Anthrax

Anthrax is also known as

• Woolsorters’ Disease

• Cumberland Disease

• Maladi Charbon

• Malignant Pustule

• Malignant Carbuncle

• Milzbrand

• Splenic Fever

• Siberian Fever

Causative agent of Anthrax

Bacillus anthracis

Anthrax morphology

• spore-forming

• Gram-positive

• aerobic rods

Anthrax Family

Bacillaceae

Virulence Factors of Anthrax

• pXO1

• pXO2

• biofilm formation

• toxins

  • edema toxin

  • lethal toxin

• capsule

exotoxin complex and is associated with symptoms

pXO1

interferes with phagocytosis

pXO2

serves as a pivotal strategy in B. anthracis virulence by augmenting its survival in hostile environments → enabling resistance to antimicrobial agents & facilitating its persistent environmental presence → contributing to the persistent and chronic nature of anthrax infection

biofilm formation

Epidemiology of Anthrax: Global

• 80% of herbivore deaths

• occurs worldwide

Epidemiology of Anthrax: Philippines

• Only 82 suspected anthrax cases were recorded from January 2017 to December 2023

• In 2022, 3 cases were confirmed

Transmission of Anthrax

• ingestion

• inhalation

• penetration through disrupted skin

• infectious dose not known

• aerosol challenge is estimated to be 8,000-50,000 spores

• infectious dose may be as low as 1-3 spores

Occupational Risk

• veterinarian

• animal health officers

• livestock workers, particularly in anthrax endemic area

• workers handling animal products (wool, meat, hair, skin, bone, or bone products)

• households or breeders who have discovered their livestock died and consumed meat contaminated with anthrax spores

• military personnel

• laboratory workers handling anthrax samples

• emergency response workers handling bioterrorism are among those at high risk of contracting anthrax

Clinico-pathological features in animals

• incubation period: 1-14 days

• in herbivores: 3-7 days (inoculated orally)

• in pigs: 1-2 weeks (laboratory experiment (oral inoculation) resulted in clinical signs after 1-8 days)

• peracute, acute - susceptible species

• subacute, chronic - more likely to be reported in resistant hosts

Clinico-pathological features of anthrax in ruminants

• peracute systemic disease is common

• sudden death is often the only sign

• staggering, trembling, dyspnea

  • sometimes noted shortly before death

  • followed by rapid collapse and terminal convulsions (in some cases)

• acute form

  • ill for a short period (up to 2 days) before they die

• fever and excitement may be noted initially, followed by depression, stupor, anorexia

• disorientation

• muscle tremors

• dyspnea

• hematuria

• diarrhea

• congested mucous membranes

• small scattered hemorrhages on the skin and mucous membranes

• pregnant cows may abort

• decreased milk production

• milk may appear bloody or discolored with yellow tinge

• bloody discharges from orifices such as nose mouth and anus

• some may develop subcutaneous edematous swellings often in the ventral neck, thorax, and shoulders, but sometimes at other sites including the genitalia

• pulmonary anthrax

  • with productive cough and an acute course

  • rare

• dying animals are usually found bloated

• without or incomplete rigor mortis

• absence of clotting - most prominent characteristic

Clinico-pathological features in horses

• acute course is common

• fever

• anorexia

• depression

• sepsis

• severe colic

• bloody diarrhea (some)

• death within 48-96 hours

• some have swelling on the neck, sternum, lower abdomen, genitalia

• usually die within 3 days but some survive longer

Clinico-pathological features in pigs

• septicemia and sudden death occur occasionally

• mild subacute to chronic cases

• localized swelling

• fever

• enlarged lymph nodes

• throat can swell rapidly in pigs that develop anthrax lesions in the oropharynx

• intestinal involvement can result in anorexia, vomiting, diarrhea (may be bloody) or constipation

• some pigs may recover

Clinico-pathological features in other animals

• naturally-acquired anthrax in dogs, cats, wild carnivores resemble the disease in pigs, with gastrointestinal and or pharyngeal signs

• anthrax in birds is reported to be an acute septicemic disease with death occuring soon after clinical signs appear

Clinico-pathological features in humans

• incubation period:

  • cutaneous: 1-20 days; but most develop within 7-10 days

  • gastrointestinal: 1-7 days

  • injectional: 1-10 days

  • inhalational: highly variable

• cutaneous

• gastrointestinal

• inhalation

  • uncommon

Diagnosis of Anthrax

• detecting the agent in a blood sample from a carcass (blood culture)

  • obtained by making a small cut in an ear vein

  • syringe at any available vein

• bacteremia is rare in pigs

  • small piece of affected lymphatic tissue is often collected aseptically

• tissue aspirates

• pharyngeal swabs

• nasal turbinates

  • useful in older carcasses (more than 3 days)

• stained smear

  • Gram-stain:

    • Gram-positive, thick, long, straight bacilli with square or truncated ends with parallel sides, usually arranged in single pairs or chains of three or four bacilli

  • polychrome methylene blue (M’Fadyean stain) stain:

    • capsulated bacilli (pink capsule surrounding dark blue bacilli, often square-ended, singly, or in short chains)

• PCR

• anthrax immunochromatographic test (AICT)

• skin hypersensitivity test using anthraxin (AnthraxinT)

• serology

  • mainly used in research, rarely in diagnosis

Treatment for Anthrax

• penicillins

  • streptomycin may be given to act synergistically with penicillin

  • tetracyclines

Prevention and Control

• modified live vaccines

• quarantine

• proper carcass disposal

  • infected carcasses should not be opened, it should

    be burned and discharged

    • carcass disposal by deep burial (6 feet), quicklime

    (calcium oxide) carcass covered with soil mixed

    with quicklime (3:1).

• improvements in industry standards to reduce occupational exposure

• protective clothing and equipment when examining sick animals

• postexposure antibiotic prophylaxis, continued for at least 60 days, and vaccination - people exposed to aerosolized anthrax spores