Which mechanism explains how Xenopsylla cheopis efficiently transmits Yersinia pestis to humans during bubonic plague?

• A The bacillus is inoculated directly through the salivary glands during probing
• B Multiplying bacilli form a mass in the proventriculus, and the blocked flea regurgitates organisms during repeated feeding attempts ✓
• C The flea contaminates the bite site with faeces containing the bacillus
• D Crushing the flea into the bite wound releases organisms from its haemolymph

Explanation

Yersinia pestis multiplies in the foregut of the flea and forms a gelatinous mass that blocks the proventriculus. Such a 'blocked' flea becomes starved, bites repeatedly, and due to the obstruction, blood mixed with bacteria is regurgitated back into the wound. This classic blockage model is central to plague epidemiology. Faecal contamination is the route in rickettsial transmission by lice and fleas, not in plague, and direct salivary gland inoculation characterises viruses such as yellow fever rather than plague.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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