Anthrax

What is anthrax?

Anthrax is a disease primarily found in animals, caused by the bacterium Bacillus anthracis. Humans can be infected with it when they are exposed to infected animals, tissue from infected animals or exposed to the spores of the bacterium.

The commonly affected animals include cattle, sheep, goats, camels, antelopes and other herbivores. Anthrax was described more than 3,500 years ago and may have been to blame for two of the plagues of Egypt in 1491 B.C.

What is the cause?

The bacterium, Bacillus anthracis, is the causative organism. Under a microscope with appropriate staining, the bacteria look like small rods. The spores are usually spherical structures, smaller than the bacteria, and are the dormant form of the bacteria. They can survive in the soil for years, and can withstand hot or cold temperatures.

What are the spores of anthrax?

Spores are the hardy form of the bacteria and can survive for years in the dry form. They can withstand boiling for 10 minutes and can resist most disinfectants. A high temperature of 120°F for at least 15 minutes (autoclaving) can be used to inactivate them.

Where does it occur?

Anthrax is found globally but infection in man is not very common. It is most common in farming regions in developing countries in South and Central America, Southern and Eastern Europe, Asia, Africa, the Caribbean and the Middle East.

Does it occur in India?

A few sporadic cases and outbreaks of anthrax have occurred in India. Detailed information collected for three southern Indian states, Andhra Pradesh, Karnataka, and Tamil Nadu, has confirmed the endemic nature of anthrax. During the last two decades, about 70 cases of human anthrax have been encountered at Christian Medical College, Vellore, including 26 cases of cutaneous anthrax. Recent outbreak of human anthrax has been reported from Jawaharlal Institute of Postgraduate Medical Education and Research (JIPMER), Pondicherry (1998-2001), during which 25 cases of cutaneous anthrax and a few cases of anthrax meningitis (brain) were recorded.

How is it transmitted?

Humans can get infected through the skin, by inhaling it, and rarely by eating or drinking the spores. Infection occurs by handling products from infected animals or by inhaling the spores from contaminated animal products. Anthrax can also be spread by eating undercooked meat from infected animals.

Since it is not contagious, it is extremely unlikely to spread from an infected person to others.

What is the infective dose?

It should be remembered that cattle or sheep (together with guinea pigs) are extremely susceptible to infection, as few as 1—10 spores being sufficient to produce the disease. The infective dose for humans ranges from 100,000 to 1000 spores. It is estimated that inhalation of 100,000 spores would infect 50% of the people exposed to the spores.

What are the symptoms?

The symptoms vary depending on the route of infection. Symptoms usually appear within seven days.

1. Cutaneous anthrax: Most anthrax infections (about 95 percent) occur when the bacteria or spores enter a cut or scrape on the skin. Skin infection begins as a raised, itchy bump that resembles an insect bite but within 1-2 days develops into a vesicle and then a painless ulcer, usually 1-3 cm. in diameter, with a characteristic black necrotic (dying) area called the eschar in the center. The nearby lymph glands swell. About 20 percent of untreated cases of cutaneous anthrax are fatal, but death is rare when it is treated.
   
2. Inhalation anthrax: It is also known as woolsorter’s disease. The initial symptoms may resemble a common cold. Later on the symptoms may progress to breathing problems and shock. Untreated inhalation anthrax is usually fatal.
   
3. Intestinal anthrax: The intestinal form is rare and is characterized by swelling of the intestines. The initial symptoms include nausea, loss of appetite, vomiting and fever, followed by abdominal pain, vomiting of blood, and severe diarrhoea. Intestinal anthrax may be fatal in 25-60 percent of cases.

Can it be prevented?

An effective vaccine is available - about 93 percent effective in protecting against anthrax. But supplies are limited, and are usually used to immunize the armed forces.

Taking antibiotics as a preventative measure is foolish. It will do more harm than good to take antibiotics without medical supervision. The antibiotics commonly used for treatment are effective against other illnesses also and their misuse may lead to development of resistance and consequently they will not work against other diseases. Prophylaxis for asymptomatic patients with suspected exposure to anthrax spores can be achieved with a 6-week course of doxycycline or ciprofloxacin.

How is it diagnosed?

The diagnosis can be made at most microbiology laboratories by smear examination and isolating the bacteria from the blood, skin lesions, or respiratory secretions by culture. Bacillus anthracis is an organism which is very easy to culture and identify.

The anthraxin skin test, consisting of subdermal injection of a commercially produced chemical extract of an attenuated strain of B. anthracis, is available for the diagnosis of acute and previous cases of anthrax. It can also be diagnosed by looking for specific antibodies in the blood or by molecular biology techniques like PCR.

How is it treated?

Antibiotics like Penicillin, Ciprofloxacin or Doxycycline are used for treatment and are effective in most cases if treatment is started in the early stages. These broad-spectrum antibiotics are used for other illnesses too. Cutaneous anthrax lesions should be covered with sterile dressings that should be changed regularly. Soiled dressings should be autoclaved and properly disposed of.

Can anthrax spores be used as a biological weapon?

Anthrax spores have several characteristics suitable for a biological weapon such as low visibility, high potency, accessibility, and relatively easy delivery, and could be used not only in war but also during terrorist activities. A millionth of a gram of anthrax spores constitutes a lethal inhalation dose; a kilogram, depending on meteorologic conditions and means of delivery, has the potential to kill hundreds of thousands of people in a metropolitan area. Vaccine may not protect against some rare B. anthracis strains. It is possible to produce B. anthracis that are resistant to antibiotics.