Question

Arrange the following stages in sequential order of their development during the life cycle of Plasmodium gallinaeceum in domestic fowl:
A. Phanerozoites
B. Metacryptozoites
C. Cryptozoites
D. Gametocytes
Choose the correct answer from the options given below:

• A. A, B, C, D
• B. C, B, A, D
• C. C, B, D, A
• D. A, C, B, D

Hint:

To remember this sequence, use the alphabetical mnemonic: Cryptozoites (1st tissue stage) $\rightarrow$ Metacryptozoites (later tissue stages) $\rightarrow$ Phanerozoites (late endothelial stages) $\rightarrow$ Gametocytes (final blood stages).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Plasmodium gallinaceum is the causative agent of avian malaria in poultry.
Its life cycle involves an asexual phase (schizogony) in the avian host and a sexual phase (sporogony) in the mosquito vector.
In the avian host, the parasite undergoes a series of tissue-dwelling exoerythrocytic stages before invading red blood cells to produce erythrocytic stages and gametocytes.

Step 2: Detailed Explanation:
Let us trace the development of the parasite inside the avian host from inoculation onward:
1. Cryptozoites (C):
When an infected mosquito bites a bird, it inoculates sporozoites into the skin.
These sporozoites enter cells of the reticuloendothelial system (macrophages and fibroblasts).
Inside these tissue cells, they undergo the first generation of exoerythrocytic schizogony, forming cryptozoites.
2. Metacryptozoites (B):
Merozoites released from the ruptured cryptozoites infect new reticuloendothelial cells to undergo subsequent generations of tissue schizogony.
These second and subsequent generations of tissue-dwelling stages are called metacryptozoites.
3. Phanerozoites (A):
As the infection progresses, some merozoites invade endothelial cells lining the blood capillaries of various organs, especially the brain.
These late-occurring endothelial schizonts are termed phanerozoites.
They can block brain capillaries, leading to cerebral damage and mortality.
4. Gametocytes (D):
Eventually, merozoites released from these tissue phases invade red blood cells.
Inside the erythrocytes, they undergo erythrocytic schizogony or differentiate into the sexual stages, gametocytes (macrogametocytes and microgametocytes), which circulate in the blood waiting to be ingested by a mosquito.
Thus, the correct developmental sequence is:
Cryptozoites (C) $\rightarrow$ Metacryptozoites (B) $\rightarrow$ Phanerozoites (A) $\rightarrow$ Gametocytes (D).
This corresponds to the sequence: C, B, A, D.

Step 3: Final Answer:
The sequential order of development in the avian host is C, B, A, D.
Therefore, the correct answer is option (B).