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Tuesday, February 2, 2010 @ 4:58 PM
Entry01: Introduction to Virology The study of viruses is known as Virology. Virus is a tiny pathogen that replicates itself in the cells of other living organism. Without a host cell, viruses cannot carry out their life-sustaining functions or reproduce. They are unable to undergo protein synthesis because they lack ribosomes and would have to facilitate the ribosomes of their host cells to translate viral messenger RNA into viral proteins. Viruses cannot generate or store their energy in the form of Adenosine Triphosphate(ATP), but derive their energy ad other metabolic functions from the host cell. In addition, they parasitize the host cell for basic building materials, such as amino acids, nucleotides and lipids. Viruses contains nucleic acid that is either Deoxyribonucleic Acid(DNA) or Ribonucleic Acid(RNA) and a protein coat that encases the nucleic acid. All viruses have a protein coat that protects the genes and some consist of an additional envelope of fat or protein molecules. In its infective form outside the cell, a virus particle is known as a "virion". Each of these virions consists of at least one unique protein synthesized by specific genes in its nucleic acid. Viruses are generally classified by the organisms that they infect. They are then further classified into: 1. The type and size of their nucleic acid. 2. The size and shape of the capsid. 3. If the nucleocapsid is enclosed by a lipid envelope.  http://biologyjunction.com/
Labels: #entry Monday, February 1, 2010 @ 5:37 PM
Entry02: Classification of Viruses Classifications of viruses involves placing viruses into taxonomic system: Kingdom, Phylum, Class, Order, Family, Genus and Species. Viruses are classified according to morphology, chemical composition and mode of replication. Today, there are more than 30 000 virus isolates known and are grouped in more thwn 3 600 species, in 164 genera and 71 families. Viral morphology aids in grouping viruses into families. A viral family might only consists of viruses that only replicate in vertebrates, invertebrates, plants, or bacteria. Certain families contain viruses that can replicate in more than one of these hosts. International Committe of Taxanomy of Viruses(ICTV) Classification The International Committe of Taxonomy of Viruses(ICTV) began devising and implementing rules for the naming and classification of viruses in the early 1990s which is an effort that continues to the present day. The ICTV Classification system:1. Order -virales 2. Family -viridae 3. Subfamily -virinae 4. Genus -virus 5. Species Currently, the 6 orders that have been established by ICTV are: Caudovirales, Herpesvirales, Mononegavirales, Nidovirales, Picornavirales, and Tymovirales. So far, 6 orders, 87 families, 19 subfamilies, 348 genera, and 2,288 species of virus have been defined. There are several rules that have been set to classification and nomenculture. General Rules: 1. Classification and nomenclature of viruses and sub-viral agents shall be international and applied universally. 2. The universal virus classification system shall employ the hierarchical levels of Order, Family, Subfamily, Genus, and Species . 3. The ICTV is not responsible for classification and nomenclature of taxa below the rank of species. The classification and naming of serotypes, genotypes, strains, variants and isolates of virus species is the responsibility of acknowledged international specialist groups. 4. Artificially created viruses and laboratory hybrid viruses will not be given taxonomic consideration. Their classification will be the responsibility of acknowledged international specialist groups. 5. Taxa will be established only when representative members are sufficiently well characterized and described in the published literature so as to allow them to be identified unambiguously and the taxon to be distinguished from other similar taxa. 6. When it is uncertain how to classify a species into a genus but its classification in a family is clear, it will be classified as an unassigned species of that family. 7. Names will only be accepted if they are linked to taxa at the hierarchical levels described in Rule 2 and which have been approved by the ICTV. Rules Pertaining to Naming Taxa: 8. Names proposed for taxa are "valid names" if they conform to the Rules set out in the Code and they pertain to established taxa. Valid names are "accepted names" if they are recorded as approved international names in the 6th ICTV Report or become "accepted names" by an ICTV vote of approval for a taxonomic proposal. 9. Existing names of taxa and viruses shall be retained whenever feasible. 10. The rule of priority in naming taxa and viruses shall not be observed. 11. No person's name shall be used when devising names for new taxa. 12. Names for taxa shall be easy to use and easy to remember. Euphonious names are preferred. 13. Subscripts, superscripts, hyphens, oblique bars and Greek letters may not be used in devising new names. 14. New names shall not duplicate approved names. New names shall be chosen such that they are not closely similar to names that are in use currently or have been in use in the recent past. 15. Sigla may be accepted as names of taxa, provided that they are meaningful to virologists in the field, normally as represented by Study Groups. 16. In the event of more than one candidate name being proposed, the relevant Subcommittee will make a recommendation to the Executive Committee of the ICTV, which will then decide among the candidates. 17. If no suitable name is proposed for a taxon, the taxon may be approved and the name will be left undecided until the adoption of an acceptable international name when one is proposed to and accepted by ICTV. 18. Names shall be selected such that they, or parts of them, do not convey a meaning for the taxon which would either (1) seem to exclude viruses which lack the character described by the name but which are members of the taxon being named, or (2) seem to exclude viruses which are as yet undescribed but which might belong to the taxon being named, or (3) appear to include within the taxon viruses which are members of different taxa. 19. New names shall be chosen with due regard to national and/or local sensitivities. When names are universally used by virologists in published work, these or derivatives shall be the preferred basis for creating names, irrespective of national origin. 20. Proposals for new names, name changes, establishment of taxa and taxonomic placement of taxa shall be submitted to the Executtive Committee of the ICTV in the form of taxonomic proposals. All relevant ICTV subcommittees and study groups will be consulted prior to a decision being taken. Rules Pertaining to Species: 21. A species is defined as a polythetic class of viruses or sub-viral agents that constitutes a replicating lineage and occupies a particular ecological niche. 22. When an ICTV Subcommittee is uncertain about the taxonomic status of a new species or about the assignment of the new species to an established genus, the new species will be listed as a tentative species in the appropriate genus or family. Names of tentative species, as of taxa generally (Rule 14), shall not duplicate approved names and shall be chosen such that they are not closely similar to names that are in use currently, names that have been in use in the recent past, or names of definitive species. 23. A species name shall consist of as few words as practicable but shall not consist only of a host name and a formal ending such as "virus". 24. A species name, usually together with a strain designation, must provide an appropriately unambiguous identification without mention of the genus or family to which it belongs. 25. Numbers, letters, or combinations thereof may be used as species epithets where such numbers and letters are already widely used. However, newly designated serial numbers, letters or combinations thereof are not acceptable alone as species epithets. If a number or letter series is in existence it may be continued. Rules Pertaining to Genera: 26. A genus is a group of species sharing certain common characters. 27. A name for a genus containing virus species shall be a single word ending in "...Virus"; a name for a genus containing viroid species shall be a single word ending in "...Viroid". 28. Approval of a new genus must be accompanied by the approval of a type species. Rules Pertaining to Subfamilies: 29. A subfamily is a group of genera sharing certain common characters. The taxon shall be used only when it is needed to solve a complex hierarchical problem. 30. A name for a subfamily containing virus genera shall be a single word ending in "...Virinae." Rules Pertaining to Families: 31. A family is a group of genera (whether or not these are organized into subfamilies) sharing certain common characters. 32. A name for a family containing virus genera shall be a single word ending in "...Viridae"; a name for a family containing viriod genera shall be a single word ending in "...Viroidae." Rules Pertaining to Orders: 33. An order is a group of families sharing certain common characters. 34. A name for an order containing virus families shall be a single word ending in "...Virales" Baltimore Classification The Balitmore Classification is based on the genetic contents and the replicaion strategies of the virus. The genetic material that is consistant in all cells is the double-stranded Deoxyribonucleic Acid(DNA), but some viruses uses Ribonucleic Acid(RNA) or single-stranded DNA to containt the gentetic information. According to Baltimore Classification, viruses are classified into 7 classes: 1. Double-stranded DNA viruses 2. Single-stranded DNA viruses 3. Double-stranded RNA viruses 4. (+)-sense Single-stranded RNA viruses 5. (-)-sense Single-stranded RNA viruses 6. RNA reverse transcribing viruses 7. DNA reverse transcribing viruses Labels: #entry Sunday, January 31, 2010 @ 5:43 PM
Entry03: Methods of Studying Viruses The indirect methods fall into 3 categories: 1. Multiplication in a suitable culture system of the virus by the effects that it causes. 2. Serology which makes use of the interaction between a virus and antibody directed specifically against it. 3. Detection of viral nucleic acid. Different techniques used to study viruses: * Agarose gel electrophrosis * Polyacrylamide gel electrophrosis (PAGE) - Formamide or urea added to denature nucleic acic - Sodium dodecyl sulfate added to denature proteins (SDS- PAGE) * ELISA * Western Blot * Northern Blot * Southern Blot * Column Chromatography - Molecular Sieve - Ion- Exchange - Affinity * Centrifugation * Ultracentrifugation - Density Gradient Based (Buoyant Density) - Rate Zonal (Isokenetic) Northern Blot 1. RNA is separated by gel electrophoresis, usually an agarose gel. Because there are so many different RNA molecules on the gel, it usually appears as a smear. 2. The RNA is transferred to a sheet of special blotting paper called nitrocellulose. The RNA molecules retain the same pattern of separation they had on the gel. 3. The blot is incubated with a probe which is single-stranded DNA. This probe will form base pairs with its complementary RNA sequence and bind to form a double-stranded RNA-DNA molecule. The probe cannot be seen but it is either radioactive or has an enzyme bound to it. 4. The location of the probe is revealed by incubating it with a colourless substrate that the attached enzyme converts to a coloured product that can be seen or gives off light which will expose X-ray film. If the probe was labelled with radioactivity, it can expose X-ray film directly. Southern Blot 1. DNA (genomic or other source) is digested with a restriction enzyme and separated by gel electrophoresis, usually an agarose gel. The DNA is denatured into single strands by incubation with NaOH. 2. The DNA is transferred to a membrane which is a sheet of special blotting paper. The DNA fragments retain the same pattern of separation they had on the gel. 3. The blot is incubated with many copies of a probe which is single-stranded DNA. This probe will form base pairs with its complementary DNA sequence and bind to form a double-stranded DNA molecule. The probe cannot be seen but it is either radioactive or has an enzyme bound to it. 4. The location of the probe is revealed by incubating it with a colourless substrate that the attached enzyme converts to a coloured product that can be seen or gives off light which will expose X-ray film. If the probe was labelled with radioactivity, it can expose X-ray film directly. Western Blot 1. Denatured or native proteins, by length of the polypeptide or by 3-D structure of the protein, are separated by the means of gel electrophoresis. 2. After the proteins are transferred to a nitrocellulose membrane, the proteins are then detected using antibodies. 3. Each protein is attached to an antibody, and an antibody is used to detect antigen. A sensitive indicator is used to label an antibody, and there will be a colour reaction with streptavidin.  http://google.com ELISA The antigen is detected by antibody and an indicator, such as horse radish peroxidise, is used to label the antibody. A colour reaction is shown. In this method, one molecule must be binded to a solid surface.  http://google.com Agarose Gel Electrophoresis of DNA Agarose gels, the most commonly-used means of isolating and purifying fragments of DNA, which is a prerequisite for building any type of recombinant DNA molecule. Equipments: •An electrophoresis chamber and power supply •Gel casting trays, The open ends of the trays are closed with tape while the gel is being cast, then removed prior to electrophoresis. •Sample combs, around which molten agarose is poured to form sample wells in the gel. •Electrophoresis buffer, usually Tris-acetate-EDTA (TAE) or Tris-borate-EDTA (TBE). •Loading buffer, which contains something dense (e.g. glycerol) to allow the sample to "fall" into the sample wells, and one or two tracking dyes, which migrate in the gel and allow visual monitoring or how far the electrophoresis has proceeded. •Ethidium bromide, a fluorescent dye used for staining nucleic acids. Transilluminator (an ultraviolet lightbox), which is used to visualize ethidium bromide-stained DNA in gels. NOTE: always wear protective eyewear when observing DNA on a transilluminator to prevent damage to the eyes from UV light. Agarose Concentration: By using gels with different concentrations of agarose, one can resolve different sizes of DNA fragments. Higher concentrations of agarose facilite separation of small DNAs, while low agarose concentrations allow resolution of larger DNAs. Electrophoresis Buffer: Several different buffers have been recommended for electrophoresis of DNA. The most commonly used for duplex DNA are TAE (Tris-acetate-EDTA) and TBE (Tris-borate-EDTA). DNA fragments will migrate at somewhat different rates in these two buffers due to differences in ionic strength. Buffers not only establish a pH, but provide ions to support conductivity. If you mistakenly use water instead of buffer, there will be essentially no migration of DNA in the gel! Conversely, if you use concentrated buffer (e.g. a 10X stock solution), enough heat may be generated in the gel to melt it. SDS-Polyacrylamide Gel Electrophoresis (PAGE) In their native form, proteins fold into a variety of shapes, some compact, some elongated. The rate of migration of native proteins through a sieving medium is therefore more a reflection of their relative compactness, and less an accurate measure of molecular weight. Denaturing the proteins nullifies structural effects on mobility, allowing separation on a true charge/mass ratio basis. It also separates subunits in multimeric proteins, allowing analysis of large, complex aggregates. The most commonly used denaturant is sodium dodecyl sulfate (SDS). SDS is an amphipathic surfactant. It denatures proteins by binding to the protein chain with its hydrocarbon ‘tail’, exposing normally buried regions and ‘coating’ the protein chain with surfactant molecules. The polar ‘head’ group of SDS adds an additional benefit to the use of this denaturant. Proteins solubilized in SDS bind the detergent uniformly along their length to a level of 1.4 g SDS/g protein. This creates a charge/mass ratio which is consistent between proteins. For this reason, separation on a polyacrylamide gel in the presence of SDS occurs by mass alone SDS is the most commonly used detergent in protein electrophoresis. Treatment with SDS creates a uniform charge to mass ratio between different proteins. PAGE + Urea or Formamide Acid urea PAGE allows the electrophoretic separation of different forms of a tRNA, discriminated by changes in bulk, charge, and/or conformation that are brought about by aminoacylation, formylation, or modification of a tRNA. Preparation of acid urea polyacrylamide gel - Gel dimension: • 0.4 mm × 20 cm × 45 cm - Gel composition: • 6.5% polyacrylamide (19:1 acrylamide/bisacrylamide) • 0.1 M sodium acetate pH 5.0 • 8 M urea • Dissolve the above ingredients under stirring (without heating the solution); adjust • Volume to 50 ml and degas for 5−10 min • Add TEMED (0.15% v/v) and ammonium persulfate (0.7% w/v) • Cast gel and allow to polymerize for approximately 2 hours - Acid urea sample buffer: • 0.1 M sodium acetate pH 5.0 • 8 M urea • 0.05% bromophenol blue • 0.05% xylene cyanol FF Gel electrophoresis •It is recommended that a short pre-electrophoresis (~30 minutes) be performed prior to loading the samples and that the sample wells be cleaned carefully. The electrophoresis buffer is 0.1 M sodium acetate pH 5.0. •Typically, 0.01−0.5 OD of tRNA (<>SDS-PAGE Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) is a method to resolve proteins in a mixture based on their molecular size. Negatively charged sodium dodecyl sulfate (SDS) in the sample buffer binds to heat denaturated proteins. The proteins migrate toward the positive pole in an electrical gradient, impeded by the polymerized and cross-linked polyacrylamide. (To convert all proteins to the same shape - we use SDS)  Labels: #entry Saturday, January 30, 2010 @ 8:01 PM
Entry04: Virus-Host Interaction Animal Viruses 1. Attachment Attachment is the binding of attachment sites on the viral surface with receptor sites on the host cell cytoplasmic membrane. For a virus to infect a host cell, that cell must have receptors for the virus on its surface and also be capable of supporting viral replication. These host cell receptors are normal surface molecules involved in routine cellular function, but since a portion of a molecule on the viral surface resembles the chemical shape of the body's molecule that would normally bind to the receptor, the virus is able to attach to the host cell's surface. 2. Penetration • Enveloped viruses Enveloped viruses enter the host cell in one of two ways: • In some cases, the viral envelope may fuse with the host cell cytoplasmic membrane and the nucleocapsid is released into the cytoplasm • Usually they enter by endocytosis, whereby the host cell cytoplasmic membrane invaginates and pinches off, placing the virus in an endocytic vesicle • Naked viruses Naked viruses enter the cell in one of two ways: • In some cases, interaction between the viral capsid and the host cell cytoplasmic membrane causes a rearrangement of capsid proteins allowing the viral nucleic acid to pass through the membrane into the cytoplasm • Most naked viruses enter by receptor-mediated endocytosis whereby the host cell cytoplasmic membrane invaginates and pinches off, placing the virus in an endocytic vesicle 3. Uncoating Before viruses can replicate within the infected host cell, the viral genome needs to released from the remainder of the virus. This process is sometimes referred to as uncoating. In the case of most viruses with an RNA genome, the viral RNA genome is released from the capsid and enters the cytoplasm of the host cell 4. Replication and expression The viral genome directs the host cell's metabolic machinery (ribosomes, tRNA, nutrients, energy, enzymes, etc.) to synthesize viral enzymes and viral parts. The viral genome has to both replicate itself and become transcribed into viral mRNA molecules. The viral mRNA can then be translated by the host cell's ribosomes into viral structural components and enzymes need for replication and assembly of the virus. 5. Maturation During maturation, the capsid is assembled around the viral genome • Maturation of an enveloped virus • Maturation of a naked virus 6. Release a. Naked viruses Naked viruses are predominantly released by host cell lysis. While some viruses are cytolytic and lyse the host cell more or less directly, in many cases it is the body's immune defenses that lyse the infected cell. b. Enveloped viruses With enveloped viruses, the host cell may or may not be lysed. The viruses obtain their envelopes from host cell membranes by budding. As mentioned above, prior to budding, viral proteins and glycoproteins are incorporated into the host cell's membranes. During budding the host cell membrane with incorporated viral proteins and glycoproteins evaginates and pinches off to form the viral envelope. Budding occurs either at the outer cytoplasmic membrane, the nuclear membrane, or at the membranes of the Golgi apparatus Two types of Replication Cycle Lytic Cycle One of the two cycles of viral reproduction (the other being the lysogenic cycle), which is usually considered as the main method of viralo reproduction because it ends in the lysis of the infected cell releasing the progeny viruses that will in turn spread and infect other cells. Lysogenic Cycle One of the ways of virus reproduction. ( other one:lyticcycle )Bacteriophage's nucleic acid fuses together with hosts, nucleic acid, so that genetic information of the virus is transmitted through daughter cells. Animation Link Viral replication cycle in which the virus's nucleic acid is integrated into the host cells chromosome; a provirus is formed and replicated each time the host cell reproduces; the host cell is not killed until the lytic cycle is activated. VIRUS GROWTH PHASES: 1. ECLIPSE PHASE - Phase during which the virion has entered the cell and before progeny virus are made. NO INFECTIOUS VIRUS is present during this phase. - Period in which virus gains control of host synthetic machinery and produce components required to assemble into virus. - Defined as the period between addition of virus and the appearance of assembled virus progeny inside the cell. 2. LATENT PHASE - Period following the eclipse phase from the time of disappearance of the infecting virus to the appearance of infectious virus in the surroundings. - Viruses are internal and must be released to be assayed because animal viruses may not have a classic burst of viruses but rather release virus slowly over a long period of time. Thus, it is possible to find large internal pools of virus - Virus yield is determined on the number of virus released per cell. Viral Infections: It should be noted that even when we consider viral diseases that replication and death of cells occurs cell by cell. Virus-host interaction: Virus can enter into our body via: - Skin - Mucous membrane - Placenta - Parenteral route Skin: formidable barrier to most viruses and only after this barrier is breached will viruses be able to infect the host. Some pathogens can enter via hair follicles, sweat glands, cuts and bruises. Mucous membrane: a thin, moist warm and cells within the mucous membrane are living. Examples of mucous membrane includes: respiratory, gastrointestinal, urinary, reproductive and conjunctiva (eyes) Placenta: Pathogens can cross placenta and infect the foetus. Thus, the foetus may have birth defections, the baby is prematurely born or the mother had gone through spontaneous abortion. Parenteral route: Pathogens also may deposit via punctures (nail, thorn), bites, cuts, wounds or through surgery. When viruses enter the body, it must leave the body too. Most of the portals of entries are the same as exits. The viruses leave the infected body so as to infect other healthy bodies. Some example of portals of exit includes: secretion (tears, saliva, vaginal, semen) and excretion (urine, faeces). Virus human relationship: When one of the organism benefit and the other is unaffected, then it’s commensalism. When one of the organism benefit and the other is harmed, then it’s parasitism. When both the organisms are benefitted, then it’s mutualism. Microflora is also known as microbiota. In a healthy individual, the internal tissues (blood, brain, muscle, etc.) are normally free from microbes. However, the surface tissues (skin and mucous membrane), are colonized by various microbial species, typically bacteria, fungi and rarely protists. The normal flora of humans consists of a few eukaryotic fungi and protists, but bacteria are the most numerous and obvious microbial components of the normal flora. 1. Virulence Factor 2. Stages of Infectious Disease 3. Sources of Pathogen 4. Modes of Transmission Virulence Factor Virulence factor is the ability of a microorganism to cause disease. Virulence may also be used to indicate the degree of pathogenicity. Virulence involved a complex interplay between the parasite and the host and is often multifactorial. Various host factors, including age, sex, nutritional status, genetic constitution, and the status of the immune system, affect the outcome of the parasite-host interaction. 1. Bacterial Virulence • Adhesion To cause infection, many bacteria must first adhere to a mucosal surface. To accomplish this, bacteria have evolved attachment mechanisms, such as pili (fimbriae), that recognize and attach the bacteria to cells. Colonization factors (as they are often called) are produced by numerous bacterial pathogens and constitute an important part of the pathogenic mechanism of these bacteria. • Invasion Factor Mechanisms that enable a bacterium to invade eukaryotic cells facilitate entry at mucosal surfaces. Some of these invasive bacteria (such as Rickettsia and Chlamydia species) are obligate intracellular pathogens, but most are facultative intracellular pathogens. The specific bacterial surface factors that mediate invasion are not known in most instances, and often, multiple gene products are involved. • Capsules and other surface components Bacteria have evolved numerous structural and metabolic virulence factors that enhance their survival rate in the host. Capsule formation has long been recognized as a protective mechanism for bacteria. Encapsulated strains of many bacteria (e.g., pneumococci) are more virulent and more resistant to phagocytosis and intracellular killing than are nonencapsulated strains. • Endotoxins Endotoxin is comprised of toxic lipopolysaccharide components of the outer membrane of Gram-negative bacteria. Endotoxin exerts profound biologic effects on the host and may be lethal. The term endotoxin was coined in 1893 by Pfeiffer to distinguish the class of toxic substances released after lysis of bacteria from the toxic substances (exotoxins) secreted by bacteria Basic structure of endotoxin (lipopolysaccharide) from Gram-negative bacteria 2. Viral Virulence Viral virulence factors determine whether infection occurs and how severe the resulting viral disease symptoms are. Viruses often require receptor proteins on host cells to which they specifically bind. Typically, these host cell proteins are endocytosed and the bound virus then enters the host cell. Five stages of Infectious Disease • Incubation The time between the exposure to an infectious disease and its development. This period may last from a few minutes to a few days, weeks, months or even years. • Prodormal An early sympton (or set of symptoms) that might indicate the start of a disease before specific symptoms occur. • Illness Most severe signs or symptons • Decline This is the period during which symptons (and signs) decrease as the infection is brought further under control. • Convalescence This is the time during which the host repairs the damage wrought by the infection. Individuals are not necessarily, depending on disease/pathogen, no-longer contagious. The body returns to normal health. Sources of Infectious Disease Animal reservoirs Zoonoses are diseases that can be transmitted from animals to humans. Sources of infection: • Direct contact with animals • Direct contact with the animal feaces • Ingesting the infected animal • Via animal vector Human reservoirs Direct or indirect contact with infected carriers for example contact with an ill person or their secretions, or objects touched by them. Nonliving reservoirs These infecting agents may also be transmitted through liquids, food, body fluids, contaminated objects, airborne inhalation, or through vector-borne spread. Videos! Labels: #entry Friday, January 29, 2010 @ 6:30 PM
Entry05: Emerging Viruses Emerging Viruses Introduction: Emerging virus are viruses that has newly appeared in a human population and is rapidly increasing in disease incidence. The virus has adapted and emerged as a new disease or pathogenic strain, with attributes facilitating pathogenicity in a field not normally associated with the original virus. This includes viruses that are the cause of diseases which has notably increased in incidence; this is often a result of a wide variety of causes from both the influence of man and nature. Most emergent viruses can be categorized as zoonotic (an animal disease that can be transmitted to humans), this has the advantage of possibly having several natural reservoirs for the disease. Reason for Emergence There are 2 main factors as to why for the emergence, they are Virus Factors & Human Factors. Under Virus factor: 1. Spontaneous evolution of new virus entity 2. Generation of a novel strain due to co-infection of different strains in an individual(random assortment) Viral population is heterogenous which mean it can only be derived from a different individual or species and viral have high mutation rates due to selection pressure. Random assortment which only happens in virus with segmented genome is where Lego blocks of 2 different viruses, after penetrating the cell membrane; it dissembles and reassembles randomly which cause co-infection of both virus. The Viruses next replicate inside the host, RNA strands are being transcribed thus synthesis of new viral proteins and the new virus is produced. New virus particles are release. Click here for image All together, there are a total of 16 different H - Hemagglutinin types & 9 different N – Neuraminidase types, e.g H1N1, H3N2 , etc. however there are only 4 strains of avian influenza virus that are known to cause disease in humans. However how many permutation are there actually the answer is still really unknown, in the near future there may appear a new avian influenza breakout. Human Factors: Because of the concentration of population and they many different habit and lifestyle makes is easier for virus break out. For example; the transmission of HIV and Hepatitis C among drug users this due to the sharing of unsterile needles. In undeveloped countries due to poverty there is a lack of education which leads to the lack of knowledge of proper hygiene and personal care thus causing breakdown in public health. e.g. HIV in Africa and china Because of climate changes the temperatures in different region of the world starts to changes .The early effects of global warming have already been observed in different geographical areas. In Europe elevated average temperatures in West-Central Europe have been associated with more frequent Puumala hantavirus outbreaks, through high seed production (mast year) and high bank vole densities. On the other hand, warm winters in Scandinavia have led to a decline in vole populations as a result of the missing protective snow cover. Additional effects can be caused by increased intensity and frequency of extreme climatic events, or by changes in human behaviour leading to higher risk of human virus exposure. Regardless of the extent of climate change, it is difficult to predict the impact on hantavirus survival, emergence and epidemiology. Nevertheless, hantaviruses will undoubtedly remain a significant public health threat for several decades to come. Man invading natural habitat of animal Due to population pressure human are forces into new areas where potentially virulent viruses may be lurking. More land is needed for example agricultural thus bring human closer to the wild animals. Virus on infected wild animals may jumped to humans as a result causing new virus to form , which lead to the increase possibility of zoonoses. Here are some examples of emerging viruses over last 10 years! H1N1 virus Swine influenza (also know as swine flu) is an infection by any one of several types of swine influenza virus. Swine influenza virus is any strain of the influenza family of viruses that is endemic in pigs. A subtypes of influenza A known as H1N1, H1N2, H3N1, H3N2, and H2N3. Swine influenza virus is common throughout pig populations worldwide. Transmission of the virus from pigs to humans is not common and does not always lead to human influenza, often resulting only in the production of antibodies in the blood. If transmission does cause human influenza, it is called zoonotic swine flu. People with regular exposure to pigs are at increased risk of swine flu infection. The meat of an infected animal poses no risk of infection when properly cooked. Dengue Dengue The incubation period is 3-15 days; most common is 5-6 days. Classic Dengue has symptoms of fever, chilly sensation, severe headache, nausea, severe bone and joint pain. Dengue Hemmorrhagic Fever has the same symptoms as the classic form, also with internal bleeding and shock. If the patient survives the infection, it causes a sensitization instead of immunization. Classic Dengue virus infects approximately 1 million people per year; 15% of the infections progress into Dengue Hemorrhagic Fever. It is an arbovirus that is transmitted by Aedes Aegypti. All infections are from a mosquito vector. SARS Severe acute respiratory syndrome (SARS) is a new viral respiratory illness first identified in humans in early 2003. The SARS virus spreads primarily by close human contact, either through the air or by touching a contaminated surface. The time between exposure to the SARS virus and the onset of symptoms of SARS is called the incubation period. The incubation period for SARS is typically two to seven days, although in some cases, it may be as long as 10 days. Symptoms of SARS usually begin with a high fever, marked by a temperature greater than 100.4°F (38.0°C). Other early SARS symptoms may include: • Headache • An overall feeling of discomfort • Body aches • Chills. However in some patients, body aches and headaches may appear 12 to 24 hours before fever. Some people may also have mild respiratory symptoms such as sore throat or runny nose at the outset. About 10 to 20 percent of patients with symptoms of SARS have diarrhea. After two to seven days, SARS patients may develop a dry cough and shortness of breath. These SARS symptoms may be accompanied by or progress to a condition in which the oxygen levels in the blood are low (hypoxia). In 10 to 20 percent of cases, patients require mechanical ventilation and most patients develop pneumonia. Labels: #entry |
