Anthrax Testing

Anthrax is a serious bacterial disease caused by Bacillus anthracis. It is a gram-positive, spore-forming bacteria that has a protective capsule and produces anthrax lethal factor toxin. Bacillus anthracis exists naturally in soil and can infect livestock and wild animals when they inhale, eat or drink spores that are present in contaminated soil, water or plants. 

Humans usually become ill after contacting infected animals or contaminated animal products. Routes of transmission include inhalation of anthrax spores, ingestion of food containing spores, drinking water contaminated with spores, or embedding spores in a skin lesion.

Anthrax can enter the body through the skin, respiratory tract or gastrointestinal system. The route of infection determines the clinical disease. Cutaneous anthrax occurs when anthrax spores enter a skin lesion. It usually occurs when a person handles infected animals or contaminated products like wool, hides, or hair. Lesions most commonly occur on the head, neck, forearms, and hands. Cutaneous anthrax can causes blisters or black sores with prominent swelling. 

Inhalation anthrax occurs when a person breathes in spores. People working in wool mills, slaughterhouses, and tanneries are at highest risk of infection. Infection starts in the mediastinal lymph nodes and then spreads throughout the body. Patients typically have fever, chills, sweating, chest pain, cough, and shortness of breath. It is the most deadly form of anthrax. 

Gastrointestinal anthrax can happen when a person eats raw or undercooked meat from an infected animal. It can infect the throat, esophagus, stomach and intestines. Symptoms include fever, chills , lymphadenopathy, sore throat, pain with swallowing, nausea, vomiting, diarrhea, hematemesis, and hematochezia. 

Welder’s anthrax is a more recently described disease that occurs in welders and metalworkers. As of September 2024, nine cases have been identified in Texas and Louisiana. Welding fumes damage the respiratory tract and predispose welders to lung infections.  results in rapidly progressive pneumonia and can be fatal. 

Injection anthrax has been reported in heroin users in northern Europe. It is similar to cutaneous anthrax and causes abscesses deep in the skin or muscle where the drug was injected. 

Anthrax is a reportable disease in all U.S. states and territories. Anthrax cases must be reported to state and territorial jurisdictions when identified by a healthcare provider, hospital, or laboratory. Specific requirements vary by jurisdiction.

Anthrax infections can be confirmed by measuring anthrax lethal factor toxin in blood, pleural, and ascites fluid. Biopsies can be tested for Bacillus anthracis by culture and for the anthrax toxin gene by RT-PCR.  Patient samples should be collected prior to starting antibiotics. 

Plasma is the preferred specimen for anthrax lethal factor toxin testing. Samples can be collected from zero to 18 days after expected exposure or the onset of symptoms. Blood should be collected in a lavender-top tube (EDTA).

A full thickness biopsy of a papule or vesicle, including adjacent skin, can be used to diagnose cutaneous anthrax. This biopsy should be taken preferably before the patient has started antibiotic treatment. Skin lesions can also be swabbed for culture and RT-PCR. 

A bronchial or pleural biopsy should be obtained for patients with symptoms of inhalation anthrax. If the biopsy samples are formalin-fixed, they should be shipped to CDC at room temperature. Do not freeze. If the biopsy samples are fresh-frozen, they should be stored at -70°C and shipped to CDC using dry ice. Pleural fluid can also be tested by RT-PCR and for LF toxin. 

Gastrointestinal anthrax can be diagnosed by collecting swabs for culture and RT-PCR from the oropharyngeal cavity and the rectum. Ascites fluid can also be tested by RT-PCR and for LF toxin.

References

Bower WA, et al. CDC guidelines for the prevention and treatment of anthrax, 2023. MMWR Recomm Rep 2023;72 (No. RR-6):1–47.

Sabin SJ, et al. Investigating anthrax-associated virulence genes among archival and contemporary Bacillus cereus group genomes. Pathogens 2024;13:884–905

Dawson P, et al. Notes from the field: fatal anthrax pneumonia in welders and other metalworkers caused by Bacillus cereus group bacteria containing anthrax toxin genes—U.S. Gulf Coast States, 1994–2020. MMWR Morb Mortal Wkly Rep 2021;70:1453–4.

Thompson JM, et al. Welder’s Anthrax Treated with Obiltoxaximab — Louisiana, 2024. MMWR Morb Mortal Wkly Rep 2026;74:641–647.