Page 184 - Concise Pathology for Exam Preparation ( PDFDrive )

7 Infections 169

Q. Write briefly about the various types of viral diseases.

Ans. Common viral diseases include

Measles
Pathogenesis
• Measles is usually seen in unvaccinated individuals or in cases of vaccination failure.
It is caused by an ssRNA virus of the paramyxovirus family (Rubeola virus) and spreads
by respiratory droplets.
• The virus initially multiplies within upper respiratory epithelial cells, and then spreads
to lymphoid tissues, where it can replicate in mononuclear cells, including T lympho-
cytes, macrophages and dendritic cells.
• Attachment to respiratory epithelial cells is via receptors, mainly, CD 46 (a complement
regulatory protein) and SLAM (signalling lymphocyte activation molecule). The virus
then spreads by blood throughout the body.
Clinical Manifestations
• The incubation period of measles (from exposure to onset of rash) is generally 14 days
(range 7–18 days). Patients are usually contagious from 4 days before until 4 days after
onset of the rash.
• Patient presents with fever, cough, coryza (running nose), conjunctivitis and an
erythematous maculopapular rash (a hypersensitivity reaction to viral antigens in
the skin).
• Koplik spots—a rash (enanthem) present on mucous membranes—is considered
pathognomonic of measles. This is typically seen as clustered, white lesions on the buccal
mucosa near each Stenson’s duct (opposite to the maxillary 2nd molars). On microscopy,
Koplik spots appear as ulcerated mucosal lesions with neutrophilic exudate.
Complications
• Diarrhoea
• Middle-ear infection
• Keratitis
• Pneumonia
• Encephalitis, frequently resulting in permanent brain damage (subacute sclerosing
panencephalitis or SSPE).

Histopathology
• Skin vessels are dilated and surrounded by a mononuclear perivascular infiltrate.
• Lymphoid organs show follicular hyperplasia.
• Random giant cells called Warthin–Finkeldey cells may be observed.
• Eosinophilic intranuclear and intracytoplasmic inclusions may be seen in the mono-
nuclear epithelial and giant cells.
Investigations
• Measles serology
• Viral culture (rarely done)

Mumps
Pathogenesis
• It is a transient inflammation of salivary glands caused by an RNA virus that usually also
involves testes, pancreas and CNS (causes aseptic meningitis and encephalitis).
• It spreads by respiratory droplets to enter respiratory epithelium, salivary gland tissue
and T cells in lymph nodes.
• It can then spread to other sites, including CNS, testis and ovary and pancreas. Aseptic
meningitis is the most common extrasalivary complication of mumps infection. Others
include orchitis leading to sterility, pancreatitis and encephalitis.

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