these cells. In that period, LLC-MK2 cells infected with the Group B arboviruses, Japanese encephalitis virus and dengue 2 virus, became progressively refractory to the complement-dependent antivirus immune cytolysis as measured by 51-Cr release. In addition, the LLC-MK2 cells themselves exhibited a decreasing susceptibility to immune lysis with anticell anti-body. In contrast, during the same period, similar immune cytolysis experiments with the Group A arboviruses, Sindbis virus and Eastern equine encephalitis virus, remained constant. It was observed that arboviral infection of lytic refractory LLC-MK2 cells restored their susceptability to immune cytolysis with anticell antibodies. The kinetics of this restoration were unique for both Group A and B arboviruses and exhibited a constant relationship to the viral growth curve. It was concluded that the above findings could be explained on the basis of differential membrane antigenic density coupled with changes in the properties of the plasma membrane on which subculture and arboviral infection had antagonistic effects.     

Polykaryocytosis induced by certain arboviruses in monolayers of BHK-21-528 cells

Multinucleated giant cell formation in a clone of BHK-21 cells, BHK-21-528, was tested with certain arboviruses. Eleven out of 19 viruses tested, Chikungunya, Getah, Sagiyama, Sindbis, Western equine encephalitis, St. Louis encephalitis, Japanese encephalitis, West Nile, Bunyamwera, Germiston and California encephalitis virus induced cell fusion after infection. All cases where giant cells were observed during the experiments, involved the B type cell fusion (fusion from within).     

Modulation of immune responses in the central nervous system by Zika virus,West Nile virus,and dengue virus

Arthropod-borne viruses (arboviruses) pose significant threats to global public health by causing a spectrum of diseases ranging from mild febrile illnesses to severe neurological complications. Understanding the intricate interplay between arboviruses and the immune system within the central nervous system is crucial for developing effective strategies to combat these infections and mitigate their neurological sequelae. This review comprehensively explores the mechanisms by which arboviruses such as Zika virus, West Nile virus, and Dengue virus manipulate immune responses within the CNS, leading to diverse clinical manifestations.     

Serological survey for the prevalence of certain arboviruses in the human population of the south-east area of Central African Republic (author's transl)

A serological survey of antibodies to arboviruses was carried out in the human population of the south-east part of Central African Republic in April 1979. Four hundred and fifty nine serum samples were tested using the haemagglutination inhibition test (H. I.) and fifty of them by the complement fixation test (C. F.). Only 11% of the population tested had no H. I. antibodies against the following arboviruses: Chikungunya, Semliki-forest, Sindbis, Yellow fever, Uganda S, West-Nile, Zika, Bunyamwera and Zinga. It seems that Chikungunya virus has recently been very active mainly in adult population. The same observation was reported for Zika virus. The following antigens were used for complement fixation test: Ilesha, Bwamba, CHF-Congo, Dugbe, Bhanja, Tataguine, Nyando, Bangui and Orungo. A positive reaction was noted in 88% of serum samples tested for Orungo virus. Antibodies were also detected by CF for CHF-Congo and Bhanja viruses.     

Arboviroses in the region of Nosy-Bé, Madagascar. Serologic and entomologic data

Since 1977, the Pasteur Institute of Madagascar has been studying, during six surveys, the arboviruses of Nosy-Be area, in the north-west of Madagascar. 47.2% out of 271 human sera and 11.3% out of 151 sera of Lemurs, tested for antibodies to 16 arboviruses by the haemagglutination inhibition test, are positive. The results show an important prevalence of Flaviviruses. West Nile and Dengue 1 viruses were probably circulating some years before the surveys. Antibodies against Sindbis and Rift Valley Fever viruses, were found only in few subjects. Bunyamwera and California groups of virus are absent. The rate of positive Lemurs is weak, particularly in Lemur macaco macaco. Flaviviruses are the most frequent. 12,262 haematophagous diptera (11,965 Culicidae belonging to 40 species) were caught. Aedes aegypti and Aedes albopictus are both present. Arbovirus isolation attempts from 394 mosquito pools failed; only Mengo virus was isolated from four pools of Eretmapodites quinquevittatus and one pool of Aedes (Skusea) sp.     

RNA interference, arthropod-borne viruses, and mosquitoes

RNA interference (RNAi) probably functions as an antiviral mechanism in most eukaryotic organisms. Variations in the activity of this antiviral pathway in mosquitoes could explain, in part, why some mosquitoes are competent vectors of medically important, arthropod-borne viruses (arboviruses) and others are not. There are three lines of evidence that show the RNAi pathway exists in Aedes species that transmit arboviruses. The first is that recombinant Sindbis viruses expressing a RNA fragment from a genetically unrelated dengue-2 virus (DENV-2) interfere with DENV-2 replication in Aedes aegypti mosquitoes by a mechanism similar to virus-induced gene silencing described in plants. The second is that transfection of C6/36 (Aedes albopictus) cells with either double-stranded RNA or synthetic small interfering RNAs derived from an arbovirus genome interferes with replication of the homologous virus. The third is that a hairpin DENV-2-specific RNA transcribed from a plasmid can generate virus-resistant C6/36 cells. We hypothesize that genetically modified mosquitoes can be generated that transcribe a flavivirus-specific dsRNA, triggering the RNAi response soon after ingestion of a blood meal. This could induce the RNAi pathway in the midgut prior to establishment of virus infection and profoundly change vector competence. Towards this goal, we are developing transgenic A. aegypti lines that are refractory to DENV by exploiting the RNAi pathway.     

Comparison of the transmission potential of two genetically distinct Sindbis viruses after oral infection of Aedes aegypti (Diptera: Culicidae)

Within mosquitoes, arboviruses encounter barriers to infection and dissemination that are critical determinants of vector competence. The molecular mechanisms responsible for these barriers have yet to be elucidated. The prototype Sindbis (SIN) strain, AR339, and viruses derived from this strain, such as TR339 virus, have limited infection and transmission potential in the medically important arthropod vector, Aedes aegypti (L.). However, the Malaysian SIN virus strain, MRE16, disseminates in nearly 100% of Ae. aegypti 14 d after oral infection. Here, we compare the spatial and temporal infection patterns of MRE16 and TR339 viruses in Ae. aegypti. The results indicate that a midgut escape barrier is primarily responsible for the significantly lower dissemination and transmission potentials observed after oral infection with TR339 virus. MRE16 and TR339 viruses now represent a well-characterized model system for the further study of virus determinants of vector infection, particularly determinants affecting the midgut escape barrier in Ae. aegypti.     

Electron microscopic study of sindbis virus morphogenesis

Summary An electron microscopic study of the growth and development of Sindbis virus in chick embryo fibroblast cultures demonstrated that the morphogenesis of this virus is essentially like that of other group A arboviruses hitherto studied.     

Specific markers for the detection of circulation of Tahyna,Inko and Batai viruses (Bunyaviridae,Bunyavirus) in humans,mosquitoes, ticks and cattle of the Ul'ianovsk region

Comprehensive examinations of the population, sanguivorous arthropoda and domestic animals were for the first time held in the territory of the Ulyanovsk region. An active circulation of certain arboviruses was detected and a predominantly ecological relation of California encephalitis serogroup viruses with Aedes mosquitoes, on the one hand, and of Batai viruses with Anopheles mosquitoes, on the other hand, was established. The most reliable detection of antibodies to California encephalitis viral complex was pointed out.     

Can pesticides and larval competition alter susceptibility of Aedes mosquitoes (Diptera: Culicidae) to arbovirus infection?

Density-dependent processes such as larval competition may be important regulatory factors among some mosquito species. The application of pesticides used for control may alter these density-dependent interactions with consequences for the number of survivors and associated sublethal and chronic effects on these individuals. We examined how intraspecific competition among larvae and low concentrations of malathion alter Aedes aegypti L. and Aedes albopictus Skuse adult life history traits and competence for arboviruses using Sindbis virus as a model system. Larvae were reared at densities of 150 and 300 larvae per container and in the absence or presence of 0.04 parts per million of malathion, before surviving females were exposed to an infectious blood meal containing 10(5) plaque-forming units/ml Sindbis virus. For both species, competition and the presence of malathion reduced survival to adulthood. The presence of malathion eliminated the negative effects of competition that resulted in lengthened development time and smaller-sized adults. For Ae. aegypti, but not Ae. albopictus, high competition conditions and the presence of malathion independently and not interactively led to an increase in virus dissemination from the midgut. Our results suggest that larval competition and chemical contaminants may influence disease transmission directly by altering adult mosquito fitness and indirectly by altering vector interactions with arboviruses.     

A survey of the relationships among the viruses not considered arboviruses, vertebrates, and arthropods

No single group of organisms demonstrates more extensive and diverse associations with animal viruses than the phylum Arthropoda. Compared with the well-recognized relationship found in arboviruses, however, most of the atypical arthropod-vertebrate relationships of the viruses normally not considered arboviruses have received much less attention, as they remain in the marginal areas of interest for most researchers in animal virology, veterinary medicine, medical entomology, and invertebrate pathology. However, this comprehensive review of the information gathered from several branches of virology by profession reveals highly valuable information potentially useful in the fields of research ranging from investigations of the mode of transmission of poorly understood or emerging viral diseases to studies of the evolution of biological transmission of animal viruses by arthropod vectors. The observations and data obtained for the animal virus relationships with arthropods and vertebrates outside the boundaries of arboviruses, in turn, can be used to reexamine more closely the definition of arboviruses. With increasing number of reports challenging one of the basic tenets of the definition of arbovirus (requirement of viremia in vertebrate host) and others describing virus-host relationships that complicate the definition of arbovirus, the accumulated information clearly demonstrates the difficulty of defining the boundaries of arboviruses.     

Sikhote-Alin virus, a new member of the cardiovirus group (Picornaviridae) isolated from Ixodes persulcatus ticks in Primorie Region.

A virus, designated Sikhote-Alin, was isolated in 1970 from Ixodes persulcatus ticks collected from a wild boar in the Primorie region (U.S.S.R.) Sikhote-Alin virus showed no haemagglutinating activity and no antigenic relationships with arboviruses of 12 antigenic groups, 17 ungrouped tick-borne arboviruses, porcine enteroviruses and coxsackie A (types 1-18) viruses. An one-way antigenic relationship was demonstrated by complement fixation with cardioviruses (Mengo and Columbia-SK strains). The virus contains RNA, is resistant to lipid solvents, highly thermostable in the presence of 1 M MgCl2 and its size is over 20 nm but less than 25 nm. All these properties make it possible to consider it as a new member of the cardiovirus group (genus Enterovirus; Picornaviridae).     

A monoclonal antibody study of the receptor area of the Venezuelan encephalitis virus]

The receptor region for virus-cell interaction in Venezuelan equine encephalomyelitis (VEE) and Eastern equine encephalomyelitis (EEE) viruses was studied using a panel of 17 monoclonal antibodies (MCA). They were able to block agglutination of goose erythrocytes. The dominant role of glycoprotein E2 in the formation of viral receptor for EEE and VEE viruses was demonstrated. Competitive radioimmunoassay identified three antigenic sites in this region. These sites were also responsible for virus neutralization. MCAs to these sites protected outbred mice against lethal infection. The presence of a highly conservative region in VEE (site E2-3) and EEE (site E2a) which produced cross-reacting antibodies blocking hemagglutination of Western equine encephalomyelitis, Semliki Forest, Sindbis, Getah, Aura, Chikungunya, and Pixuna viruses was established. A hypothesis is suggested concerning the existence of similar regions for the entire alphavirus genus, and the role of this region in virus-cell interaction.