Which is a vector of Rocky Mountain Spotted Fever (RMSF)?

NORCET 5 Prelims - Sept 2023 (Shift-2)

Microbiology

Easy

Appeared in: NORCET 5 Prelims - Sept 2023 (Shift-2)

Explanation

Rocky Mountain Spotted Fever (RMSF) is a potentially fatal tick-borne disease caused by the bacterium Rickettsia rickettsii.
The primary mode of transmission to humans is through the bite of an infected hard-bodied tick (family Ixodidae).
Key vectors in North America include the American dog tick (Dermacentor variabilis) and the Rocky Mountain wood tick (Dermacentor andersoni).
Hard ticks are distinguished by a hard shield-like plate called a scutum on their back, which is absent in soft ticks.

Option B: The rat flea (Xenopsylla cheopis) is the classic vector for murine (endemic) typhus, caused by Rickettsia typhi, and bubonic plague, caused by Yersinia pestis. It does not transmit RMSF.
Option C: Soft ticks (family Argasidae) lack the hard scutum of hard ticks. While they are vectors for other diseases, such as tick-borne relapsing fever (caused by Borrelia species), they are not the primary vectors for RMSF.
Option D: Mites are vectors for other rickettsial diseases, notably rickettsialpox (caused by Rickettsia akari) and scrub typhus (caused by Orientia tsutsugamushi). They are not involved in the transmission of RMSF.

Visual 1: Infographic - A chart comparing different rickettsial diseases, their causative agents, and their specific arthropod vectors (tick, flea, mite, louse).
Visual 2: Image - A side-by-side comparison of a hard tick (showing the scutum) and a soft tick to highlight the physical difference.
Visual 3: Map - A map of North America showing the geographic distribution of the American dog tick and the Rocky Mountain wood tick, highlighting areas with high incidence of RMSF.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Vector-borne transmission of Rocky Mountain Spotted Fever (RMSF) as background academic context rather than a clinical decision trigger.
Nurses play a vital role in patient education regarding tick-bite prevention, especially for individuals living in or traveling to endemic areas. This includes advising on the use of insect repellents, wearing protective clothing, and performing thorough tick checks after outdoor activities.
Proper tick removal is a critical nursing intervention to teach patients. Using fine-tipped tweezers to grasp the tick close to the skin's surface and pulling upward with steady, even pressure helps prevent the mouth-parts from breaking off in the skin.
Early recognition of RMSF symptoms (fever, headache, rash starting on wrists and ankles) is crucial. A nurse's prompt assessment and reporting can lead to timely administration of doxycycline, which is most effective when started within the first few days of illness and can be life-saving.

How to Approach the Question

First, identify the key terms in the question: 'vector' and 'Rocky Mountain Spotted Fever (RMSF)'. This establishes that the question is asking for the specific arthropod that transmits this particular disease.
This is a factual recall question. Access your knowledge of microbiology and infectious diseases, specifically focusing on common vector-borne illnesses.
Systematically evaluate each option. Consider what diseases are typically associated with each arthropod.
Recall or deduce that 'tick' is the correct category. Then, differentiate between 'Hard tick' and 'Soft tick'. RMSF is classically associated with specific hard tick species.
Eliminate the other options by linking them to the diseases they are known to transmit: Rat Flea with typhus/plague and Mite with rickettsialpox/scrub typhus.
Select 'Hard tick' as the most precise and correct answer based on established medical knowledge.

Concept Tested & Keywords

Concept Tested: Vector-borne transmission of Rocky Mountain Spotted Fever (RMSF)
Stem keywords: vector, Rocky Mountain Spotted Fever, RMSF
Lead-in keywords: Which is

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