Classification of Viruses PDF

Batterjee Medical College Batterjee Medical College Classification of DNA Viruses Virus Family Papillomavirus No Icosahedral Adenovirus Hepadnavirus No Yes Icosahedral Icosahedral Herpesvirus Yes Icosahedral DNA Structure SS, linear DS, circular, supercoiled DS, circular, supercoiled DS, linear DS,...

Batterjee Medical College Batterjee Medical College Classification of DNA Viruses Virus Family Papillomavirus No Icosahedral Adenovirus Hepadnavirus No Yes Icosahedral Icosahedral Herpesvirus Yes Icosahedral DNA Structure SS, linear DS, circular, supercoiled DS, circular, supercoiled DS, linear DS, incomplete circular DS, linear Poxvirus Yes Complex DS, linear Parvovirus Polyomavirus Envelope Present No No 1SS = single-stranded; DS = double-stranded. Capsid Symmetry Icosahedral Icosahedral Medically Important Viruses B19 virus JC virus, BK virus Smallpox virus, molluscum contagiosum virus Human papilloma virus Adenovirus Hepatitis B virus Herpes simplex virus, varicella-zoster virus, cytomegalovirus, Epstein-Barr virus Batterjee Medical College 1-Herpesviruses Virus Primary Infection Usual Site Recurrent of Latency Infection HSV-1 Gingivostomatitis Cranial Herpes labialis, Vesicular lesions above sensory encephalitis, the waist ganglia keratitis HSV-2 Herpes genitalis Lumbar or Herpes genitalis Vesicular lesions sacral below the waist sensory Perinatal ganglia disseminated disease VZV Varicella Cranial or Zoster Initial infection in thoracic reactivate years oropharynx. sensory later, in older and It spreads via blood to ganglia immunoliver then to skin. compromised individuals. Route of Transmission Via respiratory secretions, direct contact with virus vesicle & saliva Sexual contact, perinatal infection Via respiratory secretions Batterjee Medical College 1-Herpesviruses Virus EBV Primary Infection Usual Site of Recurrent Infection Route of Latency Transmission B lymphocytes None Via respiratory secretions & saliva Infectious mononucleosis It start in pharyngeal epithelium, spreads to cervical lymph nodes, then travels via blood to liver & spleen. CMV Congenital infection Uncertain (in utero) Mononucleosis in transfusion recipients. Pneumonia & hepatitis in immunocompromised patients Retinitis & enteritis, in AIDS patients HSV-8 Uncertain Uncertain Asymptomatic shedding Dissemination in immunocompromised patients Intrauterine infection transfusions, sexual contact, & secretions Kaposi's sarcoma in AIDS patients Sexual or organ transplantation Batterjee Medical College 1-Herpesviruses Herpes viruses-1 Batterjee Medical College Herpesviruses Varicella viruses Batterjee Medical College Herpesviruses Zoster viruses Batterjee Medical College Herpesviruses Epstein-Barr virus Batterjee Medical College Adenovirus Upper & lower tract (pharyngitis & pneumonia). respiratory disease Enteric strains cause diarrhea. Transmitted by respiratory droplet , iatrogenic in eye disease & fecal–oral with enteric strains. Live vaccine against types 3, 4, & 7 is used in military to prevent pneumonia Batterjee Medical College Papillomavirus Human Papillomavirus Papillomas (warts); condylomata acuminata (genital warts); carcinoma of cervix & penis. Transmitted by direct contact of skin & genital lesion Two early viral genes, E6 & E7, encode proteins that inhibit activity of proteins encoded by tumor suppressor genes, p53 gene & retinoblastoma gene, respectively. Vaccine containing capsid proteins of four HPV types (6, 11, 16 and 18) is available. Batterjee Medical College Papillomavirus Human Papillomavirus Batterjee Medical College Hepadnavirus Hepatitis B Virus Hepatitis B & hepatocellular carcinoma. Transmitted by blood, during birth & sexual intercourse. Hepatocellular injury due to immune attack by cytotoxic (CD8) T cells. Antigen–antibody complexes glomerulonephritis. cause arthritis, rash, & 5% of HBV infections result in a chronic carrier. Chronic hepatitis, cirrhosis & hepatocellular carcinoma can occur (integration of part of viral DNA into hepatocyte DNA). Batterjee Medical College Hepadnavirus Hepatitis B Virus Laboratory Diagnosis Three serologic tests are commonly used: 1- Surface antigen (HBsAg) 2- Surface antibody (HBsAb) 3- Core antibody (HBcAb). Detection of HbsAg ≥6 months Presence of e antigen chronic carrier. infectious chronic carrier. “Window" phase : HBV-infected person has neither detectable HBs antigen nor HBs antibody & diagnosed by detecting HB core antibody. Batterjee Medical College Hepadnavirus Hepatitis B Virus Treatment Alpha interferon & lamivudine reduce inflammation associated with chronic hepatitis B but does not cure carrier state. Prevention (1) vaccine that contains HBsAg as immunogen (2)hyperimmune serum globulins obtained from donors with high titers of HBsAb Batterjee Medical College Classification of RNA Viruses Virus Family Envelope Present Picornavirus No Capsid Symmetry Icosahedral Hepevirus No Icosahedral Calicivirus No Icosahedral Reovirus No Icosahedral Flavivirus Yes Icosahedral Togavirus Yes Icosahedral RNA Structure SS linear, nonsegmented, positive polarity SS, linear non-segmented positive polarity SS linear, nonsegmented, positive polarity DS linear, 10 or 11 segments SS linear, nonsegmented, positive polarity SS linear, nonsegmented, positive polarity Medically Important Viruses Poliovirus Rhinovirus hepatitis A virus Hepatitis E virus Norwalk virus Rotavirus Yellow fever virus, dengue virus West Nile virus, hepatitis C virus Rubella virus Batterjee Medical College Classification of RNA Viruses Virus Family Envelope Capsid Present Symmetry Retrovirus Yes Icosahedral Orthomyxovirus Yes Helical Paramyxovirus Yes Helical Rhabdovirus Yes Helical Filovirus Yes Helical RNA Structure Medically Important Viruses SS linear, 2 identical HIV strands (diploid), human T-cell positive polarity leukemia virus SS linear, 8 Influenza virus segments, negative polarity SS linear, Measles virus, nonsegmented, mumps virus, negative polarity respiratory syncytial virus SS linear, Rabies virus nonsegmented, negative polarity SS linear, Ebola virus nonsegmented, Marburg virus negative polarity Picornavirus Batterjee Medical College Enteroviruses: Poliovirus Range of responses to poliovirus infection includes: (1) inapparent, asymptomatic infection (2) abortive poliomyelitis (3) nonparalytic poliomyelitis (4) paralytic poliomyelitis. Transmission by fecal–oral route & humans are natural reservoir. Virus replicates in pharynx & GI tract & spread to local lymph nodes & then through blood to CNS. Batterjee Medical College Picornavirus Enteroviruses: Poliovirus Most infections are asymptomatic or very mild. Aseptic meningitis is more than paralytic polio. Paralysis is the result of death of motor neurons, anterior horn cells in the spinal cord. Virus in spinal fluid indicates CNS infection. Virus in stools indicates infection ( not necessarily disease) as it is found in GIT of asymptomatic carriers. Batterjee Medical College Picornavirus Enteroviruses: Poliovirus Disease can be prevented by: - Salk: inactivated vaccine - Sabin: live, attenuated vaccine both induce humoral antibody that neutralizes virus in bloodstream. Sabin vaccine has been preferred vaccine as : Oral vaccine Induces intestinal IgA, that prevent GIT infection Induces immunity of longer duration Batterjee Medical College Picornavirus Enteroviruses: Hepatitis A Virus Hepatitis A. Transmission by fecal–oral route. Blood-borne transmission is uncommon because viremia is brief & of low titer. Virus replicates in GIT then spreads to liver during brief viremic period. Virus is not cytopathic for hepatocyte & hepatocellular injury is caused by immune attack by cytotoxic T cells. Vaccine contains killed virus. Administration of immune globulin during incubation period Batterjee Medical College Picornavirus Enteroviruses:Coxsackie Viruses It causes the following diseases: -Aseptic meningitis, Myocarditis, pericarditis -Herpangina (fever, sore throat & tender vesicles in oropharynx) -Pleurodynia (fever & severe pleuritic-type chest pain due to an infection of the intercostal muscles not of pleura - Hand, foot &mouth disease (vesicular rash on hands & feet & ulcerations in mouth, mainly in children). - Coxsackie virus B4 may cause juvenile diabetes Transmission by fecal–oral route. Initial site of infection is oropharynx, but main site is GI tract then spreads through blood to various organs. Batterjee Medical College Picornavirus Rhinoviruses Common cold. There are more than 100 serotypes,which explains why the common cold is so common. They are destroyed by stomach acid Transmission by aerosol droplets & hand-to-nose contact Infection is limited to mucosa of upper respiratory tract & conjunctiva. Virus replicates best at low temperatures of nose & less well at 37°C. Batterjee Medical College Orthomyxovirus Influenza Virus Influenza. Influenza A cause worldwide epidemics. It has two major antigens ; hemagglutinin (HA) & neuraminidase (NA) on separate surface spikes. Antigenic shift in these proteins as a result of reassortment of RNA segments accounts for the epidemics of influenza Antigenic drift due to mutations also contributes. Batterjee Medical College Orthomyxovirus Influenza Virus Antigenicity of internal nucleocapsid protein determines virus is A, B or C influenza virus. Transmission by respiratory droplets. Infection limited to epithelium of respiratory tract. Neuraminidase inhibitor, oseltamivir (Tamiflu, drug of choice) & Zanamivir is used in treatment. Batterjee Medical College Orthomyxovirus Influenza Virus Two types of vaccines are available: 1-killed (subunit) vaccine: purified HA & NA. 2- Live, temperature-sensitive mutant of influenza virus. The virus replicates in cool nasal passages & induces secretory IgA, but not in warm lower respiratory tract. Batterjee Medical College Paramyxovirus Measles Virus Measles & Subacute sclerosing panencephalitis. Transmission by respiratory droplets. Initial site of infection is upper respiratory tract & spreads to local lymph nodes then via blood to other organs & skin. Maculopapular rash is due to cell-mediated immune attack by cytotoxic T cells on virus-infected vascular endothelial cells in the skin. Vaccine contains live, attenuated virus, combination with mumps & rubella vaccines. given in Batterjee Medical College Paramyxovirus Mumps Virus Mumps. Bilateral orchitis & sterility is rare Transmission by respiratory droplets. Initial site of infection is upper respiratory tract & spreads to local lymph nodes then via blood to other organs, especially the parotid glands, testes, ovaries, meninges & pancreas. Vaccine contains live, attenuated virus, given in combination with measles and rubella vaccines Batterjee Medical College Paramyxovirus Respiratory Syncytial Virus Bronchiolitis &pneumonia in infants & otitis media in older children. Transmission by respiratory droplets. Paramyxovirus Parainfluenza Virus Bronchiolitis in infants, croup in young children & common cold in adults. Transmission by respiratory droplets. Batterjee Medical College Togavirus Rubella Virus Rubella & Congenital rubella syndrome (congenital malformations, affecting cardiovascular & CNS) Transmission by respiratory droplets & across the placenta from mother to fetus (during first trimester) Initial site of infection is nasopharynx, then to local lymph nodes & disseminates to skin via blood. Rash due to viral replication & immune injury. Vaccine contains live, attenuated virus, combination with measles and mumps vaccine. given in Batterjee Medical College Coronavirus Coronavirus Common cold & SARS (severe acute respiratory syndrome). Transmission by respiratory droplets. It Infects mucosal cells of respiratory tract. Batterjee Medical College Rhabdovirus Rabies Virus Rabies (encephalitis) Transmission by animal bite & aerosols of bat saliva. Viral receptor is the acetylcholine receptor. Replication of virus at site of bite, followed by axonal transport up nerve to CNS then replicating in brain & migrates to salivary glands & saliva. Tissue stained with fluorescent antibody to detect cytoplasmic inclusions (Negri bodies). Batterjee Medical College Rhabdovirus Rabies Virus Preexposure prevention: Rabies vaccine Postexposure prevention: 1. Washing wound 2. Giving rabies immune globulins (passive immunization) into wound 3. Giving inactivated vaccine (active immunization) made in human cell culture. Batterjee Medical College Hepevirus Hepatitis E Virus Outbreaks of hepatitis in developing countries. Similar to hepatitis A virus in the following ways: - Transmitted by fecal–oral route - No chronic carrier state - No cirrhosis - No hepatocellular carcinoma. Batterjee Medical College Calicivirus Norwalk Virus (Norovirus) Gastroenteritis (watery diarrhea). Transmission by Fecal–oral route. Infection is limited to the mucosal cells of the intestinal tract. Batterjee Medical College Reovirus Rotavirus Gastroenteritis (diarrhea) in young children. Rotavirus is resistant to stomach acid Transmission by the fecal–oral route. There are two rotavirus vaccines. Live attenuated vaccine contains single most common rotavirus serotype (G1) Live reassortant vaccine contains 5 rotavirus strains. Batterjee Medical College Flavivirus Hepatitis C Virus Hepatitis C & hepatocellular carcinoma. Transmission is via blood. Sexual transmission & from mother to child probably occurs. Hepatocellular injury caused by cytotoxic T cells & HCV does not cause a cytopathic effect. 50% of infections result in chronic carrier which predisposes to chronic hepatitis & hepatocellular carcinoma. Batterjee Medical College Flavivirus Hepatitis C Virus Serologic testing detects antibody to HCV. PCR-based assay for "viral load" can be used to evaluate whether active infection is present. Alpha interferon plus ribavirin mitigates chronic hepatitis but does not eradicate carrier state. Post transfusion hepatitis can be prevented by detection of antibodies in donated blood. Batterjee Medical College Deltavirus Hepatitis D Virus Hepatitis D (hepatitis delta). Defective virus that uses HBs Ag as its protein coat & replicate only in cells infected with HBV (HBV is helper virus). Transmitted by blood, sexually & from mother to child. Hepatocellular injury caused by cytotoxic T cells. Chronic hepatitis & chronic carrier state occur. Treatment by Alpha interferon mitigates symptoms but does not eradicate carrier state. HBV vaccine & HBV hyperimmune globulins will prevent HDV infection also. Batterjee Medical College Retrovirus Human Immunodeficiency Virus Acquired immunodeficiency syndrome (AIDS). RNA-dependent DNA polymerase (reverse transcriptase) makes a DNA copy of the genome, which integrates into host cell DNA. Precursor polypeptides cleaved by virus–encoded protease to produce functional viral proteins. Antigenicity of gp120 protein changes rapidly there are many serotypes. Batterjee Medical College Retrovirus Human Immunodeficiency Virus Transmission by body fluids, e.g., blood & semen, transplacental & perinatal transmission. Two receptors are required for HIV to enter cells: 1 - CD4 protein : it is found on helper T cells. HIV infects and kills helper T cells, which predisposes opportunistic infections. 2 - chemokine receptor such as CCR5. to Batterjee Medical College Retrovirus Human Immunodeficiency Virus Detecting antibody with ELISA as screening test and Western blot as confirmatory test. Determine the "viral load," i.e., the amount of HIV RNA in the plasma, using PCR-based assays. High viral load predicts more rapid progression to AIDS Batterjee Medical College Retrovirus Human Immunodeficiency Virus Treatment Highly active antiretroviral therapy (HAART) consists of two nucleoside inhibitors (inhibit HIV replication by inhibiting reverse transcriptase) & one protease inhibitor (prevent cleavage of precursor polypeptides). Clinical improvement occurs, but virus persists. Batterjee Medical College Retrovirus Human Immunodeficiency Virus Screening of blood prior to transfusion for the presence of antibody. "Safe sex," including the use of condoms. Nucleoside inhibitors (zidovudine) with or without a protease inhibitor should be given to HIVinfected mothers and their newborns. Nucleoside inhibitors (Zidovudine & lamivudine ) & protease inhibitor should be given after a needlestick injury. Batterjee Medical College Arboviruses Classification of Major Arboviruses Family Genus Viruses of Medical Interest Alphavirus Eastern equine encephalitis virus western equine encephalitis virus Flavivirus Flavivirus St. Louis encephalitis virus Yellow fever virus Dengue virus, West Nile virus California encephalitis virus Bunyavirus Bunyavirus All arboviruses are transmitted by arthropods (arthropodColorado tickfrom feverthe virus borne) such Orbivirus as mosquitoes & ticks wild animal Reovirus reservoir to humans. Togavirus Batterjee Medical College Arboviruses Flavivirus: Yellow Fever Virus Yellow fever "Jungle" yellow fever is transmitted from monkeys to human by mosquitoes. "Urban" yellow fever is transmitted from human (reservoir) to human by Aedes mosquitoes It is severe, life-threatening disease characterized by jaundice & fever. There is a live, attenuated vaccine for humans. Batterjee Medical College Arboviruses Flavivirus: Dengue Virus Dengue fever. Transmitted by Aedes mosquitoes from one human to another. Classic dengue (worldwide) (breakbone fever) begins suddenly with influenzalike syndrome consisting of fever, malaise, cough, & headache. Severe pains in muscles & joints (breakbone) occur. Enlarged lymph nodes, maculopapular rash & leukopenia After a week, symptoms regress but weakness may persist. Batterjee Medical College Arboviruses Flavivirus: Dengue Virus The diagnosis : Isolation of virus in cell culture & Serologic tests that demonstrate presence of: IgM antibody & fourfold or greater rise in antibody titer in acute & convalescent sera. Outbreaks are controlled by using: Insecticides Raining stagnant water serves as breeding place for mosquitoes Personal protection includes: Using mosquito repellent & Wearing clothing that covers the entire body. Batterjee Medical College Prions Creutzfeldt-Jakob disease (CJD), variant CJD & kuru (transmissible spongiform encephalopathies) There is a hereditary form of CJD called Gerstmann-Sträussler-Scheinker (GSS) syndrome. Prions are composed of protein only. They have no detectable nucleic acid & highly resistant to UV light, formaldehyde & heat. They are encoded by a cellular gene. Batterjee Medical College Prions Pathogenic form (beta-pleated sheet) increases in amount by inducing conformational change in normal form (alpha helix). In GSS syndrome, a mutation occurs that enhances conformational change to beta-pleated sheet form. CJD is transmitted by pituitary extracts, brain electrodes & corneal transplants. Kuru was transmitted by ingestion or inoculation of human brain tissue. Variant CJD is transmitted by ingestion of cow brain tissue in undercooked food Batterjee Medical College Prions Aggregation of prion filaments within neurons occurs, vacuoles within neurons cause spongiform changes in brain, no inflammation or immune response occurs. Brain biopsy shows spongiform changes. Prions cannot be grown in culture.