Anthrax or bacillary anthrax

What is anthrax?

Anthrax, also known as bacillary anthrax, is caused by the Bacillus anthracis bacterium.  It affects many species of mammals, mainly herbivores (cattle, sheep, goats and horses) and certain birds.  It is a zoonotic disease, since in very rare cases it can be transmitted to humans.  

As it multiplies, the bacterium produces toxins capable of completely neutralising the host's immune response.  It is on the list of potential bioterrorism agents due to its ability to persist for long periods in the form of spores, and is listed in Annex A of the list of highly pathogenic micro-organisms or toxins.

How can animals become infected? 

In ruminants, infection most often occurs through grazing on contaminated grass, particularly in areas close to anthrax-contaminated carcasses, or through ingestion of fodder harvested from contaminated fields.  The bacterium can survive in the soil in spore form for many years.  The spores can rise to the surface, particularly when periods of drought are followed by heavy rainfall, or after earthworks.  In France, the disease generally occurs during the summer, although cases can occur in other seasons, for example if spore-contaminated  fodder is distributed in winter.  The burial of animals that died from anthrax over the centuries has contributed to the contamination of certain fields known as champs maudits (‘cursed fields’), particularly in Burgundy, the Alps and in the Massif Central.

How is the anthrax bacterium transmitted to humans? 

There are several possible routes of contamination for humans:

• One is through the skin, in the event of contamination of wounds or accidental punctures when handling carcasses, foodstuffs (meat, offal) and products (skins, hair, wool, horns, bones or carcasses) from infected animals.  Historically, these cases were found in Europe among people working with animals or animal products (butchers, slaughterhouse and tannery workers, farmers, veterinarians, etc.). 
• Contamination through inhalation of bacterial spores suspended in dust is also possible. 
• Finally, humans can also become infected by ingesting meat or offal from an animal that is sick or has died from anthrax, as is still the case in some developing countries.

Anthrax fever is recognised as an occupational disease.

What are the symptoms of the disease in animals?

In animals, anthrax most often presents as internal symptoms that rapidly progress to death, particularly in ruminants, sometimes without any clinical signs.  The most commonly observed symptoms are fever, difficulty breathing, uncoordinated movements, convulsions, bleeding from natural orifices and sometimes oedema.  In some cases, particularly in less susceptible species such as pigs or carnivores, the disease can take an external form characterised by oedema of the tongue or pharynx, which can lead to death by asphyxiation.

How serious is the disease in humans?

In humans, the most common form is skin infection.  The prognosis is generally favourable, but death can nevertheless occur in 5 to 20% of untreated patients.  Internal, visceral, gastrointestinal and respiratory forms, depending on the route of entry of the bacteria, cause septicaemia, i.e. a generalised infection via the blood, which is fatal if left untreated. The respiratory form is the most serious.

What are the means of control? 

Prevention of the disease in animals is the main means of control.  In order to avoid contamination of pastures and livestock, the carcasses of infected animals must not be autopsied on site and must be incinerated.

In the event of an outbreak of anthrax in livestock, antibiotics are effective at the early stage of the disease.  However, vaccination is the most effective means of limiting the spread of the bacterium and is recommended for healthy animals in affected herds. 

Regulations require that all suspected cases of animal anthrax must be reported to the departmental authorities responsible for population protection and be subject to sampling for laboratory analysis. 

What is ANSES’s role regarding anthrax?

The Bacterial Zoonoses Unit of ANSES’s Animal Health Laboratory is the National Reference Laboratory for anthrax. It systematically intervenes to confirm suspected cases of anthrax in animals. In addition, ANSES’s Hydrology Laboratory in Nancy carries out analyses of drinking and recreational water at the request of health authorities.

Sequencing of the genome of isolated bacteria is used to conduct epidemiological investigations aimed at identifying the geographical origin of bacterial strains and monitoring the evolution of outbreaks over time.

Furthermore, ANSES, through the National Agency for Veterinary Medicines (ANMV), grants marketing authorisations for vaccines and antibiotics used against anthrax in animals.