Chapter 25- Pathogenic RNA Viruses Flashcards
What are general characteristics of RNA viruses?
Only infective agents that store genetic information in RNA molecules
Broken into 15 families: genomic structure, presence of an envelope, and size and shape of capsid
Many RNA viruses have more than only molecule of RNA- genomes are segmented
What is the first class of naked, +ssRNA viruses?
Picornaviridae
Smallest of the animal viruses (22-30nm)
Picornaviruses that cause disease are in several genera
What are rhinoviruses?
Class of Picornaviridae
Cause most cases of the common cold - infections limited to the upper respiratory tract
Single virus is sufficient to cause a cold
Transmitted by aerosols, bomites, or hand-to-hand contact (most common)
Some immunity can be acquire against serotypes infected with in the pact
Number of infections decrease with age
How is a rhinovirus diagnosed, treated, and prevented?
Diagnosis- manifestations are characteristic
Treatment- medication for the management of symptoms, will not reduce duraction of disease
Prevention- handwashing
What are characteristics of enteroviruses?
Group of picornaviridae family
Transmitted via the fecal- oral route- by ingestion of contaminated substance, fomites, oral contact
Infect the pharynx and intestine- spread via the blood infecting various targets in the body, are cytolytic
3 main genera: Poliovirus, coxsackievirus, and echovirus
What is poliomyelitis?
Polio is caused by one of the three serotypes of poliovirus
Last case of wild-type poliomyelities in the Americas was in 1979
What are the 4 conditions caused by poliovirus?
Asymptomatic
Minor polio- fever, headache, and sore throat
Nonparalytic polio- virus invades the meninges and CNS producing muscle spasms and back pain
Paralytic polio- virus invades the cells of the spinal cord and motor cortex of the brain, producing paralysis by limiting nerve impulse conduction, may results in bulbar poliomyelitis (brain stem and medulla are infected in the paralysis of muscles in limbs)
What is postpolio syndrome and what are the vaccines against polio?
Postpolio syndrome- crippling deterioration in the function of polio-affected msucles
Near elimination of polio due to development of two vaccines
Inactivated polio vaccine (IPV)- Joan Salk
Oral Polio vaccine (OPV)- Albert Sabin
What are characteristics of Hepatitis A?
Hepatitis A virus- noncytolytic picornavirus is the causative agent
Survives on various surfaces and is resistant to common household disinfectants
Transmitted through the fecal-oral route
Fever, nausea, and jaundice are due to patient’s immune response- infection does not cause chronic liver disease
Complete recovery occurs most of the time
Two doses of Hepatitis A vaccine are recommended
What are some characteristics of Hepeviridae?
Hepatitis E- enteric hepatitis- hepatitis E virus
Formerly classified as calicivirus
Fatal in 20% of pregnant women
No treatment
Prevent by interrupting fecal-oral route
What are characteristics of Togaviridae and Flaviviridae?
Enveloped, +ssRNa virus
Designated as Arboviruses
Mosquitoes and ticks transmit arboviruses among animal hosts causing zoonotic diseases
Arthropod vectors remain infected
Are a continual source of new infections
Most infections result in mild, flu-like symptoms
Arboviruses can occasionally result in second-stage infections
Encephalitis (caused by togavirus), dengue fever and yellow fever (caused by flavivirus)
Diagnosis by serological tests like ELISA
No treatment available
Prevention by vaccination for EE, JE, West Nile encephalitis, Yellow fever; no vaccine available for dengue
What are characteristics of Togaviridae?
Enveloped, +ssRNA viruses
Rubella- also called “German measles”
Rubella virus/ rubivirus is the causative agent
One of the five childhood diseases that causes skin lesions- rash of falt, pink red spots
Infection begins in respiratory system but spreads throughout the body
Infections in children are not usually serious- may result in arthritis or encephalitis in adults
Infection in pregnant women can cause congenital defects
Vaccination is effective
What are characteristics of Hepatitis C? What type of virus causes Hepatitis C?
Flaviviridae- enveloped, +ssRNA virus
Hepatitis C caused by Hepatitis C virus
Accounts for most non-A, non-B hepatitis infections in US
Spread through use of needles, organ transplants, sexual activity, but not arthropod vectors
Chronic infection with few or any symptoms- results in severe liver damage and failure
No treatment or vaccine
What are the characteristics and the disease caused by coronaviridae?
Named due to corona-like halo formed by their envelopes
Transmitted via large droplets from upper respiratory tract
2nd most common cause of colds
Severe Acute Respiratory Syndrome- SARS, emerging disease caused by previously unknown coronavirus, rapid progressive respiratory illness, symptoms include fever, dypnea, cough, may lead to respiratory failure or death
No treatment or vaccine
What are the physical characteristics of retroviridae?
Studied more than any other virus
Have polyhedral capsules with spiked envelopes- 2 glycoprotein spikes, gp120 and gp41
Genomes contain 2 identical molecules of +ssRNA, have enzymes reverse transcriptase, protease, and integrase, tRNA (primer to make dsDNA)
Do not conform to central dogma
Transcribe dsDNA from ssRNA using reverse transcriptase
What are the two types of retroviruses?
Primarily oncogenic- Human T-lymphotrophic viruses- cancer of lymphocytes
Primarily immunosuppressive- Lentivirus human immunodeficiency virus (HIV 1 & 2)
What is AIDS?
Acquired Immunodeficiency Syndrome- not a disease
Certain opportunistic or rare infections that occur in the presence of antibodies against HIV and a CD4 white blood cell count below 200 cells per microliter of blood
What is HIV?
Human Immunodeficiency Syndrome
Likely arose from a mutation of simian immunodeficiency virus, emerged in African populations around 1930
Only replicates in humans and destroys immune system
Two major types of HIV: 1- US and Europe, 2- West Africa
How do the two glycoproteins serve in the attachment of the HIV virus?
Two antigenic glycoproteins
- gp 120- primary attachment molecule, responsible for antigenic variability, binds to CD4 receptor molecules on a host cell
- gp 41- promotes fusion of viral envelope with the target cell, form syncyticum
Both glycoproteins impede immune clearance of HIV
How does the reverse transcriptase enzyme function?
+ssRNA taken up by enzyme to form a -ssDNA strand, use of tRNA molecules
+ssRNA is degraded
+ssDNA strand is made as complementary strand to form dsDNA
What is the replication cycle of HIV?
- Attachment by gp120
- Uncoating - gp 41
- Synthesis of dsDNA by reverse transcriptase, etnry into nucleus
- Integration by integrase- latency
- Synthesis of viral proteins
- Assembly and budding
- Maturation of virion (protease)
What is the pathogenesis of AIDS?
- Initial burst of virion production and release from infected cells
- Immune system produces antibodies and number of free virions falls, no symptoms, loss of T cells
- Virions are replenished in blood, body cannot replace helper T cells, over 5-10 years helper T cells decline to a level that impairs immune response
- Rate of antibody formation falls
- HIV production climbs, and patient dies from infections
What are the opportunistic infections associated with AIDS?
Tuberculosis, Kaposi’s Sarcoma, Herpes, Pneumonia, Fungal infections
What is the epidemiology of AIDS?
AIDS first recognized in young male homosexuals in US
AIDS is now found throughout the world, approximately 33 million infected individuals
HIV found in blood, semen, saliva, vaginal secretions, and breast milk
Blood and semen are more infective than other secretions
Infected fluids must contact a tear or lesion in the skin or mucous membranes
Infected fluids can be injected into the body
What are the most common modes of tranmission of HIV?
Females- high risk heterosexual contact followed by intravenous drug use
Males- homosexual contact followed by intravenous drug use
How is AIDS diagnosed?
Patient has one or more rare disease, antibodies against HIV, fewer than 200 CD4 lymphocytes per microliter of blood, unexplained weight loss, fatigue
Serological diagnosis- test for antibodies through ELISA, Western blot, agglutination, PCR gives definitive answer
Signs and symptoms vary according to the disease present
Long term non-progressors appear not to develop AIDS- may be due to defective virions or lack of effective coreceptors of virus
How is an HIV infection treated?
HAART (highly active antiretroviral therapy)- used to reduce viral replication
Cocktail of antiviral drugs including nucleoside analogs, protease inhibitors, reverse transcriptase inhibitors
Various problems must be overcome to develop a vaccine
How is an HIV infection prevented?
Behavioral changes can slow progression of AIDS epidemic
Abstinence and safe sex
Use of clean needles
Screening of blood products
Administer AZT to infected pregnant women
What are characteristics of paramyxoviridae?
Enveloped, unsegemnted, -ssRNA
Causes cells to fuse and form giant, multinucleate syncytia, syncytia enable virus to evade immune system
4 Genera infect humans:
Morbillivirus (measles virus)
Paramyxovirus- causes croup
Rubulavirus (mumps virus)
Pneumovirus (respiratory syncytia virus)
What are some characteristics of measles?
1 of 5 clasical childhood diseases caused by paramyxovirus
Spread in the air via respiratory droplets
Viruses infect the respiratory tract and spread throughout the body
Koplik’s spots appear on mucous membrane of the mouth
Lesions then appear on the head and spread over body
Rare complications- pneumonia, encephalities, and subacutre sclerosing panencephalitis (SSPE)
How is measles diagnosed, treated, and prevented?
Signs of measles, particuarly Koplik’s spots, are diagnostic
No antiviral treatment available
Vaccine (MMR) has eliminated endemic measles in USA
Measles remain a frequent cause of death in other countries
What are some characteristics of mumps?
Causative agent: Mumps virus, paramyxovirus
Transmission occurs via respiratory secretions
Viruses infect respiratory system and spreads to other organs
Results in parotitis- painful enlargement of the parotid salivary glands
Infections are often asymptomatic
No specific treatment is available
Vacccine has almost eradicated mumps in industrialized world
What are some characteristics of Rhabdoviridae?
Enveloped, unsegmented, -ssRNA virus
Rabies virus - a rhabdovirus (bullet-shaped)
Classic zoonotic disease of animals
Primary reservoir of urban areas is a dog, bats are the source of most cases of rabies in humans
Transmission occurs via a bite- virus sometimes introduced through break in skin or inhalation
Virus attaches to nerve cells and travels to CNS - results in rabies specific neurological symptoms (hydrophobia, seizures, hallucinations, paralysis, and death)
Death results from respiratory paralysis and other complications
How is rabies diagnosed, treated, and prevented?
Diagnosis- neurological symptoms, characteristic negri bodies in the brain
Treatment- too late to intervene by the time symptoms and antibodies occur, treat at site of infection with injection of human rabies immune globulin, vaccination with human diploid cell vaccine at days 0,3,7, and 14
Prevention- vaccination of domestic cats and dogs
What are some characteristics of Respiratory Syncytial Virus?
Disease is limited to respiratory tract
Transmission occurs via fomites, hands, and respiratory droplets
Virus causes formation of syncytia in lungs
Result in difficult breathing known as dyspnea
Leading cause of fatal respiratory disease in infants and children
Infection is asymptomatic or a mild cold in older children and adults
Diagnosis based on signs of respiratory distresss - verified by immunoassay
Treatment is supportive
What are some characteristics of Filoviridae?
Hemorraghic fevers- caused by Marburg Virus and Ebola Virus
Found in Germany, Zimbabwe, Kenya, Uganda, Angola, etc.
Natural reservoir and mode of transmission to humans unknown
Spread person to person by contaminated body fluids and syringes
Virions attack many cells of the body, especially the macrophages and liver cells
Uncontrolled bleeding under the skin from every body opening due to jelly like consistency of organs (viral glycoprotein prevents the neighboring cells from adhering- allows blood to leak out of vessels)
Only treatment is fluid replacemtn
90% of human victims die
What are some characteristics of Orthomyxoviridae? What are some characteristics of the disease it causes?
Influenza- Orthomyxovirus Type A and B
Infection occurs primarily through inhalation of airborne viruses
Rarely attack cells outside the lungs
Death of infected epithelial cells eliminates the lungs epithelial linings
Patients more susceptible to secondary bacterial infections
Symptoms include fever, malaise, headache, and myalgia
Induced by cytokines released as part of immune response
What are the characteristics of the genome and envelope of influenza virus?
Genome consists of 8 different -ssRNA molecules
Envelope components- highly variable with respect to glycoprotein spikes, contains:
Hemagglutinin- entry, attachment to pulmonary epithelial cells or trigger endocytosis
Neuraminadase- exit, provide virus access to cell surfaces by hydrolyzing mucus
How are new strains of the influenza virus produced?
Mutations result in production of new strains of influenza
Antigenic drift- minor variations
Antigenic shift- major antigenic changes
How is influenza diagnosed, treated, and prevented?
Diagnosis- signs and symptoms, community wide outbreak
Treatment- drugs prevent viral uncoating or block virion release from infected cells
Oseltamivir pills or inhaled zanamivir mist are neuramindase inhibitors, must be administered within 48h of infection
Prevention- multi valent vaccine
What are some characteristics of Hepatitis D? What virus is it caused by?
Arenavirus- Hepatitis D is caused by Hepatitis D virus
Transmitted through bodily fluids via sexual contact and contaminated needles
Hepatitis D requires Hepatitis B to be virulent- cannot attach to liver cells
Hepatitis D plays a role in triggering liver cancer
Vaccination against Hepatitis B limits Hepatitis D
What are some characteristics of reovirdiae?
Only microbes with genomes composed of dsRNA
Originally considered respiratory enteric orphans (REO)
Not initially associated with any diseases
Includes Rotavirus- most common cause of infantile gastroenteritis, unique wheel-like appearance, significant cause of death in developing countries
