Anthrax is a serious bacterial disease caused by Bacillus anthracis. Anthrax most commonly occurs in wild and domestic lower vertebrates (livestock), but can also infect humans. Anthrax bacteria form hardy spores that can lie dormant in the soil for many years until they encounter a susceptible host. While rare, anthrax infections can be deadly to humans if left untreated.
B. anthracis bacteria are rod-shaped, gram-positive, aerobic bacteria that can form dormant endospores. In its dormant spore form, it is highly resistant to heat, radiation, disinfection, and desiccation. It can survive in this state for decades until conditions are favorable for germination. The spores germinate into vegetative bacteria when they encounter nutrients in a susceptible host. In the host, the vegetative form will multiply, ultimately causing disease and death as toxin-producing cells are formed.
Anthrax naturally occurs in many parts of the world where it exists in an enzootic cycle between wild and domestic herbivores. Ruminants such as cattle, sheep, goats are particularly susceptible. Infected animals will experience high fever, respiratory distress, edema (swelling), and often sudden death. They shed B. anthracis spores in body fluids, tissues, and exhaled air which can then contaminate grazing pastures and water sources. Spores persist in soil for many years. Grazing animals that ingest spores can become newly infected, continuing the enzootic cycle.
Anthrax can infect humans through contact with infected animals or contaminated animal products such as hides, wool, meat or bones. Historically, processing of animal hides and wool was a significant occupational risk factor for anthrax exposure before modern industrialization. Cutaneous anthrax is the most common form in humans, occurring when spores enter through skin abrasions. Some inhaled or ingested spores may cause pulmonary or gastrointestinal anthrax respectively, which have higher fatality rates if untreated.
Symptoms of anthrax in humans depend on the route of infection. Cutaneous anthrax causes a skin lesion that progresses from a small papule (raised bump) to a darkened eschar with surrounding swelling. Pulmonary anthrax begins with non-specific symptoms of fever, fatigue and chest discomfort but can lead to severe breathing problems and septic shock. Gastrointestinal anthrax presents with nausea, loss of appetite, fever, and abdominal pain and may cause vomiting of blood. Without prompt antibiotic treatment, death rates for pulmonary and gastrointestinal anthrax can exceed 80%. Cutaneous anthrax is seldom fatal if treated properly.
While rare today in developed nations, anthrax outbreaks can still occur through contact with infected animals or contaminated animal products. Anthrax spores have also been deliberately used as a biological weapon, raising more concern about its potential for intentional misuse. Anthrax spores were used in mail-based bioterrorism attacks in the United States in 2001, resulting in 22 confirmed or suspected cases and 5 deaths. This highlighted the potential for anthrax to be weaponized and intentionally dispersed to cause disease. Rigorous biosafeguards and disease surveillance help protect global public health security from natural and intentional anthrax exposure risks.
Veterinary vaccination programs and improved animal husbandry practices have helped control anthrax outbreaks in livestock herds and reduce human exposure in many endemic regions. Anthrax remains a threat wherever it exists naturally in the soil and grasslands. Significant endemic foci persist in parts of sub-Saharan Africa, Central and Southeast Asia, the Middle East, southern and central Europe, and parts of North and South America. Anthrax monitoring and outbreak response depends on integrated veterinary and public health collaboration.
Fortunately, anthrax is readily treatable with appropriate antibiotic therapy, especially if started early in the course of infection before toxic shock occurs. The antibiotics of choice are ciprofloxacin or doxycycline which are very effective against Bacillus anthracis. Treatment durations depend on the form of anthrax but are typically 10 days for cutaneous anthrax and 60 days for inhalation anthrax. Prompt diagnosis and administration of the correct antibiotics can greatly improve chances of survival, even in cases of severe pulmonary or gastrointestinal anthrax exposure.
Prevention of anthrax involves a combination of measures that vary based on the exposure risk. For high-risk veterinarians, farmers and animal workers in endemic regions, routine vaccination of livestock to interrupt disease transmission is an important control method along with personal protective measures when handling sick or dead animals. Proper disposal of infected carcasses helps prevent environmental contamination and wildlife exposure. Additionally, public education about risks from contact with infected animals or contact is crucial. In laboratories where anthrax research takes place, rigorous biosafety level requirements strictly regulate handling of pathogens. In terms of bioterrorism defense, ongoing detection, facility monitoring and vaccines for at-risk populations are key preparedness strategies.
While anthrax remains a serious bacterial zoonosis with public health implications, ongoing prevention and control efforts have significantly reduced its impact globally. Through integrated veterinary and public health approaches that include livestock vaccination, infection surveillance, antimicrobial stewardship and emergency preparedness – the risks from both natural occurrences and intentional misuse of anthrax can continue to be managed effectively. With continued vigilance and collaboration across disciplines, anthrax can be contained to protect human and animal health worldwide.
Andrew Stroud