Question
Read the following clinical history and answer the following questions A one year old child presented with h/o inability to move the limbs associated with neck stiffness following a bout of fever. Immunization history was not available. O/E the child had flaccid paralysis.
- (a) What is the probable clinical diagnosis and name the etiologic agent 2 mark(s)
- (b) Describe the pathogenesis of the disease . 3 mark(s)
- (c) How it is diagnosed in the lab and mention the prophylaxis available 5 mark(s)
Answer
a) Probable clinical diagnosis and etiologic agent: Poliomyelitis — acute flaccid paralysis following a febrile illness, with neck stiffness, in an unimmunized/incompletely immunized young child is classical. Etiologic agent: poliovirus (an enterovirus, family Picornaviridae; serotypes 1, 2, or 3).
b) Pathogenesis Poliovirus is transmitted by the faecal-oral route; after ingestion, it replicates initially in the oropharyngeal and intestinal lymphoid tissue (tonsils, Peyer’s patches), then spreads to regional lymph nodes and into the bloodstream (minor viraemia), producing a non-specific febrile illness in most infected individuals (the majority of infections are subclinical or cause only this minor illness). In a small proportion of cases, the virus undergoes a major viraemia and crosses into the CNS, where it shows a striking tropism for the anterior horn motor neurons of the spinal cord (and sometimes brainstem motor nuclei — bulbar poliomyelitis). Viral replication within and destruction of these motor neurons produces the characteristic lower motor neuron, asymmetric, flaccid paralysis — since sensory neurons are spared, sensation remains intact despite the paralysis, an important distinguishing clinical feature.
c) Laboratory diagnosis and prophylaxis Laboratory diagnosis:
- Virus isolation — from stool (the most reliable and standard specimen, given prolonged faecal shedding) and, less reliably, throat swab/CSF, inoculated onto susceptible cell culture lines, with identification by characteristic cytopathic effect and neutralization with type-specific antisera.
- RT-PCR — for rapid detection and genomic sequencing (distinguishing wild-type from vaccine-derived strains, important for surveillance).
- Serology — demonstration of a rising neutralizing antibody titre in paired sera; less commonly used now given the sensitivity of virus isolation/PCR.
- CSF typically shows a lymphocytic pleocytosis with normal/mildly raised protein and normal glucose (viral meningitis pattern).
Prophylaxis:
- Oral Polio Vaccine (OPV) — live attenuated trivalent (or now, with wild poliovirus type 2 eradicated, bivalent) vaccine, inducing both systemic (IgG) and local intestinal mucosal (secretory IgA) immunity, important for interrupting faecal-oral transmission; the mainstay of global polio eradication campaigns given its ease of administration and ability to induce herd/community immunity via contact spread of the vaccine strain.
- Inactivated Polio Vaccine (IPV) — killed vaccine, given by injection, inducing systemic immunity without the (very rare) risk of vaccine-associated paralytic poliomyelitis seen with OPV; increasingly incorporated into national schedules, often alongside or replacing OPV as countries approach/achieve polio-free status.