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virus(vi'rus) [L. virus, poison]
Some of the most virulent diseases are caused by viruses, e.g., the hemorrhagic fever caused by Ebola virus. Viruses are also responsible for the common cold, childhood exanthems (such as chickenpox, measles, rubella), latent infections (such as herpes simplex), some cancers or lymphomas (such as Epstein-Barr virus), and diseases of all organ systems.
Although viral architecture is very complex, every virus contains at least a genome and a capsid.Most animal viruses are also surrounded by a lipid envelope, a bilayered membrane analogous to a cell membrane. The envelope may be parasitized from host cells. Its chemical components are phospholipids and glycoproteins. The lipid envelope is frequently dotted by spikes.
Viruses with lipid envelopes have a greater ability to adhere to cell membranes and to avoid destruction by the immune system. Both the capsid and envelope are antigenic. Frequent mutations change some viral antigens so that the lymphocytes are unable to create an antibody that can neutralize the original antigen and its replacement. The common influenza viruses have antigens that mutate or combine readily, requiring new vaccines with each mutation. The body's primary immune defenses against viruses are cytotoxic T lymphocytes, interferons, and, to some extent, immunoglobulins; destruction of the virus often requires destruction of the host cell.
When viruses enter a cell, they may immediately trigger a disease process or remain quiescent for years. They damage the host cell by blocking its normal protein synthesis and using its metabolic machinery for their own reproduction. New viruses are then released either by destroying their host cell or by forming small buds that break off and infect other cells. See: illustration; table
The 400 known viruses are classified in several ways: by genome core (RNA or DNA), host (animals, plants, or bacteria), method of reproduction (such as retrovirus), mode of transmission (such as enterovirus), and disease produced (such as hepatitis virus).
Antiviral drugs include such agents as acyclovir (for herpes simplex); oseltamivir and zanamivir (for influenza A); interferons (for chronic hepatitis B and C); ribavirin (for respiratory syncytial virus and chronic hepatitis C); and lamivudine (for HIV).
B virusCercopithecine herpesvirus 1.
Banna virusAbbreviation: BAV
Barmah Forest virus
cercopithecine virus 1Cercopithecine herpesvirus 1.
cowpea mosaic virus
coxsackie virusSee: coxsackievirus
cytomegalic virusAbbreviation: CMV
deer tick virus
delta hepatitis virusAbbreviation: HDV
See: hepatitis D
EB virusEpstein-Barr virus.
enteric cytopathogenic human orphan virusAbbreviation: echovirus
enteric orphan virusSee: enteric cytopathogenic human orphan virus
Epstein-Barr virusSee: Epstein-Barr virus
Eyach virusAbbreviation: EYAV
GB virus type CHepatitis G virus.
hepatitis G virus
herpes simplex virusAbbreviation: HSV-1, HSV-2
In immunosuppressed patients, the virus can cause a widely disseminated rash. Some infections with HSV may involve the brain and meninges; these typically cause fevers, headaches, altered mental status, seizures, or coma, requiring parenteral therapy with antiviral drugs. In newborns, infection involving the internal organs also may occur. Experienced ophthalmologists should manage ocular infection with HSVs. Health care providers are at risk for herpetic whitlow (finger infections) from contact with infected mucous membranes if gloves and meticulous hand hygiene are not used.
Acyclovir and related drugs, e.g., famciclovir, valacyclovir, may be used to treat outbreaks of HSV-1 and HSV-2 and are also effective in preventing recurrences of disease.
Standard precautions prevent spread of the virus. Prescribed antiviral agents and analgesics are administered; their use is explained to the patient, with instruction given about adverse effects to report.
The patient with HSV-1 is instructed to avoid skin-to-skin contact with uninfected individuals when lesions are present or prodromal symptoms are felt. To decrease the discomfort from oral lesions, the patient is advised to use a soft toothbrush or sponge stick, a saline- or bicarbonate-based (not alcohol-based) mouthwash, and oral anesthetics such as viscous lidocaine if necessary. He or she should eat soft foods. Use of lip balm with sunscreen reduces reactivation of oral lesions.
The patient with genital herpes should wash the hands carefully after bathroom use. He or she also should avoid sexual intercourse during the active stage of the disease and should practice safe sex. A pregnant woman must be advised of the potential risk to the infant during vaginal delivery and the use of cesarean delivery if she has an HSV outbreak when labor begins and her membranes have not ruptured. The patient with genital herpes may experience feelings of powerlessness. He requires assistance to identify coping mechanisms, strengths, and support resources; should be encouraged to voice feelings about perceived changes in sexuality and behavior; and should be provided with current information about the disease and treatment options. A referral is made for additional counseling as appropriate.
CAUTION!Caregivers with active oral or cutaneous lesions should avoid providing patient care.
herpes virusSee: herpesvirus
human immunodeficiency virusAbbreviation: HIV
human papilloma virusSee: papillomavirus
human T-cell lymphotropic virus type IAbbreviation: HTLV-I
human T-cell lymphotropic virus type IIAbbreviation: HTLV-II
human T-cell lymphotropic virus type IIIAbbreviation: HTLV-III
Inkoo virusAbbreviation: INK
Kyasanur Forest virus
Langat virusAbbreviation: LGT
Nipah virusAbbreviation: NiV
Norwalk virusAbbreviation: NLV
Omsk hemorrhagic fever virus
oncogenic virusTumor virus.
Puumala virusAbbreviation: PUUV
Rauscher leukemia virusSee: Rauscher leukemia virus
respiratory syncytial virusAbbreviation: RSV
Three to five days following exposure to RSV, the patient typically develops an upper respiratory infection lasting 1 to 2 weeks with cough, mild to moderate nasal congestion, runny nose, and low-grade fever. If the infection spreads to the lower respiratory tract, symptoms worsen and may include wheezing and difficulty breathing. Infants and children with RSV pneumonia exhibit retractions; rapid grunting respirations, poor oxygenation, and respiratory distress. Vomiting, dehydration, and acidosis may occur.
Diagnosis is based on signs and symptoms and confirmed by isolating RSV from respiratory secretions (sputum or throat swabs). Immunofluorescence techniques, enzyme immunoassays, or rapid chromatographic immunoassays provide rapid identification of viral antigens for diagnosis.
Treatment is mainly supportive. Antibiotics are not effective. Acetaminophen or ibuprofen are given for pain or fever. Oxygen is administered if the patient’s oxygen saturation SpO2 falls below 92%. Bronchodilators, such as albuterol and epinephrine, are used to treat wheezing. In patients with severe RSV infections, noninvasive positive-pressure ventilation or intubation and mechanic ventilation are required. Intravenous fluids are administered as prescribed if the patient cannot take enough fluid orally. Nasopharyngeal suction may be needed to clear congestion (by bulb syringe for infants).
Strict adherence to infection control measures is important in preventing an outbreak in any facility. This includes using meticulous hand hygiene (the most important step in preventing RSV spread) before donning gloves for patient care, after removing gloves, and if any potentially contaminated surfaces have been touched. Standard and contact precautions should be observed for all patients with known or suspected RSV (gown, mask and eye protection for direct contact with respiratory secretions or droplets). Protective coverings should be removed in this order: gloves (followed by hand hygiene), goggles or face shield, gown, and finally mask or respirator, discarding them in an infectious waste container in the patient’s room. The patient with RSV should be in a private room and dedicated equipment should be used in patient care, with terminal equipment disinfection by the appropriate agency facility. Room assignments should be arranged to avoid cross-contamination whenever possible. Individuals with symptoms of respiratory infection should be prevented from caring for or visiting pediatric, immunocompromised, or cardiac patients.
The administration of high doses of respiratory syncytial virus immune globulin is an effective means of preventing lower respiratory tract infection in infants and young children at high risk for contracting this disease. Palivizumab, a monoclonal antibody given intramuscularly, can prevent RSV disease in high-risk infants and children.
Rift Valley virus
Ross River virus
sandfly fever virusToscana virus
Serra do Navio virusAbbreviation: SDNV
simian immunodeficiency virus
SV 40 virus
Tacaribe complex virus
Tahyna virusAbbreviation: TAH
transfusion-transmissible virusAbbreviation: TTV
West Nile virus
In 2009 45 states in the U.S. reported having human cases of West Nile fever. There were 720 reported cases of this viral infection in the U.S. in 2009 and 32 fatalities. Infected patients with neuroinvasive disease sometimes suffer long-term consequences of infection, including fatigue and malaise, difficulty concentrating or thinking, or movement disorders. The disease is sometimes spread from patient to patient by blood transfusion or organ transplantation.
Disease transmission can be prevented with mosquito control and mosquito avoidance measures. Health care professionals should advise patients and families to limit time out of doors, esp. at dusk and dawn, to wear protective clothing (long sleeves, long pants, and socks), to place mosquito netting over infant carriers or strollers, and to apply an FDA-approved insect repellant (e.g., DEET, picaridin, or oil of lemon eucalyptus). Mosquito breeding grounds should be eliminated: standing water should be removed from flower pots, bird baths, pool covers, rain gutters, and discarded tires. Window and door screens should be installed and kept in good repair to prevent mosquitoes from entering homes.
xenotropic murine leukemia virus–related virusAbbreviation: XMRV virus
|RNA||HIV, hepatitis A, polio, measles, mumps, rhinovirus, influenza|
|DNA||Herpesviruses, hepatitis B, adenoviruses, human papilloma viruses, cytomegalovirus|
|Humans||Measles, mumps, rubella, varicella-zoster, poliovirus|
|Humans and animals||Rabies, influenza, hantavirus, encephalitis virus|
|Plants||Tobacco mosaic virus, cowpea mosaic virus|
|Present||Herpesviruses, rabies, HIV|
|Absent||Rotavirus, Norwalk virus, adenovirus|
|Respiratory||Influenza, parainfluenza, hantavirus|
|Teratogenic||Varicella-zoster virus, cytomegalovirus, rubella|
|Neurological and fatal||Rabies|
|Paralytic encephalitic||Polio, many encephalitis viruses|
|Fulminant||Yellow fever, hantavirus, Ebola-Marburg|
|Cancer causing||Human T-cell lymphotrophic virus, hepatitis viruses, papillomavirus|
human immunodeficiency virusAbbreviation: HIV
HIVThe human immunodeficiency virus and the cause of AIDS. HIV binds avidly to CD4 cell surface receptors so its greatest affinity is for helper T cells. It will, however, also infect MACROPHAGES and the microglial cells of the brain, which also have CD4 receptors. HIV is an RNA retrovirus and uses the enzyme reverse transcriptase to convert its RNA into DNA which is then incorporated into the genome of the host cell where it can remain latent for years. The host DNA produces more HIV RNA by transcription and the cell then releases large numbers of new HI viruses which infect other cells. The virus was identified in 1983 by Dr Francoise Barré-Sinoussi (1950–) working at the Pasteur Institute in Paris. Two years later she proved that it was the cause of AIDS. She is now Head of the Retrovirus Biology Unit at the Institute and was awarded one of the French Republic's highest honours-the Chevalier de l'Ordre National de Merité.
HIVhuman immunodeficiency virus which in some individuals gives rise to AIDS. It is a RETROVIRUS, at one time referred to as Aids-associated retrovirus. The association of HIV with AIDS has been known since 1983, and a second related virus was found in West Africa in 1987; these two viruses are now designated HIV 1 and HIV 2 respectively.
Difficulties have occurred in developing an effective anti-HIV vaccine, particularly because of variations in the antigenic viral surface protein. see ANTIGENIC VARIATION. It is thought that HIV was introduced to the human population from chimpanzees. HIV has significant potential in the field of medicine. Once stripped of its lethal elements it is probably capable of delivering genes to tissues in the brain, spinal cord, liver and heart muscle and it is unique in that it is able to insert genes into cells which are not dividing. Techniques are at present being developed, using HIV, to protect transplanted organs such as liver and heart from both infection and rejection by the immune system.
HIV (human immunodeficiency virus)
Patient discussion about HIV
Q. HIV - does it infect specific Blood Types? A friend of mine joined the army and they took him to an experiment and infected him with HIV. But he was not infected- he said because he has a certain blood type. Is this true?
Q. what is HIV? how do i stay a way of it? is there a cure for it?
Q. What are the early symptoms of an HIV infection? Can I define it from other diseases? I heard that there is a sore throat and fever- but that can be anything…anything special?