Changing patterns of chikungunya virus: re-emergence of a zoonotic arbovirus

Molecular and virological investigation of a focal chikungunya outbreak in northern India

Chikungunya (CHIK) fever is one of the most important arboviral infections of medical significance. The objective of the present study is to identify and characterize the etiology of a focal febrile arthritis outbreak from Gwalior, northern India, during October-November 2010. A detailed virological (isolation) and molecular (end-point RT-PCR, quantitative RT-PCR, and nucleotide sequencing) investigation of this outbreak was carried out by collecting and studying 52 clinical samples and 15 mosquito pools from the affected region. The investigation revealed the presence of CHIK viral RNA in 29% of clinical samples and 13% mosquito pool by RT-PCR. The quantification of CHIK viral RNA in samples varied from 10^2.50 to 10^6.67 copies/mL, as demonstrated through quantitative RT-PCR. In addition, six CHIK viruses were isolated from RT-PCR positive samples. The nucleotide sequences of partial E1 gene of five representative CHIK viruses were deciphered, which revealed that all the viral strains from this outbreak belong to the recently emerging ECS African genotype. Identification of Chikungunya virus ECSA African genotype as the etiology of the present outbreak confirms the continued circulation of the novel genotype, since 2006, in India. The identification of CHIK virus in Aedes aegypti also confirmed it as the major vector in northern India.

Identical strength of the T cell responses against E2, nsP1 and capsid CHIKV proteins in recovered and chronic patients after the epidemics of 2005-2006 in La Reunion Island

To characterize the immunity developed by patients infected by chikungunya virus (CHIKV), we studied the intensity and specificity of CHIKV-specific T cells mediated responses in chronic and recovered patients at 12 to 24 months post-infection. T cells were challenged in vitro against CHIKV synthetic peptides covering the length of three viral proteins, capsid, E2 and nsP1 proteins as well as all inactivated virus particles. Cytokine production was assessed by ELISPOT and intracellular labeling. T cells producing IFN-γ were detected against CHIKV in 85% patient’s cells either by direct ELISPOT assay (69% of patients) or after expansion of memory T cells allowing the detection of both CD4 and CD8 specific-T cells in 16% additional cases. The IFN-γ response was mainly engaged in response to nsP1 or E2 (52% and 46% cases, respectively) but in only 27% cases against the capsid. The anti-E2 response represented half the magnitude of the total CHIKV IFN-γ production and was mainly directed against the C-terminal half part of the protein. Almost all patients had conserved a T cell specific response against CHIKV with a clear hierarchy of T cell responses (CD8 > CD4) engaged against E2 > nsP1 > capsid. More importantly, the intensity of responses was not significantly different between recovered and chronic patients. These findings constitute key elements to a better understanding of patient T cell immunoreactivity against CHIKV and argue against a possible defect of T cell immunoresponse in the chronicity post-CHIKV infection.

Medical entomology--back to the future?

Some of problems and challenges facing Medical/Veterinary Entomology are presented from my perspective, focusing on the current millennium. Topics include anthropogenic environmental changes created by population growth, administrative problems hindering science's response to these changes, and some of the scientific discoveries potentially providing solutions. As the title implies, many recent research discoveries have yet to be translated into major changes in control approaches for the major vectorborne public health problems, thereby providing an interesting mix of modern surveillance technology used to track problems and direct historical intervention solutions.

Development of a stable virus-like particle vaccine formulation against Chikungunya virus and investigation of the effects of polyanions

Chikungunya virus (CHIKV) is an alphavirus that infects millions of people every year, especially in the developing world. The selective expression of recombinant CHIKV capsid and envelope proteins results in the formation of self-assembled virus-like particles (VLPs) that have been shown to protect nonhuman primates against infection from multiple strains of CHIKV. This study describes the characterization, excipient screening, and optimization of CHIKV VLP solution conditions toward the development of a stable parenteral formulation. The CHIKV VLPs were found to be poorly soluble at pH 6 and below. Circular dichroism, intrinsic fluorescence, and static and dynamic light scattering measurements were therefore performed at neutral pH, and results consistent with the formation of molten globule structures were observed at elevated temperatures. A library of generally recognized as safe excipients was screened for their ability to physically stabilize CHIKV VLPs using a high-throughput turbidity-based assay. Sugars, sugar alcohols, and polyanions were identified as potential stabilizers and the concentrations and combinations of select excipients were optimized. The effects of polyanions were further studied, and while all polyanions tested stabilized CHIKV VLPs against aggregation, the effects of polyanions on conformational stability varied.

Identification of novel compounds inhibiting chikungunya virus-induced cell death by high throughput screening of a kinase inhibitor library

Chikungunya virus (CHIKV) is a mosquito-borne arthrogenic alphavirus that causes acute febrile illness in humans accompanied by joint pains and in many cases, persistent arthralgia lasting weeks to years. The re-emergence of CHIKV has resulted in numerous outbreaks in the eastern hemisphere, and threatens to expand in the foreseeable future. Unfortunately, no effective treatment is currently available. The present study reports the use of resazurin in a cell-based high-throughput assay, and an image-based high-content assay to identify and characterize inhibitors of CHIKV-infection in vitro. CHIKV is a highly cytopathic virus that rapidly kills infected cells. Thus, cell viability of HuH-7 cells infected with CHIKV in the presence of compounds was determined by measuring metabolic reduction of resazurin to identify inhibitors of CHIKV-associated cell death. A kinase inhibitor library of 4,000 compounds was screened against CHIKV infection of HuH-7 cells using the resazurin reduction assay, and the cell toxicity was also measured in non-infected cells. Seventy-two compounds showing ≥50% inhibition property against CHIKV at 10 µM were selected as primary hits. Four compounds having a benzofuran core scaffold (CND0335, CND0364, CND0366 and CND0415), one pyrrolopyridine (CND0545) and one thiazol-carboxamide (CND3514) inhibited CHIKV-associated cell death in a dose-dependent manner, with EC₅₀ values between 2.2 µM and 7.1 µM. Based on image analysis, these 6 hit compounds did not inhibit CHIKV replication in the host cell. However, CHIKV-infected cells manifested less prominent apoptotic blebs typical of CHIKV cytopathic effect compared with the control infection. Moreover, treatment with these compounds reduced viral titers in the medium of CHIKV-infected cells by up to 100-fold. In conclusion, this cell-based high-throughput screening assay using resazurin, combined with the image-based high content assay approach identified compounds against CHIKV having a novel antiviral activity - inhibition of virus-induced CPE - likely by targeting kinases involved in apoptosis.

Recent outbreaks and expanding global distribution of Chikungunya virus (CHIKV) in different regions of Asia, Africa and Europe necessitates the development of effective therapeutic interventions. At present, only two antiviral compounds (chloroquine and ribavirin) that inhibit viral infection in vitro have been used in clinical cases of chikungunya infections. However, neither of these compounds have shown strong efficacy in vivo. Recent attempts to identify new antiviral candidates for CHIKV using cell-based phenotypic approach have been reported. In this study, we developed a simple cell-based high-throughput assay using resazurin to identify potential anti-CHIKV compounds. This high-throughput assay is based on the metabolic reduction of resazurin to the highly fluorescent resorufin by viable cells as an indicator of activity against CHIKV-induced CPE. We screened 4,000 small molecules belonging to the BioFocus kinase inhibitor chemical library and found a cluster of related molecules with antiviral activity against CHIKV. Finally, we characterized the putative mode of action of these active compounds using an image-based high content assay and conventional virological methods (i.e., virus yield reduction assay, microneutralization assay).

HLA class II allele polymorphism in an outbreak of chikungunya fever in Middle Andaman, India

A sudden upsurge of fever cases with joint pain was observed in the outpatient department, Community Health Centre, Rangat during July-August 2010 in Rangat Middle Andaman, India. The aetiological agent responsible for the outbreak was identified as chikungunya virus (CHIKV), by using RT-PCR and IgM ELISA. The study investigated the association of polymorphisms in the human leucocyte antigen class II genes with susceptibility or protection against CHIKV. One hundred and one patients with clinical features suggestive of CHIKV infection and 104 healthy subjects were included in the study. DNA was extracted and typed for HLA-DRB1 and DQB1 alleles. Based on the amino acid sequences of HLA-DQB1 retrieved from the IMGT/HLA database, critical amino acid differences in the specific peptide-binding pockets of HLA-DQB1 molecules were investigated. The frequencies of HLA-DRB1 alleles were not significantly different, whereas lower frequency of HLA-DQB1*03:03 was observed in CHIKV patients compared with the control population [P = 0·001, corrected P = 0·024; odds ratio (OR)  = 0, 95% confidence interval (95% CI) 0·0-0·331; Peto's OR = 0·1317, 95% CI 0·0428-0·405). Significantly lower frequency of glutamic acid at position 86 of peptide-binding pocket 1 coding HLA-DQB1 genotypes was observed in CHIKV patients compared with healthy controls (P = 0·004, OR = 0·307, 95% CI 0·125-0·707). Computational binding predictions of CD4 epitopes of CHIKV by NetMHCII revealed that HLA-DQ molecules are known to bind more CHIKV peptides than HLA-DRB1 molecules. The results suggest that HLA-DQB1 alleles and critical amino acid differences in the peptide-binding pockets of HLA-DQB1 alleles might have role in influencing infection and pathogenesis of CHIKV.

Enhanced arbovirus surveillance with deep sequencing: Identification of novel rhabdoviruses and bunyaviruses in Australian mosquitoes

Viral metagenomics characterizes known and identifies unknown viruses based on sequence similarities to any previously sequenced viral genomes. A metagenomics approach was used to identify virus sequences in Australian mosquitoes causing cytopathic effects in inoculated mammalian cell cultures. Sequence comparisons revealed strains of Liao Ning virus (Reovirus, Seadornavirus), previously detected only in China, livestock-infecting Stretch Lagoon virus (Reovirus, Orbivirus), two novel dimarhabdoviruses, named Beaumont and North Creek viruses, and two novel orthobunyaviruses, named Murrumbidgee and Salt Ash viruses. The novel virus proteomes diverged by ≥ 50% relative to their closest previously genetically characterized viral relatives. Deep sequencing also generated genomes of Warrego and Wallal viruses, orbiviruses linked to kangaroo blindness, whose genomes had not been fully characterized. This study highlights viral metagenomics in concert with traditional arbovirus surveillance to characterize known and new arboviruses in field-collected mosquitoes. Follow-up epidemiological studies are required to determine whether the novel viruses infect humans.

Chikungunya virus: emerging targets and new opportunities for medicinal chemistry

Chikungunya virus is an emerging arbovirus that is widespread in tropical regions and is spreading quickly to temperate climates with recent epidemics in Africa and Asia and documented outbreaks in Europe and the Americas. It is having an increasingly major impact on humankind, with potentially life-threatening and debilitating arthritis. There is no treatment available, and only in the past 24 months have lead compounds for development as potential therapeutics been reported. This Perspective discusses the chikungunya virus as a significant, new emerging topic for medicinal chemistry, highlighting the key viral target proteins and their molecular functions that can be used in drug design, as well as the most important ongoing developments for anti-chikungunya virus research. It represents a complete picture of the current medicinal chemistry of chikungunya, supporting the development of chemotherapeutics through drug discovery and design targeting this virus.

Chronic joint disease caused by persistent Chikungunya virus infection is controlled by the adaptive immune response

Chikungunya virus (CHIKV) is a reemerging mosquito-borne pathogen that causes incapacitating disease in humans characterized by intense joint pain that can persist for weeks, months, or even years. Although there is some evidence of persistent CHIKV infection in humans suffering from chronic rheumatologic disease symptoms, little is known about chronic disease pathogenesis, and no specific therapies exist for acute or chronic CHIKV disease. To investigate mechanisms of chronic CHIKV-induced disease, we utilized a mouse model and defined the duration of CHIKV infection in tissues and the associated histopathological changes. Although CHIKV RNA was readily detectable in a variety of tissues very early after infection, CHIKV RNA persisted specifically in joint-associated tissues for at least 16 weeks. Inoculation of Rag1(-/-) mice, which lack T and B cells, resulted in higher viral levels in a variety of tissues, suggesting that adaptive immunity controls the tissue specificity and persistence of CHIKV infection. The presence of CHIKV RNA in tissues of wild-type and Rag1(-/-) mice was associated with histopathological evidence of synovitis, arthritis, and tendonitis; thus, CHIKV-induced persistent arthritis is not mediated primarily by adaptive immune responses. Finally, we show that prophylactic administration of CHIKV-specific monoclonal antibodies prevented the establishment of CHIKV persistence, whereas therapeutic administration had tissue-specific efficacy. These findings suggest that chronic musculoskeletal tissue pathology is caused by persistent CHIKV infection and controlled by adaptive immune responses. Our results have significant implications for the development of strategies to mitigate the disease burden associated with CHIKV infection in humans.

Differential regulation of TLR mediated innate immune response of mouse neuronal cells following infection with novel ECSA genotype of Chikungunya virus with and without E1:A226V mutation

Chikungunya virus (CHIKV) has received global attention due to the series of large-scale outbreaks in different parts of the world including Africa, Indian Ocean Islands, India and South-East Asia. The appearance of many unusual severe manifestations including neurological disorders was reported in post resurgence epidemics with implication of novel East Central South African (ECSA) genotype with E1:A226V mutation. The molecular mechanism of CHIKV neuropathogenesis is not yet understood and very little is known about the host-pathogen interactions. In the present study replication kinetics and innate immune response of ECSA genotype of CHIKV with and without A226V mutation were determined in mouse neuroblastoma cell line (N2a). The 226V mutant strain was more replication competent in N2a cells with a peak titer of 10(8)PFU/ml compared to 10(6)PFU/ml for A226 virus. Besides, the 226V mutant virus showed relatively less induction of antiviral genes i.e. IFN-β, OAS-3, MX-2, ISG-15 and Toll like receptors 3 and 7 as compared to non mutant strain (A226). Further pretreatment of N2a cells either with Poly I: C, IFN-β or TNF-α resulted in inhibition of CHIKV replication hence confirming the role of TLR mediated innate immune response in CHIKV pathogenesis. Differential regulation of TLRs and associated down stream antiviral genes might have attributed for increased pathogenesis of the 226V mutant novel ECSA genotype of CHIKV during the recent epidemics.

Proof of concept for a novel insecticide bioassay based on sugar feeding by adult Aedes aegypti (Stegomyia aegypti)

Aedes aegypti L. (Stegomyia aegypti) (Diptera: Culicidae) is the principal vector of dengue and yellow fever viruses in tropical and subtropical regions of the world. Disease management is largely based on mosquito control achieved by insecticides applied to interior resting surfaces and through space sprays. Population monitoring to detect insecticide resistance is a significant component of integrated disease management programmes. We developed a bioassay method for assessing insecticide susceptibility based on the feeding activity of mosquitoes on plant sugars. Our prototype sugar-insecticide feeding bioassay system was composed of inexpensive, disposable components, contained minimal volumes of insecticide, and was compact and highly transportable. Individual mosquitoes were assayed in a plastic cup that contained a sucrose-permethrin solution. Trypan blue dye was added to create a visual marker in the mosquito's abdomen for ingested sucrose-permethrin solution. Blue faecal spots provided further evidence of solution ingestion. With the sugar-insecticide feeding bioassay, the permethrin susceptibility of Ae. aegypti females from two field-collected strains was characterized by probit analysis of dosage-response data. The field strains were also tested by forced contact of females with permethrin residues on filter paper. Dosage-response patterns were similar, indicating that the sugar-insecticide feeding bioassay had appropriately characterized the permethrin susceptibility of the two strains.

Chikungunya virus capsid protein contains nuclear import and export signals

BACKGROUND

Chikungunya virus (CHIKV) is an alphavirus of the Togaviridae family. After autoproteolytic cleavage, the CHIKV capsid protein (CP) is involved in RNA binding and assembly of the viral particle. The monomeric CP is approximately 30 kDa in size and is small enough for passive transport through nuclear pores. Some alphaviruses are found to harbor nuclear localization signals (NLS) and transport of these proteins between cellular compartments was shown to be energy dependent. The active nuclear import of cytoplasmic proteins is mediated by karyopherins and their export by exportins. As nuclear and cytoplasmic trafficking may play a role in the life cycle of CHIKV, we have sought to identify nuclear localization and nuclear export signals in CHIKV CP in a virus-free system.

METHODS

EGFP-fusion proteins of CHIKV CP and mutants thereof were created and used to monitor their intracellular localization. Binding of cellular proteins was confirmed in pull-down assays with purified CP using co-immuoprecipitation. Nuclear localization was demonstrated in a virus-free system using fluorescence microscopy.

RESULTS

Here we show that CHIKV CP is a nuclear-cytoplasmic shuttling protein with an active NLS that binds to karyopherin α (Karα) for its nuclear translocation. We also found that the Karα4 C-terminal NLS binding site is sufficient for this interaction. We further demonstrate that CHIKV CP interacts directly with the export receptor CRM1 to transport this viral protein out of the nucleus via a nuclear export signal (NES). The CHIKV CP NES was mapped between amino acids 143 and 155 of CP. Deduced from in silico analyses we found that the NES has a mode of binding similar to the snurportin-1 CRM1 complex.

CONCLUSIONS

We were able to show that in a virus-free system that the CHIKV capsid protein contains both, a NLS and a NES, and that it is actively transported between the cytoplasma and the nucleus. We conclude that CHIKV CP has the ability to shuttle via interaction with karyopherins for its nuclear import and, vice versa, by CRM1-dependent nuclear export.

Chikungunya virus infection results in higher and persistent viral replication in aged rhesus macaques due to defects in anti-viral immunity

Chikungunya virus (CHIKV) is a re-emerging mosquito-borne Alphavirus that causes a clinical disease involving fever, myalgia, nausea and rash. The distinguishing feature of CHIKV infection is the severe debilitating poly-arthralgia that may persist for several months after viral clearance. Since its re-emergence in 2004, CHIKV has spread from the Indian Ocean region to new locations including metropolitan Europe, Japan, and even the United States. The risk of importing CHIKV to new areas of the world is increasing due to high levels of viremia in infected individuals as well as the recent adaptation of the virus to the mosquito species Aedes albopictus. CHIKV re-emergence is also associated with new clinical complications including severe morbidity and, for the first time, mortality. In this study, we characterized disease progression and host immune responses in adult and aged Rhesus macaques infected with either the recent CHIKV outbreak strain La Reunion (LR) or the West African strain 37997. Our results indicate that following intravenous infection and regardless of the virus used, Rhesus macaques become viremic between days 1–5 post infection. While adult animals are able to control viral infection, aged animals show persistent virus in the spleen. Virus-specific T cell responses in the aged animals were reduced compared to adult animals and the B cell responses were also delayed and reduced in aged animals. Interestingly, regardless of age, T cell and antibody responses were more robust in animals infected with LR compared to 37997 CHIKV strain. Taken together these data suggest that the reduced immune responses in the aged animals promotes long-term virus persistence in CHIKV-LR infected Rhesus monkeys.

Chikungunya virus (CHIKV) is a re-emerging Alphavirus that has caused recent massive outbreaks in the Indian Ocean region. In addition, outbreaks have been documented in Europe and elsewhere in the world, initiated by infected travelers returning to their homelands. The recent outbreak strains possess extended vector range and as such, raise the potential of CHIKV outbreaks in the Southeastern parts of the United States. In this study, we examined CHIKV immunity in adult and aged Rhesus macaques following infection with two different CHIKV strains (recent outbreak strain CHIKV-LR and a West African Strain CHIKV-37997). CHIKV-LR causes persistent infection in the aged animals and replicates, on average, to higher levels than CHIKV-37997. Irrespective of the viral strain used, aged animals had delayed and/or reduced immunity compared to adult animals. Our data support the clinical findings of CHIKV susceptibility in vulnerable populations including the aged and provide mechanistic evidence that an effective immune response directed against the virus is required for preventing persistent CHIKV infection.

Structure based design towards the identification of novel binding sites and inhibitors for the chikungunya virus envelope proteins

Chikungunya virus is an emerging arbovirus that is widespread in tropical regions and is spreading quickly to temperate climates with recent epidemics in Africa, Asia, Europe and the Americas. It is having an increasingly major impact on humans with potentially life-threatening and debilitating arthritis. Thus far, neither vaccines nor medications are available to treat or control the virus and therefore, the development of medicinal chemistry is a vital and immediate issue that needs to be addressed. The viral envelope proteins play a major role during infection through mediation of binding and fusion with the infected cell surfaces. The possible binding target sites of the chikungunya virus envelope proteins have not previously been investigated; we describe here for the first time the identification of novel sites for potential binding on the chikungunya glycoprotein complexes and the identification of possible antagonists for these sites through virtual screening using two successive docking scores; FRED docking for fast precise screening, with the top hits then subjected to a ranking scoring using the AUTODOCK algorithm. Both the immature and the mature forms of the chikungunya envelope proteins were included in the study to increase the probability of finding positive and reliable hits. Some small molecules have been identified as good in silico chikungunya virus envelope proteins inhibitors and these could be good templates for drug design targeting this virus.

Chikungunya fever: epidemiology, clinical syndrome, pathogenesis and therapy

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Chikungunya fever is caused by a mosquito-borne alphavirus originating in East Africa.

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During the past 7 years, the disease has spread to islands of the Indian Ocean, Asia and Europe.

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Its spread has been facilitated by a mutation favouring replication in the mosquito Ae. albopictus.

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No vaccines or antiviral drugs are available to prevent or treat chikungunya fever.

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This paper provides an extensive review of the virus and disease, including Supplementary Tables.

Chikungunya virus (CHIKV) is the aetiological agent of the mosquito-borne disease chikungunya fever, a debilitating arthritic disease that, during the past 7 years, has caused immeasurable morbidity and some mortality in humans, including newborn babies, following its emergence and dispersal out of Africa to the Indian Ocean islands and Asia. Since the first reports of its existence in Africa in the 1950s, more than 1500 scientific publications on the different aspects of the disease and its causative agent have been produced. Analysis of these publications shows that, following a number of studies in the 1960s and 1970s, and in the absence of autochthonous cases in developed countries, the interest of the scientific community remained low. However, in 2005 chikungunya fever unexpectedly re-emerged in the form of devastating epidemics in and around the Indian Ocean. These outbreaks were associated with mutations in the viral genome that facilitated the replication of the virus in Aedes albopictus mosquitoes. Since then, nearly 1000 publications on chikungunya fever have been referenced in the PubMed database. This article provides a comprehensive review of chikungunya fever and CHIKV, including clinical data, epidemiological reports, therapeutic aspects and data relating to animal models for in vivo laboratory studies. It includes Supplementary Tables of all WHO outbreak bulletins, ProMED Mail alerts, viral sequences available on GenBank, and PubMed reports of clinical cases and seroprevalence studies.

Deciphering the protective role of adaptive immunity to CHIKV/IRES a novel candidate vaccine against Chikungunya in the A129 mouse model

Chikungunya virus (CHIKV), a mosquito-borne alphavirus, recently re-emerged in Africa and spread to islands in the Indian Ocean, the Indian subcontinent, and to South East Asia. Viremic travelers have also imported CHIKV to the Western hemisphere highlighting the importance of CHIKV in public health. In addition to the great burden of arthralgic disease, which can persist for months or years, epidemiologic studies have estimated case-fatality rates of ∼0.1%, principally from neurologic disease in older patients. There are no licensed vaccines or effective therapies to prevent or treat human CHIKV infections. We have developed a live CHIKV vaccine (CHIKV/IRES) that is highly attenuated yet immunogenic in mouse models, and is incapable of replicating in mosquito cells. In this study we sought to decipher the role of adaptive immunity elicited by CHIKV/IRES in protection against wild-type CHIKV infection. A single dose of vaccine effectively activated T cells with an expansion peak on day 10 post immunization and elicited memory CD4(+) and CD8(+) T cells that produced IFN-γ, TNF-α and IL-2 upon restimulation with CHIKV/IRES. Adoptive transfer of CHIKV/IRES-immune CD4(+) or CD8(+) T cells did not confer protection against wtCHIKV-LR challenge. By contrast, passive immunization with anti-CHIKV/IRES immune serum provided protection, and a correlate of a minimum protective neutralizing antibody titer was established. Overall, our findings demonstrate the immunogenic potential of the CHIKV/IRES vaccine and highlight the important role that neutralizing antibodies play in protection against an acute CHIKV infection.

An essential role of antibodies in the control of Chikungunya virus infection

In recent years, Chikungunya virus (CHIKV) was responsible for epidemic outbreaks in intertropical regions. Although acquired immunity has been shown to be crucial during CHIKV infection in both humans and mice, their exact role in the control of CHIKV infection remains unclear. In this study, wild-type (WT), CD4(-/-), and B cell (μMT) knockout mice were infected with CHIKV. Sera were taken at different days postinfection and measured for anti-CHIKV Ab levels. Isotype and neutralizing capacity of these Abs were assessed in vitro, and specific linear epitopes were mapped. Viremia in CHIKV-infected μMT mice persisted for more than a year, indicating a direct role for B cells in mediating CHIKV clearance. These animals exhibited a more severe disease than WT mice during the acute phase. Characterization of CHIKV-specific Abs revealed that anti-CHIKV Abs were elicited early and targeted epitopes mainly at the C terminus of the virus E2 glycoprotein. Furthermore, CD4(-/-) mice could still control CHIKV infection despite having lower anti-CHIKV Ab levels with reduced neutralizing capacity. Lastly, pre-existing natural Abs in the sera of normal WT mice recognized CHIKV and were able to partially inhibit CHIKV. Taken together, natural and CHIKV infection-induced specific Abs are essential for controlling CHIKV infections.

Profile of The Chikungunya Infection: A Neglected Vector Borne Disease which is Prevalent In The Rajkot District

BACKGROUND

Chikungunya Virus has been responsible for significant human morbidity probably for several hundred years; yet in spite of its prevalence, the Chikungunya Virus epidemiology and the mechanisms of virulence and pathogenesis are still poorly understood and undetermined.

AIMS

This study was done to show that the Chikungunya infection has shown a change in its pattern of occurrence with respect to the clinical features, the gender and the age group which are predominant and the season of the outbreak. The present study was conducted to evaluate the features of the Chikugunya infection in patients with acute febrile illness from various geographical regions of Rajkot district, Gujarat, India.

TYPE OF STUDY

A cross-sectional study, multi centric study.

STATISTICAL METHOD

The Chi-square test for the goodness of the fit and independence.

METHODS

One hundred ninty three serum samples of suspected cases of patients who attended the outdoor and indoor patients departments at a tertiary care hospital, Rajkot and the primary health centres, the community health centre and the urban health centres that were covered in the Rajkot district, which were collected during the period of one year from 1(st) January 2011 to 25(th) December 2011, were studied. The sera were processed and tested for the detection of the Chikungunya IgM antibody by using a solid phase, capture micro well ELISA technology.

RESULTS

Out of the total 193 cases, 84 were positive for the Chikungunya IgM antibody. Out of the total 84 positive cases, 32 were males (38.09%) and 52 were females (61.9%). Female patients showed more prevalence of this disease. A majority of the patients presented with fever, headache and joint pain: 44(52.38%). The highest prevalence of Chikungunya was found in the 40-50 years age group, which occurred in 34 (40.47%) cases. In the months of November and December, the occurrence of Chikungunya was more.

CONCLUSION

This study emphasizes the need for a continuous surveillance on the disease burden by using multiple diagnostic tests and it also warrants the need for appropriate molecular diagnostic techniques for an early detection of the Chikungunya virus.

Travel-Associated Chikungunya Cases in South Korea during 2009-2010

Objectives

Chikungunya (CHIK) has been classified as a communicable disease group IV in South Korea since late 2010. Based on this, we investigated the extent of imported cases of CHIK in dengue-suspected individuals returning from dengue-endemic regions.

Methods

A total of 486 dengue-suspected serum samples were screened for CHIK by enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR) analysis. Further RT-PCR-positive samples were used for the viral culture, and CHIK was subsequently confirmed by sequence analysis of the culture samples.

Results

Five out of 107 dengue-positive samples were found to be positive for CHIK and 15 out of 379 dengue-negative samples were found to be positive for CHIK by immunoglobulin M ELISA. Further, a CHIK virus was isolated from one of the two RT-PCR-positive sera by cell culture and confirmed by sequence analysis.

Conclusion

The present study documents the first evidence of travel-associated CHIK infection in South Korea. Considering the intense international traffic between countries, our finding emphasizes the urgent need for active patient and vector surveillance for timely response to reduce the introduction of CHIK in Korea.

Development of a highly protective combination monoclonal antibody therapy against Chikungunya virus

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that causes global epidemics of a debilitating polyarthritis in humans. As there is a pressing need for the development of therapeutic agents, we screened 230 new mouse anti-CHIKV monoclonal antibodies (MAbs) for their ability to inhibit infection of all three CHIKV genotypes. Four of 36 neutralizing MAbs (CHK-102, CHK-152, CHK-166, and CHK-263) provided complete protection against lethality as prophylaxis in highly susceptible immunocompromised mice lacking the type I IFN receptor (Ifnar^−/−) and mapped to distinct epitopes on the E1 and E2 structural proteins. CHK-152, the most protective MAb, was humanized, shown to block viral fusion, and require Fc effector function for optimal activity in vivo. In post-exposure therapeutic trials, administration of a single dose of a combination of two neutralizing MAbs (CHK-102+CHK-152 or CHK-166+CHK-152) limited the development of resistance and protected immunocompromised mice against disease when given 24 to 36 hours before CHIKV-induced death. Selected pairs of highly neutralizing MAbs may be a promising treatment option for CHIKV in humans.

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that causes outbreaks of polyarthritis in humans, and is currently a threat to spread to the United States due to the presence of its mosquito vector, Aedes albopictus. At present, there is no licensed human vaccine or therapeutic available to protect against CHIKV infection. The primary goal of this study was to develop an antibody-based therapeutic agent against CHIKV. To do this, we developed a panel of 230 new mouse anti-CHIKV MAbs and tested them for their ability to neutralize infection of different CHIKV strains in cell culture. We identified 36 MAbs with broad neutralizing activity, and then tested several of these for their ability to protect immunocompromised Ifnar^−/− mice against lethal CHIKV infection. In post-exposure therapeutic trials, administration of a single dose of a combination of two neutralizing MAbs limited the development of resistance and protected Ifnar^−/− mice against disease even when given just 24 to 36 hours before CHIKV-induced death. Analogous protection against CHIKV-induced arthritis was seen in a disease model in wild type mice. Our data suggest that pairs of highly neutralizing MAbs may be a therapeutic option against CHIKV infection.

Chikungunya virus and prospects for a vaccine

In 2004, chikungunya virus (CHIKV) re-emerged from East Africa to cause devastating epidemics of debilitating and often chronic arthralgia that have affected millions of people in the Indian Ocean Basin and Asia. More limited epidemics initiated by travelers subsequently occurred in Italy and France, as well as human cases exported to most regions of the world, including the Americas where CHIKV could become endemic. Because CHIKV circulates during epidemics in an urban mosquito-human cycle, control of transmission relies on mosquito abatement, which is rarely effective. Furthermore, there is no antiviral treatment for CHIKV infection and no licensed vaccine to prevent disease. Here, we discuss the challenges to the development of a safe, effective and affordable chikungunya vaccine and recent progress toward this goal.

Structural analyses at pseudo atomic resolution of Chikungunya virus and antibodies show mechanisms of neutralization

A 5.3 Å resolution, cryo-electron microscopy (cryoEM) map of Chikungunya virus-like particles (VLPs) has been interpreted using the previously published crystal structure of the Chikungunya E1-E2 glycoprotein heterodimer. The heterodimer structure was divided into domains to obtain a good fit to the cryoEM density. Differences in the T = 4 quasi-equivalent heterodimer components show their adaptation to different environments. The spikes on the icosahedral 3-fold axes and those in general positions are significantly different, possibly representing different phases during initial generation of fusogenic E1 trimers. CryoEM maps of neutralizing Fab fragments complexed with VLPs have been interpreted using the crystal structures of the Fab fragments and the VLP structure. Based on these analyses the CHK-152 antibody was shown to stabilize the viral surface, hindering the exposure of the fusion-loop, likely neutralizing infection by blocking fusion. The CHK-9, m10 and m242 antibodies surround the receptor-attachment site, probably inhibiting infection by blocking cell attachment. DOI:http://dx.doi.org/10.7554/eLife.00435.001.

Photochemical inactivation of chikungunya virus in human apheresis platelet components by amotosalen and UVA light

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that recently re-emerged in Africa and rapidly spread into countries of the Indian Ocean basin and South-East Asia. The mean viremic blood donation risk for CHIKV on La Réunion reached 1.5% at the height of the 2005-2006 outbreaks, highlighting the need for development of safety measures to prevent transfusion-transmitted infections. We describe successful inactivation of CHIKV in human platelets and plasma using photochemical treatment with amotosalen and long wavelength UVA illumination. Platelet components in additive solution and plasma units were inoculated with two different strains of high titer CHIKV stock (6.0-8.0 logs/mL), and then treated with amotosalen and exposure to 1.0-3.0 J/cm² UVA. Based on in vitro assays of infectious virus pre- and post-treatment to identify endpoint dilutions where virus was not detectable, mean viral titers could effectively be reduced by > 6.4 ± 0.6 log₁₀ TCID₅₀/mL in platelets and ≥ 7.6 ± 1.4 logs in plasma, indicating this treatment has the capacity to prevent CHIKV transmission in human blood components collected from infected donors in or traveling from areas of CHIKV transmission.

A tyrosine-to-histidine switch at position 18 of the Ross River virus E2 glycoprotein is a determinant of virus fitness in disparate hosts

Arthritogenic alphaviruses are human pathogens maintained in nature through alternating replication in vertebrates and mosquitoes. Using chimeric viruses, we previously reported that replacement of the PE2 coding region of the T48 strain of Ross River virus (RRV-T48) with that from the attenuated DC5692 strain, which differ by 7 amino acids, resulted in an attenuated disease phenotype in a mouse model of RRV-induced rheumatic disease. Here, we demonstrate that introduction of one of these amino acid differences, a tyrosine (Y)-to-histidine (H) change at position 18 of the E2 glycoprotein (E2 Y18H), into the RRV-T48 genetic background was sufficient to generate a virus that caused dramatically less severe musculoskeletal disease in mice. The attenuated phenotype of RRV-T48 E2 Y18H was associated with reduced viral loads in musculoskeletal tissues, reduced viremia, and less efficient virus spread. Consistent with these findings, RRV-T48 E2 Y18H replicated less well in mammalian cells in vitro due to significantly reduced PFU released per infected cell. In contrast, RRV-T48 E2 Y18H replicated more efficiently than RRV-T48 in C6/36 mosquito cells. Competition studies confirmed that RRV-T48 E2 Y18H had a fitness advantage in mosquito cells and a fitness disadvantage in mammalian cells. Interestingly, all sequenced Ross River viruses encode either a tyrosine or a histidine at E2 position 18, and this holds true for other alphaviruses in the Semliki Forest antigenic complex. Taken together, these findings suggest that a tyrosine-to-histidine switch at E2 position 18 functions as a regulator of RRV fitness in vertebrate and invertebrate cells.

Dendritic cell immunoreceptor regulates Chikungunya virus pathogenesis in mice

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus responsible for recent epidemic outbreaks of debilitating disease in humans. Alphaviruses are known to interact with members of the C-type lectin receptor family of pattern recognition proteins, and given that the dendritic cell immunoreceptor (DCIR) is known to act as a negative regulator of the host inflammatory response and has previously been associated with rheumatoid arthritis, we evaluated DCIR's role in response to CHIKV infection. Although we observed an increase in the proportion of dendritic cells at the site of CHIKV infection at 24 to 36 h postinfection, these cells showed decreased cell surface DCIR, suggestive of DCIR triggering and internalization. In vitro, bone marrow-derived dendritic cells from DCIR-deficient (DCIR(-/-)) mice exhibited altered cytokine expression following exposure to CHIKV. DCIR(-/-) mice exhibited more severe disease signs than wild-type C57BL6/J mice following CHIKV infection, including a more rapid and more severe onset of virus-induced edema and enhanced weight loss. Histological examination revealed that DCIR-deficient animals exhibited increased inflammation and damage in both the fascia of the inoculated foot and the ankle joint, and DCIR deficiency skewed the CHIKV-induced cytokine response at the site of infection at multiple times postinfection. Early differences in virus-induced disease between C57BL6/J and DCIR(-/-) mice were independent of viral replication, while extended viral replication correlated with enhanced foot swelling and tissue inflammation and damage in DCIR(-/-) compared to C57BL6/J mice at 6 to 7 days postinfection. These results suggest that DCIR plays a protective role in limiting the CHIKV-induced inflammatory response and subsequent tissue and joint damage.

Dissemination and transmission of the E1-226V variant of chikungunya virus in Aedes albopictus are controlled at the midgut barrier level

Emergence of arboviruses could result from their ability to exploit new environments, for example a new host. This ability is facilitated by the high mutation rate occurring during viral genome replication. The last emergence of chikungunya in the Indian Ocean region corroborates this statement since a single viral mutation at the position 226 on the E1 glycoprotein (E1-A226V) was associated with enhanced transmission by the mosquito Aedes albopictus in regions where the major mosquito vector, Aedes aegypti, is absent.

We used direct competition assays in vivo to dissect out the mechanisms underlying the selection of E1-226V by Ae. albopictus. When the original variant E1-226A and the newly emerged E1-226V were provided in the same blood-meal at equal titers to both species of mosquitoes, we found that the proportion of both variants was drastically different in the two mosquito species. Following ingestion of the infectious blood-meal, the E1-226V variant was preferentially selected in Ae. albopictus, whereas the E1-226A variant was sometimes favored in Ae. aegypti. Interestingly, when the two variants were introduced into the mosquitoes by intrathoracic inoculations, E1-226V was no longer favored for dissemination and transmission in Ae. albopictus, showing that the midgut barrier plays a key role in E1-226V selection.

This study sheds light on the role of the midgut barrier in the selection of novel arbovirus emerging variants. We also bring new insight into how the pre-existing variant E1-226V was selected among other viral variants including E1-226A. Indeed the E1-226V variant present at low levels in natural viral populations could rapidly emerge after being selected in Ae. albopictus at the midgut barrier level.

Development of a pseudotyped-lentiviral-vector-based neutralization assay for chikungunya virus infection

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that causes chikungunya fever in Africa, South Asia, and Southeast Asia. Because the mosquito vector Aedes albopictus is present in habitats across Europe, North America, and East Asia, CHIKV has become a serious worldwide public health concern. Infection with CHIKV typically causes fever, rash, myalgia, and arthralgia. One of the important questions yet to be answered is how the host immune system is involved in the development of this disease. In this study, we prepared a CHIKV-pseudotyped lentiviral vector for use in a safe and convenient neutralization (NT) assay and analyzed its efficacy. The CHIKV-pseudotyped lentiviral vector was prepared by cotransfection with plasmids encoding the CHIKV glycoproteins E3, E2, 6k, and E1, packaging elements, and a luciferase reporter. This alternative to native CHIKV can be safely handled in a biosafety level 2 facility. The NT assay was optimized using sera from CHIKV-immunized mice and then applied to human patient sera. The majority of the serum samples from patients with chikungunya in Thailand showed robust neutralization activities, with titers that were tightly correlated with those determined by a conventional NT assay. Moreover, there was a strong correlation with the CHIKV antibody titers as determined by enzyme-linked immunosorbent assay. Thus, the CHIKV-pseudotyped-lentiviral-vector-based NT assay system is a powerful tool for examining the neutralization activity of patient sera, which will lead to a better understanding of the immune responses involved in CHIKV infection.

Chikungunya and the eye: a review

Chikungunya is a self-limited, systemic viral infection that has been a major health problem since the past few years. Ocular manifestations of the disease have become more prevalent in the recent years. Currently, there is neither a specific treatment nor vaccine available for chikungunya fever. This review highlights the current understanding on the pathogenesis, systemic changes with an emphasis on ocular findings, laboratory investigations, and prevention and treatment of this disease.

Emergence of chikungunya seropositivity in healthy Malaysian adults residing in outbreak-free locations: chikungunya seroprevalence results from the Malaysian Cohort

BACKGROUND

In 1998, Malaysia experienced its first chikungunya virus (CHIKV) outbreak in the suburban areas followed by another two in 2006 (rural areas) and 2008 (urban areas), respectively. Nevertheless, there is still a lack of documented data regarding the magnitude of CHIKV exposure in the Malaysian population. The aim of this study was to determine the extent of chikungunya virus infection in healthy Malaysian adults residing in outbreak-free locations.

METHODS

A cross sectional study of chikungunya (CHIK) seroprevalence was carried out in 2009 amongst The Malaysian Cohort participants living in four states (Kuala Lumpur, Selangor, Pahang and Negeri Sembilan). A total of 945 participants were randomly identified for the study. Potential risk factors for CHIK infection were determined via questionnaires, and IgG antibodies against CHIK were detected by an enzyme-linked immunosorbent assay. Logistic regression identified risk factors associated with CHIK seropositivity, while geographical information system was used for visual and spatial analysis.

RESULTS

From the 945 serum samples tested, 5.9% was positive for CHIK IgG. Being male, Malay, rural occupancy and Negeri Sembilan residency were identified as univariate predictors for CHIK seropositivity, while multivariate analysis identified being male and rural occupancy as risk factors.

CONCLUSIONS

This study provided evidence that CHIK is slowly emerging in Malaysia. Although the current baseline seroprevalence is low in this country, increasing number of CHIK cases reported to the Malaysia Ministry of Health imply the possibility of CHIK virus becoming endemic in Malaysia.

Differential unfolded protein response during Chikungunya and Sindbis virus infection: CHIKV nsP4 suppresses eIF2α phosphorylation

Chikungunya (CHIKV) and Sindbis (SINV) are arboviruses belonging to the alphavirus genus within the Togaviridae family. They cause frequent epidemics of febrile illness and long-term arthralgic sequelae that affect millions of people each year. Both viruses replicate prodigiously in infected patients and in vitro in mammalian cells, suggesting some level of control over the host cellular translational machinery that senses and appropriately directs the cell's fate through the unfolded protein response (UPR). The mammalian UPR involves BIP (or GRP78), the master sensor in the endoplasmic reticulum (ER) together with the three downstream effector branches: inositol-requiring ser/thr protein kinase/endonuclease (IRE-1), PKR-like ER resident kinase (PERK) and activating transcription factor 6 (ATF-6). Through careful analysis of CHIKV and SINV infections in cell culture we found that the former selectively activates ATF-6 and IRE-1 branches of UPR and suppresses the PERK pathway. By separately expressing each of the CHIKV proteins as GFP-fusion proteins, we found that non-structural protein 4 (nsP4), which is a RNA-dependent-RNA polymerase, suppresses the serine-51 phosphorylation of eukaryotic translation initiation factor, alpha subunit (eIF2α), which in turn regulates the PERK pathway. This study provides insight into a mechanism by which CHIKV replication responds to overcome the host UPR machinery.

Utility of IgM ELISA, TaqMan real-time PCR, reverse transcription PCR, and RT-LAMP assay for the diagnosis of Chikungunya fever

Chikungunya fever a re-emerging infection with expanding geographical boundaries, can mimic symptoms of other infections like dengue, malaria which makes the definitive diagnosis of the infection important. The present study compares the utility of four laboratory diagnostic methods viz. IgM capture ELISA, an in house reverse transcription PCR for the diagnosis of Chikungunya fever, TaqMan real-time PCR, and a one step reverse transcription-loop mediated isothermal amplification assay (RT-LAMP). Out of the 70 serum samples tested, 29 (41%) were positive for Chikungunya IgM antibody by ELISA and 50 (71%) samples were positive by one of the three molecular assays. CHIKV specific nucleic acid was detected in 33/70 (47%) by reverse transcription PCR, 46/70 (66%) by TaqMan real-time PCR, and 43/70 (62%) by RT-LAMP assay. A majority of the samples (62/70; 89%) were positive by at least one of the four assays used in the study. The molecular assays were more sensitive for diagnosis in the early stages of illness (2-5 days post onset) when antibodies were not detectable. In the later stages of illness, the IgM ELISA is a more sensitive diagnostic test. In conclusion we recommend that the IgM ELISA be used as an initial screening test followed one of the molecular assays in samples that are collected in the early phase of illness and negative for CHIKV IgM antibodies. Such as approach would enable rapid confirmation of the diagnosis and implementation of public health measures especially during outbreaks.

O'nyong nyong virus molecular determinants of unique vector specificity reside in non-structural protein 3

O'nyong nyong virus (ONNV) and Chikungunya virus (CHIKV) are two closely related alphaviruses with very different infection patterns in the mosquito, Anopheles gambiae. ONNV is the only alphavirus transmitted by anopheline mosquitoes, but specific molecular determinants of infection of this unique vector specificity remain unidentified. Fifteen distinct chimeric viruses were constructed to evaluate both structural and non-structural regions of the genome and infection patterns were determined through artificial infectious feeds in An. gambiae with each of these chimeras. Only one region, non-structural protein 3 (nsP3), was sufficient to up-regulate infection to rates similar to those seen with parental ONNV. When ONNV non-structural protein 3 (nsP3) replaced nsP3 from CHIKV virus in one of the chimeric viruses, infection rates in An. gambiae went from 0% to 63.5%. No other single gene or viral region addition was able to restore infection rates. Thus, we have shown that a non-structural genome element involved in viral replication is a major element involved in ONNV's unique vector specificity.

Predictors of Chikungunya rheumatism: a prognostic survey ancillary to the TELECHIK cohort study

Introduction

Long-lasting relapsing or lingering rheumatic musculoskeletal pain (RMSP) is the hallmark of Chikungunya virus (CHIKV) rheumatism (CHIK-R). Little is known on their prognostic factors. The aim of this prognostic study was to search the determinants of lingering or relapsing RMSP indicative of CHIK-R.

Methods

Three hundred and forty-six infected adults (age ≥ 15 years) having declared RMSP at disease onset were extracted from the TELECHIK cohort study, Reunion island, and analyzed using a multinomial logistic regression model. We also searched for the predictors of CHIKV-specific IgG titres, assessed at the time of a serosurvey, using multiple linear regression analysis.

Results

Of these, 111 (32.1%) reported relapsing RMSP, 150 (43.3%) lingering RMSP, and 85 (24.6%) had fully recovered (reference group) on average two years after acute infection. In the final model controlling for gender, the determinants of relapsing RMSP were the age 45-59 years (adjusted OR: 2.9, 95% CI: 1.0, 8.6) or greater or equal than 60 years (adjusted OR: 10.4, 95% CI: 3.5, 31.1), severe rheumatic involvement (fever, at least six joints plus four other symptoms) at presentation (adjusted OR: 3.6, 95% CI: 1.5, 8.2), and CHIKV-specific IgG titres (adjusted OR: 3.2, 95% CI: 1.8, 5.5, per one unit increase). Prognostic factors for lingering RMSP were age 45-59 years (adjusted OR: 6.4, 95% CI: 1.8, 22.1) or greater or equal than 60 years (adjusted OR: 22.3, 95% CI: 6.3, 78.1), severe initial rheumatic involvement (adjusted OR: 5.5, 95% CI: 2.2, 13.8) and CHIKV-specific IgG titres (adjusted OR: 6.2, 95% CI: 2.8, 13.2, per one unit increase). CHIKV specific IgG titres were positively correlated with age, female gender and the severity of initial rheumatic symptoms.

Conclusions

Our data support the roles of age, severity at presentation and CHIKV specific IgG titres for predicting CHIK-R. By identifying the prognostic value of the humoral immune response of the host, this work also suggest a significant contribution of the adaptive immune response to the physiopathology of CHIK-R and should help to reconsider the paradigm of this chronic infection primarily shifted towards the involvement of the innate immune response.

Human-Wildlife Contact and Emerging Infectious Diseases

The majority of all emerging pathogens in humans are zoonotic (nonhuman animal) in origin. Population, ecological, and behavioral changes that increase contact with wildlife exacerbate emergence of these pathogens. Anthropogenic modification of the physical environment has altered not only our risk of zoonotic infection from wildlife but also the likelihood of pathogen transmission from human to nonhuman animal populations. This is particularly the case for primates that share a number of common infections with humans. In this chapter, I use a series of case studies involving SARS, HIV, Nipah virus, Lyme disease, malaria, and Ebola to exemplify how various anthropogenic factors have facilitated pathogen transmission between human and nonhuman animal populations. The costs and benefits of primate-based ecotourism are also reviewed to better illustrate how human-wildlife contact can affect both populations. Responsible health monitoring of human-wildlife interactions is a necessary prerequisite for prevention of the transmission of future emerging infectious diseases.

Animal Models of Human Viral Diseases

As the threat of exposure to emerging and reemerging viruses within a naive population increases, it is vital that the basic mechanisms of pathogenesis and immune response be thoroughly investigated. By using animal models in this endeavor, the response to viruses can be studied in a more natural context to identify novel drug targets, and assess the efficacy and safety of new products. This is especially true in the advent of the Food and Drug Administration's animal rule. Although no one animal model is able to recapitulate all the aspects of human disease, understanding the current limitations allows for a more targeted experimental design. Important facets to be considered before an animal study are the route of challenge, species of animals, biomarkers of disease, and a humane endpoint. This chapter covers the current animal models for medically important human viruses, and demonstrates where the gaps in knowledge exist.

Genomes to hits in silico - a country path today, a highway tomorrow: a case study of chikungunya

These are exciting times for bioinformaticians, computational biologists and drug designers with the genome and proteome sequences and related structural databases growing at an accelerated pace. The post-genomic era has triggered high expectations for a rapid and successful treatment of diseases. However, in this biological information rich and functional knowledge poor scenario, the challenges are indeed grand, no less than the assembly of the genome of the whole organism. These include functional annotation of genes, identification of druggable targets, prediction of three-dimensional structures of protein targets from their amino acid sequences, arriving at lead compounds for these targets followed by a transition from bench to bedside. We propose here a "Genome to Hits In Silico" strategy (called Dhanvantari) and illustrate it on Chikungunya virus (CHIKV). "Genome to hits" is a novel pathway incorporating a series of steps such as gene prediction, protein tertiary structure determination, active site identification, hit molecule generation, docking and scoring of hits to arrive at lead compounds. The current state of the art for each of the steps in the pathway is high-lighted and the feasibility of creating an automated genome to hits assembly line is discussed.

Infection of Aedes albopictus with chikungunya virus rectally administered by enema

Chikungunya virus (CHIKV) is an alphavirus transmitted by Aedes albopictus and Aedes aegypti mosquitoes in tropical areas of Africa, Asia, and the islands of the Indian Ocean. In 2007 and 2009, CHIKV was transmitted outside these tropical areas and caused geographically localized infections in people in Italy and France. To temporally and spatially characterize CHIKV infection of Ae. albopictus midguts, a comparison of viral distribution in mosquitoes infected per os or by enema was conducted. Ae. albopictus infected with CHIKV LR 5' green fluorescent protein (GFP) at a titer 10(6.95) tissue culture infective dose(50) (TCID(50))/mL, were collected and analyzed for virus dissemination by visualizing GFP expression and titration up to 14 days post inoculation (dpi). Additionally, midguts were dissected from the mosquitoes and imaged by fluorescence microscopy for comparison of midgut infection patterns between orally- and enema-infected mosquitoes. When virus was delivered via enema, the anterior midgut appeared more readily infected by 3 dpi, with increased GFP presentation observed in this same location of the midgut at 7 and 14 dpi when compared to orally-infected mosquitoes. This work demonstrates that enema delivery of virus is a viable technique for use of mosquito infection. Enema injection of mosquitoes may be an alternative to intrathoracic inoculation because the enema delivery more closely models natural infection and neither compromises midgut integrity nor involves a wound that can induce immune responses. Furthermore, unlike intrathoracic delivery, the enema does not bypass midgut barriers to infect tissues artificially in the hemocoel of the mosquito.

Modeling dynamic introduction of Chikungunya virus in the United States

Chikungunya is a mosquito-borne viral infection of humans that previously was confined to regions in central Africa. However, during this century, the virus has shown surprising potential for geographic expansion as it invaded other countries including more temperate regions. With no vaccine and no specific treatment, the main control strategy for Chikungunya remains preventive control of mosquito populations. In consideration for the risk of Chikungunya introduction to the US, we developed a model for disease introduction based on virus introduction by one individual. Our study combines a climate-based mosquito population dynamics stochastic model with an epidemiological model to identify temporal windows that have epidemic risk. We ran this model with temperature data from different locations to study the geographic sensitivity of epidemic potential. We found that in locations with marked seasonal variation in temperature there also was a season of epidemic risk matching the period of the year in which mosquito populations survive and grow. In these locations controlling mosquito population sizes might be an efficient strategy. But, in other locations where the temperature supports mosquito development all year the epidemic risk is high and (practically) constant. In these locations, mosquito population control alone might not be an efficient disease control strategy and other approaches should be implemented to complement it. Our results strongly suggest that, in the event of an introduction and establishment of Chikungunya in the US, endemic and epidemic regions would emerge initially, primarily defined by environmental factors controlling annual mosquito population cycles. These regions should be identified to plan different intervention measures. In addition, reducing vector: human ratios can lower the probability and magnitude of outbreaks for regions with strong seasonal temperature patterns. This is the first model to consider Chikungunya risk in the US and can be applied to other vector borne diseases.

Chikungunya fever is a mosquito-borne viral infection showing a surprising potential for geographic expansion. Similar to other tropical infectious diseases having no vaccine and no specific treatment, the main control strategy for Chikungunya remains reduction of mosquito population size. We developed a model for disease introduction that combines a climate based mosquito population dynamics stochastic model with an epidemiological model in order to identify temporal windows during which disease introduction through one exposed individual might compromise the health status of the entire human population. We ran this model with temperature data from different locations showing the geographic sensitivity of this risk. The identification of temporal windows with epidemic risk at different spatial locations is key to guiding mosquito population control campaigns. Locations with marked seasonal variation also have a season with high epidemic risk matching the period in which mosquito populations survive and grow, therefore controlling mosquito population sizes might be an optimal strategy in those areas. However, locations with other temperature patterns may need additional control strategies to avoid epidemics. To our knowledge, this is the first model to explore Chikungunya introduction in the USA. Our modeling approach can be used for other vector borne diseases and can be expanded to compare the outcome with different control strategies.

Viperin restricts chikungunya virus replication and pathology

Chikungunya virus (CHIKV) is a mosquito-borne arthralgia arbovirus that is reemergent in sub-Saharan Africa and Southeast Asia. CHIKV infection has been shown to be self-limiting, but the molecular mechanisms of the innate immune response that control CHIKV replication remain undefined. Here, longitudinal transcriptional analyses of PBMCs from a cohort of CHIKV-infected patients revealed that type I IFNs controlled CHIKV infection via RSAD2 (which encodes viperin), an enigmatic multifunctional IFN-stimulated gene (ISG). Viperin was highly induced in monocytes, the major target cell of CHIKV in blood. Anti-CHIKV functions of viperin were dependent on its localization in the ER, and the N-terminal amphipathic α-helical domain was crucial for its antiviral activity in controlling CHIKV replication. Furthermore, mice lacking Rsad2 had higher viremia and severe joint inflammation compared with wild-type mice. Our data demonstrate that viperin is a critical antiviral host protein that controls CHIKV infection and provide a preclinical basis for the design of effective control strategies against CHIKV and other reemerging arthrogenic alphaviruses.

Mouse models for Chikungunya virus: deciphering immune mechanisms responsible for disease and pathology

Chikungunya virus (CHIKV), an alphavirus, has been responsible for large epidemic outbreaks with serious economic and social impact during the last 6 years. Transmitted by Aedes mosquitoes, it causes Chikungunya fever, an acute illness in patients with a stooped posture often associated with chronic and incapacitating arthralgia. The unprecedented re-emergence has stimulated renewed interest in CHIKV. This review discusses the advantages and disadvantages of different animal models for CHIKV infections and their importance to study the role of the immune system in different pathologies caused by CHIKV. We also reveal how such studies still present a difficult challenge, but are indispensible for mechanistic studies to further understand the pathophysiology of CHIKV infections.

Infectious disease emergencies in returning travelers: special reference to malaria, dengue fever, and chikungunya

This review article discusses important infectious illnesses, namely malaria, dengue, and chikungunya, in travelers returning from endemic areas. Malaria and dengue are two of the most common systemic illnesses reported in returning travelers. Because chikungunya is gaining importance, it is also briefly discussed. The clinical significance of these diseases is mainly due to the possibility of sudden deterioration with high mortality in clinically healthy looking patients. The key clinical features, their diagnosis, and treatment algorithms are discussed in detail to help in early diagnosis and appropriate clinical management of such travelers presenting in emergency departments.

A chimeric vesiculo/alphavirus is an effective alphavirus vaccine

While a large number of mosquito-transmitted alphaviruses are known to cause serious human diseases, there are no licensed vaccines that protect against alphavirus infections. The alphavirus chikungunya virus (CHIKV) has caused multiple recent outbreaks of chikungunya fever. This virus has the potential to cause a worldwide epidemic and has generated strong interest in development of a prophylactic CHIKV vaccine. We report here on the development of a potent experimental vaccine for CHIKV based on a chimeric vesicular stomatitis virus (VSV) expressing the entire CHIKV envelope polyprotein (E3-E2-6K-E1) in place of the VSV glycoprotein (G). These VSVΔG-CHIKV chimeras incorporated functional CHIKV glycoproteins into the viral envelope in place of VSV G. The chimeric viruses were attenuated for growth in tissue culture but could be propagated to high titers without VSV G complementation. They also generated robust neutralizing antibody and cellular immune responses to CHIKV in mice after a single dose and protected mice against CHIKV infection. VSVΔG-alphavirus chimeras could have general applicability as alphavirus vaccines.

Complete genome sequence of a chikungunya virus isolated in Guangdong, China

Chikungunya virus belongs to the genus Alphavirus in the family Togaviridae. Here we report the complete genome sequence of a chikungunya virus strain, GD05/2010, isolated in 2010 from a patient with chikungunya fever in Guangdong, China. The sequence information is important for surveillance of this emerging arboviral infection in China.