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A viral disease (or viral infection) occurs when an organism's body is invaded by pathogenic viruses, and infectious virus particles (virions) attach to and enter susceptible cells. [ 1] Examples are the common cold, gastroenteritis and pneumonia. [ 2]
Such viruses are called attenuated. Live vaccines can be dangerous when given to people with a weak immunity (who are described as immunocompromised), because in these people, the weakened virus can cause the original disease. [166] Biotechnology and genetic engineering techniques are used to produce subunit vaccines.
Virus classification. Virus classification is the process of naming viruses and placing them into a taxonomic system similar to the classification systems used for cellular organisms . Viruses are classified by phenotypic characteristics, such as genderlogy, nucleic acid type, mode of replication, host organisms, and the type of disease they cause.
Visna-maedi virus. The human immunodeficiency viruses ( HIV) are two species of Lentivirus (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), [ 1][ 2] a condition in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive. [ 3]
The specimen came to be known as the Beaudette strain. In the late 1940s, two more animal coronaviruses, JHM that causes brain disease (murine encephalitis) and mouse hepatitis virus (MHV) that causes hepatitis in mice were discovered. [19] It was not realized at the time that these three different viruses were related. [20] [12]
Poliomyelitis (/ ˌ p oʊ l i oʊ ˌ m aɪ ə ˈ l aɪ t ɪ s / POH-lee-oh-MY-ə-LY-tiss), commonly shortened to polio, is an infectious disease caused by the poliovirus. [1] Approximately 75% of cases are asymptomatic; [5] mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe symptoms develop such as headache, neck stiffness, and paresthesia.
Symptoms, when they occur, may include watery blisters in the skin of any location of the body, or in mucous membranes of the mouth, lips, nose, genitals, [ 1 ] or eyes ( herpes simplex keratitis ). [ 7 ] Lesions heal with a scab characteristic of herpetic disease. Sometimes, the viruses cause mild or atypical symptoms during outbreaks.
Co-infection of these two viruses can cause a more severe liver disease and increase the risk for primary liver cancer (Hepatocellular Carcinoma). Reporting of this co-infection may be underreported due to hepatitis C's ability to become the dominant liver virus during coinfection, reducing the detectable amount of HBV found in the body. [ 81 ]