Concept:
In modern microbiology, certain infectious conditions are initiated by agents that do not fit into the standard categories of bacteria, fungi, or viruses. These sub-viral pathogens consist either of naked genetic material or completely protein-based structures capable of altering host cellular proteins.
Step 1: Understand the nature of Prions
Prions are abnormally folded, infectious proteins that lack any type of nucleic acid (neither DNA nor RNA). They cause progressive neurodegenerative disorders by interacting with normal cellular proteins in the central nervous system, forcing them to misfold into the same pathogenic configuration. This accumulation causes brain tissue to develop microscopic vacuoles, giving it a sponge-like appearance under a microscope.
Step 2: Link Prions to Mad Cow Disease
In cattle, this specific spongiform encephalopathy is clinically called Bovine Spongiform Encephalopathy (BSE), commonly recognized by its popular name,
Mad cow disease.
The human analog variant of this prion-mediated neurological disease is known as Cr-Jacob disease (CJD). Hence, prions are the causative agents of Mad cow disease.
Step 3: Analyze and eliminate other options
• Option (1) Mycoplasma sp.: These are cell-wall-less prokaryotic bacteria known to cause atypical pneumonia in humans and pleuropneumonia in animals, not spongiform encephalopathies.
• Option (3) Viroids: Discovered by T.O. Diener, these are infectious agents composed purely of a low-molecular-weight free RNA strand without a protein coat. They primarily target plants, causing diseases like Potato spindle tuber disease.
• Option (4) Aspergillus sp.: This is a genus of filamentous fungi responsible for respiratory fungal infections like aspergillosis or producing aflatoxins, completely unrelated to BSE.
This firmly establishes option (2) as the correct choice.
