Question
30 years male admitted in hospital with h/o high grade fever, head ache, nasal discharge and cough and breathing difficulty. Answer the following.
- (a) Name the main group of viruses causing respiratory infections 2 mark(s)
- (b) Classify this group of viruses and describe the morphology and antigenic 2 mark(s)
- (c) What is antigenic drift and shift. Briefly describe 3 mark(s)
- (d) How do you confirm the diagnosis 2 mark(s)
- (e) Name two drugs used for treatment 1 mark(s)
Answer
a) Main group of viruses causing respiratory infections: Orthomyxoviruses — specifically Influenza viruses (A, B, C) — a leading cause of acute febrile respiratory illness, particularly relevant given this patient’s fever, nasal discharge, cough, and breathing difficulty. (Other respiratory virus families include Paramyxoviridae — RSV, parainfluenza; Coronaviridae; Rhinovirus/Picornaviridae; Adenovirus — but influenza is the classical answer given the specific antigenic-shift/drift context of the question.)
b) Classification, morphology, and antigenicity Influenza virus (family Orthomyxoviridae) is a spherical to pleomorphic, enveloped, single-stranded, negative-sense, segmented RNA virus (8 gene segments for types A/B). Types: A, B, and C (and D), distinguished by antigenic differences in internal nucleoprotein/matrix protein; type A is further subtyped by its surface antigens. Morphology: an outer lipid envelope studded with two glycoprotein spikes — haemagglutinin (HA), mediating attachment to host sialic acid receptors, and neuraminidase (NA), facilitating release of progeny virions; beneath the envelope, the matrix (M1) protein; internally, a helical nucleocapsid with each RNA segment individually encapsidated by nucleoprotein and associated RNA polymerase. Antigenicity: HA and NA are the major antigens, targets of neutralizing antibody and the basis of strain nomenclature (e.g., H1N1, H3N2); influenza A has 18 HA and 11 NA subtypes recognized.
c) Antigenic drift and shift Antigenic drift — gradual, minor accumulation of point mutations in the HA/NA genes (due to the error-prone viral RNA polymerase), occurring in both influenza A and B; responsible for seasonal epidemics and the need for annual vaccine reformulation. Antigenic shift — a major, abrupt change in HA/NA through genetic reassortment (exchange of whole gene segments between two different strains co-infecting the same cell, e.g., in a pig “mixing vessel”), occurring only in influenza A (requiring an animal reservoir); produces a completely novel HA/NA combination against which the population has little immunity, capable of causing a pandemic.
d) Confirmation of diagnosis: RT-PCR (rapid, sensitive, now the standard); rapid antigen detection tests (point-of-care, less sensitive); viral culture with haemadsorption/CPE (traditional method, now largely research/reference use); serology (rise in antibody titre, retrospective).
e) Two drugs used for treatment: Oseltamivir and Zanamivir (neuraminidase inhibitors) — administered early in illness to reduce duration/severity of symptoms.