Introduction to Virology - MIMM 211

Lecture 1: Introduction to Virology

• The lecture is titled "Introduction to Virology" and was presented by Dr. Jasmin Chahal on November 1st, 2024.
• The course is MIMM 211 (Introductory Microbiology).
• Interactive polling will be used (Slido).
• The Slido code is #3031727
• Lecture slides will be posted a day ahead of the lecture
• All the content for the final exam is contained within the lecture slides.
• The lecture will cover: an overview of viruses, virus structure, genomes and classification, genome classification, the infectious cycle, cultivation and detection of viruses, viruses and cancer, and some pathogenic viruses.

Administrative Information (I)

• Email: [email protected]
• Office: Room 408A, Duff Medical Building
• Office hours: By appointment on Calendly (link provided).
• Students should describe any steps they have already taken to answer questions regarding course content or assessments.

Administrative Information (II)

• Previously taught by Dr. Jacques Archambault
• Currently teaching MIMM 324
• Research on Human Papillomaviruses
• Some slides are adapted from his lectures

Resources

• Wellness Hub: mcgill.ca/wellness-hub/ (contact info provided).
• Office for Sexual Violence Response, Support and Education: mcgill.ca/osvrse
• Laptop loaning: mcgill.service-now.com/itportal?id=kb_article&sysparm_article=KB0010885 (Audiovisual Equipment loans, 2 business days' notice).

Viral Evolution/Origin

• No definitive explanation for the origin of viruses exists.
• Viruses might have originated prior to or from cells ( ~ 4 billion years ago).
• Viruses may have arisen during an "RNA world" period, when RNA was the sole genetic carrier.

Why Viruses Appeared?

• Viruses enriched genetic diversity in hosts by facilitating gene transfer.
• Earliest viruses may have coexisted with host cells (later possibly harming them).
• Viruses may have played a crucial role in the RNA to DNA transition.
• Some RNA viruses evolved DNA genomes to protect them from cellular ribonucleases.
• DNA is more stable than RNA.
• Viruses use cellular replication machinery to replicate.

Viruses are Everywhere!

• Viruses occupy nearly all organisms.
• They can live in various habitats (air, ocean).
• They affect bacteria, fungi, animals, plants, and humans.
• They are the most abundant microorganisms.
• There are ~94% of nucleic-acid-containing particles and only ~5% of total biomass.

Climate Change Affecting Pathogenic Diseases

• Climate change might shift geographic ranges of ~3,100 mammal species, also impacting the viruses they carry.
• Increasingly driving encounters between mammal species, risking new diseases.
• In the next 50 years, could drive more than 15,000 new cases of mammals transmitting viruses to other mammals.
• 58% of human infectious diseases have been (at some point) influenced by climatic hazards.

General Characteristics of Viruses (I)

• Viruses are genetic elements that reproduce only inside living cells.
• They're not living organisms and can't independently reproduce.
• They're obligatory intracellular parasites, needing host cells for energy and metabolic intermediates.

General Characteristics of Viruses (II)

• Viruses have an extracellular state (virion), containing a protein coat (capsid) surrounding nucleic acid.
• Some viruses have a phospholipid envelope (nucleocapsid).
• Some may contain glycoproteins as projections.
• These projections allow the virus to recognize and bind to host receptors/cells.

Discovery of Viruses

• The term "virus" (poison) was coined in the late 1800s.
• In 1886, Adolf Mayer's work showed that tobacco mosaic disease was transmissible.
• In 1892, Dimitri Iwanowski filtered sap from diseased plants, finding the infectious agent passed through filters that retained bacteria.
• In 1946, Wendell Stanley received a Nobel Prize for isolating, characterizing and crystallizing TMV.
• In 1957, Sarah Stewart connected some viruses to cancer development.

Giant Viruses

• Mimivirus (2003), a "mimicking microbe" was discovered.
• Mimiviruses were initially mistaken for bacteria, but their large capsid (~400 nm ) and protein filaments containing ~100nm, distinguishable them.
• These viruses have a large DNA genome (~1000 genes).
• Called Nucleocytoplasmic Large DNA viruses (NLDV) and can replicate inside the host's nucleus and cytoplasm.

Giant Viruses Challenging Evolution

• Giant viruses infect eukaryotic unicellular organisms like amoebas.
• Their genomes are diverse and complex
• Some genes in giant viruses may have originated from bacteria, archaea, or other viruses.

Giant Viruses Have Their Own Viral Parasites

• Virophages are small DNA viruses that replicate only in cells already co-infected with giant viruses
• Sputnik (discovered virophage), replicates in Mimivirus-infected amoebas, reducing replication of Mimiviruses by ~70%.
• Virophages may improve the host cell survival by preventing cell lysis by giant viruses.

Are All Viruses Bad?

• Most viruses aren't pathogenic; they're crucial elements in many ecosystems and regulate population diversity and evolution.
• Viruses that infect bacteria (bacteriophages/phages) can be used in phage therapy.

Most Viruses Are Not Pathogenic

• Biologists estimate trillions of viruses in and on our bodies (10x bacteria).
• While some cause illness, most don't.
• They play an essential ecological role in controlling bacterial populations.

This quiz covers the key concepts from Lecture 1 of MIMM 211, focusing on the fundamental aspects of virology. You will explore virus structure, classification, the infectious cycle, and the relationship between viruses and cancer. Prepare to delve into various pathogenic viruses as well.