Basic Course in HIV - Pathophysiology and Natural History of HIV Infection | Summary and Q&A

Transcript

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Summary

This video discusses the pathophysiology and natural history of HIV. It answers questions about how HIV works, the immune system's role in fighting off viruses, the different types of white blood cells, and the specific cells that HIV infects. It also explains the process of HIV replication and the importance of targeting certain enzymes. The video further explores the different strains of HIV, the time line of infection from initial stages to symptomatic disease, and the differences in progression between adults and children.

Questions & Answers

Q: What is the role of the immune system in protecting against viruses?

The immune system's main function is to protect the body from infections. It consists of immune cells, lymph tissue, organs, vessels, and skin. It fights off viruses, germs, bacteria, and fungi constantly to keep the body healthy.

Q: How does HIV affect the immune system?

HIV damages a specific type of white blood cell called the CD4 cell, which is a major part of the immune system. CD4 cells act as soldiers and generals, directing and organizing the immune response. When HIV infects the CD4 cell, the immune system becomes compromised, leading to a decreased ability to fight off infections.

Q: Why is the CD4 cell important in the immune system?

CD4 cells, specifically the CD4 T-cells, are like the generals of the immune system. They plan and direct the immune response by summoning other types of cells, such as B-cells, natural killer cells, and macrophages, to locate and attack infected cells. They are crucial in coordinating the immune system's defense against infections.

Q: How does HIV infection differ in infants and children compared to adults?

Infants and children have an immature immune system, which means they do not have the same ability to fight off infections as adults. When infants are infected with HIV, their viral load remains consistently high because their immune system is not yet developed enough to control the infection. Additionally, their CD4 cell counts are initially very high but gradually decrease with age.

Q: Why is CD4 percent used instead of absolute CD4 count in children?

CD4 percent is used in children, especially those younger than six, because their absolute CD4 counts are naturally higher and constantly changing. CD4 percent provides a more stable measure of immune system health in children, whereas absolute CD4 count is more useful in older children and adults.

Q: What is the structure of the HIV virus?

HIV is a lentivirus, which means it is a slow virus. It has an outer membrane with proteins that serve as markers for the body to recognize it as a foreign invader. Inside the virus, there are enzymes called reverse transcriptase, integrase, and protease, which are necessary for the virus to replicate and infect new cells.

Q: How does HIV replicate and infect new cells?

When HIV enters a host cell, it uses reverse transcriptase to convert its RNA into DNA. This DNA is then integrated into the host cell's genome by the enzyme integrase. The host cell then activates the virus's genes, leading to the production of new viral components. Finally, the components are assembled by the enzyme protease, and the virus is released to infect other cells.

Q: How do antiretroviral drugs work against HIV?

Antiretroviral drugs target specific enzymes in the HIV replication process. Nucleoside reverse transcriptase inhibitors (NRTIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs) inhibit reverse transcriptase, preventing the virus from converting RNA to DNA. Integrase inhibitors block the action of integrase, preventing the virus from integrating its DNA into the host cell's DNA. Protease inhibitors block the action of protease, preventing the assembly of new viral components.

Q: Why does HIV mutate and change over time?

HIV's reverse transcriptase enzyme is prone to making errors during DNA replication, leading to genetic mutations in the virus. These mutations result in different strains and subtypes of HIV. Additionally, HIV replicates billions of times per day, resulting in a high rate of mutation and genetic diversity within the infected individual.

Q: What is the natural history of HIV infection in adults and children?

In adults, HIV infection typically involves an initial asymptomatic stage, followed by a prolonged clinical latency period where the virus is actively replicating but symptoms are minimal. Eventually, the CD4 cell count decreases, leading to increased susceptibility to opportunistic infections and progression to AIDS. The timeline from infection to symptoms is around 7-10 years, but there are variations among individuals. In children, the progression can be different, with a higher viral load and rapid decline in CD4 cell count, leading to faster disease progression.

Takeaways

Understanding the pathophysiology and natural history of HIV is crucial in managing the infection. HIV infects and damages the immune system, particularly the CD4 cells, leading to compromised immunity and increased vulnerability to infections. Antiretroviral drugs target specific enzymes in the virus to stop its replication. HIV is a rapidly mutating virus, leading to various strains and subtypes. The progression of HIV varies between adults and children, with children often experiencing faster disease progression. Early diagnosis, regular testing, and adherence to antiretroviral therapy are essential in preventing HIV-related complications and improving outcomes.