Endemic foci of tick-borne relapsing fever persist for years even when small mammal populations in the area are sparse. Which property of the soft tick Ornithodoros best explains this maintenance of Borrelia infection in nature?

• A The tick dies shortly after transmitting the spirochaete
• B The spirochaete undergoes sexual reproduction within the tick gut, increasing virulence
• C The tick requires a blood meal at every nymphal moult from a different host species
• D Spirochaetes are passed transovarially to offspring and across all life stages, making the tick itself a reservoir ✓

Explanation

Ornithodoros is long-lived, tolerates prolonged starvation between meals, and transmits Borrelia both transstadially and transovarially, so infected progeny hatch from infected females. Because the spirochaete persists through generations of ticks, the tick population alone can maintain the infection cycle independent of high rodent densities, which explains persistent endemic foci. Option A is wrong because the tick survives feeding and remains infective for years, and option C confuses the biology with hard tick feeding patterns.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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