Question:
Which of the following is the carrying agent (vector) for the disease with the given characteristic on polarized microscopy?
Which of the following is the carrying agent (vector) for the disease with the given characteristic on polarized microscopy?
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The Maltese-cross tetrad inside RBCs means babesiosis - which arthropod transmits it?
Updated On: Jun 23, 2026
- Anopheles
- Ixodes scapularis ticks
- Louse
- Rat flea
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The Correct Option is B
Solution and Explanation
Step 1: The microscopy shows the Maltese cross, a tetrad of four intraerythrocytic parasites whose pointed ends meet, which is pathognomonic of babesiosis. Babesia infects and resides inside red blood cells (intraerythrocytic).
Step 2: Babesiosis is transmitted by Ixodes scapularis ticks (the same vector as Lyme disease), so the carrying agent is the Ixodes tick.
Step 3: Babesiosis is easily confused with Plasmodium falciparum malaria, but two features distinguish it: the Maltese cross is present in babesiosis and absent in malaria, and the malarial pigment haemozoin is absent in babesiosis but present in malaria. This is why recognising the tetrad is key.
Step 4: Why the distractors are wrong: Anopheles transmits malaria, the louse transmits epidemic typhus, relapsing fever and trench fever, and the rat flea (Xenopsylla) transmits plague and endemic typhus. None of these carries Babesia. The vector is Ixodes scapularis. (Note: a Maltese-cross appearance can also be seen with Cryptococcus and Aspergillus, but those are fungi, not RBC parasites.)
Step 2: Babesiosis is transmitted by Ixodes scapularis ticks (the same vector as Lyme disease), so the carrying agent is the Ixodes tick.
Step 3: Babesiosis is easily confused with Plasmodium falciparum malaria, but two features distinguish it: the Maltese cross is present in babesiosis and absent in malaria, and the malarial pigment haemozoin is absent in babesiosis but present in malaria. This is why recognising the tetrad is key.
Step 4: Why the distractors are wrong: Anopheles transmits malaria, the louse transmits epidemic typhus, relapsing fever and trench fever, and the rat flea (Xenopsylla) transmits plague and endemic typhus. None of these carries Babesia. The vector is Ixodes scapularis. (Note: a Maltese-cross appearance can also be seen with Cryptococcus and Aspergillus, but those are fungi, not RBC parasites.)
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