Pathophysiology of Sexually Transmitted Infections

Pathophysiology of Sexually Transmitted Infections

• HIV is a retrovirus, enveloped, positive-sense, single-stranded RNA virus. It has a reverse transcriptase enzyme, a polyhedral capsid, and a spiked envelope. Its size ranges from 80-146 nm.
• Two main variants exist: HIV-1, predominant globally, and HIV-2, primarily found in West Africa. HIV-2 shares 50% sequence homology with HIV-1.
• HIV-1's life cycle involves binding to CD4 cells (Helper T cells), fusion, core delivery, reverse transcription initiation, uncoating and reverse transcription completion, integration, transcription, translation, assembly, budding, release, and maturation.
• HIV's replication utilizes reverse transcriptase to convert RNA into DNA, creating a DNA-RNA hybrid intermediate.
• Reverse transcriptase degrades the RNA portion of this hybrid, then synthesizes a complementary strand of DNA using the DNA strand as a template, eventually forming double-stranded DNA.

Pathogenicity of HIV

• Body fights the virus initially, killing millions of CD4 cells in the latent phase.
• The body's inability to produce enough CD4 cells results in a decline in their numbers over 5-10 years.
• HIV virus numbers increase during this time.
• Other infections easily invade the system due to a compromised immune system (AIDS).

Epidemiology of HIV

• Discovered in young homosexual males in 1981, in the USA.
• Now a global issue.
• Estimated 39 million people were living with HIV in 2022, with two-thirds in the WHO African Region (25.6 million).
• In 2022, 630,000 people died from HIV-related causes and 1.3 million people acquired HIV.
• Sub-Saharan Africa is most affected by HIV, representing 71% of the global caseload.
• Transmission occurs through sexual contact and intravenous drug use, with contact with bodily fluids being comparatively rare.

HIV Symptoms

• Initial infections present symptoms like fever, fatigue, weight loss, diarrhea, and body aches.
• AIDS onset is characterized by opportunistic infections: Kaposi's sarcoma, disseminated herpes, toxoplasmosis, and pneumocystis pneumonia. These infections are not usually lethal in people with healthy immune systems.

Diagnosis of HIV

• Often initially mistaken for the flu because the initial symptoms are similar.
• The diagnosis involves monitoring CD4 cell counts.
• Serology testing for antibodies, rapid point-of-care testing, and PCR of RNA are diagnostic methods.

Treatment of HIV

• Antiretroviral therapy (ART) involves a cocktail of 3-4 antiviral drugs including nucleotide analogs, integrase inhibitors, protease inhibitors, and reverse transcriptase inhibitors.
• ART must be taken on a strict schedule; otherwise, its efficacy may be compromised.
• ART is expensive.
• ART stops HIV replication.

HIV Vaccine Development

• Vaccine development is difficult due to HIV's high mutability, ability to spread through syncytia, and ability to infect vital cells like macrophages, dendritic cells, and Helper T cells, which are normally stimulated by vaccines.
• Another challenge is the ethical difficulty of testing the vaccine on humans only.

Human Papillomavirus (HPV)

• Non-enveloped, double-stranded circular DNA virus.
• Causes genital warts, a common STI in the UK.
• Transmission mostly occurs through sexual contact.
• Genital warts appear as small, rough lumps around the vagina, penis, or anus.
• In 90% of cases, the body's immune system manages the infection on its own.
• Persistent high-risk HPV infections can lead to cervical cancer, the most common HPV-related cancer.

Trichomonas vaginalis

• A protozoan parasite, an obligate parasite that lives only in human hosts.
• Transmitted exclusively via sexual contact.
• Most often observed in people with other STIs or multiple sex partners.
• Characterized by four anterior flagella, an undulating membrane, a body approximately 15 μm in length, and a posterior flagellum (axostyle).
• The parasite replicates by binary fission within the human host.
• Existence in a cyst form is not observed, and it does not survive well in the external environment.

Trichomonas vaginalis - Symptoms

• Women: vaginosis, purulent, and odorous discharge, vaginal and cervical lesions, abdominal pain, painful urination, and painful sexual intercourse.
• Men: typically asymptomatic, but may present with urethra/bladder inflammation.

Trichomonas vaginalis - Treatment and Diagnosis

• Diagnosis: microscopic observation of trophozoites in vaginal/urethral secretions.
• Treatment: Nitroimidazole drugs are typically effective, but resistance in some strains exists.

Summary of STIs

• This presentation covered the pathogenesis (development and progression) of various STIs, including Chlamydia, Gonorrhea, Syphilis, Genital Warts/HPV, Genital Herpes, HIV/AIDS, and Trichomonas vaginalis.

This quiz covers the pathophysiology and pathogenicity of HIV, including its structure, life cycle, and replication process. Test your knowledge on the key differences between HIV-1 and HIV-2, and understand how the virus interacts with the immune system. Dive into the complexities of retroviral infections and their impact on human health.