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Virus Particles To Infect

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Last Updated: 02 July 2021

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General | Latest Info

The amount of SARS - CoV - 2 virus that needs to be present in the body to trigger infection is unclear. Other respiratory viruses could offer insight into this number. For example, SARS, another coronavirus, requires just a few hundred viral particles for infective dose, while the dose for MERS is several thousands of particles. Much of the data collected on transmission of SARS - CoV - 2 has been inconsistent. Patients who are asymptomatic have been found to have viral loads equal to patients who are critically ill. The phenomenon of super - spreaders who can pass viruses to many people could provide a clue, but it is unclear yet whether these cases are due to people's biology or behavior. Factors like nostril shape, presence of nose hair and mucus, and even distribution of cellular receptors in the airway can all influence how much virus needs to be received to cause infection. Dose may also vary depending on whether particles are ingested or inhale. The Centers for Disease Control and Prevention has publicly said that they do not believe ingestion is a major way virus is spreading, but rather via aerosol transmission. Sneezing, coughing, and talking can spread thousands of respiratory droplets carrying viruses into the air. Larger droplets fall quickly due to their weight and will not penetrate surgical masks, but droplets less than 5 microns in diameter, called aerosols, can remain in the air for hours. Proximity to an infected person, air flow, and timing all seem to be critical factors for aerosol transmission. Using spray nozzle design to simulate expulsion of saliva droplets, Dutch researchers found that opening windows or doors introduces enough air flow to expel present aerosols. Data published in the journal Nature from hospitals in Wuhan, China finds more aerosolized particles in unventilated restrooms than in in ventilated patient rooms or even crowded public areas. Researchers note that aerosols, due to their size, would contain lower quantity of viruses than much larger droplets. Experts agree that in addition to avoiding unventilated and crowded indoor areas, most effective way to avoid infection is to wear a mask. Even if a mask does not fully shield from respiratory droplets containing viruses, it can help keep the amount of virus wearer receive below the infective dose.

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* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Other factors to consider

Data about the influence of other microorganisms on virus survival is contradictory. Virus survival may increase or decrease with the number of microbes present on the surface. Bacteria or microscopic fungi are able to attack and inactivate infectious viral particles. Some bacteria can produce low molecular weight substances that apparently inactivate viruses. Others appear to use viral capsid proteins as substrates. By contrast, increasing amount of microbes can protect viruses from desiccation and disinfection. Interactions of pathogenic viruses with bacterial biofilms have been report. As biofilms can form on a wide spectra of surfaces, their influence on virus survival is also discussed in this review. One proposed mechanism of viral loss in the environment is inactivation by direct or indirect action of microorganisms. Environmental isolates of bacteria with antiviral ability have been found on several occasions. These microbes are able to produce metabolites, which adversely affect viral particles, or can use viral capsid as a nutrient source. Inactivation of viruses by bacterial cultures is temperature dependent. The lower temperature of mixed waste, longer virus is able to persist. Moreover, temperature could strongly influence microbial activity, and thus influence viral persistence. Ward investigates the influence of mixed - liquor suspended solids of inactivated sludge on poliovirus 1 survival. The first experiment was conducted in order to determine the effect of MLSS on recovery of poliovirus after different periods of time. The second experiment was designed to find out the role of different MLSS components in virus loss. Results of these studies indicate that MLSS contains components which can inactivate poliovirus 1. These components were pelleted during centrifugation, destroyed by autoclaving, and removed by filtration. Consecutively, residual activity of MLSS supernatant fraction was also studied to confirm absence of antiviral activity in non - living heat - sensitive material in MLSS. Subsequent increasing activity of this supernatant, coupled with previous results, strongly indicate antiviral activity of some microbial species. Deng and Cliver demonstrate antiviral effect of several bacterial cultures from swine manure slurry and mixed septic tank effluent. These cultures were identified as Micrococcus luteus, Staphylococcus epidermidis, Bacillus sp. And Streptococcus sanguis group. The Comparison of poliovirus 1 inactivation in raw mixed waste, autoclave mixed waste, and bacterium - free filtrate of raw mixed waste demonstrates that virus inactivation is relate, at least in part, to microbial activity in similar environmental conditions. Inhibition of poliovirus 1 inactivation by protease inhibitors suggests that antiviral activity of mixed waste was partially due to proteolytic enzymes produced by bacteria in wastes. Bacteria may also produce substances that inactivate viruses by processes other than enzymatic ones,. Eg Pseudomonas aeruginosa can produce substances with molecular weights below 500 Da which appear to inactivate viral particles. Substances with such low molecular weights cannot act enzymatically and they are referred to as virolytic substances. Deng and Cliver study the role of microbial activity of animal wastes in inactivation of HAV. Ten out of 31 bacterial isolates were able to efficiently inactivate HAV.


Conclusions

Viral infections of the respiratory tract are common acute illnesses among humans, and virus transmission, by either direct or indirect routes, occurs in disparate regions around the globe. More detailed understanding of how these viruses transmit can have broad public health implications. Indeed, variety of meteorological factors have at times been associated with rates of virus infection as well as transmission among individuals. As present in this review, precipitation, humidity, temperature, and airflow can be determinants of virus infection and transmission; However, despite robust investigation of the effects of these environmental factors, inconsistencies and uncertainties in data remain. It is possible that meteorological determinants play greater roles in some geographic regions than others, or simply that differences in experimental design affect outcomes and data interpretation. Non - environmental effects, including but not limited to seasonal changes in behavior, family and social structures, and pre - existing immunity, could also play a role in respiratory virus transmissibility and rates of infection. Discrepancies in collected data suggest that more vigilant surveillance over large geographic regions and further control experiments in animal models and perhaps in humans will probably be necessary to determine with increased certainty role that environmental factors play on transmission of viral pathogens.

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Premade Virus Particles

AAV Serotypes Available

SerotypePrimary Target TissuesDescription
AAV-1MuscleBest for cardiac muscle, skeletal muscle, neuronal and glial tissue.
AAV-2Muscle, Liver, RetinaOldest and most commonly-used serotype. Best for neurons, muscle, liver, and brain.
AAV-3MegakaryocytesBest for megakaryocytes, muscle, liver, lung, and retina.
AAV-4RetinaBest for neurons, muscle, brain, and retina.
AAV-5LungBest for lung, neurons, synovial joint, retina, and pancreas.
AAV-6Muscle, LungBest for lung, liver, and heart.
AAV-7Muscle, Retina, NeuronsBest for muscle, neurons, and liver.
AAV-8LiverBest for muscle, brain, liver, and retina.
AAV-9VariousBest for muscle, heart, liver, lung, and brain.
AAV-10Pleura, CNSCloned from Cynomolgus, almost identical with AAVrh10 except for 12 amino acids in VP1. Best for lung, muscle, heart, CNS, and liver.
AAV-DJVariousA mixture of 8 naturally-occurring serotypes. Efficiently transduces a wide variety of cell types in vitro .
AAV-DJ/8VariousA variant of AAV-DJ with a mutation that permits infection of liver as well as other tissues i n vivo.

Lentivirus Vector system and lentivirus production service: lentiviral Vector cloning, lentivirus packaging, purification, premade lentivirus. Hiv - 1 base defective lentivirus has been one of the most widely used gene therapy vectors. It is a powerful tool for introduction of exogenous genes. The most advantageous feature of lentivirus vectors is to mediate efficient transfection and long - term expression of exogenous genes in both dividing and non - dividing cells. The Lentivirus system has been widely used in various cell lines for gene overexpression, RNA interference, microRNA research and in vivo animal experiments. Genemed provides lentiviral Vector construction, lentivirus packaging for RNA interference, miRNA, overexpression constructs and stable transfected cell line construction services. Genemed offers high titer, high purify and ready - to use lentivirus in just two weeks. Please refer to lentivirus packaging options before you order. Our optimized production of lentiviral vectors and strict quality control systems supply customers with high titer of functional recombinant lentiviral vectors. Two methods are employed to determine viral titers: physical titer and functional titer. Physical titer is calculated by the level of protein, such as p24, or Viral nucleic acid. Functional titer, calculation of active virus that can infect cells, is much less than physical titer. The method we adopt is functional titer, which is an accurate solution for testing virus accurate activity and MOI. Physical titer can only reflect the number of virus particles, but not reflect true viral activity, which will cause large errors in subsequent infection experiments.

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Burst Size

The number of virus particles released during lysis of host cells is term burst size. The size of this viral offspring is a critical parameter in regulating population dynamics of both cellular host and viruses themselves. Estimates of burst size are used to relate in situ viral production to lysis rates of host cells and virus - mediate mortality of prokaryotes. Burst size estimates can be obtained by one - step growth curve experiments or, better, by in situ observation of virus particles within intact or thin - sectioned cells. Another approach is to use batch cultures and calculate the burst size necessary to balance viral production with measurements of viral decay, or from observed net production of viruses over incubation period. In many studies, burst size has been reported AS average of inspected cells or AS range of individual observations. A wide range of burst size values can be found in literature, probably also reflecting differences in methodologies apply. Phage and host species AS well AS environmental parameters such AS temperature and trophic state of aquatic system seem to be important. Further, burst size may also be positively correlated to the size of host cells and, moreover, tend to be higher in freshwater than in marine environments. Examples from inland water environments are provided in Table 2.

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Parasitism

Viruses are obligate intracellular parasites having no metabolism on their own. Instead, they employ resources from their hosts. Because of their high adaptability and diversity, viruses are the most abundant biological objects on Earth. Indeed, they can parasitise all cellular types; cases of simultaneous co - infection by different viral species are widespread. This observation indicates a deep evolutionary connection between cells and viruses, possibly dating back to the origin of life itself. Understandably, virus research is mostly focused on disease - causing agents of humans and livestock. However, rise of methods for massively parallel nucleic acid sequencing enables broad - scale studies of viral ecology and diversity in those groups of hosts, which were previously neglect. In particular, this led to significant progress in the study of viruses in protists. One of better study groups in this respect is trypanosomatids, flagellate parasites of vertebrates, including humans and domestic animals, plants and invertebrates. Methods of RNA viruses detection in parasitic protists - Early reports of virus - like particles in various protists were mostly based on transmission electron microscopy, which has part of routine species description procedures since 1950s. Unfortunately, for the most part, microscopic images were inconclusive and insufficient to prove viral infection. Moreover, nucleic acid sequencing methods were not well developed at that time, further complicating description of new viruses from protists. Standards of Virology require enrichment of viral particles by ultracentrifugation with subsequent demonstration of their infectivity in the original host. This technique had limited success with viruses of protists, since it usually causes only latent infections. Not all early descriptions of putative protist - infecting viruses withstood further scrutiny. For example, nuclear filamentous and cytoplasmic polyhedral VLPs from Entamoeba histolytica were extensively studied by TEM throughout the 1970s. However, all attempts to purify VLPs failed and the nature of the supposed viral agent has not been revealed thus far. Another, more fruitful approach of studying viruses in protists is based on observation of double - strand RNA in cellular RNA extracts. This method facilitates discovery of dsRNA viruses, but has also successfully applied to single - strand RNA viruses, which produce small amounts of dsRNA replication intermediates. Originally, it was based on ribonuclease treatment of DNA - free RNA samples at various salt concentrations, as this enzyme has lower affinity toward dsRNA at higher ionic strength of reaction buffer. Other methods of dsRNA isolation include salting - out ssRNA molecules with high concentration of LiCl or digestion with single - strand - specific S1 nuclease. Regardless of the exact method used, viral dsRNA was visualise in agarose gel and used for downstream applications. These methods allowed viral discoveries in Trichomonas, Giardia, and Leishmania spp. Also, virus particles were isolated from these cells using CsCl gradient ultracentrifugation, and association of dsRNA with these particles was confirm. Recently, developed real time quantitative polymerase chain reaction / ultracentrifugation - base protocol for viral purification couples molecular identification with TEM and has potential to greatly facilitate viral detection.

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* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

VII.B Surfactants and Self-Assembly

Self - assembly is a hallmark of biological systems, including assembly of protein subunits into holoenzymes, of proteins and nucleic acids into virus particles, and of tropocollagen into collagen fibers. There has been increasing interest in synthetic self - assembly. In addition to assembly of molecules with complementary hydrogen bonding to form supramolecular clusters, there are many papers on assembly of charge polymers and particles to form multilayers and on assembly of particles or particles and films coated with complementary biological recognition molecules, such as biotin - streptavidin system. Work at Mobil Corporation shows that mesoporous silica could be formed by hydrolysis of tetraethoxysilane entrained in highly concentrated water / silane / surfactant system. In this regime, three - component mixture forms order structures with a range of symmetries. In one hexagonal phase, rods of water are surrounded by surfactant and embed in hydrophobic silane matrix. Hydrolysis of silane under suitable conditions, followed by drying and sintering, results in porous silica with aligned pores of a few nanometers in diameter. The growth of lyotropic liquid crystal precursors is very sensitive to the environment. Ozin and co - workers have shown that complex particle morphologies can result from growth of these mesoporous structures in quiescent solutions as diffusion fields and surface forces interact. Several workers have shown how the direction of rods or plates of silica can be control. Polymers can be introduced to form composite structures that are very reminiscent of some biological composites. This does seem to parallel the proposed importance of liquid crystals in the growth of many biological structures. While one would expect that this approach could extend to many other material combinations, rules are not understood. Efforts to form similar structures other than oxides, such as titania, or various crystalline materials, have been only partly successful. Possibly, any rapid or localized conversion process also disrupt liquid crystalline organization. Stupp and co - workers have produced a range of amphiphiles that assemble into various ribbon and wedge structures, and authors have explored their catalytic activity.


Discussion

Vlps, composed of viral structural proteins without genetic materials, are self - assembled macromolecules. Because of their ability to stimulate strong immune response and plentiful antibody production, they are regarded as candidates for novel vaccines. Vlps provide more safety in use and the possibility of large scale production of vaccines with reproducible high quality results compared with traditional live - attenuate or inactivated virus vaccines. Some VLPs, such as Hepatitis B surface antigen VLPs, human papillomavirus VLPs and Malaria VLP - base vaccines have already been clinically used for prevention of infectious diseases. In recent years, technology of expressing capsid protein of PCV2 and self - assembly into virus - like particles has advance, and can be used in multiple recombinant protein expression systems including baculovirus, yeast and E. Coli. Many commercial vaccines based on VLPs have effectively prevented infection of PCV2. Similar to PCV2, there are two major open reading frames, ORF1 and ORF2, in the PCV3 genome. Orf2 encodes immunogenic Cap which is the sole structural protein of viral coat. Whether the idea of forming recombinant Cap into VLPs is equally applicable to PCV3 is the main purpose of our research. In this study, E. Coli expression system has been used successfully for expression of PCV3 VLPs due to its relative simplicity, low cost, and fast high - density cultivation, which is significant in future diagnosis and vaccine development. However, N - terminal NLS domain of Cap protein is abundant in arginine residues and contains several rare codons for E. Coli that impede foreign gene expression, which is disadvantageous for full - length Cap expression. Using codon optimization can overcome the difficulty of high - level expression of full - length Cap. Removing of NLS has also been used to improve expression efficiency and stability of expressed protein in E. Coli but has failed to self - assemble into VLPs. The diameter of the circovirus is around 17 nm, similar to beak and feather disease virus, bat circovirus and PCV2. Morphological study of PCV3 has not been conduct, whether 10 nm particles is the true size of the virus remains to be determine. Previous studies have shown that expressing full - length PCV3 Cap gene and NLS domains presenting within N - terminal arginine rich motif may cause misfolding of protein and induce formation of circular virus complexes of 10 - 12 nm. Other groups have published that, different sizes of VLPs appear in different expression systems,. A number of factors, including storage conditions as well as process design, also influence characteristics of VLPs. 10 nm particles can be used as preliminary evaluation standard before real virus morphology of PCV3 is discover. Hydrophobic interaction chromatography has also been used as a step in the purification process. But eCap cannot be elute under any conditions even if the least hydrophobic filler was select. Therefore, it is suspected that PCV3 VLPs are highly hydrophobic. This conclusion can also be derived from genetic analysis as the entire Cap gene contains many hydrophobic amino acids.

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Microscopy of Soil Viruses

Sampling was conducted at Hainich Critical Zone Exploratory in Thuringia, Germany, within the framework of DFG fund AquaDiva project. A detailed description of the study site is provided by Kusel et Al. Briefly, Hainich National Park is the largest connected deciduous forest in Germany. Hainich CZE was established at eastern slope of the Hainich range, which has mean inclination of ~2. Underlying geological units building soil bedrocks belong to Middle and Upper Muschelkalk and Lower Keuper. Soil sampling sites were taken from transect oriented in W - E direction and covered land types forest, pasture and cropland. Viruses were extracted from triplicate subsamples of each soil as described by Williamson et Al. Briefly, 5 - G samples of field - moist soil were weighed into 25 - mL Teflon - coat polyethylene centrifuge tubes, and 15 mL of one of the following eluants was add: 1% potassium citrate, 10 mM sodium pyrophosphate, or 250 mM glycine. All tubes were vortexed, sonicated on ice for 3 min, and centrifuge at 10 000 G to sediment soil particles. Supernatants passed through 0. 20 - M syringe filters to remove bacteria and small soil particles. To assess potential differences in extractability of viruses across soils, sequential extractions were performed on triplicate subsamples of each soil, using 1% potassium citrate. After removing supernatant from initial extraction, soil pellets were resuspend in fresh eluant and the extraction procedure was repeated two more times. Bacteria were extracted from triplicate subsamples of each soil by using methods adapted from those of van Elsas and Smalla. Ten grams of moist soil was transferred to a glass bottle containing 95 mL of 1% potassium citrate, representing 10 1 dilution. Serial 10 - fold dilutions were prepared in glass bottles containing sterile 1% potassium citrate. Bottles were manually shaken for 3 min and allowed to settle for 15 seconds prior to each transfer. Vlps were enumerated as described by Williamson et Al. Aliquots of 0. 2 - mfiltered soil extracts were suspended in 900 L of sterile deionized water and vacuum filtered through a stack of 25 - mM filters consisting of 0. 02 - M Anodisc, which was supported by 0. 22 - M Supor, and glass fiber filter. Anodisc filters containing capture Virus particles were stained by adding 400 L of 1 SYBR Gold directly to filter on vacuum manifold. Filters were incubated for 15 min in the dark and analyzed by EFM using Zeiss Axioskop 2 microscope with fluorescein isothiocyanate excitation filter. Ten fields per sample were digitally photographed at magnification of 1 000 using the Hamamatsu ORCA - ER camera. Virus - Like Particles were counted using Fovea Pro plug - in for Adobe Photoshop. Vlps were discriminated from bacteria or detritus based on pixel dimensions: pixel area of the smallest known bacterium was established as the maximum cutoff; all objects smaller than this were counted as VLPs.


INTRODUCTION

Virus particles are abundant in the environment and exceed the number of cellular organisms in marine and soil habitats by at least order of magnitude. Global population size is estimated to be > 10 30 virus particles, and the advent of deep sequencing of environmental samples has shown that virus genome sequences in sequence databases are bias representation of virus diversity in the environment, as novel virus lineages are increasingly being discover. Many studies of virus populations in the environment have been performed in marine or aquatic habitats, which are amenable to concentration and purification of relatively large virus biomass. Surveying viruses in soils has started recently, despite the recalcitrant character of many soil samples, and initial estimates of concentrations of viruses in soils are on the order of 1. 5 10 8 g 1 to 10 9 virus particles g 1. Data on changes to soil virus abundance and diversity caused by environmental factors has recently been report; for example, it was shown that virus abundance and diversity are greater in wetland forest soil than in drier agricultural soils. Most of soil virus particles identified by electron microscopy were tail phage types resembling Caudovirales, which account for 95% of all known bacteriophages. However, complex morphology of soil debris makes it difficult to distinguish virus particles other than tailed phage, and improved virus purification techniques show that while numbers of tailed bacteriophage were similar to previous reports, they comprise only 4% of total virus particles present, and the remaining, overwhelming majority of particles consist of spherical particles of various sizes, along with bacilliform, rod - shape, and filamentous virus - like entities. Recent studies have also shown that 51 to 92% of virus particles in ocean samples are nontailed. One type of spherical virus that has been the subject of a number of recent studies is viruses containing circular Rep - encoding single - strand DNA genomes, which have been found to be more prevalent in a number of environments than previously think. In this work, we examine viruses in several contrasting soil types, including agricultural and alpine soils and rare coastal Machair soil, which is found only on the west coast of Scotland and in Ireland. Our analysis gives an initial outline of virus loads in soils and reveals contrasts between viruses in different soils, which may be related to soil pH and / or water content. Taking into account the abundance and potential importance of ssDNA viruses, we have performed metagenomic analysis of virus populations from Machair and brown Earth soils using multiple - displacement amplification to preferentially amplify DNA from genomes of viruses containing circular ssDNA genomes. This analysis again reveals potentially important differences in populations of ssDNA viruses in two soils that may be related to soil physicochemical characteristics and host populations.

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What is an infectious dose?

Influenza Virus infection is a highly contagious respiratory disease that can spread easily and is responsible for considerable morbidity and mortality each year. Influenza is caused by the RNA Virus of the family Orthomyxoviridae and is classified into three types, influenza, B, and C. Influenza is essentially avian viruses that periodically transmit to other species, including mammals. However, they are the most virulent human pathogens among the three influenza types and cause the most severe disease. Furthermore, influenza viruses comprise a large variety of antigenically distinct subtypes that replicate asymptomatically in the intestine of birds and constitute a large reservoir of potentially pandemic viruses. Influenza C infects humans and some other animals such as pigs, while influenza B almost exclusively infects humans. Three different modes of influenza transmission have been identify: droplet, airborne, and contact transmission. Which of three modes is responsible for most influenza infections remains highly controversial. Numerous studies report infectious doses of influenza Virus in human volunteers using various strains of influenza or B Virus administered either by nasal drops or aerosols. Results of these studies suggest that nasal infectious dose of influenza Virus is several orders of magnitude higher than that of airborne infection. Many of published infectious doses of influenza Virus come from studies into the prophylactic or therapeutic effect of various compounds and investigations into their role in preventing or treating experimentally induced influenza infection in human volunteers. These studies have often used high doses of virus inoculated intranasally to produce disease in as many subjects as possible. For example, approximately 10 7 TCID 50 of influenza B strain B / Yamagata / 16 / 88 infect over 80% of inoculated subjects but produce illness in only a few. A similar dose of influenza B / Panama / 45 / 90 infected 55% of 11 inoculated subjects, four of whom developed illness. Doses between 10 5 and 10 7 TCID 50 of H 1 N 1 influenza, infect most intranasally inoculated volunteers and cause illness in the majority of subjects in some but not all studies. Another H 1 N 1 influenza strain, / Kawasaki / 986, infects most subjects and causes disease in about half of them when administered intranasally at dose of 10 7 TCID 50. H 3 N 2 influenza strain / England / 42 / 72 infected and caused disease in just over half of the inoculated population when 3. 5 10 3 TCID 50 or 1 000 times higher doses were used. Infection rate with 1. 2 10 4 TCID 50 of / England / 40 / 83 strain was reported to be over 90% and this dose caused illness in 40% of subjects. Two H 3 N 2 influenza strains, / University of Maryland / 170 and / University of Maryland / 274, cause illness in the majority of volunteers inoculated with about 10 4 TCID 50. 6. 4 10 4 TCID 50 of 2 / Rockville / 165 Virus delivered to nasopharynx infected most inoculated subjects with approximately half of them developing influenza symptoms.


Respiratory Viruses

In 1956, novel virus was recovered from a chimpanzee with respiratory symptoms and designated chimpanzee coryza agent. In the ensuing decade, virus was renamed respiratory syncytial virus to reflect giant syncytia which forms in tissue cultures, and epidemiological studies clearly establish RSV as one of most important causes of severe respiratory tract infection in infants and young children as well as elderly persons and adults with underlying cardiopulmonary diseases. Human RSV is an enveloped RNA virus and is a member of the genus Pneumovirus, classified within the family Paramyxoviridae. The virus is highly contagious and is believed to spread primarily by large droplets and fomites and can survive on non - porous surfaces, skin, and gloves for many hours. Hence, close person - to - person contact or contact with contaminated environmental surfaces and autoinoculation are required for transmission. Rsv is shed in high titers from infants hospitalized for lower respiratory tract disease for up to 21 days and with a mean maximal nasal wash titer of 2. 2 10 4 TCID 50 / ml. In adult challenge studies, volunteers excrete virus for up to 8 days with peak virus titer of up to 10 5 TCID 50 / ml of nasal wash. Isolate of RSV passaged twice in rhesus monkey kidney cells was administered by intraoral and intranasal spray to adult volunteers with serum antibody titers of 1: 16 or higher. Dose ranging between 160 and 640 TCID 50 caused illness in 20 of 41 volunteers inoculated with an additional 14 subjects shedding virus or developing serological evidence of infection. This study suggests that the HID 50 of the virus is less than 640 TCID 50. When 32 healthy, susceptible adult volunteers were inoculated intranasally with a dose of approximately 10 6 pfu of safety - tested clinical isolate of RSV type B, 18 subjects became infected as determined by either viral shedding or nasal antigen detection or 4 - fold rise in virus - specific antibody titer. Higgins et al. Report that intranasal inoculation of 10 healthy adult volunteers with 6. 3 10 4 TCID 50 of bacteriologically sterile MRC 5 tissue culture fluid of RSS - 2 strain of RSV of 11 passage containing 3. 1 10 5 TCID 50 / ml failed to produce symptoms in any of the volunteers. Out of 19 volunteers challenge with 0. 5 ml of above fluid to each nostril, 14 show laboratory evidence of infection as shown by viral isolation and / or antibody raise, and seven developed colds. A number of studies report infectious doses of RSV A2. A safety - tested pool of virus used for inoculation had undergone six passages in human embryonic kidney cells, ten passages in calf kidney cells, and several additional passages in bovine embryonic kidney cells. In one study, 5. 0 10 2 pfu of RSV A2 administered as intranasal drop to male volunteers with varying levels of serum and nasal antibodies, infected 100% of challenged subjects but produced no illness.

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What is the viral load?

We include in this quantitative virologic study 154 patients WHO fulfil modified World Health Organization definition of SARS and whose treatment was managed in United Christian Hospital and Caritas Medical Centre of Hong Kong Special Administration Region of China. All patients infections were either serologically confirmed or RT - PCR was positive for SARS - CoV RNA. Case definitions include temperature of > 38C, cough or shortness of breath, and new pulmonary infiltrates shown on chest x - ray or high - resolution compute tomographic scan in absence of alternative diagnosis to explain clinical signs and symptoms. Treatment protocol, Clinical manifestations, and progression of disease in part of this cohort have been previously report. In brief, patients were prospectively monitored for diarrhea, oxygen desaturation, mechanical ventilation; laboratory evidence of lymphopenia, renal impairment, liver dysfunction, or abnormal urinalysis during the first 15 days; and death. Diarrhea was defined as bowel movements > 3 times per day for 2 consecutive days. Oxygen desaturation was defined as < 90% oxygen saturation measured by pulse oximetry while breathing room air. Some of these patients later required mechanical ventilation. Hepatic dysfunction was defined as mean level of alanine aminotransferase, alkaline phosphatase, or both, greater than the upper limit of normal from day 10 to day 15 after onset of symptoms. Impaired renal function was defined as serum creatinine level higher than the reference range on 2 consecutive days. Lymphopenia was defined as absolute lymphocyte count < 1 000 / L on 2 consecutive days. Abnormal urinalysis results were defined as proteinuria, microscopic hematuria, pyuria on dipstick test, or casts in urine examined with an inverted microscope by experienced technician. To diagnose SARS - CoV infection, NPA and serum samples were taken on admission. Convalescent - phase serum samples were taken between days 7 and 28 after symptom onset. In all patients, RT - PCR for SARS - CoV RNA was performed on NPA collect on admission. Rt - qPCR was performed for patients WHO had NPA, serum, stool, and urine specimens collected on days 10 to 15 after onset of symptoms. All virologic diagnostic laboratory tests, including Viral culture, RT - PCR, RT - qPCR, and immunofluorescent antibody Detection for immunoglobulin g, were performed according to our previously published protocols. Npa was obtained by suction through both nostrils with a Pennine 6 mucus extractor and mucus specimen trap. A catheter was connected midway between the tip of nose and the auditory meatus; it was rotated continuously and slowly retrieved with intermittent suction at negative pressure of 100 mm Hg for 15 s. Procedure was repeated in other nostril. Secretions stuck to the lumen of the catheter were transferred to the mucus trap by flushing with 1 mL of Viral transport medium, which consists of Earle's balance Salt Solution, 4. 4% bicarbonate, 5% bovine serum albumin, vancomycin, amikacin, and nystatin. The 10% stool suspension was made by swirling approximately 1 g of stool in 10 mL of Viral transport medium. Midstream urine was collected in a sterile container.

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Overview

A virion is an entire virus particle consisting of an outer protein shell called capsid and an inner core of nucleic acid. Core confers infectivity, and capsid provides specificity to virus. In some virions capsid is further enveloped by fatty membrane, in which case virion can be inactivated by exposure to fat solvents such as ether and chloroform. Many virions are spheroidalactually icosahedral with regularly arranged units called capsomeres, two to five or more along each side. Nucleic acid is densely coiled within. Other virions have capsids consisting of an irregular number of surface spikes, with nucleic acid loosely coiling within. Virions of most plant viruses are rod - shape; capsid is a naked cylinder within which lies a straight or helical rod of nucleic acid. Virion capsids are formed from identical protein subunits called capsomeres. Viruses can have lipid envelope derived from the host cell membrane. Capsid is made from proteins encoded by the viral genome and its shape serves as the basis for morphological distinction. Virally cod protein subunits will self - assemble to form capsid,s in general requiring presence of virus genome. Complex viruses code for proteins that assist in construction of their capsid. Proteins associated with nucleic acid are know as nucleoproteins, and the association of viral capsid proteins with viral nucleic acid is called nucleocapsid. Capsid and entire virus structure can be mechanically probed through atomic force microscopy. Virus has either DNA or RNA genes and is called DNA virus or RNA virus, respectively. The vast majority of viruses have RNA genomes. Plant viruses tend to have single - strand RNA genomes and bacteriophages tend to have double - strand DNA genomes. Viral genomes are circular, as in polyomaviruses, or linear, as in adenoviruses. The type of nucleic acid is irrelevant to the shape of the genome. Among RNA viruses and certain DNA viruses, genome is often divided up into separate parts, in which case it is called segmented. For RNA viruses, each segment often cod for only one protein, and they are usually found together in one capsid. However, all segments are not required to be in the same virion for a virus to be infectious, as demonstrated by brome mosaic virus and several other plant viruses. The viral genome, irrespective of nucleic acid type, is almost always either single - strand or double - strand. Single - strand genomes consist of unpaired nucleic acid, analogous to one - half of ladder split down middle. Double - strand genomes consist of two complementary pair nucleic acids, analogous to ladder. Virus particles of some virus families, such as those belonging to Hepadnaviridae, contain a genome that is partially double - strand and partially single - strand.


Discovery and Detection of Viruses

Viruses were first discovered after development of porcelain filter, called Chamberland - Pasteur filter, which could remove all bacteria visible in microscope from any liquid sample. In 1886, Adolph Meyer demonstrated that disease of tobacco plants, tobacco mosaic disease, could be transferred from diseased plant to healthy one via liquid plant extracts. In 1892, Dmitri Ivanowski showed that this disease could be transmitted in this way even after the Chamberland - Pasteur filter had removed all viable bacteria from extract. Still, it was many years before it was proven that these filterable infectious agents were not simply very small bacteria, but were new type of tiny, disease - causing particle. Virions, single virus particles, are very small, about 20 - 250 nanometers in diameter. These individual virus particles are infectious form of virus outside the host cell. Unlike bacteria, we cannot see viruses with a light microscope, with the exception of some large virions of the poxvirus family. It was not until the development of the electron microscope in late 1930s that scientists got their first good view of the structure of tobacco mosaic virus and other viruses. The surface structure of virions can be observed by both scanning and transmission electron microscopy, whereas internal structures of viruses can only be observed in images from transmission electron microscope. Use of these technologies has enabled the discovery of many viruses of all types of living organisms. They were initially grouped by shared morphology. Later, groups of viruses were classified by type of nucleic acid they contain, DNA or RNA, and whether their nucleic acid was single - or double - strand. More recently, molecular analysis of viral replicative cycles has further refined their classification.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Sources

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

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