Page 171 - Concise Pathology for Exam Preparation ( PDFDrive )

156 SECTION I General Pathology

• There are two clinically significant Neisserial species:
• N. gonorrhoeae (gonococcus): Causes gonorrhoea
• N. meningitides (meningococcus): Causes meningitis
• N. gonorrhoeae normally colonizes mucosal surfaces. Humans are the only host and
transmission is via sexual contact. The bacteria need to have fimbriae (pili) to be
virulent as the latter enable the gonococcus in attaching to host cells.
• N. meningitides normally inhabits the human nasopharynx and can sometimes over-
come the body defences to cause meningitis and septicaemia. Its virulence is mainly
due to its antiphagocytic capsule and meningococcal LPS.
Clinical Manifestations
• N. gonorrhoeae causes painful urethritis in men. In women, the infection is often asymp-
tomatic and so might go untreated. Untreated chronic infection can lead to pelvic inflam-
matory disease, which in turn can cause infertility or ectopic pregnancy. Disseminated
infection can cause septic arthritis accompanied by a haemorrhagic rash.
• Neisseria meningitidis causes meningitis and meningococcemia, a life-threatening sepsis.

Chancroid (Soft Chancre)

Chancroid is a sexually transmitted infection caused by Haemophilus ducreyi, a small,
Gram-negative and facultative anaerobic bacillus that is highly infective. It is one of the
most common causes of genital ulcers in Southeast Asia, where it probably serves as an
important cofactor in the transmission of HIV-1 infection. It is known to spread to other
anatomical sites by autoinoculation.
Clinical Features
• The disease has an incubation period of 5–7 days. It typically begins as a small inflam-
matory papule at the site of inoculation; within days, the papule may erode to form an
extremely painful deep irregular ulceration.
• In males, the primary lesion is usually located on the penis; in females, most lesions
occur in the vagina or the periurethral area. Unlike the primary chancre of syphilis, the
ulcer of Chancroid is not indurated and multiple lesions may be present.
• Regional lymphadenopathy is very common. In untreated cases, inflamed nodes may
erode overlying skin to produce chronic, draining ulcers.
Morphology
• Microscopically, the ulcer of Chancroid contains three zones, a superficial zone of neu-
trophilic debris and fibrin; a middle zone of granulation tissue and oedema; and a deep
zone of lymphoplasmacytic inflammation. Coccobacilli can sometimes be demonstrated
by Gram or silver stains.
• H. ducreyi is a fastidious bacterium requiring a relatively expensive nutritive base to
grow on and is an extremely difficult organism to culture from clinical specimens. DNA
amplification techniques have shown a somewhat improved diagnostic sensitivity but
are only performed in a few laboratories.

Granuloma inguinale
Granuloma inguinale (donovanosis) is a sexually transmitted, chronic inflammatory disease
caused by Klebsiella granulomatis, formerly Calymmatobacterium granulomatis, a Gram-
negative rod. It is endemic in tropical and subtropical climates.
Clinical Features
• The average incubation period varies between 2 and 4 weeks.
• The initial lesion may be a papule, a subcutaneous nodule or an ulcer, which weeks later
converts into a raised, soft, painless, beefy-red, superficial ulcer with characteristic
rolled edges.

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