An epidemiologist investigating an outbreak of epidemic typhus among displaced persons notes that Rickettsia prowazekii is transmitted by the body louse. Which biological behaviour of the infected louse best explains the explosive spread of the disease in crowded populations?

• A The louse injects rickettsiae directly with its saliva during biting
• B The louse transmits the rickettsiae transovarially to its offspring
• C The louse defecates while feeding, contaminating the bite wound
• D The louse leaves the febrile or dead host to seek a new host ✓

Explanation

Rickettsia prowazekii multiplies in the gut of the body louse and kills it within about two weeks. Infected lice leave a febrile or dying host and move rapidly to new hosts in crowded, unhygienic settings, which drives explosive epidemics. Transmission occurs when infective louse faeces are scratched into skin or mucosa, not via saliva, so option A is wrong. Lice do not transmit Prowazekii transovarially, unlike ticks in rickettsial spotted fevers.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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