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INFORMATION ON THE ANTHRAX
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Anthrax
What is anthrax? Effective
treatment (antibiotic medicines) and vaccination means that Anthrax is
much less common nowadays than it used to be in animals. This information has therefore
been taken from the Merck Veterinary Manual Second Edition (1961) and The
Merck Veterinary Manual Seventh Edition (1991) in combination. Anthrax is
an acute, infectious, febrile (causing a fever) disease. It can affect virtually all
warm-blooded animals, including man.
In its most common form, it is essentially a septicaemia, and is
characterised particularly by its rapidly fatal course. In man, it
may be more or less localised (e.g., a malignant pustule, malignant
carbuncle) on the skin or, if acquired by inhaling the spores, a rapidly
fatal pneumonia (woolsorters’ disease) may develop. In countries where the flesh of
animals dead of disease is eaten, an intestinal form of anthrax sometimes
follows the consumption of contaminated meat. Anthrax is
caused by a bacterium, Bacillus Anthracis. This is a grampositive, nonmotile,
spore-forming rectangular shape bacterium of relatively large size (4-8µ x
1-1.5µ). The bacilli are
usually arranged in chain formation, but may occur singly or in
pairs. When bacilli from an opened
carcass are exposed to free oxygen, or after discharge from an infected
animal, they form spores that are resistant to extremes of temperature,
chemical disinfectants, and desiccation. For this reason, the carcass of an
animal dead of anthrax should not be autopsied (post-mortem). These spores are situated centrally in the
cell. When properly stained,
the bacilli in blood and tissue smears of animals dead of the disease
usually reveal a distinct capsule. The organisms are highly
virulent. Upon entering the
body, they multiply rapidly, invade the blood stream and produce
septicaemia (blood poisoning).
In the presence of oxygen, sufficient moisture and a favourable
temperature, the bacilli develop spores of remarkable tenacity. It is generally believed that
spores do not form in the unopened carcass, but sporulation occurs readily
when organisms are discharged from the body of an infected animal or when
the carcass is opened for autopsy. Anthrax spores are highly resistant to heat, low
temperatures, chemical disinfectants and prolonged drying and may retain
their viability for many years in the soil, in water, on hides and on
contaminated objects in storage.
In certain areas subject to flooding, in low-lying marshy land or
in soils that are rich in decomposed vegetable or animal remains, the
organisms survive for long periods. Observations indicate that outbreaks are more likely to occur on
neutral or slightly alkaline soils, which serve as “incubator areas” for
the organisms. In these
areas, the spores apparently revert to the vegetative form and multiply to
infectious levels when optimal environmental conditions of soil, moisture,
temperature and nutrition appear.
Outbreaks originating from soil-borne infection occur primarily in
seasons when the minimal daily temperature is >60°F (16°C). Epidemics tend to occur in
association with marked climatic or ecologic change, such as heavy
rainfall, flooding, or drought and subsequent to periods of drought that
have been preceded by heavy rains or followed by hot, humid weather. In endemic areas, there is a
marked tendency for the disease to be seasonal in character, occurring in
epizootic form during summer and early fall, but sporadic outbreaks may
occur at any time. Even in
endemic areas, anthrax occurs irregularly, often with many years between
occurrences. Incidence and
Dissemination - who gets it and where?
Man may develop localized skin lesions (malignant
carbuncle) from contact of broken skin with infected blood or tissues, or
acquire a highly fatal hemorrhagic mediastinitis (woolsorters’ disease)
from spore inhalation when handling contaminated wool or hair, or
intestinal anthrax from consumption of undercooked
meat. But
virtually all animals are susceptible to anthrax in some degree. Cattle, horses, sheep, goats and
the wild herbivores are most commonly affected. Man and swine appear to possess a
greater natural resistance to the disease. Under certain conditions, dogs,
cats, mink, wild animals of prey and birds may become infected. Mice, guinea pigs and rabbits,
which are commonly used in the laboratory diagnosis of anthrax, are
susceptible to the disease, whereas rats show considerable
resistance. Infection
in cattle, horses, mules, sheep and goats usually is the result of grazing
on infected pastureland.
Infection also may be caused by contaminated fodder or artificial
feedstuffs, such as bone-meal, blood-meal, oil-cake and tankage; by drinking from contaminated
pools or by the bites of contaminated flies. Swine, dogs, cats, mink and wild
animals held in captivity usually acquire the infection from the
consumption of infected meat. Anthrax has a worldwide distribution. Districts where repeated anthrax
outbreaks occur exist in southern Europe, parts of Africa, Australia, Asia
and North and South America.
In the United States, there are large recognized areas of infection
in South Dakota, Nebraska, Arkansas, Mississippi, Louisiana, Texas and
California, and small areas exist in a number of other States. Anthrax is spread from one country to another,
principally through the interchange of infected objects closely associated
with animal life, such as hides, hair, wool, bone meal, meat scraps,
fertilizer, forage and other materials. The disease may spread from
infected areas to adjoining localities and even to distant points by: (1)
Contamination of soil, drinking water and pasture plants with
discharges from diseased animals; (2)
Dogs, cats, coyotes and other carnivores that have fed on infected
carcasses; (3)
Carrion-eating birds; (4)
Flies and possibly other types of insects; (5)
Streams contaminated with surface-drainage from anthrax-infected
soil and tannery wastes;
and (6)
Mixed feeds containing contaminated bone meal, meat scraps and
other animal proteins. Symptoms
Lesions – Overall Symptoms
A general picture of septicaemia is commonly observed
in carcasses of animals dead of anthrax. There may be oozing of blood from
the nostrils and anus, rapid decomposition and marked bloating; the blood fails to clot readily
and is darker in colour than normal;
rigor mortis is frequently absent or incomplete, haemorrhages
beneath the skin are common;
clear or blood-tinged gelatinous exudates are found at the site of
swellings; the spleen usually
is greatly enlarged and the splenic pulp is soft or semi-fluid in
consistency and dark red to blackish in colour. The liver, kidneys and lymph nodes
are usually congested and enlarged. Other Symptoms
Symptoms of anthrax vary according to the species of
animals affected and the acuteness of the attack. The average period of incubation
ranges from 1 to 5 days, but may be longer. The disease may occur in a peracute, acute, subacute,
chronic or cutaneous (skin) form. The peracute, apoplectic or fulminant
form, most common in cattle, sheep and goats, occurs at the beginning of
an outbreak and is characterized by its sudden onset and rapidly fatal
course. Victims present a
picture of cerebral apoplexy (sudden staggering, difficult breathing,
trembling, collapse, a few convulsive movements) and die, frequently
without showing any previous evidence of illness. In acute anthrax of cattle and
sheep, there is an abrupt rise in body temperature and a period of
excitement followed by depression, stupor, respiratory or cardiac
distress, staggering, convulsion, and death. The body temperature may
reach 107°F (41.5°C), rumination ceases, milk production is materially
reduced, and pregnant animals may abort. There may be bloody discharges
from the natural body openings. Chronic
infections are characterized by localized, subcutaneous, oedematous
swelling that can be quite extensive. Areas most frequently involved are
the ventral neck, thorax, and shoulders. The disease in horses is acute. They may show fever,
chills, severe colic, anorexia, depression, weakness, bloody diarrhoea,
and swellings in the region of the neck, sternum, lower abdomen, and
external genitalia. Death usually occurs within 2-3 days of onset. Some pigs in a group may die of acute anthrax without
having shown any previous signs. Others may show rapidly progressive
swelling about the throat, which may cause death by suffocation. Many of the group may develop the
disease in a mild chronic form and recover gradually. However, some of these, when
slaughtered as normal animals, may show evidence of anthrax infection in
the cervical lymph nodes and tonsils. Chronic anthrax with local lesions confined to the
tongue and throat is observed mostly in swine, but occurs occasionally in
cattle, horses and dogs. A cutaneous or localized form of anthrax characterized
by swellings in various parts of the body may occur in cattle and horses
when anthrax organisms lodge in wounds or abrasions of the skin. This form of the disease may occur
following bites by infected flies or in highly susceptible animals
subsequent to vaccination. The methods commonly used in identifying the organism
comprise: (1)
Microscopic examination of blood smears properly stained with
polychrome methylene blue or Giemsa for the presence of encapsulated
bacilli having the morphologic characteristics of Bacillus
anthracis; (2)
Culture tests on plain and blood agar plates for characteristic,
“medusa head” anthrax colonies showing no hemolysis, followed by tests for
motility and reactions on diagnostic media; (3)
Regardless of whether the microscopic and cultural tests are
negative or positive, pathogenicity tests should be carried out on guinea
pigs or mice. Subcutaneous
injection or cutaneous scarification are the methods of exposure
preferred. If the material
injected contains anthrax organisms, the laboratory animal dies, usually
within 48 hours, revealing characteristic lesions, such as an inflammatory
area at the site of injection, gelatinous oedema in the subcutaneous
tissue dark-coloured, uncoagulated blood, an enlarged dark-coloured
friable spleen and a congested mahogany-coloured liver. Anthrax organisms
are present in large numbers in the blood, spleen, liver and other organs
and can be readily recovered in culture tests. Diagnosis
Anthrax should be suspected when animals die suddenly
on or near premises where the disease has appeared previously. Diagnosis based on clinical
symptoms may be difficult, especially when the disease occurs in a new
area. Peracute anthrax may be
confused with other conditions producing sudden death, such as lightning
stroke, sunstroke, lead poisoning and other acute, fatal maladies. Less acute cases may be mistaken
for malignant oedema, hemorrhagic septicaemia, tick fever, anaplasmosis,
blackleg and sweet clover poisoning in cattle; for purpura haemorrhagica,
acute swamp fever and colic in horses and for malignant oedema and acute
hog cholera in swine. A tentative diagnosis based on clinical symptoms
should always be confirmed by a laboratory examination. When anthrax is
suspected, it is inadvisable to make a post-mortem examination because
opening or skinning the carcass may result in spreading the disease and
transmitting the infection to the operator. Specimens
selected for laboratory examination should be obtained a short time after
death, since specimens from carcasses showing evidence of decomposition
are unsuitable for laboratory examination. Blood smears on clean glass slides or sterile cotton
swabs, gauze or suture tape saturated with a sample of blood collected
aseptically from a peripheral blood vessel and allowed to dry, or a few
drops of blood drawn with a sterile syringe and transferred to a sterile
vial and sealed, make excellent specimens for sending to the laboratory
for examination. Specimens should be placed in clean glass containers
labelled “suspected anthrax” and sent to the laboratory in a sealed metal
mailing tube. Ears and spleen tissue, unless properly collected and
prepared for shipment, are dangerous to ship and handle and frequently
arrive at the laboratory in an unsatisfactory condition for examination.
When anthrax in swine is suspected, specimens of the cervical lymph nodes
packed in borax should be submitted for examination, as anthrax organisms
rarely occur in the blood stream of this species. Prophylaxis
(Prevention) Anthrax of
livestock can be largely controlled by annual prophylactic vaccination of
all animals in endemic areas. Vaccination of exposed animals in an
infected herd together with strictly sanitary police measures will reduce
losses and assist in controlling the disease. The agents available for immunization of animals
against the disease are of two types: (a)
Sterile products, anti-anthrax serum (II, III) and anthrax bacterin
(IV); and (b)
Live-spore vaccines (V, VI, VII, VIII, IX) which consist of suspensions
of living anthrax spores of different degrees of attenuation in
physiological salt solution and glycerine for intradermal or subcutaneous
use, with saponin or alum added for subcutaneous injections only. (a) Anti-anthrax
serum (II, III), which rapidly produces passive immunity of about 2 weeks'
duration, is of value both as a prophylactic and as a therapeutic
agent. Its use, however, is
now limited by the efficiency and economy of other immunizing agents and
antibiotics. Anthrax bacterin
(IV) produces an immunity of low degree without danger to non-exposed
animals or to premises. Its
use is indicated where there is a minimum exposure. The live-spore vaccines, on the
other hand, produce a higher degree of immunity than do bacterins and are
widely used in all parts of the world for the immunization of livestock
against anthrax. (b) There are two
kinds of spore vaccines now in general use: - The
Sterne-type nonencapsulated avirulent vaccine (V); and The Sterne spore vaccine, developed in South Africa,
has been used with excellent results there; in England and in many other
countries, and, since 1957, has been steadily gaining in favour for
vaccination of livestock in endemic areas in the United States. It can be used with comparative
safety on all species of livestock and produces a high degree of
immunity. This type of spore
vaccine is now being produced and marketed in the United States under
different trade names. The
No. 1 spore vaccine, of low virulence, is used for the preliminary
injection in the double- or triple-injection method of vaccination. The No. 2 spore vaccine is used in
areas where an ordinary type of infection exists and the No. 3 and No. 4
spore vaccines are used in areas where a highly virulent type of infection
prevails. Satisfactory results have been
obtained with spore vaccines given subcutaneously by the single-, double-
or triple-injection method, but in known anthrax areas, exceptionally good
results are obtained with single-injection intradermal spore vaccine of
selected virulence which produces a rapid, solid, durable immunity with
little or no reaction and is especially useful for immunizing exposed
animals in an infected herd. The simultaneous administration of anti-anthrax serum
and subcutaneous spore vaccines (No. 2, 3 or 4) is likewise an effective
method of immunization and is the method preferred by some veterinarians
for vaccinating exposed animals during an outbreak The use of spore vaccines requires considerable
discretion, and immunization should be carried out in accordance with the
recommendations of the appropriate livestock sanitary officials. Ordinarily, No. 1 or No. 2 Pasteur-type spore
vaccines, when properly administered, should cause little or no reaction
in the majority of vaccinated animals. However, in highly susceptible
animals, severe reactions and an occasional death may occur following
vaccination with spore vaccines, especially with the more virulent No. 3
and No. 4 types. Oedematous
swellings may also occur following vaccination with Sterne-type
vaccine. Since sheep, goats
and horses are very susceptible to anthrax, spore vaccines should be used
with discretion on these species of animals. Certain other factors such as the
site of inoculation, fatigue, general condition of the animal, temperature
and humidity, may to some extent influence the type of reaction following
vaccination. It is ordinarily inadvisable to use anthrax spore
vaccines on premises where the disease has not existed previously unless
danger from exposure is imminent.
Where spore vaccines are used, due care should be taken to prevent
contamination of the surroundings. In anthrax areas, vaccination with the proper type of
immunizing agent usually affords protection for a season, but not more
than a year and should be repeated annually. In some endemic areas that have a
long anthrax season, a booster dose of vaccine is administered 4 to 6
months after the date of the first vaccination. Since
anthrax is often fatal, early treatment and vigorous implementation of a
preventive program are essential. For many years, anti-anthrax serum (I) was most
commonly used for the treatment of anthrax in animals. In recent years, however, this has
been largely supplanted by penicillin (R30) and other antibiotics, such as
oxytetracycline (R26), which have proved to be extremely effective in the
treatment of the disease in animals. When
a soil-borne outbreak occurs, it is best to use antibiotics for the sick
animals and immunize all apparently well animals in the herd and on
surrounding premises. If the
outbreak is associated with a discrete source, such as contaminated bone
meal, antibiotic treatment of exposed animals and removal of the source
may be more effective than vaccination in reducing losses. Domestic livestock respond well to
penicillin if treated in the early stages of the disease. Oxytetracycline given daily in
divided doses also is effective.
Other antibacterials, e.g., erythromycin or sulphonamides, also can
be used, but their effectiveness in comparison to penicillin and the
tetracyclines has not been evaluated under field
conditions. Anthrax of
livestock can be controlled largely by annual vaccination of all grazing
animals in the endemic area and implementing control measures during
outbreaks. The
non-encapsulated Sterne-strain vaccine is used almost universally for
livestock immunization.
Vaccination should be done 2-4 weeks before the season when
outbreaks may be expected.
Animals should not be vaccinated within 2 months of anticipated
slaughter. Because this is a
live vaccine, antibiotics should not be administered within 1 week of
vaccination. Before
vaccination of dairy cattle during an outbreak, the procedures required by
local laws should be determined. Excellent results in the treatment of infected
livestock by penicillin therapy have been reported from different parts of
the United States and France.
In cattle, intramuscular administration of 1 to 3 million units or
more of penicillin during the early stages of the disease resulted in
marked improvement in 36 hours or less, with complete recovery in 1 to 5
days. Large doses of
penicillin (9 to 12 million units) in combination with injections of
anthrax antiserum have given good results in the treatment of animals
affected with postvaccination anthrax. Postvaccination anthrax in cattle
and horses showing advanced symptoms has been successfully treated with a
combination of penicillin intramuscular and oxytetracycline intravenously,
or oxytetracycline alone intravenously. The administration of anthrax
antiserum or penicillin, singly or in combination, to infected swine also
hastens recovery. In the
past, veterinary officials in some States recommended prophylactic
treatment of exposed cattle in an infected herd with penicillin in lieu of
vaccination. Control
Measures
In
outbreaks in livestock, the following control measures will assist in
checking the disease and preventing its spread to other areas: (1)
Notification of appropriate regulatory officials; (2)
A strict quarantine of the infected premises, rigidly enforced to
prevent the movement of livestock from or into the infected areas; (3)
Prompt disposal of dead animals by complete cremation or deep
burial under a layer of quick-lime; (4)
Destruction of manure, bedding and other contaminated material by
burning; (5)
Isolation
of visibly sick animals and immediate treatment with anti-anthrax serum
(I), penicillin (R30) or oxytetracycline (R26); (6)
Vaccination of the apparently well but exposed animals with the
immunizing agents recommended by the livestock sanitary officials; (7)
Changes of pastures if practicable; (8)
Disinfection of contaminated stables and sterilization of all
milking equipment if the outbreak occurs in a dairy herd; (9)
Fly control with effective repellents; (10)
Observation of general sanitary measures by persons who are in
contact with diseased animals, both for their own safety and to prevent
spread of the disease; (11)
Maintenance of good sanitation; and (12)
Due precaution to prevent spreading the infection through rats,
dogs, eats, swine, chickens, buzzards and crows feeding on the carcasses
of animals dead of anthrax.
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