Clinical Overview

Anthrax, is a zoonotic disease caused by Bacillus anthracis. It occurs in domesticated and wild animals, primarily herbivores, including goats, sheep, cattle, horses and swine. Humans usually become infected by contact with infected animals or contaminated animal products. Infection occurs most commonly via the cutaneous route and only very rarely via the respiratory or gastrointestinal routes.

Due to the infectiousness of anthrax spores by the respiratory route and the high mortality of inhalational anthrax, there is great concern about its possible use as a biolgical weapon. Bacillus anthracis is a large, Gram-positive, spore-forming, nonmotile bacillus. The organism grows readily on sheep blood agar aerobically. The vast majority of cases have been cutaneous. Under natural conditions, inhalational anthrax is exceedingly rare, with only 18 cases having been reported in the United States in the 20th century.

Clinical Presentation

Depending on the mode of transmission, anthrax infections can present as cutaneous, gastrointestinal or inhalational disease.

Cutaneous Anthrax

The disease first appears as a small papule that progresses over 1 to 2 days to a vesicle containing serosanguinous fluid with many organisms and a paucity of leukocytes. After inoculation, the incubation period is 1 to 5 days. The vesicle, which may be 1 to 2 cm in diameter, ruptures, leaving a necrotic ulcer. The lesion is usually painless and varying degrees of edema may be present around it. Patients usually have fever, malaise and headache, which may be severe in those with extensive edema. The ulcer base develops a characteristic black eschar and after a period of 2 to 3 weeks the eschar separates, often leaving a scar. Septicemia is very rare and with treatment mortality is less than 1 percent.

Inhalational Anthrax

Inhalational anthrax begins after an incubation period of 1 to 6 days with nonspecific symptoms of malaise, fatigue, myalgia and fever. There may be an associated nonproductive cough and mild chest discomfort. These symptoms usually persist for 2 or 3 days and in some cases there may be a short period of improvement. This is followed by the sudden onset of increasing respiratory distress with dyspnea, stridor, cyanosis, increased chest pain, and diaphoresis. There may be associated edema of the chest and neck. Chest X-ray examination usually shows the characteristic widening of the mediastinum and often, pleural effusions. Notably rhinorrea is absent, in contrast with other acute respiratory infections. Meningitis is present in up to 50percent of cases, and some patients may present with seizures. The onset of respiratory distress is followed by the rapid onset of shock and death within 24 to 36 hours. Mortality rates are high, although 6 out of 11 cases in 2001 survived with early aggressive treatment. Predictions are that mortality could be much higher (100percent if untreated).

Gastrointestinal Anthrax

Oropharyngeal and gastrointestinal anthrax result from the ingestion of infected meat that has not been sufficiently cooked. After an incubation period of 2 to 5 days, patients with oropharyngeal disease present with severe sore throat, cervical or submandibular lymphadenitis and edema. Gastrointestinal anthrax begins with nonspecific symptoms of nausea, vomiting and fever; these are followed in most cases by severe abdominal pain. Mortality in both forms may be as high as 50 percent, especially in the gastrointestinal form.

Diagnosis

The most critical aspect in making a diagnosis of anthrax is a high index of suspicion associated with a compatible history of exposure. Cutaneous anthrax should be considered following the development of a painless pruritic papule, vesicle or ulcer often with surrounding edema that develops into a black eschar. With extensive or massive edema, such a lesion is almost pathognomonic. Gram’s stain or culture of the lesion will usually confirm the diagnosis. The differential diagnosis should include tularemia, staphylococcal or streptococcal disease, and orf (a viral disease of sheep and goats, transmissible to humans).

The diagnosis of inhalational anthrax is extraordinarily difficult, unless it is a known event. The disease should be suspected with a history of exposure to a B. anthracis containing aerosol. The early symptoms are entirely nonspecific. However, the development of respiratory distress in association with radiographic evidence of a widened mediastinum and the presence of hemorrhagic pleural effusion or hemorrhagic meningitis should suggest the diagnosis. Sputum examination is not helpful in making the diagnosis, since pneumonia is not usually a feature of inhalational anthrax.

Gastrointestinal anthrax is also difficult to diagnose in the absence of a recognized exposure because of the rarity of the disease and its nonspecific symptoms. Only with a history of ingesting contaminated meat in the setting of an outbreak is this diagnosis usually considered. Microbiologic cultures are not helpful in confirming the diagnosis. Serology is generally only of use in making a retrospective diagnosis.

Treatment

Current recommendations from the CDC in the event of clinical disease: Ciprofloxacin, 400 mg IV every 12 hr or Doxycycline, 100 mg IV every 12 hr and one or two additional antimicrobials (agents with in vitro activity include rifampin, vancomycin, penicillin, ampicillin, chloramphenicol, imipenem, clindamycin and clarithromycin). In mass prophylaxis situations, treat with Ciprofloxacin, 500 mg PO twice daily or Doxycycline, 100 mg PO twice daily. Postexposure prophylaxis for exposure to airborne spores of B. anthracis generally involves the use of antimicrobial therapy, although vaccination also may have utility in certain situations. Postexposure prophylaxis is recommended for the following persons:

• Those exposed to an air space where a suspicious material may have been aerosolized
• Those who have shared the air space likely to be the source of an inhalational anthrax case

In addition to Cipro and Doxycyline, Penicillin G procaine has been approved by the FDA for anthrax treatment. Antimicrobial therapy should be continued for at least 60 days for treatment or prophylaxis. Over 10,000 people were placed on post-exposure prophylaxis during the 2001 anthrax outbreak; no cases of anthrax occurred among this group. A follow-up study of those persons who were offered antimicrobial prophylaxis in 2001 demonstrated that 5,343 took at least one dose of antimicrobial therapy. Of this group, 3,032 (57percent) reported medication related adverse events during the first 60 days of therapy. Statistical modeling suggested that about nine cases were prevented through the use of post-exposure antibiotics. The Working Group on Civilian Biodefense has concluded that antibiotic administration for 60 days, in conjunction with vaccination, provides optimal protection for persons exposed to anthrax following an aerosol release.

There is a vaccine available for anthrax, but it is not for general use. Studies are ongoing to develop new safer vaccines.

Transmissibility and Infection Control

Person to person spread of anthrax has not been reported and is unlikely. General infection control precautions are thought to be adequate for those treating anthrax patients. Patients exposed to anthrax should remove contaminated clothing and store it in labeled, plastic bags. Clothing should be handled as little as possible to avoid agitation and releasing spores. Patients should shower thoroughly with soap and water. Questions remain about proper procedures for the decontamination of areas with the intentional release of anthrax. Attempts to decontaminate a contaminated area require specialized training.

As with any bioterrorism agent, a case or suspected case of anthrax in someone living or working in the County should be immediately reported by phone to the Anne Arundel County Department of Health at 410-222-7256. To report communicable diseases, click here for instructions.