02_2025S_MICR490_Intro to viruses
Definition of Viruses
Obligate parasites needing host cell machinery for reproduction.
Spread through infectious particles (virions).
Microscopic agents with RNA or DNA genomes surrounded by protective coats.
Mechanism of Viral Action
Entry into a host cell leads to the viral genome directing the synthesis of viral components through host cell systems.
Progeny virus particles assemble within the infected cell.
Viral Presence
Viruses' ubiquity in nature: 10^{15} viruses associated with the human body; 10^{30} in oceans, and significant excretion rates by infected animals.
Viruses in Living Organisms
Viruses can infect a variety of hosts including humans, animals, plants, etc.
They can cause significant economic and social impacts by affecting agriculture.
Human Diseases Caused by Viruses
Examples include COVID-19, smallpox, yellow fever, and more significant global health concerns.
Viruses account for approximately 15% of the cancer burden in humans.
Benefits of Viruses
Viruses play crucial roles in biogeochemical cycles and maintaining microbiome homeostasis.
Certain viral infections could mitigate the pathogenesis of other virus infections or bacterial pathogens.
Endogenous Retroviral DNA
Approximately 8% of the human genome is derived from endogenous retroviruses, influencing evolutionary biology.
Retroviral proteins contribute to essential reproductive processes like cell fusion in placentation.
Cross-Species Infection
Viruses may cross species barriers, leading to zoonotic diseases.
The rise in human populations and expansion into wilderness increases the frequency of such infections.
Historical Context of Viral Infections
Co-evolution of viruses and humans leading to virulent strains over 10,000 years.
Evidence of viral diseases documented in historical texts (e.g., The Iliad and Egyptian hieroglyphs).
The Evolution of Vaccination
Variolation as a precursor to vaccination, with Cowpox leading to the discovery and term 'vaccination' by Edward Jenner.
Importance of variolation in protecting against smallpox but with unpredictable outcomes.
Microbiology and Pathogenicity
Antony van Leeuwenhoek's advancements in microscopy allowed the observation of microorganisms.
Pasteur's experiments debunking spontaneous generation and establishing links between specific microorganisms and diseases.
Koch’s Postulates
Criteria established by Robert Koch to link specific microorganisms to particular diseases, foundational to microbiology.
Discovery of Viruses
Identification of virus-like infectious agents smaller than bacteria, beginning with Dimitrii Ivanovsky’s work on TMV.
Beijerinck’s contributions in classifying these agents and naming them as viruses.
Defining Properties of Viruses
Viruses are obligate intracellular parasites requiring host cells for propagation.
Simplicity of virus structures identified via electron microscopy.
Viral Propagation Mechanisms
Compartments containing viral genomes assembled in the host, relying on host biosynthetic machinery.
Distinction between viral assembly and cellular reproduction.
Classification of Viruses
Viruses classified based on nucleic acid type, symmetry of the capsid, presence of an envelope, and other characteristics.
Baltimore classification based on mRNA production steps from diverse viral genomes.
Common Strategies for Viral Propagation
Viral cycles include attachment, genome entry, replication, and particle assembly/release, reflecting shared strategies across virus types.