Control and Prevention of Anthrax, Texas, USA, 2019

Tom Sidwa; Johanna S. Salzer; Rita Traxler; Erin Swaney; Marcus L. Sims; Pam Bradshaw; Briana J. O'Sullivan; Kathy Parker; Kenneth A. Waldrup; William A. Bower; Kate Hendricks

Disclosures

Emerging Infectious Diseases. 2020;26(12):2815-2824. 

In This Article

Control and Prevention Measures

Control Measures for Animal Outbreaks

Because naturally occurring human anthrax cases in endemic countries are almost always related to exposure to infected animals or their byproducts, control of animal anthrax essentially eliminates human risk. The primary control measure for animal anthrax is annual preventive vaccination; however, once an outbreak occurs, other control measures include ring vaccination, proper carcass disposal to avoid further environmental contamination, and quarantine (i.e., limit animal movement from the affected and nearby properties, animal contact with anthrax-contaminated sites, and contact between affected and nonaffected herds).[9] On the basis of anecdotal reports and 1 small study, tabanid flies (e.g., deer and horse flies) might play a role in transmission; whether fly control is achievable or would be effective remains an open question.[2,12,13]

The attenuated Sterne-strain of B. anthracis is used globally for vaccination among domestic livestock.[14] Because the vaccine is live-attenuated, concurrent antibiotic administration can substantially diminish efficacy. If an animal is given antibiotics either 10 days before or after vaccination, revaccination is recommended.[9,15] Whether concurrent administration of antibiotics played a role in diminished vaccine efficacy in the Texas outbreak is unclear.

Proper and safe carcass disposal is critical for controlling anthrax outbreaks in enzootic areas because inappropriate carcass disposal seeds the soil with spores and increases the risk for future epizootics. Global recommendations[9] and codified Texas regulations[16] for carcass disposal are similar: the carcass should be burned in place, using a pyre or other method that leaves only ash and allows the destruction of the contaminated soil as well (i.e., "burnt until it is thoroughly consumed").[9,16] When a carcass cannot be burned, global recommendations are to bury it deeply.[9] The historic practice of adding lime should be avoided.[17] High soil calcium levels, either from the addition of lime or as occur naturally in southwest Texas, are conducive to B. anthracis spore survival[6,7] and increase the likelihood of future outbreaks. The least desirable disposal method is leaving the carcass in place, because scavenging can further disseminate the spores and increase future exposure risks for susceptible animals. Alternative carcass disposal methods are needed in areas where the standard recommendations to burn or bury carcasses are impractical. This need is particularly pronounced where there is an abundance of susceptible wildlife species that are not vaccinated or where there is poor vaccination coverage of domestic hoofstock.

Prevention of Human Cases in Endemic Areas

Human and animal health authorities should remind at-risk populations of the following prevention measures when animal cases are first identified. During animal outbreaks of anthrax, persons who handle and dispose of infected animals are at highest risk for exposure. However, exposure can be minimized through use of personal protective equipment, which should include gloves that can be disinfected or disposed of, long sleeves and pants, and footwear suitable to the terrain that can be disinfected.[9] Even in the absence of a recognized anthrax outbreak, veterinarians and ranchers in endemic areas should always keep anthrax in mind as they interact with members of susceptible species that are ill. To do otherwise can result in inadvertent exposure to anthrax.

Antibiotic postexposure prophylaxis (PEP) is another important component of prevention. In the former Soviet Union, before 1965, 58/339 (17%) of patients who did not receive antibiotic prophylaxis after cutaneous exposures had onset of anthrax; in contrast, only 5/287 (2%) who received prophylaxis had onset of anthrax.[18]

If skin or mucus membrane contact occurs during carcass disposal, persons should seek medical attention and receive antibiotic PEP for 7 days (Table 1) and have their symptoms monitored for 14 days. Although aerosol exposure is unlikely in cases of natural cutaneous exposures, if potential aerosol exposure also occurred, antibiotic PEP should be administered for up to 60 days and anthrax vaccine may be considered.

Persons who live and work in anthrax-endemic areas and who anticipate interacting with animals that are dying or have died of anthrax might wish to consider preexposure prophylaxis with anthrax vaccine adsorbed (AVA). For preexposure prophylaxis of persons at high risk for B. anthracis exposure, AVA is administered intramuscularly as a priming series at 0, 1, and 6 months, with booster doses at 12 and 18 months and annually thereafter.[19] Health departments in endemic areas that have existing vaccination programs can acquire AVA from the manufacturer.

Healthcare Infection Control Issues for Cutaneous Anthrax

A person with cutaneous or other type of anthrax (e.g., injection, ingestion, or inhalation) cannot transmit disease through aerosol or droplet. However, spores that could remain on a person's skin, hair, or clothing after an exposure before they bathe or shower and change clothes might possibly transfer to someone else's skin and cause cutaneous anthrax.[20–22] Although incubation periods of ≤1 day are reported, patients usually wait a few days to seek care, making it likely that they would already have bathed and changed clothes before seeking care. It is therefore unlikely that healthcare personnel would be secondarily exposed to spores.

Although cutaneous anthrax lesions can be contagious before the institution of effective antibiotic therapy, they become sterile in <1 day once therapy has begun.[23] Lesions should be covered until the patient has had 24 hours of effective antibiotics. Contact precautions should be used for the first day; after that, standard precautions are sufficient.

Disposable items that have been in direct contact with the anthrax lesion, any tissue removed during debridement, and potentially infectious wound care materials[24,25] should be disposed of in a biohazard bag according to guidelines for disposal of any potentially infectious material. No additional disinfection is needed beyond what is regularly scheduled for the facility. Nondisposable surfaces in direct contact with the anthrax lesion or wound drainage can be disinfected with a 0.5% hypochlorite solution, a commercial product such as SporGon (Decon Labs, https://deconlabs.com), or other sporicidal agents such as an Environmental Protection Agency–registered antimicrobial product effective against B. anthracis spores;[26–28] products effective against Clostridium difficile spores might also be appropriate[29,30]

Diagnosis

Although an eschar is the cardinal sign of cutaneous anthrax, in its early stages, anthrax can manifest as a group of small vesicles that might be pruritic. The lesion might be surrounded by erythema and swelling but is usually painless. Lymphadenopathy can occur, and constitutional symptoms including fever and headache are also possible. Localized cutaneous anthrax can disseminate to become a systemic disease. Although a substantial portion (10%–40%) of patients with cutaneous anthrax would die if left untreated,[4] most can recover with treatment.[31] Meningitis is also a possible, and typically fatal, complication.[32]

In the United States, cutaneous anthrax is decidedly rare: other causes of eschars and eschar-like lesions include poxvirus infections (e.g., cowpox, vaccinia, orf), rickettsial infections (e.g., scrub typhus and Rickettsia parkeri rickettsiosis), ulceroglandular tularemia, staphylococcal or streptococcal infections, and noninfectious causes such as insect or spider bites. Obtaining a good exposure history is key to determining the likelihood of various etiologies among the differential diagnoses and determining the best specimens to collect. Patients seeking care with an eschar or eschar-like lesion should be asked about recent exposure to dead or dying herbivores or biting flies in an anthrax enzootic area; recent animal bites or scratches; and recent contact with lagomorphs, rodents, fleas, ticks, and spiders.

A Gram stain of a swab specimen from the lesion can often quickly identify possible cases and narrow the differential diagnosis.[23] Specimens for tests such as Gram stain, culture, and PCR to rule anthrax in or out (Table 2) must be collected before the use of antibiotic therapy because they will rapidly become negative after the implementation of therapy.[23] Specimens can be sent to sentinel laboratories for preliminary assessment. Specimens for which B. anthracis is not ruled out by a sentinel laboratory should promptly be sent to a Laboratory Response Network (LRN) laboratory for confirmation.[33] LRN is a network of laboratories established to respond to biologic and chemical threats and other public health emergencies that consists of 3 types of laboratories. Private and commercial laboratories comprise the first tier of the LRN and are described as sentinel laboratories. Laboratories that receive reagents, protocols, and specialized training to perform confirmatory testing for multiple agents in high-risk environmental or clinical samples comprise the second tier of LRN and are referred to as reference laboratories. Specialized characterization of organisms, bioforensics, select agent activity, and handling of highly infectious biologic agents is performed at national laboratories, the third tier of LRN. However, with approval from public health authorities, specimens from lesions that are highly suspicious based on clinical or epidemiologic grounds can be sent directly from clinicians to an LRN laboratory.[34]

Notification

Clinicians should promptly notify their local or state health department when they suspect anthrax, although the mandated timing varies by jurisdiction. State and territorial health departments should notify the Centers for Disease Control and Prevention (CDC) within 4–24 hours[24] of the initial report for patients whose illness meets the probable or confirmed case definition.[35] Presumptive positive results from an LRN laboratory must be reported within 2 hours to the state and CDC.

Treatment

Cutaneous anthrax lacking systemic manifestations such as fever, tachycardia, tachypnea, hypotension, leukocytosis, or leukopenia can usually be treated with 7 days of an oral antibiotic. Patients with cutaneous anthrax should only continue oral antibiotics for PEP after antibiotic treatment is complete if the patient was also exposed to aerosolized spores; this would rarely be indicated for naturally acquired cutaneous infections because aerosol exposures are unlikely (Table 1).

Systemically ill patients should be evaluated for meningitis; if meningitis can be ruled out, they should be treated with at least 2 intravenous antibiotics (1 that is bactericidal and 1 that inhibits protein synthesis to block toxin production). Antibiotic therapy should continue for ≥2 weeks or until the patient is stable. If meningitis is present, ≥3 antibiotics should be used (≥1 should be bactericidal, ≥1 should inhibit protein synthesis, and all should have good central nervous system penetration). Antibiotic options for treatment and prevention of anthrax are listed in Table 1 and Table 3.

Systemically ill patients (whether from cutaneous, ingestion, inhalation, or injection exposures) are candidates for 1 of the Food and Drug Administration–approved anthrax antitoxins. The antitoxins are available through the Strategic National Stockpile pending a consultation with an anthrax subject matter expert at CDC, which can be reached by calling the Emergency Operations Center (770-488-7100).

Surgery might occasionally be indicated for lesions complicated by compartment syndrome. However, surgery usually is not necessary for cutaneous anthrax.[36]

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