27: Infections of the genitourinary tract

Chapter 27 Infections of the genitourinary tract

Normal flora and the natural defences of the genitourinary tract

The predominant vaginal flora in adult women consists of lactobacilli. They keep the vaginal pH low and appear to prevent the growth of potential pathogens. For instance, their suppression by antibiotics may lead to overgrowth of the yeast Candida albicans found in relatively low numbers in the healthy vagina. Other common groups of vaginal organisms include diphtheroids, streptococci, anaerobes and coliforms. Most of these organisms may behave as opportunistic pathogens when appropriate conditions supervene. Approximately 20% of women of child-bearing age carry group B β-haemolytic streptococci in the vagina. These may be acquired by a baby during its passage through the birth canal, resulting in serious infections such as meningitis and sepsis.

The urine in the bladder is normally sterile, but the voided urine often becomes contaminated by flora from the distal portions of the urethra, such as Staphylococcus epidermidis, coliforms, diphtheroids and streptococci. Additionally, in females, the organisms present in the distal part of the urethra may include contaminants from the gut flora such as enterobacteria and lactobacilli. The flushing action of the urine is arguably the most important defence factor of the urethra in both males and females. Bactericidal mechanisms in the bladder mucosa, including local antibody response and lysozyme, play an important role in preventing ascending infection of the urinary tract.

Important pathogens

Important pathogens are listed in Figure 27.1 and Table 27.1.

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Fig. 27.1 Major infectious agents of the genitourinary tract.

Table 27.1 Sexually transmitted diseases

Disease Agent
Bacterial infections  
Gonorrhoea Neisseria gonorrhoeae (the gonococcus)
Syphilis Treponema pallidum
Vaginitis Gardnerella vaginalis, anaerobes
Chancroid Haemophilus ducreyi
Viral infections  
Genital herpes Herpes simplex virus (type 2 mainly)
Genital warts Papillomavirus
Hepatitis Ba Hepatitis B virus
AIDSa Human immunodeficiency virus (HIV)
Others  
Lymphogranuloma venereum Chlamydia trachomatis types L1–L3
Granuloma inguinale (donovanosis) Calymmatobacterium granulomatis (a Klebsiella-like microorganism)
Pubic lice (crabs) Phthirus pubis
Genital scabies Sarcoptes scabiei
Non-specific urethritis Chlamydia trachomatis types D–K
Trichomoniasis Trichomonas vaginalis
Vaginal thrush Candida albicans

AIDS, acquired immune deficiency syndrome.

a Not always sexually transmitted.

Sexually transmitted diseases

A large group of infections are essentially transmitted by sexual intercourse; they may affect both heterosexual and homosexual partners. Varying patterns of sexual behaviour can result in such infections manifesting in the oral cavity, oropharynx and the rectum; sexually transmitted diseases frequently – but not invariably – produce genital lesions; several produce severe systemic disease that may even lead to death, such as human immunodeficiency virus (HIV) infection and hepatitis B.

Gonorrhoea

Gonorrhoea is caused by Neisseria gonorrhoeae (the gonococcus).

Clinical features

In women: acute urethritis, increased vaginal secretions with purulent discharge. In men: acute gonococcal urethritis with severe dysuria and purulent discharge. The disease may involve the rectum and oropharynx. Pharyngitis, sore throat, tonsillitis and gingivitis may occur as a result of gonococcal infection, especially from orogenital contact in homosexual men. Asymptomatic infection is common in both men and women. Complications include prostatitis, salpingitis and occasionally haematogenous spread, causing arthritis, septicaemia and meningitis.

Pathogenesis and epidemiology

Gonococcal infection has been reported only in humans. The infection is limited to the mucosa of the anterior urethra in men and the cervix of women. In the newborn, gonococcal conjunctivitis may occur due to cross infection from the mother’s birth canal.

Three virulence factors have been identified:

1. an endotoxin that inhibits the ciliary activity of the fallopian tubes and retards the expulsion of the gonococcus
2. an enzyme that destroys the protective immunoglobulins (secretory IgA) of the mucosa
3. β-lactamase is produced by some strains – penicillinase-producing N. gonorrhoeae (PPNG).

Diagnosis

Gram smears show Gram-negative pairs of the typical kidney-shaped gonococci inside neutrophils (Fig. 27.2). Swabs from the urethra cultured on lysed blood or chocolate agar yield oxidase-positive, translucent colonies, and rapid carbohydrate utilization tests are also diagnostic (see Chapter 14).

image

Fig. 27.2 Smear of a urethral pus exudate in gonorrhoea showing polymorphs and intracellular Gram-negative gonococci.

Treatment

A choice of antibiotics is available: a large, single, curative oral dose of amoxicillin (with probenecid to delay renal excretion); ceftriaxone; spectinomycin (for β-lactamase-positive gonococci); or erythromycin (children or pregnant women).

Non-specific urethritis

One of the most common sexually transmitted diseases, non-specific urethritis is seen more in men than in women. It is caused by more than one agent, but Chlamydia trachomatis is the most common cause. A mycoplasmal organism (‘bacteria’ without a cell wall), Ureaplasma urealyticum, may also cause significant morbidity.

Clinical features

Acute purulent urethral discharge resembles that of gonorrhoea; cervicitis occurs in women.

Diagnosis

Smears and swabs of urethral or cervical discharge are diagnostic. Culture is now rarely done. Smears are examined for intracytoplasmic inclusions by immunofluorescence. Serology for chlamydial antigens by indirect immunofluorescence with monoclonal antibody or by enzyme-linked immunosorbent assay (ELISA).

Treatment

Tetracycline is given for up to 10 days; relapses are common owing to the diverse aetiology of the disease.

Syphilis

The incidence of syphilis worldwide has increased in recent years, and in 2006, the figure was estimated to be 12 million worldwide and 70 000 new cases were reported in the USA.

Syphilis is one of the classic diseases with protean manifestations (i.e. affecting virtually all organ systems of the body), and has re-emerged as an important disease associated with HIV infection and sexual promiscuity. The disease, important due to its late and severe sequelae, is preventable, and treatable with effective and inexpensive antibiotics.

The disease is caused by Treponema pallidum, the syphilis spirochaete.

Clinical features

Syphilis has an incubation period of 10–90 days (average 3 weeks) and is characterized by four main clinical stages: primary, secondary, tertiary and late or quaternary (Fig. 27.3).

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Fig. 27.3 Natural history of untreated syphilis. *Approximate figures.

Primary syphilis

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Related posts:

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  2. 18: Fusobacteria, Leptotrichia and spirochaetes
  3. 11: Streptococci, staphylococci and micrococci
  4. 32: Microbiology of dental caries
  5. 26: Infections of the gastrointestinal tract
  6. 4: Viruses and prions

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Jan 4, 2015 | Posted by in General Dentistry | Comments Off on 27: Infections of the genitourinary tract

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