Virus - an infectious PATHOGEN that must invade a host cell to replicate, technically called an obligate intracellular PARASITE. A virus is a particle of living material that contains an inner core of nucleic acid (DNA or RNA), called the genome, encased in an outer shell of protein, called a capsid. Some viruses contain a third layer composed of lipids, called an envelope, that further protects and nourishes the virus. These components, collectively called a virion, cannot themselves support a full life cycle, which obligates the virus to find a host to maintain its survival. A virus can attach only to the type of cell capable of supporting it, binding to specific protein molecules on the surface of the cell membrane.
ANTIBIOTIC MEDICATIONS are not effective in treating illnesses that result from viral infections, such as COLDS and INFLUENZA.
|COMMON VIRUSES AND THE ILLNESSES THEY CAUSE|
|Virus or Viral Family||Genetic Configuration||Illness|
|ADENOVIRUS||DNA||PHARYNGITIS, PNEUMONIA, acute respiratory disease, cervicitis, URETHRITIS, CYSTITIS, GASTROENTERITIS|
|CYTOMEGALOVIRUS (CMV)||DNA||CMV INFECTION|
|EPSTEIN-BARR VIRUS||DNA||infectious mononucleosis, Burkitt’s lymphoma, Hodgkin’s lymphoma|
|HEPATITIS A virus (HAV), hepatitis C virus (HBV)||RNA||HEPATITIS|
|HERPES SIMPLEX virus 1 (HSV-1)||DNA||COLD SORE|
|herpes simplex virus 2 (HSV-2)||DNA||GENITAL HERPES|
|human herpesvirus 8 (HHV-8)||DNA||KAPOSI’S SARCOMA|
|human immunodeficiency virus 1 (HIV-1),
human immunodeficiency virus 2 (HIV-2)
|human papillomavirus (HPV)||DNA||genital WARTS, CERVICAL CANCER, vaginal cancer|
|human parainfluenza viruses||RNA||acute upper respiratory disease, CROUP, bronchiolitis, BRONCHITIS, pneumonia|
|INFLUENZA viruses||RNA||influenza (flu)|
|Norwalk-like viruses||RNA||acute gastroenteritis|
|respiratory syncytial virus||RNA||bronchiolitis, pneumonia, acute upper respiratory disease|
|RUBELLA virus||RNA||rubella (German or three-day measles)|
|varicella-zoster||DNA||CHICKENPOX, HERPES ZOSTER (shingles)|
After invading a host cell, a virus hijacks the cell’s structures and functions to serve its own needs and to replicate itself. DNA viruses produce proteins that the host cell’s RNA transcribe as instructions to replicate the virus’s DNA, which the cell does. DNA contains the instructions for the cell’s functions; RNA forms the messenger proteins that carry out the directives of the DNA. Eventually the virus’s copies of DNA crowd out the cell’s copies of DNA, and the cell becomes the agent of the virus. The cell either divides or ruptures, spreading the virus. RNA viruses achieve a similar result by causing the host cell to replicate their RNA, which then replaces the cell’s RNA. Retroviruses are RNA viruses that contain the enzyme reverse transcriptase, which allows RNA to instruct DNA (the reverse of normal).
Viruses are highly adaptable and have numerous mechanisms to hide from the IMMUNE SYSTEM, allowing them to become well established infections before the immune system detects their presence. Once the immune system does detect a virus, it develops antibodies that protect against subsequent infection by the same virus. Many common viruses-such as those that are responsible for COLDS (rhinoviruses), GASTROENTERITIS (enteroviruses), and the flu (INFLUENZA viruses)- frequently alter their structures, evolving into different strains that can cause the same illnesses. Some viruses, such as human T-lymphotropic virus (HTLV) and HUMAN PAPILLOMAVIRUS (HPV), cause cancer (oncoviruses). The human immunodeficiency virus (HIV) is a retrovirus that attacks the immune system, causing AIDS (acquired immunodeficiency syndrome).
Resource: Facts On File Encyclopedia Of Health And Medicine
What is a virus - definition Virus - an infectious PATHOGEN that must invade a host cell to replicate, technically called an obligate intracellular PARASITE. A virus is a particle of living material that contains an inner core of nucleic acid (DNA or RNA), called the genome, encased in an outer shell of protein, called a capsid. Some viruses contain a
A VIRUS family that causes INFECTION of mucous membrane tissues throughout the body. Adenoviruses are responsible for a wide range of illness including upper respiratory infection, viral CONJUNCTIVITIS, GASTROENTERITIS, and URINARY TRACT INFECTION (UTI). These infections primarily affect children age 10 and younger. Infection with one adenovirus confers
A parasitic INFECTION of the gastrointestinal tract. The PARASITE responsible is Entamoeba histolytica, a single-cell organism (an ameba) that enters the body by drinking water or eating food that contains E. histolytica in cyst form. The cyst is a protective encasing within which the ameba may sustain itself in a dormant stage for weeks to months outside a
Antibiotic medications - Drugs that kill BACTERIA and certain other microorganisms. Antibiotic medications are the mainstay of treatment for bacterial INFECTION. Broad-spectrum antibiotics are capable of killing numerous types of bacteria; narrowspectrum antibiotics kill specific types or strains of bacteria. There are seven primary classifications of
Drugs that kill fungi (yeast). Antifungal medications are available for topical or systemic treatment. Some fungal infections require both. Antifungal medications work through various mechanisms to interfere with the ability of fungi to survive or reproduce. Broadspectrum antifungal medications are effective for treating a variety of fungal infections;
Antiviral medications - medications to shorten the course and lessen the severity of illness due to viral INFECTION as well as reduce viral shedding to minimize contagiousness. Some antiviral medications are able to prevent viral infection from developing after exposure to the VIRUS. Antiviral medications mark a fine line because they must destroy viruses
Anthrax (disease) - an illness resulting from INFECTION with the bacterium Bacillus anthracis. Anthrax is a naturally occurring infection among wild and domestic livestock (such as cows, sheep, goats, and antelope). Anthrax is rare in people in the United States, though more common in people who live, work, or travel to countries where anthrax is more
An illness that results from INFECTION with the parasitic protozoan Babesia microti. Most people who have babesiosis do not have symptoms; the infection causes illness primarily in people who are IMMUNOCOMPROMISED or who have had SPLENECTOMY (surgical removal of the SPLEEN). The bite of the Ixodes tick, found in the northeastern United States, is the mode
What is bacteria and definition of bacteria Bacteria - single-cell microorganisms (microbes). Bacteria are the most ancient and primitive life forms known, with fossils dating back more than 3 billion years. A bacterium’s structure is very simple, consisting of a rigid cell wall that supports and contains the cytoplasm, fragments of RNA, and a single
What is Botulism Botulism is a potentially life-threatening illness resulting from INFECTION with the anaerobic bacterium Clostridium botulinum. The BACTERIA are naturally present in soil, where they encase themselves in spores. In the body, the bacteria release a toxin that blocks the release of acetylcholine, a NEUROTRANSMITTER that facilitates NERVE