Popular Science: Quick Facts on Anthrax and Key Prevention and Control Techniques

I. What is anthrax?

Anthrax is an acute, febrile, septicemic zoonotic disease caused by the bacterium Bacillus anthracis. In China, it is classified as a Category II animal epidemic disease; under the Law of the People’s Republic of China on the Prevention and Control of Infectious Diseases, it is designated as a Class B infectious disease; and the World Organisation for Animal Health (OIE) lists it as a notifiable animal disease.

II. What is the epidemiological situation of anthrax?

Anthrax is a naturally occurring zoonotic disease with a global distribution. Annual cases range from approximately 20,000 to 100,000. It occurs in Europe, Asia, Africa, the Americas, and Oceania, with outbreaks in China primarily concentrated in certain provinces in the northwest, southwest, and northeast. Epidemics can occur throughout the year, with the peak incidence occurring from June to September; drought and flooding are the main contributing factors.

III. How is anthrax transmitted?

Humans and animals are primarily infected via the gastrointestinal tract, but respiratory transmission and infection through contact with broken skin are also possible. Contaminated soil, water sources, and premises can serve as persistent reservoirs of the pathogen. In most cases, herbivores such as cattle and sheep become infected by ingesting anthrax spores while grazing; humans, in turn, become infected through contact with contaminated materials—such as the meat, hides, blood, or soil—from animals that have been infected with anthrax.

IV. What are the clinical signs of anthrax infection in animals?

This disease typically follows an acute course, characterized by sudden death, dark soy-sauce–colored blood that fails to clot, incomplete rigor mortis, and abdominal distension. Bleeding from natural orifices is commonly observed in sheep but is rare in cattle.

Cattle: Body temperature often rises above 41°C, with dark purple discoloration of the visible mucous membranes, tachycardia, and dyspnea. In chronic cases, edema is commonly observed in the neck, anterior chest, scapular region, ventral abdomen, or vulva; skin lesions exhibit increased temperature, firm consistency, and tenderness, and may undergo necrosis, sometimes developing into ulcers. Neck edema is frequently accompanied by pharyngitis and laryngeal edema, further exacerbating respiratory distress. Acute cases typically succumb within 24 to 36 hours, while subacute cases usually die after 2 to 5 days.

Horses: Body temperature rises, and edema is commonly observed in the ventral abdomen, udder, shoulders, and pharynx. Cutaneous anthrax often presents with respiratory distress and cyanosis; intestinal anthrax is characterized by marked abdominal pain. Acute cases typically succumb within 24 to 36 hours, whereas when anthrax carbuncles are present, the course of the disease may extend to 3 to 8 days.

Sheep: The disease most often presents as an extremely acute (sudden death) condition, characterized by staggering, teeth grinding, convulsions, struggling, and sudden collapse; in some cases, dark red blood with bubbles may be observed oozing from natural orifices. Even in cases with a slightly longer course, death typically occurs within a few hours.

Pigs: Lesions are mostly localized, with a chronic course and mild clinical signs; pathological changes are often observed postmortem.

V. What are the clinical symptoms of human anthrax infection?

    Cutaneous anthrax ： Cutaneous anthrax lesions commonly occur on exposed areas such as the hands, upper limbs, neck, and shoulders. The initial clinical manifestations include unexplained papules or erythematous patches on the skin, resembling mosquito-bite–like papules; most patients also present with fever. Subsequently, vesicles develop, accompanied by perilesional edema, followed by central necrosis that leads to the formation of an ulcerative black eschar. Pain is typically mild, with only slight pruritus; abscesses do not form. With prompt treatment, the case-fatality rate is less than 1%. However, a small number of severe cases do not exhibit the classic black eschar; instead, they present with extensive localized edema and necrosis, with rapid disease progression and a high mortality rate, warranting close vigilance.

    Intestinal anthrax: Intestinal anthrax may present as either an acute enteritis type or an acute abdominal syndrome type. In the acute enteritis type, patients typically experience nausea, vomiting, abdominal pain, and diarrhea. In the acute abdominal syndrome type, systemic toxic symptoms are severe, with persistent vomiting and diarrhea, passage of bloody, watery stools, abdominal distension, and abdominal pain; sepsis and infectious shock are common complications. Without prompt treatment, the condition can be fatal.

Pulmonary anthrax: Pulmonary anthrax initially presents with “influenza-like” symptoms, including low-grade fever, fatigue, general malaise, myalgia, and cough, typically lasting about 48 hours. It then progresses rapidly and abruptly, with the development of respiratory distress, dyspnea with wheezing, cough, cyanosis, and hemoptysis. Although relatively rare, it is highly contagious and associated with a high case-fatality rate.

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VI. Notice Issued on August 4, 2024, by the China Animal Disease Prevention and Control Center on the “Technical Guidelines for the Prevention and Control of Animal Anthrax during the Flood Season”

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