Picornaviridae (+)

Picornaviridae (+) Features: 1. RNA virus 2. Positive sense a. Structure similar to host mRNA b. Uses host RNA polymerase to replicate i. All RNA viruses replicate in cytoplasm (except orthomyxovirus) 3. Naked virus 4. Acid stable a. Except Rhinovirus which is acid labile 5. Divided into: a. Hepatitis A b. Rhinovirus c. Enterovirus i. Coxsachie A and B ii. Polio virus iii. Echovirus Transmission: Fecal oral route (except Rhinovirus which has respiratory transmission) Pathogenesis: Viral RNA is translated into a long polyprotein product which is inactive. It is activated when uncleaved by viral proteases. Specific details of all the subtypes are given below: Hep Hepatiti atiti atitiss A: Refer to general picornavirus overview for features. Unique features are given below: 1. 2. 3. 4. Often occurs in traveler’s going to endemic areas The duration of symptoms is usually one month It is self-limiting It has no carrier/chronic state Smokers with Hepatitis A develop an aversion to smoking Transmission: 1. Fecal oral route (in developing countries) 2. Uncooked contaminated shellfish (in USA) Diseases: 1. Anicteric Hepatitis a. Clinically silent b. No jaundice c. Often observed in young children and infants 2. Acute Viral Hepatitis a. Fever b. Jaundice c. Hepatomegaly Prevention: Inactivated vaccine Rhi Rhinovir novir novirus: us: Refer to general overview for common features. Unique features are given below: 1. Acid labile 2. Grows best in cooler temperature (33oC) 3. A lot of different serotypes Transmission: 1. Inhalation 2. Fomites Pathogenesis: Rhinovirus enters the body by attaching to ICAM-1 Disease: Common cold (upper respiratory tract infection) Hepatitis A can be inactivated in contaminated water by following techniques: 1. 2. 3. 4. Chlorination Bleaching UV Radiation Boiling (85oC for 1 minutes) En Entero tero teroviru viru virus: s: Refer to general overview for common features. Enterovirus Polio virus Coxsachie A and B Echovirus Enteroviruses are the #1 cause of aseptic meningitis. Children are mostly affected. Septic meningitis is due to bacteria. The difference between the two can be found by CSF findings. The CSF findings in viral (aseptic) meningitis are: 1. Normal glucose levels 2. No organisms are found 3. High protein content Polio Virus: Refer to general overview for common features. Pathogenesis: 1. Initially enters GIT and starts replicating in lymphoid tissues namely: a. Tonsil b. Peyer’s patches 2. Later, it moves into the anterior horns of lower motor neuron cell bodies a. Leads to paralysis Diseases: 1. Asymmetric Paralysis a. Concentrated in lower legs 2. Respiratory insufficiency a. Paralysis of diaphragm 3. Myalgia 4. Decreased tendon reflexes 5. Aseptic meningitis Prevention: 1. No treatment available 2. Vaccines a. Salk (killed vaccine; parenteral administration) i. Only forms IgG antibodies 1. Because it bypasses GIT b. Sabin (live vaccine; oral administration) i. Forms both IgG and IgA antibodies ii. Can be shed in feces and cause polio in another person Coxsachie A: 1. Infection common in summer time 2. Red vesicular rash occurring on a. Hand b. Foot c. Mouth 3. Aseptic meningitis Coxsachie B: 1. Dilated cardiomyopathy 2. Devil’s grip a. Also called Bornholm’s disease or Pleurodynia b. Characterized by extreme sharp pain in lower chest c. Often unilateral d. Difficulty in breathing Treatment: Treatment for both is supportive.