Virology Lectures 2024 #17: Persistent Infections

A persistent viral infection is one that lasts the lifetime of the host, and humans harbor multiple such infections. In this lecture we discuss the mechanisms and consequences of viral persistence, illustrated with examples of measles virus, polyomaviruses, hepatitis B and C viruses, and herpesviruses.
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*Abstract*
This lecture explores the mechanisms and consequences of persistent
viral infections, which last for the lifetime of the host. Unlike
acute infections that are cleared by the immune system, persistent
viruses employ various strategies to evade immune responses and remain
in the body. The lecture covers specific examples of persistent
viruses, including measles virus, polyomaviruses, hepatitis B and C
viruses, and herpesviruses, highlighting their unique characteristics
and disease potential.
*Summary by Timestamp:*
*General Properties of Persistent Infections:*
- 1:01: Persistent infections begin as acute infections but are never fully cleared.
- 3:35: Virus particles, proteins, or genomes continue to be produced throughout the host's life.
- 3:48: Viral genomes may remain even when proteins are undetectable.
- 4:32: Persistent viruses often exhibit reduced cytopathic effects and antagonize host defenses.
*Evasion of Cytotoxic T-cell Response:*
- 6:04: Persistent viruses often evade the cytotoxic T lymphocyte (CTL) response, which is crucial for clearing infected cells.
- 7:20: Some viruses downregulate MHC molecules, preventing antigen presentation to CTLs.
- 8:56: Certain viruses, like herpes simplex and hepatitis C, can mutate their T-cell epitopes to escape CTL recognition.
- 11:45: Some viruses can even kill CTLs through mechanisms like Fas ligand expression.
*Persistence in Immune-Privileged Sites:*
- 13:23: Some viruses persist in tissues with reduced immune surveillance, such as the central nervous system, eyes, and testes.
- 14:55: Ebola virus persistence in the eye and testes highlights the risk of transmission even after recovery.
*Infection of Immune Cells:*
- 18:14: Many persistent viruses, including measles and HIV, can infect immune cells themselves, further hindering immune clearance.
*Specific Examples of Persistent Viruses:*
- 19:45: Measles virus can cause a rare but fatal disease called subacute sclerosing panencephalitis (SSPE) years after the initial infection.
- 22:48: Polyomaviruses are widespread and typically asymptomatic, but can cause disease in immunocompromised individuals.
- 27:03: Hepatitis B virus can lead to chronic liver disease and cancer, highlighting the importance of vaccination.
- 32:43: Hepatitis C virus is transmitted through blood and can also cause chronic liver disease, emphasizing the need for effective prevention and treatment strategies.
*Latent Infections:*
- 39:59: Latent infections are characterized by the presence of viral genomes with minimal protein expression, making them difficult for the immune system to detect.
- 40:44: Herpes simplex viruses exemplify latent infections, residing in nerve ganglia and periodically reactivating to cause cold sores.
- 51:17: Epstein-Barr virus establishes latency in B cells and can contribute to various cancers.
- 55:25: Varicella-zoster virus causes chickenpox and shingles, demonstrating reactivation from latency in sensory ganglia.
- 57:59: Cytomegalovirus persists in myeloid cells and can cause severe birth defects if infection occurs during pregnancy.
- 1:01:36: Herpesviruses 6 and 7 cause a mild childhood rash and integrate their genomes into host chromosomes in some cases.
*Concluding Remarks:*
- 1:03:26: Humans harbor numerous chronic viral infections, which can potentially influence various health conditions and should be considered in clinical studies.
disclaimer: i used gemini 1.5 pro to summarize the youtube transcript using this prompt: Create an abstract and summarize the following video transcript as a bullet list. Prepend each bullet point with starting timestamp. Do not show the stopping timestamp. Also split the summary into sections and create section titles: ``````

[@mwizanyimbiri2253]

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[@anthonyrstrawbridge]

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