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Human Papillomavirus Infections

Chapter 203 | Part 5: Infectious Diseases · Part 5 – Infectious Diseases: Viral (incl. HIV) · Chapter 203

Key Clinical Points

  1. HPV is an icosahedral, nonenveloped, 8000-base-pair, double-stranded DNA virus (diameter 55 nm).
  2. Persistent HPV infection is the primary risk factor for cervical cancer; relative risks range from 10 to 20 and exceed 100 in case–control studies.
  3. HPV types 16 and 18 cause ≥70% of cervical squamous cell carcinomas and 85% of cervical adenocarcinomas worldwide.
  4. Immune response is unique due to lack of viremia; CD4+ T cells are critical for controlling infection progression.
  5. HIV infection significantly accelerates HPV disease progression, particularly in anal cancer (130/100,000 vs. 5/100,000 in MSM).
  6. Imiquimod 5% cream is a standard treatment for genital warts (bedtime application, 3x/week for up to 16 weeks; ≈56% clearance).
  7. Vaccination options include Quadrivalent (types 6, 11, 16, 18) and Nine-valent (adds 31, 33, 45, 52, 58).
  8. Cervical cancer screening is cost-effective; initiation at age 21 regardless of sexual debut.
  9. Most HPV infections are cleared within 6–9 months.
  10. Oropharyngeal cancers (linked to type 16) show a better prognosis than cervical cancer (5-year survival ≈80%).

DEFINITION & CLASSIFICATION

• Structure: Nonenveloped, double-stranded DNA virus • Morphology: Icosahedral structure; diameter of 55 nm • Genome: 8000-base-pair; contains early (E) genes, late (L) genes, and regulatory noncoding regions • Pathophysiology: E6 and E7 proteins drive oncogenesis by inactivating p53 and Rb pathways • Infection Mechanism: Occurs via microtrauma to mucosal surfaces; replication completes as keratinocytes differentiate • Classification: ◦ Low-risk: Types 6, 11 (cause genital warts; ≈10% of low-grade cervical lesions) ◦ High-risk: Types 16, 18 (cause dysplasia and 70–85% of cervical cancers) ◦ Other oncogenic types: 31, 33, 45, 52, 58 (account for remaining 30% of cervical cancers) • Scope: Over 200 HPV types identified; ≈40 infect the anogenital tract

• Other Human Parvoviruses: ◦ HBoV1: Respiratory infections in children <5 years ◦ HBoV2-4: Found in feces; role in gastroenteritis uncertain ◦ Bufavirus/cutavirus: Detected in diarrheal stools; cutavirus linked to cutaneous T-cell lymphoma ◦ Parvovirus 4 (parv4): Found in plasma donations and injection drug users; apathogenic ◦ Adeno-associated viruses (AAV): Require helper viruses for replication; used in gene therapy; linked to rare acute hepatitis

EPIDEMIOLOGY

• Prevalence: ≈50% of young women infected within months of first intercourse • Clearance: Most infections become undetectable in 6–9 months • Risk Factors: Multiple sexual partners; immunosuppression (e.g., HIV) • Cervical Cancer Burden: Peaks in low-income countries (>85% of cases occur there) • HIV Impact: Accelerates progression; anal cancer rates reach 130/100,000 in HIV-infected MSM vs. 5/100,000 in HIV-negative MSM • Specific Types: ◦ HPV 1: Causes plantar warts but not genital infections

Epidemiology of HPV Types

• Low-risk types: 6, 11 (genital warts; ≈10% of low-grade cervical lesions) • High-risk types: 16, 18 (cause dysplasia and 70–85% of cervical cancers) • Other oncogenic types: 31, 33, 45, 52, 58 (account for remaining 30% of cervical cancers)

ETIOLOGY & PATHOPHYSIOLOGY

• Transmission: Sexual contact (vaginal, anal, oral) or direct genital contact • Immune Response Characteristics: ◦ No viremic phase ◦ 60–70% of infected individuals develop detectable serum antibodies ◦ Neutralizing antibodies provide partial protection against reinfection• Cell-Mediated Immunity: CD4+ T cells regulate infection control; HIV compromises this• Oncogenic Prevention: T cell responses to E2/E6 proteins associate with cervical cancer prevention

CLINICAL FEATURES

• Genital Warts: Soft, sessile growths (types 6/11); penile lesions 2–5 mm in diameter; vulvar warts as whitish papules • Cervical Cancer: Early erosion with easy bleeding → advanced stages show ulceration or exophytic masses • Anal Cancer: Rectal bleeding, pain, or mass sensation (20% asymptomatic at diagnosis) • Oropharyngeal Cancers: Increasing incidence in men 40–50 years old; linked to HPV type 16

• Anatomic Distribution of Lesions: ◦ Male: urethra, penis, scrotum; keratotic plaques on penile lesions ◦ Female: vulva, vagina, cervix; vaginal lesions as elongated papillae ◦ Both: perianal/anal/oropharyngeal infections

DIFFERENTIAL DIAGNOSIS

• Genital warts: Molluscum contagiosum, syphilis (condyloma lata) • Cervical cancer: Benign polyps, ectropion • Anal cancer: Hemorrhoids, fissures • Oropharyngeal cancer: Tonsillitis, abscesses • Vulvar cancer: Lichen sclerosus, planus • Penile cancer: Balanitis, other dermatoses

DIAGNOSTIC APPROACH

  1. Cervical Cancer Screening (General):
  2. Age 21–29: Pap smear every 3 years
  3. Age 30–65: Co-testing (Pap + HPV DNA) → if negative, repeat in 5 years
  4. High-risk HPV types (non-16/18): Follow with cytology
  5. Cervical Cancer Screening (HIV-infected):
  6. Annual cytology starting within 1 year of diagnosis
  7. Clinical Identification:
  8. Genital warts: Identified by morphology (e.g., cauliflower-like growths)
  9. Cervical cancer: Identified via cytology/biopsy

Screening Algorithms

• Age 21–29: Pap every 3 years; no co-testing • Age 30–65: Co-testing (Pap + HPV) every 5 years if negative • Positive HPV 16/18: Colposcopy required • HIV-infected: Annual cytology starting within 1 year of diagnosis

MANAGEMENT & TREATMENT

  1. Genital Warts (Topical):
  2. Imiquimod 5% cream: Apply at bedtime, 3 times per week for up to 16 weeks → ~56% clearance
  3. Other options: podophyllin, trichloroacetic acid
  4. Cervical Dysplasia:
  5. Loop electrosurgical excision procedure (LEEP)
  6. Cryotherapy
  7. Cervical Cancer Management:
  8. Colposcopy
  9. Biopsy
  10. Cone biopsy
  11. Surgery (e.g., radical hysterectomy)
  12. Radiation therapy
  13. Chemotherapy (cisplatin-based)
  14. Vaccination:
  15. Quadrivalent: targets types 6, 11, 16, and 18
  16. Nine-valent: adds types 31, 33, 45, 52, and 58
  17. Timing: Recommended for adolescents (age 11–12); catch-up available up to age 45

Therapeutic Options

• Genital warts: Imiquimod 5% cream, podophyllin, trichloroacetic acid • Cervical dysplasia: LEEP, cryotherapy • Cancer treatment: Radical hysterectomy, radiation therapy, cisplatin-based chemotherapy

COMPLICATIONS & PROGNOSIS

• Cervical cancer: 5-year survival ≈66% in developed countries; <20% in low-income regions • Anal cancer: 5-year survival ≈60–70% • Oropharyngeal cancer: 5-year survival ≈80% (better than cervical)

• Complications of HPV Infection: ◦ Cervical cancer: Metastasis to bladder/bowel, pelvic pain ◦ Anal cancer: Bowel obstruction, bleeding ◦ Oropharyngeal cancer: Dysphagia, airway obstruction ◦ Genital warts: Recurrent lesions, psychological impact

SPECIAL POPULATIONS

• HIV-infected individuals: - Accelerated disease progression - Higher rates of persistent infection and cancer - Requirement for more frequent/earlier screening (annual cytology starting within 1 year) • Immunosuppressed patients: - Management of warts requires more aggressive therapy • Adolescents: - Vaccination recommended at age 11–12 • Global disparities: Limited screening access in low-income regions increases cervical cancer mortality

KEY PEARLS & HIGH-YIELD POINTS

• High-Risk vs Low-Risk: Types 16/18 (high) are the primary drivers of cervical cancer; types 6/11 (low) cause common genital warts. • Imiquimod Dosage: 5% cream, 3x/week for up to 16 weeks. • Screening Thresholds: Age 21 start; 3-year interval for young adults; 5-year interval for older adults with co-testing. • HIV Impact: Significant acceleration of anal cancer (130/100,000 vs. 5/100,000).