Viral Ifections
Viruses, Viroids, And Prions |
||||
Latent Viral Infections
Many viruses, especially the human herpesviruses, can remain in host cells throughout life without causing disease. They may be reactivated by immunosuppression, however, and cause disease.
Examples:
Cold sores
Shingles
Persistent Viral Infections
Persistant viral infections (formerly termed slow viral infections) are progressive over a long period of time and are usually fatal.
Persistant viral infections are different from latent viral infections in that the detectable virus builds slowly over a long period of time rather than appearing suddenly.
Examples:
Subacute sclerosing panencephalitis (Measles virus)
Progressive encephalitis (Rubella virus)
Progressive multifocal leukoencephalopathy (Papovavirus)
AIDS dementia comples (HIV)
Persistant enterovirus infection (Echoviruses)
Progressive pneumonia (retrovirus)
Prions
Prions are infectious proteins.
Insoluble aggregates of protein with normal primary sequence but exhibit altered folding pattern.
The normal protein (PrPc) is coded for by a gene on chromosome 20.
The abnormal form (PrPSc) is found in disease states.
Abnormally-folded proteins (PrPsc) cause normal proteins to assume the pathogenic conformation.
The diseases are spongiform encephalopathies that cause large vacuoles to appear in the brain.
Diseases:
Scrapie (sheep)
Transmissible mink encephalopathy
Bovine spongiform encephalitis (mad cow disease)
Kuru – New Guinea, contracted by eating infected brain tissue (cannabilism was a mourning rite among members of this particular tribe between about 1920 and 1950)
Creutzfeldt-Jakob disease (CJD) is very similar and has a heritable form and may be passed by contact (neurosurgery, corneal transplants, pituitary-derived GH preparations)
Gerstmann-Straussler-Scheinker syndrome (GSS) similar, inherited
Plant Viruses and Viroids
Examples:
Chrysanthemum stunt disease
Citrus excortis disease
Coconut cadang-cadang
Cherry chloratic mottle
Cucumber pale fruit disease
Viroids are naked (lacking a protein coat) pieces of RNA that can cause some plant diseases. They are internally base paired, so they assume a folded conformation that protects them from enzymatic degradation.
Viroids don't code for proteins and research indicates that they have similarities to introns, which suggests researchers may discover animal viroids in the future.
Example:
Potato spindle tuber viroids
Diseases With Possible Viral/Prion Etiology
Alzheimer’s senile dementia
Multiple sclerosis
Parkinson’s disease
Amyotrophic lateral sclerosis
Diabetes mellitus
Rheumatoid arthritis
Hepatitis
Lupus erythematosus
Some neoplastic diseases
Swine Flu, anyone? Or how about some avian flu?
