MLS Review - Virology

MEDICAL LABORATORY SCIENCE REVIEW • VIROLOGY OUTLINE • • • • • • • • General Characteristics Parts of a Virion Infectious Cycle Specimen Collection Cell Cultures DNA Virus RNA Virus • • • VIROLOGY • • Penetration o Enveloped virus - engulfment of virus through endocytosis (involvement of cytoplasmic vacuoles) o Naked virus - direct fusion Uncoating – release of viral content o Separation of capsid to genetic material Biosynthesis – replication and translation occur Assembly/maturation o Materials are assembled in a protein coat to enclose the genomic material, forming a new cell Release – to the extracellular fluid (through budding or cell lysis) and repeat the cycle. Virology - study of viruses Viruses - diverse due to different and varying shapes, structures, and hosts GENERAL CHARACTERISTICS • • • • • • • Smallest infectious agent - measures 20-300nm in diameter Haploid except Retrovirus Either DNA or RNA in nature Resistant to antibiotics Obligate intracellular organisms o Unable to self-replicate; requires a whole cell to multiply If virus is envelope, it is ether sensitive or labile while naked is ether resistant Naked Virus: Picornavirus, Reovirus, Calicivirus, Papovavirus, Parvovirus, and Adenovirus (PRCPPA) SPECIMEN COLLECTION • • PARTS OF A VIRION • • • • • • Capsid - Protein shell or coat that encloses nucleic acid o Can be helical, icosahedral, and complex Nucleic Acid (Viral Genome or Genomic Material) DNA (deoxyribonucleic acid) or RNA (ribonucleic acid) o Cannot be both present Nucleocapsid - Nucleic acid + Capsid (Enclosed) Capsomeres - morphological units seen on the surface of particles; composes the capsid Envelope - A lipid containing membrane that surrounds some viral particles o May contain glycoprotein, envelope proteins, matrix proteins Structural Units - Protomers are the smallest functional unit equivalent to building units of the capsid Appropriate time of collection - Acute phase reaction within 72 hours of disease Go where the manifestation of the viral disease shows o Aspirated secretions – maximum recovery o Swabs – use Synthetic Swab (Dacron or Nylon) TRANSPORT MEDIA • • Consist of buffered isotonic solution + some type of protein + antibiotic Examples include: Stuart’s, Amies, Leibovitz Emory, Hanks' Balanced Salt Solution (HBSS) and Eagle Tissue Culture Medium CELL CULTURES • Most widely used for virus isolation (shell vial). TYPES OF CELL CULTURES • • • Primary cell culture - derived from animal tissues; very expensive o example: Monkey Kidney – excellent for myxovirus Semi-continuous cell culture – derived from embryonic tissues o e.g., Human embryonic kidney and skin fibroblasts Continuous cell culture - derived from tumor cells/ malignant tissues o e.g., HeLa, Vero, Hep2, LLC-MK2, MDCK DNA VIRUS INFECTIOUS CYCLE • Attachment/Adhesion – finding of suitable host cell to invade o Aka adsorption, invasion o Viral Tropism - virus attaches to specific receptor on a suitable host cell GENERAL RULE • • • • • All are ds-DNA except: Parvovorus o ds-DNA - double-stranded DNA All are icosahedral except: Poxvirus (Complex) All are enveloped except: (PAP) Pavovirus, Adenovirus, Parvovirus All multiply in nucleus Except: Poxvirus (cytoplasm) Largest is Poxvirus while smallest is Parvovirus 1 o ADENOVIRUS • • • • • • Genus: Mastadenovirus Grapelike cluster with cytopathic effect Pathogenic to human (w/ 2 serotypes) Respiratory and Gastrointestinal are common clinical manifestation o Acquired through contaminated respiratory droplets, stool and fomite Replicates in the oropharynx Serotypes o 40 and 41 - Gastroenteritis in children o 8 - Conjunctivitis o 3 and 7 - Pharyngitis o 4 and 7 - Respiratory Disease Epidemic in Military • • HEPADNAVIRUS • • • • • • Dane particle or Australian antigen – infectious unit Only DNA hepatitis Associated with acute hepatitis but may lead to Cirrhosis and Liver carcinoma Humans are the only source of the virus Viral Hepatitis - group of clinically similar liver diseases (similar signs and symptoms) but differ in etiology and epidemiology Table of differentiation of Hepatitis MOT Virus ssRna HAV Fecal oral Picornaviridae HBV Sexual, perinatal, dsDNA (Hepadnaviridae) parenteral HCV Sharing of needles Flaviviridae HDV Intravenous drug Delta Virus (incomplete virus; use infective only in presence of HBV) HEV Fecal Oral Hepevirus o HEV - similar to HAV but differ in causative agent ▪ Originally calicivirus HERPES VIRUS • • • • • • • From Greek word “Herpes” meaning creep o Due to presence of ulcerative lesions Large (150-200 nm) Consist of 4 components (nucleic acid core, capsid, tegument and envelope) Lifelong persistence in their hosts Latency - the condition is already existing but it is not active and it may not cause symptoms yet HSV-1 and HSV-2 o Spread by direct contact with infected secretions o Recurrence of skin lesion after primary infection o HSV 1 and 2 latency is sensory nerve ganglia o HSV-1 “Cold sores” or “Fever blisters” ▪ Gingivostomatitis, Pharyngitis, Herpes Labialis, Herpetic whitlow, Keratitis, Encephalitis ▪ HSV-1 is the leading cause of fatal sporadic encephalitis and corneal infection in the United States; Encephalitis in older children and adults o HSV-2 - Genital Infection/Genital Herpes ▪ MOT: Sexual contact Varicella Zoster Virus (VZV) / HHV-3 o Transmitted through personal contact especially respiratory o Varicella - Chicken pox ▪ Common in children • • Zoster - Shingles ▪ Recurrence of HHV-3 ▪ Common in adults o VZV latency is dorsal root ganglia o Presence of skin rash with blisters that look like dew drops on a rose petal Epstein Barr Virus (EBV) or HHV-4 o Transmitted through saliva o Causative agent of Infectious mononucleosis (Glandular Fever/Kissing’s dse), Burkitt lymphoma and nasopharyngeal carcinoma o Latency is B lymphocytes Cytomegalovirus (CMV) or HHV-5 o Aka salivary gland virus o Presence of Cow’s eye appearance o Transmitted through close contact with secretions, blood transfusion (WBC), organ transplant and transplacental o CMV is the most common cause of viral mental retardation and congenital disease. ▪ Must be avoided by pregnant women especially during the first trimester o Latency is WBCs, endothelial cells Human Herpes Virus-6 (HHV-6) and HHV 7 o Transmitted through respiratory secretions; almost all children from age 2-3 years old o Lymphotropic virus and Roseola (Exanthem subitum) – fever with short rash. o Site of latency is CD4 (T helper lymphocytes) o Cause beta herpesvirus HHV-8 or Rhadinovirus - gamma herpesvirus causing Kaposi Sarcoma PAPILLOMAVIRUS • • • • • • • • • Cause warts and exhibit tropism in cutaneous and mucocutaneous HPV-1 - Plantar Warts HPV-2 and 4 - Warts of the Hand HPV-6 and 11 - Genital Warts HPV 5 and 8 - Epidermodysplasia verruciformis HPV 13 and 32 - Hecks’s Disease (Focal Epithelial Hyperplasia) HPV-16 and 18 - Condyloma Accuminate HPV-16 - Subset cancer of oropharynx and penile cancer in men HPV 41-42 - Genital Warts PARVOVIRUS B19 (Erythrema Infectiosum) • • • • Latin word “Parvus “ meaning small Smallest virus Viral replication sites are erythroid progenitor cells, adult bone marrow and fetal liver With characteristic slapped cheek appearance POLYOMA VIRUS • • • BK Virus/ Polyoma virus hominis 1 - hemorrhagic cystitis; latent state in kidney JC Virus/ Polyoma virus hominis 2 – Progressive multifocal leukoencelopathy; latent state in B lymphocytes MC virus - associated with Merkel Cell Carcinoma 2 POXVIRUS CALICIVIRUS • • • • • • • Largest and most complex of all viruses Oval or brick shape virus Variola/Orthopoxvirus – causative agent of Smallpox virus o Smallpox - eradicated by Edward Jenner Molluscum Contagiosum - small, pink, papular, wart-like benign tumors of the skin or mucous membrane. Orf virus – transmitted by direct contact with sheep in which nodules in hands may be seen Vaccinia - weak virulent; used for smallpox vaccine (Cowpox) IRIDOVIRUS • • • Large ds DNA virus which is the causative agent of African Swine Flu (ASF) Not transmissible to human but highly pathogenic to pigs (hemorrhagic fever) Known to be transmitted by arthropods (soft ticks) RNA VIRUS • • CORONAVIRUS • • • • • • GENERAL RULE • • • • • • • All are single stranded Except: Reovirus All are enveloped Except: Picornavirus, Calicivirus, & Reovirus Generally helical Except: Picornavirus, Reovirus, Retrovirus, Flavivirus, Togavirus All replicate in cytoplasm Except: Orthomyxovirus, Retrovirus Largest is Paramyxovirus Smallest is Picornavirus Arthropod borne (insect borne) – Majority of Bunyaviridae (except Hantaviridae), Flaviviridae (except HCV), and Togaviridae (except Rubella) ARENAVIRUS • • • • Sand shape appearance in electron microscope Acquired through inhalation from infected rodent or direct contact New World Arena Virus -Tacaribe, Guanarito, Junin and Machupo Old World Arena Virus - Mus musculus, Mastomys natalensis o Lymphocytic Choriomeningitis - meningitis ▪ Causes a rare case of aseptic meningitis o Lassa Virus – hemorrhagic fever + influenza like ▪ Cause hemorrhagic fever influenza-like • • • • • • Transmitted by mosquito, ticks and sandfly Type and Organ damage associated with Bunyavirus o PHLEBOV-Rift Valley Fever Virus - brain & liver o ORTHOBUNYAV-LaCrosse & California Encephalitis - Brain o NAIROVIRUS-Crimean Congo Hemorrhagic Fever - Vascular Endothelium and Liver o Hantavirus – rodent-borne bunyavirus (deer mice) ▪ Disease caused is known as hemorrhagic fever with renal syndrome (HFRS) Filo or threadlike due to long filamentous morphology in EM Most pathogenic of the hemorrhagic virus Marburg hemorrhagic fever virus o 25% fatality rate o Acquired from African green monkey in Africa Ebola Virus o Emerging virus due to eating of wild animal meat o Acquired through direct contact with wild infected animal or human o 80% fatality rate FLAVIVIRUS • • Star appearance in EM Account to 2-9% of pediatric gastroenteritis in the world BUNYAVIRUS Pleomorphic, roughly spherical Extremely fragile and difficult to culture Resemble halo/crown on external surface of the virus SARS-COV1 – acquired from civet cat that originated from Guangdong, China MERS-COV - acquired from camel that originated in middle east SARS-COV2 –possibly acquired from pangolin (bats) that originated for Wuhan, China. o SARS-COV2 Detection ▪ Direct - microscopy/viral nucleic acid ▪ Indirect - serological testing o Variants of Concern ▪ Alpha – B117 - United Kingdom ▪ Beta – B1351 - South Africa ▪ Gamma P1 - Brazil ▪ Delta B16172 - India FILOVIRUS ASTROVIRUS • • Small (30 to 38) nm rounded nonenveloped that cause gastroenteritis to humans Norovirus / Norwalk Virus o Associated with 80% of nonbacterial acute gastroenteritis in undeveloped countries o Due to ingestion of contaminated shellfish and water Sapovirus – cup shaped in EM that is also associated with gastroenteritis • • Derived from ‘flavus which means yellow’ Yellow Fever o First discovered Flavivirus o Three Cycles ▪ Sylvatic - Monkey population transmitted by mosquitoes (Aedes aegypti) ▪ Urban - Human ▪ Intermediate - Human Dengue Virus o Dengue vectors - Aedes aegypti, Aedes albopictus and Aedes polynesiansis. o It has four serotypes (1 to 4) o Major protein in dengue virus, called 'E' for envelope protein St. Louis Encephalitis (SCE) - transmitted by Culex mosquitoes and mostly in summer months. 3 • • • Zika virus o Spread by daytime Aedes aegypti & albopictus o There is preliminary evidence, that Zika is a cause of Guillain-Barré syndrome in adults. West Nile Virus o Vector is Culex mosquitos o Maintained in bird-mosquito cycle such as crows, ravens Hepatitis C virus - associated with chronic liver disease o Parenteral transmission by sharing of needles PICORNAVIRUS • • • • HEPEVIRUS • • Previously under calicivirus; High Case Fatality Rate in Pregnant Women (10-20%) ORTHOMYXOVIRUS • • • • • • • • Pleomorphic single stranded with 8 segments. Three Serotypes: o A - naturally infects animals o B, C - human Transmitted through respiratory secretions Causes influenza Influenza is further subdivided based on Hemagglutinin (HA) and neuraminidase (NA) o Hemagglutinins - rod-shaped spikes o Neuraminidase - mushroom-shaped spikes Antigenic drift refers to alteration of Influenza HA and NA antigens. Antigenic shift occurs after having a completely new novel type. Only H1 H2 H3 N1 N2 found in human population o H1N1 - Spanish Flu o H2N2 - Asian FLu o H3N2 - Hongkong Flu o H5N1 - Avian Flu • REOVIRUS (RESPIRATORY ENTERIC ORPHAN) • • PARAMYXOVIRUS • • • • • • • Do not have segments that’s why they don’t undergo antigenic shift Mumps or Rubulavirus o Characterized by inflamed salivary gland accompanied by high temperature and fatigue Parainfluenza virus o Second cause of pneumonia and bronchiolitis in children after RSV o 4 serotypes ▪ Parainfluenza 1 is associated with croup (acute larygeotracheobronchitis) ▪ Parainfluenza 3 is severe and fatal Respiratory Synctial Virus (RSV) or Pneumovirus o Most significant cause of acute RTI in children under 5 years of age worldwide. o Contains a surface F protein (Fusion protein) o Leads to giant multinucleated cells Measles or Morbilivirus or Rubeola o Highly contagious accompanied by maculopapular rash and fever Metapneumovirus o Associated with winter epidemics bronchiolitis and pneumonia which is common in children Nipah virus - can cause febrile encephalitis in human “Piccolo” means small Simplest and smallest of RNA viruses with highly structured capsid but limited surface elaboration Consists of 30% RNA and 70% Protein Enterovirus o The most common cause of aseptic meningitis or inflammation of brain parenchyma. o Primary MOT: respiratory or gastrointestinal o Enteroviruses are subdivided into: ▪ Poliovirus (1-3) - associated with paralytic poliomyelitis (classic paralysis) ▪ Coxsackie A (1-23) - assoc. with herpangina or severe febrile pharyngitis w/ small blisters in mouth ▪ Coxsackie B (1-6) - associated with epidemic myalgia (joint pain) or chronic fatigue syndrome, • Pleurodynia - pain upon breathing • Born-old disease ▪ Enterovirus (68-72) ▪ Echovirus (1-32) • Echo - enteric cytopathogenic human orphan • Characterized by cough, rash, and influenzalike syndrome ▪ Parechovirus (1-4) Rhinovirus o It is the major cause of cold virus o Resistant to detergents, lipid solvents, and temperature extremes o Sensitive to pH less than 6 Rotavirus o The most common cause of viral gastroenteritis in infants and children worldwide Coltivirus o With 12 RNA segments o Associated with Colorado tick fever RETROVIRUS • • • Requires RNA-dependent DNA polymerase Oncovirus o HTLV-1, HTLV-2 and HTLV-5 are oncovirus but not cytolytic ▪ HTLV - Human T-cell Lymphotrophic Virus o HTLV-1- known as T cell leukemia o HTLV-2- known as Hairy Cell Leukemia Lentivirus o HIV - it is causative agent of AIDS o HIV antigens are p24, gp41, gp120 and gp 160. o Screening: ELISA o Confirmatory: WB (Western Blot) o HIV has 2 groups ▪ HIV-1: Worldwide prevalence • HIV-1 main groups are M,N and O ▪ HIV-2: West Africa • A-K are subgroup 4 RHABDOVIRUS • Lyssavirus/ Rabies o Bullet-shaped appearance o Characterized by saliva frothing with painful spasm o May lead to coma or death o Associated with negri bodies in brain tissues of infected animals and humans TOGAVIRUS • • • • Arthropod-borne Alphavirus – associated with equine encephalitis and transmitted by mosquitos (Aedes) o Equine encephalitis Types ▪ Eastern equine encephalitis (EEE) ▪ Western equine encephalitis (WEE) ▪ Venezuelan equine encephalitis (VEE) Rubella or Rubivirus o German measles or 3 day measles (mild fever) – may lead to congenital defect if pregnant women is infected o Must be avoided by pregnant during 1st trimester Chikungunya virus - associated with myositis and arthritis which is transmitted by Aedes aegypti 5