(Splenic Fever, Charbon, Milzbrand)

(avec l'aimable autorisation de l'auteur)

What is anthrax?
What causes anthrax?
Incidence and Dissemination - who gets it and where?


Laboratory Examination

Prophylaxis (Prevention)

Control Measures

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.


What is anthrax?

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.


What causes anthrax?

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.



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.


Laboratory Examination

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.



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 Pasteur-type encapsulated vaccines designated in accordance with their degree of virulence as No. 1 spore (VI), No. 2 spore (VII), No. 3 spore (VIII) and No. 4 spore (IX) vaccine.

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.