Viruses, viroids, and prions are acellular infectious agents that are smaller and less complex than cells. Viruses contain nucleic acids enclosed in a protein coat, while viroids are even smaller RNA particles without a protein coat. Prions are the simplest infectious particles and are associated with brain diseases in animals. Many human diseases are caused by viruses, and viruses outside of cells cannot grow or replicate on their own. Viroids infect only plant tissues and cause crop damage, while prions cause brain diseases in animals and can transmit between animals or through meat consumption.

1. ACELLULAR INFECTIOUS AGENTS

2. Acellular infectious agents entities exist as smaller
and less complex in structure but affect our lives.
Viruses - are infectious agents made up of nucleic acids
(DNA or RNA) that are enclosed within a protein coat
called capsid.
Viroids – are infectious RNA particles with sizes even
smaller than viruses, viroids are not closed by a
protein coat.
Prions – are the simplest form of acellular infectious
particles.

3. VIRUSES

4. • A virus found outside aa cell is called virion, an inert
particle that cannot grow, cannot move, cannot replicate
on its own and cannot undergo biosynthetic or
biochemical activity.
• A number of human diseases are caused by viruses
including polio (polio virus), small pox (small pox virus),
hepatitis (hepatitis virus), dengue (dengue virus), AIDS
and many other viral diseases. Most of this diseases have
no cure or would require a vaccine to prevent them from
harming us.

5. • The different identified viroids infect only plant tissues
causing crop damages. Characterized viroids include
those that cause spindle tuber disease in potatoes, viroids
that cause the stunning growth of chrysanthemum plants.
• Viroids that cause cucumber pale fruit disease, and the
viroids that cause cadang-cadang disease in coconut
trees that almost wiped out of the Philippine coconut
industry.
• It s said that prions do not exist inside our bodies
although their function is not well understood.

6. VIROIDS

7. • Prions are identified as the main cause of several brain
diseases in animals including mad cow disease in cattle;
scrapie disease in sheep and goats.
• All diseases associated with prions cause changes n brain
tissues to results to its spongy appearance. Infected
animals exhibit abnormal behavior that may later lead to
death.
• Recent studies indicate that prions can be transmitted
from one animal to another or through the consumption
of prion-infected meat.

8. PRIONS