Application of real-time RT-PCR in vector surveillance and assessment of replication kinetics of an emerging novel ECSA genotype of Chikungunya virus in Aedes aegypti

Selective estrogen receptor modulators limit alphavirus infection by targeting the viral capping enzyme nsP1

Alphaviruses cause animal or human diseases that are characterized by febrile illness, debilitating arthralgia, or encephalitis. Selective estrogen receptor modulators (SERMs), a class of FDA-approved drugs, have been shown to possess antiviral activities against multiple viruses, including Hepatitis C virus, Ebola virus, dengue virus, and vesicular stomatitis virus. Here, we evaluated three SERM compounds, namely 4-hydroxytamoxifen, tamoxifen, and clomifene, for plausible antiviral properties against two medically important alphaviruses, chikungunya virus (CHIKV) and Sindbis virus (SINV). In cell culture settings, these SERMs displayed potent activity against CHIKV and SINV at non-toxic concentrations with EC₅₀ values ranging between 400 nM and 3.9 μM. Further studies indicated that these compounds inhibit a post-entry step of the alphavirus life cycle, while enzymatic assays involving purified recombinant proteins confirmed that these SERMs target the enzymatic activity of non-structural protein 1 (nsP1), the capping enzyme of alphaviruses. Finally, tamoxifen treatment restrained CHIKV growth in the infected mice and diminished musculoskeletal pathologies. Combining biochemical, cell culture-based studies, and in vivo analyses, we strongly argue that SERM compounds, or their derivatives, may provide for attractive therapeutic options against alphaviruses.

Development of magnetic bead based sample extraction coupled polymerase spiral reaction for rapid on-site detection of Chikungunya virus

The molecular detection system has evolved over last two decades and is rapidly replacing the conventional confirmatory techniques in diagnostic virology. However the major limitation in implementation of available molecular detection assays is the non availability of field deployable nucleic acid isolation platform coupled with gene amplification technique. The rapid and early molecular detection is crucial for employing effective measure against many viral infections. The re-emergence of chikungunya virus (CHIKV) has led to epidemics since 2004 in several parts of the world including India. The main association of CHIKV with severe arthritis and long-lasting arthralgia and closely mimics symptoms of Dengue and Zika virus infection requiring laboratory confirmation. In this study, a simple magnetic bead based ribonucleic acid extraction method was optimized, which was coupled with isothermal polymerase spiral reaction (PSR) technique for early and rapid detection. Subsequently, the polymerase spiral reaction reagents were converted to dry down format that led to a rapid user friendly field compatible sample processing to answer method for rapid and onsite detection of Chikungunya virus. Both the methods were evaluated with a panel of clinical samples. The sensitivity of the assays were compared with available commercial viral RNA extraction platform and qRT-PCR. The in-house nucleic acid extraction system based on magnetic bead followed by dry down RT-Polymerase Spiral Reaction assay was found to be highly sensitive with 10 copies of RNA as limit of detection in CHIKV clinical specimens. With respect to other closely related viruses no cross reactivity was observed. This novel methodology has the potential to revolutionize the diagnosis of infectious agents in resource limited settings around the world.

Origins, pathophysiology, diagnosis, vaccination and prevention of Chikungunya virus

Chikungunya virus is an Alphavirus that possesses characteristics similar to that of an arthropod-borne virus. Chikungunya virus has been one of the major concerns for the last few decades due to its nature of explosive spreading throughout the world. This article is intended to give detailed information about Chikungunya virus, and includes its pathogenesis, origins, diagnosis, treatment and prevention. Although, recent researches suggests various approaches to treating Chikungunya virus, extensive literature search on Chikungunya virus has revealed that, currently, there is no effective treatment available and the virus is greatly dependent on its vectors. Patients affected by Chikungunya virus mainly show symptoms of fever, arthralgia, joint pain and skin rash. Since there is no effective treatment available, public awareness is the most significant factor for potential prevention against Chikungunya virus.

Virus load and clinical features during the acute phase of Chikungunya infection in children

BACKGROUND

Chikungunya virus (CHIKV) infection is a long known mosquito-borne disease that is associated with severe morbidity, characterized by fever, headache, rashes, joint pain, and myalgia. It is believed that virus load has relation with severity of clinical features.

OBJECTIVES

We performed this study to assess the relationship between virus load and clinical features in children during the acute phase of CHIKV infection, in order to draw insights for better-informed treatment.

STUDY DESIGN

Between June 1, 2009, and May 31, 2010, 338 patients with fever and susceptive to CHIKV during first 4 days of illness were prospectively enrolled from Karnataka Institute of Medical Sciences, Hubli in our hospital based cross sectional observational study. Sybr green quantitative reverse transcription polymerase chain reaction was performed to estimate the virus load.

RESULTS

Quantitative RT-PCR was positive for CHIKV in 54 patients. The median copy number of CHIKV was 1.3x 108 copies/ml (1.7x105-9.9x109 copies/ml). Among the observed clinical features, a statistically significant difference in log mean virus load was found between patients with and without myalgia (log mean 7.50 vs 8.34, P = 0.01).

CONCLUSION

Patients with myalgia had lower virus load and those without myalgia had a higher virus load.

Dynamic distribution and tissue tropism of avian encephalomyelitis virus isolate XY/Q-1410 in experimentally infected Korean quail

Avian encephalomyelitis (AE) is an important infectious poultry disease worldwide that is caused by avian encephalomyelitis virus (AEV). However, to date, the dynamic distribution of AEV in quails has not been well described. Quantitative real-time polymerase chain reaction (qPCR) and immunohistochemistry (IHC) assays were used to investigate the dynamic distribution and tissue tropism of AEV in experimentally infected Korean quail. AEV was detected in the cerebrum, cerebellum, proventriculus, intestine, liver, pancreas, spleen, bursa, lung and kidney as early as 3 days post-infection (dpi). The viral loads in the proventriculus, intestine, spleen and bursa were relatively higher than in other tissues. According to the qPCR results, AEV XY/Q-1410 infection lasted for at least 60 days in infected Korean quail. Immunohistochemistry-positive staining signals of AEV antigen were analysed by Image-Pro Plus software. A positive correlation between qPCR and IHC results was identified in most tissues. Our results provide an insight into the dynamic distribution of AEV in various tissues after infection. The distinct dynamic distribution of the viral genome in Korean quail in the early and late stages of infection suggests that AEV replication is affected by antibody levels and the maturity of the immune system of the host.

Vector-delivered artificial miRNA effectively inhibited replication of Chikungunya virus

Chikungunya virus (CHIKV) has emerged as one of the most significant arboviral threats in many parts of the world. In spite of large scale morbidity, and long lasting polyarthralgia, no licensed vaccine or antivirals are available for the clinical management of CHIKV infection. In this study, a novel RNA interference based strategy has been adopted for effective inhibition of CHIKV. Four artificial microRNAs (amiRNAs) were designed to target different regions of CHIKV genome. These amiRNAs significantly inhibited CHIKV replication in Vero cells at both RNA and protein levels as assessed by qRT-PCR, immunoblotting and immunofluorescence techniques. Further inhibition of the infectious CHIKV up to 99.8% was demonstrated by plaque reduction assay. Concatemerization of amiRNA resulted in higher inhibition of CHIKV than individual amiRNAs. In addition, we studied the effect of combination of RNAi based therapy with other classical antivirals like chloroquine, ribavirin and mycophenolic acid, that helped in understanding the rational selection of RNAi based combination therapy. These findings provide a promising avenue for the development of novel amiRNA or combination based therapeutics against emerging CHIKV.

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amiRNAs targeting different ORF of CHIKV was designed.

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Significant Inhibition of CHIKV replication through amiRNA was demonstrated.

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Concatenated amiRNAs results in higher viral inhibition.

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Combination of RNAi with classical drugs may obliterate failure of monotherapy.

Two novel epistatic mutations (E1:K211E and E2:V264A) in structural proteins of Chikungunya virus enhance fitness in Aedes aegypti

Expansion of CHIKV outbreaks with appearance of novel mutations are reported from many parts of the world. Two novel mutations viz. E1:K211E and E2:V264A in background of E1:226A are recently identified from Aedes aegypti dominated areas of India. In this study, the role of these mutations in modulation of infectivity, dissemination and transmission by two different Aedes species was studied. Mutations were sequentially constructed in CHIKV genome and female Ae. aegypti and Aedes albopictus mosquitoes were orally infected with eight different CHIKV mutants. Double mutant virus containing E1:K211E and E2:V264A mutations in background of E1:226A revealed remarkably higher fitness for Ae. aegypti, as indicated by significant increase in virus infectivity (13 fold), dissemination (15 fold) and transmission (62 fold) compared to parental E1:226A virus. These results indicate that adaptive mutations in CHIKV are leading to efficient CHIKV circulation in Ae. aegypti endemic areas, contributing and sustaining the major CHIKV outbreaks.

Expression and Characterization of Yeast Derived Chikungunya Virus Like Particles (CHIK-VLPs) and Its Evaluation as a Potential Vaccine Candidate

Chikungunya virus (CHIKV) has emerged as a global health concern due to its recent spread in both old and new world. So far, no CHIKV specific drug or vaccine is licensed for human use. In this study, we report production of Chikungunya virus like particles (CHIK-VLPs) using novel yeast expression system (Pichia pastoris) and its evaluation as vaccine candidate. The gene encoding structural polyprotein of CHIKV from a recent epidemic strain was cloned into yeast expression system. The multicopy integrants were processed for expression of CHIK-VLPs. The VLPs were purified and confirmed through electron microscopic analysis for their morphological identity with CHIKV. The in vitro and in vivo evaluation of CHIK-VLPs as vaccine candidate was determined in Balb/c mice. Induction of both humoral and cellular immune response was observed with different doses of CHIK-VLPs. The humoral immune response was studied through different techniques like enzyme linked immunosorbent assay, IgG Isotyping and plaque reduction neutralization test. CHIK-VLPs were found to elicit high titer of antibodies that are able to recognize native CHIKV. Higher level of IgG2a and IgG1 subtypes was identified suggestive of balanced Th1/Th2 response. Both in vitro and in vivo neutralization activity of CHIK-VLPs antibodies was observed even with low concentration, which shows its high specificity and neutralizing activity against two different CHIKV strains. Neonatal mice receiving anti-CHIK-VLPs antibodies were protected from CHIKV challenge. Induction of cellular immune response was confirmed through higher level of TNF-α, IL-10 and substantial level of IL-2, IL-4 and IFN-γ indicating a balanced response. This is the first report, where CHIK-VLPs has been expressed by Pichia pastoris and evaluated for neutralizing activity against CHIKV. These promising results indicate the utility of CHIK-VLPs as a promising vaccine candidate against emerging CHIKV.

Chikungunya virus (CHIKV) has emerged in many parts of tropics in last decade. The absence of an approved vaccine or antiviral drug for CHIKV makes it one of the important public health challenges. Though attempt to develop a CHIKV vaccine was initiated in 1980s, however it has not succeeded so far. The Virus like particles (VLPs) are now explored as promising vaccine candidate against many viruses viz. HBV, HPV etc. In this study, we report the production of CHIK-VLPs using novel yeast expression system (Pichia pastoris) and its evaluation as vaccine candidate. These CHIK-VLPs share morphological identity to native CHIKV. The results indicate that CHIK-VLPs induced both cell mediated as well as humoral response in a balanced manner, which fulfils its criteria as a potent immunogen. Further, antibodies generated against CHIK-VLPs demonstrated efficient in vitro and in vivo neutralization activity, as evaluated through plaque reduction in Vero cells and protection in CHIKV infected neonatal mice respectively using two different CHIKV strains, which makes it a promising vaccine candidate. The yeast expressed CHIK-VLPs has high potential for development of an effective vaccine candidate against CHIKV during epidemic situations.

Development of a SYBR green I-based quantitative RT-PCR for Ross River virus: Application in vector competence studies and antiviral drug evaluation

Ross River virus (RRV) is an emerging Alphavirus and is presently endemic in many parts of Oceania. Keeping in mind its emergence, we developed a molecular detection system and utilized it to study vector competence and evaluate activity of antiviral compounds against RRV. A SYBR Green I-based quantitative RT-PCR for detection of RRV was developed targeting the E2 gene, with a detection limit of 100 RNA copies/reaction. The specificity was confirmed with closely related Alphaviruses and Flaviviruses. The assay was applied to study the vector competence of Indian Aedes aegypti for RRV, which revealed 100% infection and dissemination rate with 75% transmission rate. Viral RNA was found in saliva as early as 3day post infection (dpi). Further application of the assay in antiviral drug evaluation revealed the superior in vitro activity of ribavirin compared to chloroquine in Vero cells. Successful demonstration of this assay to detect RRV in low titre mosquito samples makes it a sensitive tool in vector surveillance. This study also showed that Indian Ae. aegypti are well competent to transmit RRV highlighting the risk of its introduction to naïve territories across continents. Further validation of this assay, revealed its utility in screening of potential antivirals against RRV.

Mosquito saliva induced cutaneous events augment Chikungunya virus replication and disease progression

Chikungunya virus (CHIKV) is transmitted when infected mosquito probes the host skin. While probing, mosquito saliva is expectorated into host skin along with virus which contains cocktail of molecules having anti-hemostatic and immunomodulatory properties. As mosquito saliva is a critical factor during natural arboviral infection, therefore we investigated mosquito saliva induced cutaneous events that modulate CHIKV infection. The effect of mosquito saliva on CHIKV infection was examined through inoculation of suckling mice subcutaneously with either CHIKV alone or uninfected mosquito bite followed by CHIKV. Histopathological evaluation of skin revealed infiltration of transmigrated inflammatory cells. Dermal blood vessels were hyperemic and adnexa showed degenerating lesions. Severe hemorrhage was observed in dermis and hypodermis in mosquito bite+CHIKV group compared to CHIKV group. Analysis of cytokines in skin showed significant downregulation of inflammatory genes like TLR-3, IL-2, IFN-γ, TNF-α and IFN-β in mosquito bite+CHIKV group compared to CHIKV group. In contrast, significant upregulation of anti-inflammatory genes like IL-4 and IL-10 was observed. These early events might have been responsible for increased dissemination of CHIKV to serum and peripheral organs as demonstrated through >10-fold higher viremia, antigen localization, cellular infiltration and degenerative changes. Thus mosquito saliva induced early cellular infiltration and associated cytokines augment CHIKV pathogenesis in a mouse model. This mosquito improved CHIKV mouse model simulates the realistic conditions that occur naturally during infected mosquito bite to a host. It will lead to better understanding of CHIKV pathobiology and promote the evaluation of novel medical countermeasures against emerging CHIKV.

Chikungunya virus, epidemiology, clinics and phylogenesis: A review

Chikungunya virus is a mosquito-transmitted alphavirus that causes chikungunya fever, a febrile illness associated with severe arthralgia and rash. Chikungunya virus is transmitted by culicine mosquitoes; Chikungunya virus replicates in the skin, disseminates to liver, muscle, joints, lymphoid tissue and brain, presumably through the blood. Phylogenetic studies showed that the Indian Ocean and the Indian subcontinent epidemics were caused by two different introductions of distinct strains of East/Central/South African genotype of CHIKV. The paraphyletic grouping of African CHIK viruses supports the historical evidence that the virus was introduced into Asia from Africa. Phylogenetic analysis divided Chikungunya virus isolates into three distinct genotypes based on geographical origins: the first, the West Africa genotype, consisted of isolates from Senegal and Nigeria; the second contained strains from East/Central/South African genotype, while the third contained solely Asian. The most recent common ancestor for the recent epidemic, which ravaged Indian Ocean islands and Indian subcontinent in 2004 - 2007, was found to date in 2002. Asian lineage dated about 1952 and exhibits similar spread patterns of the recent Indian Ocean outbreak lineage, with successive epidemics detected along an eastward path. Asian group splitted into two clades: an Indian lineage and a south east lineage. Outbreaks of Chikungunya virus fever in Asia have not been associated necessarily with outbreaks in Africa. Phylogenetic tools can reconstruct geographic spread of Chikungunya virus during the epidemics wave. The good management of patients with acute Chikungunya virus infection is essential for public health in susceptible areas with current Aedes spp activity.

Evidence of experimental vertical transmission of emerging novel ECSA genotype of Chikungunya Virus in Aedes aegypti

Background

Chikungunya virus (CHIKV) has emerged as one of the most important arboviruses of public health significance in the past decade. The virus is mainly maintained through human-mosquito-human cycle. Other routes of transmission and the mechanism of maintenance of the virus in nature are not clearly known. Vertical transmission may be a mechanism of sustaining the virus during inter-epidemic periods. Laboratory experiments were conducted to determine whether Aedes aegypti, a principal vector, is capable of vertically transmitting CHIKV or not.

Methodology/Principal Findings

Female Ae. aegypti were orally infected with a novel ECSA genotype of CHIKV in the 2^nd gonotrophic cycle. On day 10 post infection, a non-infectious blood meal was provided to obtain another cycle of eggs. Larvae and adults developed from the eggs obtained following both infectious and non-infectious blood meal were tested for the presence of CHIKV specific RNA through real time RT-PCR. The results revealed that the larvae and adults developed from eggs derived from the infectious blood meal (2^nd gonotrophic cycle) were negative for CHIKV RNA. However, the larvae and adults developed after subsequent non-infectious blood meal (3^rd gonotrophic cycle) were positive with minimum filial infection rates of 28.2 (1∶35.5) and 20.2 (1∶49.5) respectively.

Conclusion/Significance

This study is the first to confirm experimental vertical transmission of emerging novel ECSA genotype of CHIKV in Ae. aegypti from India, indicating the possibilities of occurrence of this phenomenon in nature. This evidence may have important consequence for survival of CHIKV during adverse climatic conditions and inter-epidemic periods.

Although vertical transmission of arboviruses has been recognized for nearly a century, rates of transmission in laboratory experiments are low and their significance in terms of survival of virus during periods of low transmission appears debatable. Recently, major urban outbreaks of chikungunya have been recorded in many parts of Asia, Africa, and Europe. The occurrence of random sporadic cases of the disease in years following a major outbreak prompted us to investigate whether these might be attributable to survival of the virus by vertical transmission. Our experiments were designed to test two hypotheses: (1) The development of an egg-batch derived from an infectious blood meal is too rapid for the infection to reach ovaries; (2) The enormous distension of the membrane enveloping ovaries and ovarioles following oviposition, might facilitate virus penetration. We conclude that after the infected blood meal, oogenesis and oviposition were complete before virus had disseminated to infect the ovaries. Because similar experiments with infection in first gonotrophic cycle did not lead to infected progenies, it is presumed that expanded parous ovaries might support efficient infection. Therefore, it may be concluded that vertical transmission is a more common phenomena in mosquitoes during subsequent gonotrophic cycles following arboviral infection.

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.