Transcript Causative agents of zoonoses

Chair of Microbiology, Virology, and Immunology
CAUSATUIVE AGENTS OF
ZOONOSES
Yersinia pestis belongs to Genus Yersinia which
includes in family Enterobacteriaceae.
The causative agent of plague, Yersinia pestis, was
discovered by the French microbiologist A. Yersin in
Hong Kong in 1894.
Ukrainian scientists D. Samoilovich, D. Zabolotny
and others contributed greatly to the study of the
mechanisms of its transmission.
The French microbiologists G. Girard and T. Robic
obtained a live vaccine from the attenuated EV
strain.
Bubonic plague, caused by Y. pestis, is an ancient disease
that has killed millions of people over the centuries. For
example, it is believed to have killed more than 100 million
persons in an epidemic in the sixth century.
Another epidemic in the 14th century killed one fourth of
the European population, and the London plague in 1665
killed more than 70,000 persons.
In 1893, an epidemic began in Hong Kong and spread to
India where more than 10 million individuals died over a
20-year period.
Morphology. The plague
bacillus, as seen in tissue
smears, is ovoid-shaped. It is
non-motile, forms no spores,
and on solid media cultures is
elongated in form. In
preparations from tissues and
cultures Y. pestis is found to
have a delicate capsule. The
organism stains with ordinary
aniline dyes and gives a
bipolar appearance, its ends
staining more intensively.
Y. pestis
Cultivation. The optimum temperature for cultivation is 2530° C.
On agar slants the culture forms a viscid translucent
mucilaginous mass. On agar plates it forms colonies with
turbid white centres and scalloped borders resembling lace or
crumpled lace handkerchiefs.
In meat broth the cultures form a pellicle on the surface with
thread-like growth resembling stalactites and a flocculent
precipitate. Sodium sulphite, fresh haemolytic blood, sarcinic
extract, and live sarcina (“feeders”) are used as growth
stimulators. They are of special value when the seeded
material contains a small number of organisms.
Differentiation of Yersinia Species
adonitol
arabinose
arabitol
arbutin
sorbitol
Production of
Hydrogen
sulphide
xylose
Carbohydrate fermentation
Y. pestis
–
+
–
–
+
+
+
Y. pseudotuberculosis
Y. enterocolitica
+
+
–
+
–
–
–
–
+
–
+
+
+
+
Species
Some diagnostic signs differentiating the bacteria of
plague from those of pseudotuberculosis in rodents
Yersinia pestis
Yersinia
pseudotuberculosis
1.Fresh strains do not usually 1. Fresh strains usually
ferment rhamnose
ferment rhamnose
2. Do not ferment adonite
2. Ferment adonite with the
formation of acid
3. Do not ferment urea
3. Ferment urea
4. On desoxycholic citrate
agar they grow with the
formation of red colonies
4. On desoxycholic citrate
agar they grow with the
formation of yellow colonies
5. Are lysed by the plague
phage to the titre
5. Do not undergo lysis
Toxin production. Y. pestis is very virulent for humans. The
important virulence factors of Y. pestis seem to be directed
toward two goals for the organisms: (1) invasion and
proliferation within host cells, and (2) resistance to killing by
the host. The incredibly high fatality rate of bubonic plague is
probably primarily because of septic shock resulting from the
bacteremia occurring in the disease.
Virulence factors that seem to be important in human
disease.
Factor
Fraction 1 capsule
V/W antigens
Fibrinolysin
Low Ca2+ response gene
YOP H
YOP K & L
Apparent Function
Antiphagocytic
Suppress granuloma
formation
Tissue invasion
YOP synthesis
Protein tyrosine phosphatase
Inhibit cell-mediated immune
response
Antigenic Makeup of Y. pestis
Antigen
Composition
Function
Protection
Envelope
(F1)
A
Soluble
polysaccharideprotein
Immunogen
+
B
Soluble
polysaccharidae
Species-specific
antigen
–
C
Insoluble
polysaccharidae
Nonimmunogen
–
Antigen
Antigenic Makeup of Y. pestis
ComposiFunction
tion
Protection
Somatic (O)
1
Unknown
Virulence antigen
+
3
Corresponds
to F1
Species-specific antigen
+
4
Heat-stable
protein
Nonimmunogen
–
5
Heat-stable
protein
Shared with Y. pseudotuberculosis
–
8
Heat-labile
polypeptide
Toxin
-
V
Protein
Associated with virukence
inhibits phagocytosis
+
Antigenic Makeup of Y. pestis
Antigen
Composition
Function
W
Protein
Shared with Y.
pseudotuberculosis
Rough
Heat-stable
polysaccharidae
Shared with Y.
pseudotuberculosis
Protection
+
–
Pathogenicity for animals. Rodents, among them black rats,
grey rats, mice, susliks, midday gerbils, tumarisks, and
marmots (tarbagans) are susceptible to plague. More than 300
rodent species may spontaneously contract the disease. In
addition, 19 rodent species are susceptible to laboratory
infection with plague. Camels died in the Astrakhan steppes
m 1911, and humans who ate camel meat contracted plague.
Pigs, sheep, goats, donkeys, mules, dogs, cats, monkeys, and
certain carnivores are susceptible to the disease in natural
environments. However, little epidemiological importance is
attached to them.
1. Reservoir: Fleas and wild
rodents (ground squirrel, gerbil,
marmot, cavy)
1. Reservoir: Rodents in contact
with man (house rat, sewer rat)
2. Vectors: Fleas on infected
rodents, flea i rodent burrows
2. Vectors: Fleas
3. Rodent – Flea – Rodent
Bubonic palgue:
Rat – Xenopsilla – Man
Man – Pulex irritans – Man
Hangling infected rodents
4. Wild Rodent to man – Sporadic 4. Sepicemic plague: Primary –
human plague. Usually direct
entry throgh mucose
contact
Secondary – complication of
bubonic
5. Wild rodent – flea – domestic
rodent
5. Pneumonic plague: Secondary
– complication of bubonic
6. Domestic rodent – flea – man:
human plague
6. Primary – droplet infection
man – to – man
The disease is transmitted
by the bites of fleas (e.g.,
Xenopsylla cheopis, the rat
flea) which have previously
sucked blood from an
infected animal. The
ingested bacilli proliferate
in the intestinal tract of the
flea and eventually block
the lumen of the
proventriculus. The hungry
flea, upon biting another
rodent, regurgitates into the
wound a mixture of plague
bacilli and aspirated blood.
Bubonic plague
Immunity. After recovery from the disease a stable
immunity of long duration is acquired. Realizing this, in
ancient times people living in countries invaded by plague
made use of convalescents for nursing plague patients and
burying corpses.
Postinfection
and
postvaccinal
immunities
are
predominantly due to the phagocytic activity of the cells of
the lymphoid-macrophage system. An important role is
played by the protective capsular antigen which serves as
the basis in the preparation of chemical antiplague vaccines.
Laboratory diagnosis. Examination is carried out in
special laboratories and in antiplague protective clothing.
A strict work regimen must be observed. Depending on the
clinical form of the disease and the location of the
causative agent, test specimens are collected from bubo
content (in bubonic plague), ulcer secretions (in cutaneous
plague), mucus from the pharynx and sputum (in
pneumonic plague), and blood (in septicaemic plague).
Test matter is also recovered from necropsy material
(organs, blood, lungs, contents of lymph nodes), rodent
cadavers, fleas, foodstuff's, water, air, etc.
1. Microscopy of smears, fixed in Nikiforov's mixture and
stained by the Gram method or with methylene blue by
Loeffler's method.
2. Inoculation of the test material into nutrient media,
isolation of a pure culture and its identification.
3. Biological tests of the isolated pure culture and of
material from which isolation of the organism is difficult
are conducted on guinea pigs
Treatment.At present streptomycin is used for treatment of
plague, the drug being very effective and curing even
pneumonic plague in a high per cent of cases. Good results
have been obtained from a combination of streptomycin
with chloromycetin or tetracycline with antiplague serum.
Antiplague gamma-globulin and a specific bacteriophage
are also used for treatment of plague patients. Penicillin,
chlortetracycline, and sulphonamides are recommended in
cases with complications.
Prophylaxis. General prophylaxis comprises the following
measures:
(1) early diagnosis of plague, particularly the first cases;
(2) immediate isolation and hospitalization of patients and
enforcement of quarantine;
(3) observation (i. e. isolation of individuals or groups of
people suspected of having been in contact with infected
material, daily inspection from house to house, temperature
measurement twice a day, and observation during the possible
incubation period);
(4) thorough disinfection and extermination of rats in disease
foci;
(5) individual protection of medical personnel and
prophylactic treatment with streptomycin and vaccination;
(6) prophylactic measures and systematic observation carried out
by plague control laboratories, stations, and institutes in endemic
areas;
(7) observance of international plague control conventions;
(8) security measures from plague invasion at frontiers. Specific
prophylaxis is accomplished with live EV vaccine.
Causative Agent of Tularaemia
The tularaemia bacteria are short coccal-shaped or rod-like
cocci measuring 0.2-0.7 mcm. In old cultures the organisms
retain the coccal form. They are non-motile,
polychromatophilic, and Gram-negative. In the animal body
they are sometimes surrounded by a fine capsule.
Cultivation. The tularaemia organism is an aerobe which
does not grow on ordinary media, but grows well at 37° C on
media rich in vitamins, e. g. yolk medium which consists of
60 per cent of yolk and 40 per cent of a 0.85 per cent sodium
chloride solution with pH 6.7-7A. The organisms are cultured
in a thermostat for 2-14 days.
Fermentative properties. Tularaemia bacteria break down
proteins with the elimination of hydrogen sulphide, and do
not produce indole. They ferment glucose, levulose,
mannose, and maltose, with acid formation. Dextrin,
saccharose, and glycerin fermentation is not a stable
property. Biochemical properties are unstable and liable to
comparatively rapid changes.
Toxin production. The existence of a soluble toxin in
tularaemia bacteria has not been demonstrated. The
organism's virulence is associated with its K-antigen. The
tularaemia bacterium grows poorly in liquid media, and for
this reason it is difficult to isolate any toxin.
Pathogenicity for animals. The organism is pathogenic
for water rats, field voles, grey rats, common field mice
and house mice, hares, susliks, chipmunks, hamsters,
muskrats, gerbils, moles, shrews, and other animals.
Among the domestic animals camels, sheep, cats, dogs,
and pigs are susceptible to the disease, and among
laboratory animals, guinea pigs and white mice.
Laboratory diagnosis. 1. Allergy develops on the thirdfifth day of the disease. For this reason, intracutaneous and
cutaneous tests with tularine are made for early diagnosis.
In tularaemia patients the test gives a positive reaction 6-12
hours after inoculation of tularine.
2. In the second week of the disease agglutinins begin to
accumulate in the blood. They are detected by carrying out
the agglutination reaction by the blood-drop and volume
methods. In some cases this test may give a positive
reaction with material containing brucella organisms, since
they possess antigens common to tularaemia bacteria.
3. The tularaemia culture is isolated by the biological
method as it is impossible to recover the pathogen directly
from a tularaemia patient. For this purpose white mice or
guinea pigs are infected by material obtained from people
suffering from the disease (bubo punctate, scrapings from
ulcers, conjunctiva! discharge, throat films, sputum, and
blood).
4. Laboratory diagnosis of rodent tularaemia is made by
microscopy of smears from organs, precipitin ring reaction
(thermoprecipitation), and biological tests.
Water, foodstuffs, and blood-sucking arthropods are
examined by biological tests.
Prophylaxis comprises the following measures:
(1) systematic observation, absolute and relative
registration of rodent invasion, and extermination of rats;
(2) prevention of mass reproduction of the rodents;
(3) protective measures in agricultural enterprises against
contamination by tularaemia-infected rodents;
(4) protection of foodstuffs and water from rodents;
(5) control of ticks, horseflies, stable-flies, mosquitoes,
and protection from these insects;
(6) specific prophylaxis with a live vaccine.
The vaccine is prepared in a dry form. A single application
is made by rubbing it into the skin and it produces
immunity for a period of 3-6 years.
Brucellae
Brucella abortus
Brucella melitensis
Brucella cuis
Brucellae are small, coccal, ovoid-shaped micro-organisms
0.5-0.7 mcm in size. Elongated forms are b.6-1.5 mem in
length and 0.4 mcm in breadth. Under the electron
microscope Brucella organisms of cattle, sheep and goats
appear as coccal and coccobacilary forms, while those of
pigs are rod-shaped. They are Gram-negative, non-motile,
and do not form spores or capsules (in some strains capsules
are sometimes present). DNA contains 56 to 58 per cent of
G+C.
Cultivation. The organisms are aerobic. When cultivated
from material recovered from patients, they grow slowly,
over a period of 8-15 days.
Brucella organisms may be cultivated on ordinary media,
but they grow best on liver-extract agar and liver-extract
broth. On liver-extract agar the organisms form round,
smooth colonies with a white or pearly hue. In liver-extract
broth they produce a turbidity, and subsequently a
mucilaginous precipitate settles at the bottom of the tubes
Brucella organisms grow well on unfertilized eggs and on
the yolk sac of a 10-12-day-old chick embryo.
The brucellae of bovine origin (Brucella abortus) only
grow in an atmosphere of 10 per cent carbon dioxide,
which serves as a growth factor.
Colonies of Brucella
Fermentative properties. Brucellae do not liquefy gelatin
and do not produce indole. Some strains produce
hydrogen sulphide, break down urea and asparagin,
reduce nitrates to nitrites, and hydrolize proteins, peptones
and amino acids, with release of ammonia and hydrogen
sulphide. No carbohydrates are fermented, although a
small number of strains ferment glucose and arabinose.
Toxin production. Brucellae do not produce soluble
toxins. An endotoxin is produced as a result of
disintegration of the bacterial cells. This endotoxin
possesses characteristic properties and may be used in
allergic skin tests
Antigenic structure. The organism contains four antigens:
A, M, O, Vi, G and R.
The M-antigen is predominant among brucellae of sheep and
goats, and the A-antigen, in the other species. Substances of
polysaccharide character, with no type specificity, have been
extracted from brucellae of cattle, sheep and goats.
Pathogenity for animals. Goats, sheep, cattle, pigs, horses,
camels, deer, dogs, cats, and rodents (rats, mice, susliks,
hamsters, rabbits, field-voles, water rats, and other animals)
are all susceptible to infection by brucellae. The high
concentration of brucellae in the placenta of cattle is
explained by the presence in this tissue of the growth
stimulator erythrol.
In human beings brucellosis is characterized by undulant
fever with atypical and polymorphous symptoms. The disease
may assume an acute septic or a chronic metastatic course.
The structural and motor systems, haemopoietic, hepatolienal,
nervous and genital systems are often involved. Pregnant
women may have miscarriages. Often brucellosis recurs,
continuing for months and years. The death rate is 1-3 per
cent. The diagnosis of mild, asymptomatic forms presents
difficulties and is based on laboratory tests.
Laboratory diagnosis. The patient's blood and urine (for
isolation of the pathogen), serum (for detection of
agglutinins), milk and dairy products (for detection of
brucellae or agglutinins in milk) are examined. The microbe
is isolated in special laboratories.
1. Culture isolation. Since brucellosis is often accompanied
by bacteraemia, blood is examined during the first days of
the disease (preferably when the patient has a high
temperature). The cultures are grown for 3-4 weeks or more.
Five to ten per cent of carbon dioxide is introduced into one
of the flasks (for growth of the 23 bovine species of the
bacteria). Inoculations on agar slants are made every 4-5
days for isolation and identification 'of the pure culture.
Brucella susceptibility to stains
An antiphage serum is introduced into the cultures for
neutralization of the phage which inhibits the growth of
brucellae.
The best results are obtained when the blood is inoculated
into the yolk of an unfertilized egg or the yolk sac of a
chick embryo. Growth is examined every 2-3 days.
If the blood culture produces a negative result bone
marrow obtained by sternum puncture is inoculated onto
solid and liquid media for isolation of myelocultures.
Susceptibility to
phages
The urine is also examined. It is obtained with a catheter,
centrifuged, and 0.1 ml of the precipitate is seeded onto
agar plates containing 1 :200000 gentian violet. In some
cases faeces, cow's and human milk, and amniotic fluid of
sick humans and animals are examined for the presence
of Brucella organisms.
Brucella cultures may be isolated by the biological
method. For this purpose healthy guinea pigs or white
mice are injected with 0.5 or 3 ml of the test material. A
month later the guinea pigs' blood is tested for agglutinins,
the allergic test is carried out, and the pure culture is
isolated. White mice are tested bacteriologically every
three weeks.
2. Serological test. The Wright (in test tubes) and
Huddleson (on glass) reactions are carried out. The Wright
reaction is valued highly positive in a 1 800 serum
dilution, positive in a 1:400-1:200 dilution, weakly
positive in 1 :100 dilution, and doubtful at a titre of 1 :50.
3. Skin allergic test. To determine allergy, Burne's test is
made beginning from the fifteenth-twentieth day of the
disease. A 0.1 ml sample of the filtrate of a 3- or 4-weekold broth culture (brucellin) is injected intracutaneously
into the forearm. The test is considered positive if a
painful red swelling 4 by 6 cm in size appears within 24
hours.
4. Opsono-phagocytic test. This test detects changes in
the phagocytic reaction. The index of healthy individuals
averages 0-1 and occasionally 3-5. In sick persons the
reaction is considered high if the index is 50-70, mild, if it
is 25-49, and low, if it is 10-24.
For detecting brucellae in the external environment the
reaction for demonstrating a rise in bacteriophage titre is
carried out.
5. In some cases the complement-fixation test, the
indirect haemagglutination reaction, and the
immunofluorescence reaction are used.
Treatment. Patients suffering from brucellosis are treated
with antibiotics (amphenicol, tetracycline, etc.). Chronic
cases are best treated by vaccine therapy. X-ray therapy,
blood transfusions, electropyrexia, and balneotherapy,
hormonotherapy.
Injection
of
antibrucellosis
gammaglobulin is recommended for the prevention of
recurrences.
Prophylaxis comprises a complex of general and specific
measures carried out in conjunction with veterinary
services.
Immunization with the live or killed vaccine is an
additional measure in districts where there are cases of
goat-sheep brucellosis.
B. anthracis belongs to the family Bacillaceae.
Anthrax bacilli are large organisms, measuring 3-5 mcm
in length and 1-1.2 mcm in breadth. In the body of
animals and man they occur in pairs or in short chains,
while in nutrient media they form long chains. In stained
preparations the ends of the bacilli appear either to be
sharply cut across or slightly concave, resembling
bamboo canes with elbow-shaped articulations. The G+C
content in DNA is 32 to 62 per cent.
B. anthracis
In the bodies of man
and animals the bacilli
produce capsules which
surround
a
single
organism
or
are
continuous over the
whole chain. Capsules
are also produced on
nutrient media which
contain blood, serum,
egg yolk, or brain
tissue.
Colony of B. anthracis
Colony of
B. anthracis
Fermentative properties. The
anthrax bacilli possess great
biochemical activity. They contain
the enzymes — dehydrogenase,
lipase, diastase, peroxidase, and
catalase. In gelatin stab-cultures
growth resembles an inverted fir
tree, the gelatin being liquefied in
layers. The organisms cause late
liquefaction of coagulated serum
and produce ammonia and
hydrogen sulphide. They slowly
reduce nitrates to nitrites and
coagulate and peptonize milk. The
organisms
ferment
glucose,
levulose, saccharose, maltose,
trehalose, and dextrin with acid
production.
Toxin production. When growing on semisynthetic
medium, B. anthracis discharges an exotoxin (oedema
factor) into the culture fluid. The capsular substance is
very toxic, it contains Brayle's aggressins. Loss of the
capsule results in loss of virulence.
It has been established that some strains of B. anthracis
produce in the animal's body a lethal toxin (mouse
factor), which on addition of the oedema factor or the
protective antigen causes death of the animal.
The serum of guinea pigs who died from anthrax
possesses the property of causing death of albino mice
and guinea pigs on being injected intra-venously in small
doses.
Components of Anthrax Toxin
Component
Function
EE
Inactive adenylate cyclase activated by
calmodulin
LF
Causes pulmonary edema and death in rats;
cytolytic for macrophages
PA
Required for the binding of both EF and
LF to host cell
EF, edema factor; LF, lethal factor; PA, protective antigen
Differential-Diagnostic Signs of B. anthracis,
Antracoides
Properties
B. anthracis
Anthracoides
Motility
Capsule formation
Hemolysis
+
+
-
+
+
Lysis with specific
phage
+
-
“Pearl necklace” test
+
-
Pathogenicity for
rabbits
+
-
Pathogenesis and diseases in man. Anthrax is a typical
zoonosis. Anthrax is primarily a disease of sheep, goats,
cattle, and, to a lesser extent, other herbivorous animals.
Once the disease is established in an area, bacterial
endospores from infected or dead animals are able to
contaminate the soil and, because of the resistant
endospores, the pasture areas remain infectious for other
animals for many years In most animal infections, the
spores enter the body by way of abrasions in the oral or
intestinal mucosa, and after entering the bloodstream, they
germinate and multiply to tremendous numbers, causing
death in 2 to 3 days.
Humans acquire the disease from sick animals or articles and
clothes manufactured from contaminated raw materials:
sheepskin coats, fur mittens, collars, hats, shaving-brushes, etc.
In summer the infection may be transmitted by blood-sucking
insects. Anthrax occurs in three main clinical forms: cutaneous,
respiratory, and intestinal.
Lesion of
cutaneous
anthrax (eighth
day of illness)
on the arm of a
person who had
been a carder in
a wool factory
Laboratory diagnosis. In cases of cutaneous anthrax the
malignant pustular exudate is examined; it is obtained
from the deep layers of the oedematous area where it
borders with the healthy tissues. Sputum is examined in
cases of the respiratory form, faeces and urine, in intestinal
form, and blood is examined in cases of septicaemia.
1. The specimens are examined under the microscope, the
smears are Gram-stained, or stained by the RomanowskyGiemsa method. The presence of morphologically
characteristic capsulated bacilli, arranged in chains, allows a
preliminary diagnosis.
2. For isolation of the pure culture the specimens are
inoculated into meat-peptone agar and meat-peptone broth.
The isolated culture is differentiated from other
morphologically similar bacteria by its morphological and
biochemical properties.
3. Laboratory animals (white mice, guinea pigs and rabbits)
are inoculated with the pathological material and with the
pure culture derived from it. B. anthracis causes the death of
white mice in 24-48 hours and of guinea pigs in 2-3 days
following inoculation. Microscopic examination of smears
made from blood and internal organs reveals anthrax bacilli
which are surrounded by a capsule.
Phagolysis of B. anthracis
A rapid biological test is also employed. The culture
obtained which has to be identified is introduced
intraperitoneally into white mice. Several hours after
inoculation smears are prepared from the peritoneal
contents. Detection of typical capsulated bacilli gives a
basis for con-firming the final result of the biological test.
The allergic test with anthracin (a purified anthrax
allergen) is employed when a retrospective diagnosis is
required in cases which have yielded negative results with
microscopical and bacteriological examination.
Postmortem material as well as leather and fur used as raw
materials
are
examined
serologically
by
the
thermoprecipitin reaction (Ascoli's test) since isolation of
the bacilli is a matter of difficulty in such cases.
As can be seen in Fig., the result in the first test tube
(containing the test material) may be either positive or
negative, in the second test tube (control) it must be only
positive, and in the third, fourth, fifth, and sixth control test
tubes the results must always be negative.
When employing laboratory diagnosis of anthrax, one
must bear in mind the possibility of the presence of
bacteria identical with B. anthracis in their biological
properties. These sporing aerobes are widely distributed in
nature and are normally sporeforming saprophytes. They
include B. cereus, B. subtilis, B. megaterium, etc.
The anthrax bacilli may be differentiated from anthracoids
(false anthrax organisms) and other similar sporing
aerobes by phagodiagnosis. The specific bacteriophage
only causes lysis of the B. anthracis culture.
Treatment comprises timely intramuscular injection of
antianthraxglobulin, and the use of antibiotics (penicillin,
tetracycline, and streptomycin).
Prophylaxis. General measures of anthrax control are
carried out in joint action with veterinary workers. These
measures are aimed at timely recognition, isolation, and
treatment of sick animals. They also include thorough
disinfection of premises for live-stock, territory an dall
objects found on it, and ploughing over of pastures.
Carcasses of animals which have died of anthrax are burnt
or buried on specially assigned territory, not less than 2
meters deep, and covered with lime chloride.
The veterinary authorities also enforce regulations banning
the use of contaminated meat for food and introduce
thorough control of manufactured articles from animal hide
and fur which are to be marketed.
Ever since Pasteur's celebrated field trial, in which animals
were successfully immunized with a living attenuated
suspension of B. anthracis, efforts have been directed
toward the production of effective vaccines that possess
little or no toxicity. Because killed vaccines are of little
value, two different approaches for the stimulation of
artificial immunity have been undertaken: (1) the isolation
and use of the protective antigenic component of the
anthrax toxin, and (2) the use of attenuated living bacteria
to induce antitoxic immunity.
At present, a vaccine, prepared from non-capsulated anthrax bacilli
and consisting of a suspension of live spores of vaccine strains, is
used. It is employed for immunization of man and domestic
animals.
The vaccine is completely harmless, producing immunity quite
rapidly (in 48 hours) and for a period of over a year. It is inoculated
in a single dose.
Vaccination is carried out among people who work at raw-material
processing factories (processing of animal hide and hair), at meatpacking factories, and at farms where anthrax is encountered.
Reinoculation is performed after a period of 12 months.
However, all effective living vaccines possess some toxicity, and
they have not been used in the United States for humans. The
vaccine licensed in the United States for use in humans is an
aluminum hydroxide-adsorbed supernatant material from ferment
or cultures of a toxigenic, but nonencapsulated strain of B.
anthracis. Unfortunately, it induces a short-lived immunity and requires annual boosters.
Individuals who have been in contact with material contaminated
with anthrax organisms (when dressing infected carcasses or
using such meat for food) are given intramuscular injections of
20-25 ml of antianthrax globulin together with penicillin.
PA seems to be the only effective component of the vaccine
because neither EF nor LF induced protection. It has been cloned
in Bacillus subtilis, and guinea pigs immunized by the
intramuscular injection of the B subtilis cell suspension were
protected against challenge by B. anthracis. PA also has been
cloned in vaccinia virus, where it induced at least partial
immunity to challenge in guinea pigs and mice. It is, therefore,
possible that a cloned source of PA will be used in future anthrax
vaccines for humans. The vaccine used in domestic animals
consists of a living spore culture, which is designated the Sterne
strain. It still carries the plasmid encoding for PA, EF, and LF, but
its avirulence is attributed to the loss of the plasmid encoding the
antiphagocytic capsule.