Viral pathogens classification, biology, diseases 2

Question 1

Describe how virus replication reflects the disease we observe (HIV)

Answer 1

Role of Viral Replication in Disease Progression for HIV:

CD4+ T Cell Depletion:

• HIV replication in CD4+ T cells eventually leads to their death, either directly by cytopathic effects or indirectly through immune responses
• This ongoing destruction leads to the progressive weakening of the immune system

Immune Activation and Exhaustion:

• Chronic HIV replication results in persistent immune activation, which is thought to contribute to the depletion and exhaustion of immune cells, further weakening the immune system

Genetic Variation:

• HIV replication is error-prone, leading to the production of many viral variants.
• This genetic diversity allows the virus to evade the immune response and develop resistance to antiretroviral therapy, contributing to disease progression

Latent Reservoir:

• Some infected CD4+ T cells become long-lived memory cells, forming a latent reservoir of HIV
• These cells can reactivate and produce new virus, contributing to ongoing disease despite therapy

HIV-Associated Conditions:

• HIV replication also causes chronic inflammation and immune activation, leading to non-AIDS related conditions such as cardiovascular disease, kidney disease, liver disease, neurological complications, and others

Question 2

Provide examples of the involvement of viral infections in cancer and immunodeficiency

Answer 2

Viral Infections and Cancer:

Integration of viral DNA into the host genome, chronic inflammation, suppression of the host’s immune response, and production of viral proteins that interfere with cell growth and proliferation controls

HPV: types 16 and 18, are strongly associated with cervical cancer

HBV & HCV: Chronic infection with either of these viruses can lead to liver cirrhosis and hepatocellular carcinoma (liver cancer)

EBV: associated with Burkitt’s lymphoma, Hodgkin’s lymphoma, certain types of stomach cancer (gastric carcinomas), and nasopharyngeal carcinoma

HTLV: cause of adult T-cell leukemia/lymphoma

MCV: associated with Merkel cell carcinoma

Viral Infections and Immunodeficiency:

HIV: HIV selectively infects and kills CD4+ T cells, leading to a progressive decline in immune function and the development of AIDS

SCID due to Adenosine Deaminase (ADA) deficiency:

• SCID from viral infection
• ADA is an enzyme that is important in the breakdown of toxic substances that can harm lymphocytes
• Infants with SCID are extremely susceptible to severe viral infections, including those caused by measles, CMV and VZV

Measles: not causing a permanent immunodeficiency, measles infection can cause an immunosuppressive state for weeks to months, leading to a higher susceptibility to other infections