Page 194 - Textbook of Pathology, 6th Edition

178 ANTHRAX aerosols results in rapid development of malignant
pustule in the bronchus. This is followed by development
Anthrax is a bacterial disease of antiquity caused by Bacillus
anthracis that spreads from animals to man. The disease is of primary extensive necrotising pneumonia and
widely prevalent in cattle and sheep but human infection is haemorrhagic mediastinitis which is invariably fatal.
rare. However, much of knowledge on human anthrax has 3. Intestinal anthrax is rare in human beings and is quite
been gained owing to fear of use of these bacteria for military similar to that seen in cattle. Septicaemia and death often
purpose by rogue countries or for “bio-terrorism” (other results in this type too. The lesions consist of mucosal
microbial diseases in this list include: botulism, pneumonic oedema, small necrotic ulcers, massive fluid loss and
plague, smallpox). A few years back, the human form of haemorrhagic mesenteric lymphadenitis.
SECTION I
disease attracted a lot of attention of the media and the Besides, anthrax septicaemia results in spread of
civilised world due to its use in the form of anthrax-laced infection to all other organs.
letters sent by possible terrorist groups as a retaliatory
biological weapon against the US interest subsequent to LABORATORY DIAGNOSIS. Anthrax can be diagnosed by
punitive attacks by the US on Afghanistan as an aftermath a few simple techniques:
of September 11, 2001 terrorist attacks in the US. In India, i) Smear examination: Gram stained smear shows rod-shaped,
anthrax in animals is endemic in South due to large spore-forming, gram-positive bacilli. Endospores are
unprotected and uncontrolled live-stock population. detectable by presence of unstained defects or holes within
the cell.
ETIOPATHOGENESIS. The causative organism, Bacillus
anthracis, is a gram-positive, aerobic bacillus, 4.5 μm long. It ii) Culture: Anthrax bacteria grow on sheep blood agar as
is a spore-forming bacillus and the spores so formed outside flat colonies with an irregular margin (medusa head).
the body are quite resistant. The disease occurs as an Anthrax contaminated work surfaces, materials and
exogenous infection by contact with soil or animal products equipment must be decontaminated with 5% hypochlorite
or 5% phenol.
contaminated with spores.
Depending upon the portal of entry, three types of human
anthrax is known to occur: WHOOPING COUGH (PERTUSSIS)
i) Cutaneous form by direct contact with skin and is most Whooping cough is a highly communicable acute bacterial
common. disease of childhood caused by Bordetella pertussis. The use
ii) Pulmonary form by inhalation, also called as “wool- of DPT vaccine has reduced the prevalence of whooping
sorters’ disease” and is most fatal. cough in different populations.
General Pathology and Basic Techniques
The causative organism, B. pertussis, has strong tropism
iii) Gastrointestinal form by ingestion and is rare. for the brush border of the bronchial epithelium. The
The mechanism of infection includes spread of bacilli organisms proliferate here and stimulate the bronchial
from the portal of entry to the regional lymph nodes through epithelium to produce abundant tenacious mucus. Within
lymphatics where the bacteria proliferate. There is delayed 7-10 days after exposure, catarrhal stage begins which is the
accumulation of polymorphs and macrophages. most infectious stage. There is low grade fever, rhinorrhoea,
Macrophages also play a role in expression of bacterial conjunctivitis and excess tear production. Paroxysms of
toxicity; bacterial toxin is quite lethal to macrophages. cough occur with characteristic ‘whoop’. The condition is self-
limiting but may cause death due to asphyxia in infants. B.
MORPHOLOGIC FEATURES. The characteristic lesions pertussis produces a heat-labile toxin, a heat-stable endotoxin,
of anthrax are haemorrhage, oedema and necrosis at the and a lymphocytosis-producing factor called histamine-
portal of entry.
sensitising factor.
1. Cutaneous anthrax is the most common and occurs in
two forms: one type is characterised by necrotic lesion due Microscopically, the lesions in the respiratory tract consist
to vascular thrombosis, haemorrhage and acellular of necrotic bronchial epithelium covered by thick
necrosis, while the other form begins as a pimple at the mucopurulent exudate. In severe cases, there is mucosal
point of entry of B. anthracis into the abraded exposed skin, erosion and hyperaemia. The peripheral blood shows
more often in the region of hands and the head and neck. marked lymphocytosis upto 90% (Fig. 7.3) and
The initial lesion develops into a vesicle or blister enlargement of lymphoid follicles in the bronchial mucosa
containing clear serous or blood-stained fluid swarming and peribronchial lymph nodes.
with anthrax bacilli which can be identified readily by
smear examination. The bursting of the blister is followed GRANULOMA INGUINALE
by extensive oedema and black tissue necrosis resulting
in formation of severe ‘malignant pustule’. Regional Granuloma inguinale is a sexually-transmitted disease
lymph nodes are invariably involved along with profound affecting the genitalia and inguinal and perianal regions
septicaemia. caused by Calymmatobacterium donovani. The disease is
common in tropical and subtropical countries such as New
2. Pulmonary anthrax (wool-sorters’ disease) occurring Guinea, Australia and India. The organism inhabits the
from inhalation of spores of B. anthracis in infectious
intestinal tract. The infection is transmitted through vaginal