Virologia - Interação Vírus Hospedeiro - Aula 4 Parte 1

Summary

In this virology class, Professor Vera Morais discusses the intricate interactions between viruses and their hosts. The lecture delves into viral pathogenesis, emphasizing how viruses replicate and cause diseases. Topics such as viral virulence, host immune responses, and factors influencing infection, like genetics and immunity, are explored. The session covers various entry points for viruses into the body, such as through the respiratory, digestive, and urogenital systems. Additionally, it highlights the body's innate defense mechanisms and the strategies viruses use to evade immune responses. The importance of understanding these principles for studying viral diseases is stressed.

Takeaways

• 😀 Viruses are everywhere, but most viral interactions with the host do not cause noticeable symptoms or infections.
• 😀 Viral infections can be apparent (showing symptoms) or inapparent (without symptoms). Both types are important for understanding viral pathogenesis.
• 😀 Viral virulence refers to a virus's ability to cause disease. Some viruses are virulent, causing significant harm, while others are attenuated and cause little or no disease.
• 😀 Virulence can depend on various factors like viral dose, host immunity, and the route of inoculation (e.g., respiratory vs. direct contact).
• 😀 The host's age, sex, nutritional status, and genetic factors all influence how severe a viral infection will be.
• 😀 Viral factors such as replication ability, immune evasion, and cell toxicity contribute to virulence.
• 😀 Inoculation routes affect the severity of viral infections, such as how a virus behaves differently when introduced via the respiratory system compared to direct injection.
• 😀 Viral infections require specific conditions: an appropriate number of virus particles, susceptible and permissive cells, and the absence of antiviral defense mechanisms.
• 😀 The immune system plays a crucial role in controlling viral infections. Defenses include innate immunity (e.g., physical barriers like the skin and mucous membranes) and adaptive immunity.
• 😀 Viruses can enter the body through various routes such as the respiratory, digestive, and urogenital tracts. Each route has its own mechanisms of defense, like mucous production or immune cells.
• 😀 Defense mechanisms against viruses include mechanisms like APOBEC3G, which mutates viral DNA to prevent replication, and the process of apoptosis to eliminate infected cells before they can spread the virus.

Q & A

What is viral virulence?

Viral virulence refers to the ability of a virus to cause disease in a host. It depends on factors like viral dose, host immunity, and the route of viral inoculation.

How can viral virulence be quantified?

Viral virulence can be quantified by the time and severity of symptoms, the percentage of mortality, and the extent of tissue damage or other markers such as the viral load or immune response.

What are some factors that influence viral virulence?

Factors influencing viral virulence include the virus's genetic composition, the host's immune response, the host’s age, nutritional status, and other physiological conditions.

What are the main viral factors of virulence?

Viral factors of virulence include viral genes that affect replication, genes that help in immune evasion, and proteins that damage host cells or tissues, as well as factors aiding viral spread.

What is the difference between symptomatic and asymptomatic viral infections?

Symptomatic viral infections show clear signs or symptoms, whereas asymptomatic infections do not show any visible signs but still involve viral replication.

How does the host's immune system affect viral infections?

The immune system's ability to recognize and respond to the virus can significantly influence the severity and outcome of an infection. Weak immunity can make an individual more susceptible to severe infections.

How does the route of inoculation impact viral infection severity?

The route of inoculation, such as respiratory or intraperitoneal, can influence the viral dose needed to cause disease and its severity. For example, some viruses cause more severe symptoms when inoculated through the respiratory route compared to others.

What is the role of viral receptors in infection?

Viral receptors on host cells are essential for viral entry. If a host lacks the appropriate receptors for a virus, infection and disease may not occur, as seen in the case of HIV resistance due to a lack of CCR5 receptors.

What mechanisms do viruses use to evade the immune system?

Viruses use various mechanisms to evade the immune system, such as inhibiting immune responses, producing proteins that interfere with immune detection, and altering host cell functions to avoid detection and destruction.

What are the main portals of entry for viruses into the host?

Viruses can enter the host through several portals, including the skin, respiratory tract, gastrointestinal tract, urogenital tract, and through direct contact with infected bodily fluids or contaminated surfaces.