What are the causes of Bacterial Vaginosis (BV)?

Causes of Bacterial Vaginosis (BV)

Bacterial vaginosis (BV) is primarily caused by a disruption in the normal vaginal microbiota, where beneficial Lactobacillus species are replaced by an overgrowth of anaerobic bacteria including Gardnerella vaginalis, Prevotella species, Bacteroides species, Mobiluncus species, and Peptostreptococcus species. 1, 2, 3

Microbiological Factors

• Microbial imbalance: BV represents a significant alteration in vaginal ecology where:

  • Protective Lactobacillus species (especially H₂O₂-producing strains) decrease dramatically
  • Anaerobic bacteria increase in number and diversity 3
  • This disruption leads to the characteristic symptoms of BV including thin, homogeneous discharge and fishy odor 1

• Key bacterial players in BV include:

  • Gardnerella vaginalis
  • Prevotella species
  • Bacteroides species
  • Mobiluncus species
  • Peptostreptococcus species
  • Mycoplasma hominis 1, 3

Risk Factors and Contributing Causes

Several factors have been identified that contribute to the development of BV:

1. Sexual activity:

   • Multiple sexual partners increase risk 2, 3
   • While not classified as a sexually transmitted infection, BV shows patterns similar to STIs 3
   • The rectum may serve as a reservoir for BV-associated bacteria 3

2. Hormonal influences:

   • Lack of estrogen can affect vaginal pH and bacterial composition
   • Hormonal contraception may offer some protection against BV 1, 2

3. Lifestyle factors:

   • Smoking is associated with increased BV risk 1, 2
   • Smoking cessation may help prevent BV 2

4. Hygiene practices:

   • Douching and other practices that disrupt normal vaginal flora
   • Use of certain lubricants or vaginal products 2

5. Biofilm formation:

   • BV-associated bacteria, particularly G. vaginalis, can form biofilms that protect bacteria from host immune responses and antibiotics 2
   • This contributes to the high recurrence rate (50-80% within one year after treatment) 2

Pathophysiological Mechanisms

The development of BV involves several interconnected processes:

• Disruption of protective mechanisms:

  • Reduction in H₂O₂-producing Lactobacillus species that normally protect against colonization by anaerobic bacteria 3
  • Increase in vaginal pH (>4.5) that facilitates growth of anaerobes 1

• Bacterial interactions:

  • Synergistic relationships between BV-associated bacteria
  • Competition for nutrients and attachment sites
  • Production of enzymes and metabolites that further alter the vaginal environment 4

• Host immune factors:

  • Genetic variations affecting immune response
  • Differences in local immunity that may explain why some women with BV-associated bacteria remain asymptomatic 4

Clinical Implications

Understanding the causes of BV is important because:

• BV increases risk of acquiring STIs including HIV 5
• BV is associated with adverse pregnancy outcomes including preterm birth 1, 5
• BV can lead to pelvic inflammatory disease and other upper genital tract infections 3
• The high recurrence rate suggests that current treatments do not address underlying causes effectively 2

Prevention Strategies

Based on the causes of BV, several prevention strategies may be effective:

• Consistent condom use 2
• Smoking cessation 1, 2
• Use of hormonal contraception 2
• Avoiding douching and other disruptive vaginal practices
• For postmenopausal women, vaginal estrogen with or without lactobacillus-containing probiotics may help maintain normal vaginal pH 1

Understanding the complex interplay of factors causing BV is essential for developing more effective prevention and treatment strategies, particularly given the high recurrence rates with current antibiotic treatments.