Page 190 - Concise Pathology for Exam Preparation ( PDFDrive )

7 Infections 175

the critical phase, which is marked by resolution of the high fever. During this phase,
there may be significant fluid accumulation in the chest and abdominal cavity due to
increased capillary permeability and leakage. The recovery phase occurs next, with
resorption of the leaked fluid into the bloodstream. This is characterized by severe itch-
ing and bradycardia, and leads to depletion of fluid from the circulation and decreased
blood supply to vital organs. Another rash may occur with either a maculopapular or
vasculitic appearance, which is followed by peeling of the skin.
• In a small proportion of cases, the disease develops into a life-threatening dengue
haemorrhagic fever, resulting in bleeding, low circulating levels of platelets and blood
plasma leakage, or into dengue shock syndrome, where dangerously low blood pres-
sure occurs. Polymorphisms in particular genes have been linked with increased risk of
severe dengue complications.

Q. Write briefly about chlamydial infections.
Ans. Chlamydia trachomatis is a small Gram-negative, aerobic, intracellular bacterium.
• Chlamydia pneumoniae is one of the main causative agents of pneumonia and bronchitis.
It has also been linked with atherosclerosis and multiple sclerosis.
• C. trachomatis infection causes urogenital infections (nongonococcal urethritis or NGU),
inclusion conjunctivitis, lymphogranuloma venereum, epididymitis, prostatitis, pelvic
inflammatory disease (PID), pharyngitis, conjunctivitis and trachoma.
• Chlamydia exists in two forms during its unique life cycle. The infectious form—the el-
ementary body (EB)—is a metabolically inactive, spore-like structure, which is taken up
by host cells, primarily by receptor-mediated endocytosis. The bacteria prevent fusion of
endosome and lysosome. Inside the endosome, the EB differentiates into a metabolically
active form called the reticulate body (RB) that is capable of infecting additional cells.
• C. trachomatis urethritis is characterized by a mucopurulent discharge which on microscopy
shows mainly neutrophils. The lesions of lymphogranuloma venereum show a suppurative
(neutrophilic inflammatory) response with an occasional granuloma. Intracytoplasmic
Chlamydial inclusions can be demonstrated in epithelial or inflammatory cells.
• Regional lymphadenopathy is common. Affected nodes show a granulomatous reaction
associated with irregular necrosis (stellate abscesses), which may heal with extensive
fibrosis to cause lymphatic obstruction with lymphoedema.
• Chlamydiae cannot be demonstrated by Gram’s staining. While culturing of the organ-
ism can confirm the diagnosis, this method is limited to research laboratories. For rou-
tine diagnostic use, newer and inexpensive diagnostic tests that depend on identification
and amplification of the genetic material of the organism have replaced the older, time-
consuming culture methods.

Q. Write briefly about rickettsial infections.
Ans. Rickettsial organisms are vector-borne, Gram-negative, obligate intracellular bacteria that
are divided into two antigenically defined groups: spotted fever group and typhus group.
• Patients present with fever and exanthem; eventually there is visceral involvement;
symptoms include nausea, vomiting, abdominal pain, encephalitis, hypotension, acute
renal failure, respiratory distress and coma.
• The organisms proliferate in the endothelial cell cytoplasm and then either burst the cell
(typhus group) or spread from cell-to-cell (spotted fever group).

Q. Write briefly about fungal infections.
Ans. Fungi are eukaryotes that possess thick chitin-containing cell walls and ergosterol-
containing cell membranes. They can grow either as budding yeast cells or as slender fila-
mentous hyphae. Hyphae may be septate (with cell walls separating individual cells) or
aseptate, which is an important distinguishing characteristic in clinical material. Fungi
may cause superficial or deep infections.
• Superficial fungal infections involve the skin, hair and nails. Fungal species that are
confined to superficial layers of the human skin are known as dermatophytes. These

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