Page 200 - Textbook of Pathology, 6th Edition

184 Monkeys carry the virus without suffering from illness and iii) coagulopathy with thrombocytopenia; and
the virus is transmitted from them to humans by Aedes aegypti iv) haemoconcentration.
as vector. The main abnormalities in investigations in DHF are
Yellow fever is characterised by the following clinical
features: Sudden onset of high fever, chills, myalgia, as under:
i) Leucopenia with relative lymphocytosis, sometimes
headache, jaundice, hepatic failure, renal failure, bleeding with atypical lymphocytes
disorders and hypotension.
ii) Thrombocytopenia
MORPHOLOGIC FEATURES. Major pathologic changes iii) Elevated haematocrit due to haemoconcentration
SECTION I
are seen in the liver and kidneys. iv) X-ray chest showing bilateral pleural effusion
Liver. The characteristic changes include: v) Deranged liver function tests (elevated transaminases,
i) midzonal necrosis; hypoalbuminaemia and reversed A:G ratio)
ii) Councilman bodies; and vi) Prolonged coagulation tests (prothrombin time,
iii) microvesicular fat. activated partial thromboplastin time and thrombin time)
Diagnosis of DHF is confirmed by:
Kidneys. The kidneys show the following changes: serologic testing for detection of antibodies;
i) coagulative necrosis of proximal tubules; detection of virus by immunofluorescence method and
ii) accumulation of fat in the tubular epithelium; and monoclonal antibodies; and
iii) haemorrhages. rapid methods such as reverse transcriptase-PCR and
Patients tend to recover without sequelae and death fluorogenic-ELISA.
rate is less than 5%, death resulting from hepatic or renal
failure, and petechial haemorrhages in the brain. At autopsy, the predominant organ changes observed
are as follows:
Dengue Haemorrhagic Fever (DHF) i) Brain: intracranial haemorrhages, cerebral oedema,
dengue encephalitis.
The word dengue is derived from African word ‘denga’ ii) Liver: enlarged; necrosis of hepatocytes and Kupffer
meaning fever with haemorrhages. Dengue is caused by virus cells, Reye’s syndrome in children.
transmitted by bites of mosquito Aedes aegypti; the iii) Kidneys: petechial haemorrhages and features of renal
transmission being highest during and after rainy season failure.
when mosquitos are numerous. DHF was first described in iv) Muscles and joints: perivascular mononuclear cell
1953 when it struck Philippines. An outbreak of DHF infiltrate.
occurred in Delhi and neighbouring cities in 1996 claiming
General Pathology and Basic Techniques
several lives. Since then, some cases of DHF have been Chikungunya Virus Infection
reported in post-monsoon period every year in North India.
Dengue occurs in two forms: The word chikungunya means “that which bends up” and
is derived from the language in Africa where this viral
1. Dengue fever or break-bone fever in an uncomplicated way disease was first found in human beings. Chikungunya virus
is a self-limited febrile illness affecting muscles and joints infection is primarily a disease in nonhuman primates but
with severe back pain due to myalgia (and hence the name the infection is transmitted to humans by A. aegypti
‘break-bone’ fever). mosquito. The disease is endemic in parts of Africa and Asia
2. Dengue haemorrhagic fever (DHF), on the other hand, is a and occurs sporadically elsewhere. A massive outbreak
severe and potentially fatal form of acute febrile illness occurred in 2004 in Indian Ocean region affecting people in
characterised by cutaneous and intestinal haemorrhages due Sri Lanka, Maldives, Mauritius and parts of India.
to thrombocytopenia, haemoconcentration, hypovolaemic Clinically, the disease is characterised by abrupt onset of
shock and neurologic disturbances. DHF is most common in fever, severe arthralgia (producing bending posture of
children under 15 years of age. patient due to pain and hence the name), migratory
Dengue virus infects blood monocytes, lymphocytes and polyarthritis affecting small joints, chills, headache, anorexia,
endothelial cells. This initiates complement activation and nausea, abdominal pain, rash, petechiae and ocular
consumptive coagulopathy including thrombocytopenia. The symptoms such as photophobia.
entire process takes place rapidly and may evolve over a Major laboratory findings include leucopenia, mild
period of a few hours. If patient is treated appropriately at thrombocytopenia, elevated transaminases and raised CRP.
this stage, there is rapid and dramatic recovery. But in
untreated cases, dengue shock syndrome develops and death INFLUENZA VIRUS INFECTIONS
occurs.
Influenza virus infection is an important and common form
MORPHOLOGIC FEATURES. The predominant organ of communicable disease, especially prevalent as a seasonal
changes in DHF are due to following: infection in the developed countries. Its general clinical
i) focal haemorrhages and congestion; features range from a mild afebrile illness similar to common
ii) increased vascular permeability resulting in oedema cold by appearance of sudden fever, headache, myalgia,
in different organs; malaise, chills and respiratory tract manifestations such as
cough, soar throat to a more severe form of acute respiratory