Anthrax in Animals | How Humans Get Infected | Anthrax Vaccination

Anthrax is a zoonotic bacterial disease of domestic herbivores that is caused by spore-forming bacteria. The word anthrax comes from a Greek word that means coal. Because of the characteristics of black skin lesions on the site of infection. Bacillus anthracis ( causative agent of Anthrax ) was used successfully as a weapon of terrorism in 2001, killing 5 people and causing disease in 22.

Other Names: Splenic Fever, Siberian plague, Siberian ulcer, Cumberland Disease, charbon, Malignant edema, woolsorter’s disease, and in Pakistan locally it is known as Goli (گولی), Sutt, Phirki.

Cause of Anthrax in Animals and Humans:

Anthrax in Animals or Humans is caused by gram +ve bacterium, Bacillus anthracis. This bacteria is present in the form of spores in the environment like on soil for a long time even decades.

Some Characteristics of Bacillus Anthracis:

• Spore-forming
• Gram+ve
• Rod shape
• Aerobic/Fucultative Anerobes
• Non-Motile
• In soil, endospores of B. anthracis can survive for more than 50 years.
• B. anthracis, does not produce capsules when grown on laboratory media.
• Bacillus anthracis colonies are up to 5 mm in diameter, flat, dry, greyish, and with a ‘ ground-glass ’ appearance after incubation for 48 hours. At low magnification, curled outgrowths from the edge of the colony impart a characteristic, ‘ medusa head ’ appearance.

The bacterium normally rests in spore form in the soil and can survive for decades in this state. Herbivores are often infected while grazing, especially when eating rough, irritant, or spiky vegetation; the vegetation has been hypothesized to cause wounds within the GI tract, permitting entry of the bacterial spores into the tissues, though this has not been proven.

How Anthrax in Animals is Transmitted?

As we mentioned, there are 2 forms of Bacillus anthracis, spore, and vegetative form. The spore form is outside the body of the host in the environment. These spores can withstand harsh environmental conditions and even survive for years to decades. So these spores are present in all the world’s continents even in Antarctica. It was reported that spores from the buried site of infected animals caused disease after 70 years.

Anthrax in Animals is transmitted by either ingestion or inhalation of spores of Bacillus anthracis. The spores can also enter the body of an animal through skin abrasion. It was said that herbivores mostly get infected by ingesting the spores during the grazing of vegetation. Sometimes it is also possible that animals ingest the spiky vegetation that causes the wounds in GIT and ultimately the spores of bacteria get the chance to enter into the tissue. But this mechanism is not yet proven.

Long story short, after the entry of spores of Bacillus anthracis into the body of animals, the spores germinate into vegetative form and then spread to lymphatics and throughout the body causing the clinical signs. In the case of inhalation, the spores are picked up by the macrophages of the lung’s alveoli and carried by lymphatics to the lymph nodes of the mediastinum. This leads to chest problems like dyspnea etc. After multiplication in lymph nodes of the mediastinum, the macrophages burst and further bacilli release into the bloodstream and then throughout the body. Whereas in the case of ingestion and cutaneous entry, the spores germinate at the site of infection, and the draining lymph nodes at the site of infection.

How do Humans get infected with Anthrax?

As it is a zoonotic disease, humans also get infection either through contact with infected animals, their byproducts, or by direct inhalation of spores under certain conditions. For example, as we mentioned, the spores are mostly found in vegetation, so those people that work in wool processing companies have greater chances of getting the spores into their bodies. But it is said that for the infection to happen at least the minimum exposure will be 2,500 to 55,000 spores. Anyhow humans are also susceptible to anthrax.

Pathogenesis of Anthrax in Animals and Humans:

The pathogenesis of Anthrax in Animals and Humans are same. After entry of spores either by ingestion, inhalation, or cutaneous route, the spores germinate in the draining lymph nodes of the infected site. During germination, they produce exotoxins (lethal toxin, edema toxin, protective antigens). These toxins enter the bloodstream (toxemia) and spread throughout the body.

Clinical Signs of Anthrax In Animals:

The Anthrax in Animals may range from peracute to acute.

Signs in Per-Acute Anthrax in Animals:

• Staggering
• Dyspnea,
• Trembling,
• Collapse,
• A few convulsive movements, and ultimately death

Signs in Acute form of Anthrax in Animals:

• Abrupt fever 107°F
• Period of excitement followed by depression
• Stupor,
• Respiratory or cardiac distress,
• Staggering,
• Convulsions, and death.
• Rumen motility stops
• Milk production is materially reduced
• Pregnant animals may abort.
• Bloody discharges from the natural body openings.
• Edematous swelling mostly on ventral neck, thorax, and shoulders

Some Clinical Signs in Humans Due to Anthrax:

The signs of anthrax in humans vary depending upon the site of infection. Briefly, the signs are

Inhalational Anthrax:

The inhalational anthrax is also known as woolsorters disease, is because by inhaling the spores of bacillus anthracis, the signs are like influenza or pneumonia

• Cough
• Chest pain
• Dyspnea
• Sometimes if bacteria first affect the lymph nodes of the chest rather than entering the lungs then this condition is known as hemorrhagic mediastinitis.

Cutaneous Anthrax:

The most common form of anthrax in humans. It is also known as Hide porter’s disease. this occurs when bacterial spores enter through the skin. the major sign in such form of anthrax is

• A boil-like skin lesion that eventually forms an ulcer with a black center

Gastrointestinal Infection:

This type of anthrax occurs due to the ingestion of bacterial spores. the clinical signs are related to gastrointestinal infections like

• Diarrhea with blood
• Abdominal pain
• Vomiting etc

Diagnosis:

It is a well-renowned saying that ” forget the treatment, diagnosis is everything. ” Diagnosis of every disease revolves around 3 things

1- History

2- Clinical signs

3- Lab test for isolation of the causative agent

So take some history from the owner of the animal and then look at the obvious clinical signs. It must be mentioned here that clinical signs are somewhat similar in different diseases so the best way of diagnosis is the confirmation by a lab test.

Various techniques may be used for the direct identification of B. anthracis in clinical material like PCR and immunofluorescence microscopy.

Check another zoonotic disease Vesicular Stomatitis

Treatment of Anthrax in Animals:

Domestic livestock responds well to penicillin @ 20000-40000 IU/kg if treated in the early stages of the disease. Oxytetracycline given daily in divided doses also is effective. Other antibacterials, including amoxicillin, chloramphenicol, ciprofloxacin, doxycycline, erythromycin, gentamicin, streptomycin, and sulfonamides also can be used, but their effectiveness in comparison with penicillin and the tetracyclines has not been evaluated under field conditions.

How to Prevent the Anthrax:

Anthrax in Animals and Humans is controlled through vaccination programs, rapid detection and reporting, quarantine, treatment of asymptomatic animals (postexposure prophylaxis), and burning or burial of suspect and confirmed cases.

1. In livestock, anthrax can be controlled largely by the annual vaccination of all grazing animals in the endemic area and by the implementation of control measures during epizootics. The nonencapsulated Sterne-strain vaccine is used almost universally for livestock immunization. Vaccination should be done at least 2–4 wk before the season when outbreaks may be expected. Because this is a live vaccine, antibiotics should not be administered within 1 wk of vaccination.

• Animals should be moved to another pasture away from where the bodies had lain and any possible soil contamination.
• The suspected contaminated feed should be immediately removed.
• Notification of the appropriate regulatory officials  
• Rigid enforcement of quarantine (after vaccination, 2 wk before movement off the farm, 6 wk if going to slaughter)
• Prompt disposal of dead animals, manure, bedding, or other contaminated material by cremation (preferable) or deep burial
• Isolation of sick animals and removal of good animals from the contaminated areas
• Cleaning and disinfection of stables, pens, milking barns, and equipment used on livestock
• Use of insect repellents
• Control of scavengers that feed on animals dead from the disease
• Observation of general sanitary procedures by people who handle diseased animals, both for their own safety and to prevent the spread of the disease. Contaminated soils are very difficult to completely decontaminate, but formaldehyde will be successful if the level is not excessive.

Conclusion:

Anthrax is a bacterial zoonotic disease caused by Bacillus anthracis. Humans also get the infection when exposed to spores of Bacillus anthracis. The symptoms in both animals and humans are somewhat different. Antibiotic therapy can help in the treatment of anthrax. Vaccination and other biosecurity measures are helpful in its prevention.