Anthrax after September 11 th 2001-What to look for and how to treat it

Anthrax is a serious bacterial infection with a particularly high mortality in its gastrointestinal, pulmonary, and meningitic forms with a worldwide distribution, although it is most common in the developing world. Gastrointestinal and pulmonary anthrax results in death within hours or a few days of the onset of serious symptoms and the diagnosis is usually made post-mortem. Treatment of wild type anthrax is usually with penicillin in high dose. The production of anthrax for large scale bioterrorism is difficult and requires sophisticated facilities. There is a greater risk that anthrax used as a bioterrorist weapon will be antibiotic resistant and ciprofloxacin is a more appropriate antibiotic choice until the antibiotic sensitivity of the anthrax strain being deployed becomes known. Post exposure prophylaxis should be continued for two months due to the long delay that sometimes occurs before spores germinate once within the human host. A live vaccine is available but requires a large number of injections and its use is largely limited to military personnel.


Introduction
In early October last year I was on my way back to Edinburgh from a meeting in London.A sig nalling failure just outside Paddington station meant that a journey on the Heathrow Express extended from 15 to 75 minutes, during which time I watched the BBC News summary more times than I would have wished, particularly since the delay threatened my return that night to Edinburgh.BBC News majored on the bioterrorist outbreak of anthrax which was then in its early phases in the USA.The index case became ill on October 2nd in Florida and died a few days later1.To my surprise a disease which I had treated several times at a teaching hospital in Tanzania 20 years previously was now appar ently of global interest.On my return to Edin burgh I offered to give a short presentation at the Grand Round at the Western General Hospi tal, since if Al Qaeda was responsible it was at least remotely possible that the UK, as the clos est ally of the USA, might also be a target.This paper is a direct result of that presentation and seeks to summarise what we know about anthrax, its clinical presentations and treatment, both in endemic and bioterrorist forms.

The causative organism and pathogenesis
Anthrax derives its name from the Greek word anthrakos meaning coal due to the appearance of a coal black centre in the lesion in the cutane ous form.Anthrax is caused by a gram positive, spore forming, toxin producing aerobic rod, Ba cillus anthracis.Although in vitro it grows as long chains, in the human host it appears as sin gle organisms or chains of 2 or 3 bacilli 1.The vegetative bacillus does not survive long in a pu trefying carcass, only 3-4 days at 25° C 2. Es caping bacilli at temperatures above 20°C form spores which may survive decades, but these are destroyed by dry heat of 150°C, boiling for 10 minutes, and autoclaving.The toxin has three parts, of which two are important, an oedema factor and a lethal factor2.Lethal factor stimu lates the release of tumour necrosis factor and interleukin-1a contributing to sudden death2.
The lethal factor is a protease with a particular amino acid substrate which could be a target for the development of an inhibitor1.Infection is initiated after introduction of a spore through a break in the skin or mucosa and the vegetative form is germ inated after ingestion by macrophages and may then pass to regional lymph nodes and the spleen.Extracellular mul tiplication then occurs with toxin production 2. Lethal factor is produced and released in a burst, causing fever, disorientation, coma, and death.In rhesus monkeys, inhaled spores are deposited in alveolar spaces and then transported to medi astinal lymph nodes where germination occurs up to 60 days later.It was this observation that has led to the recommendation that antibiotic prophylaxis should be continued for 60 days af ter inhalational exposure2.

Epidemiology of wild type anthrax
Anthrax has a worldwide distribution but is now most common in developing countries, princi pally in Africa and Asia.Historically, some out breaks have been massive.In 1945 an outbreak in Iran caused one million sheep deaths1, and between 1979 and 1985 an outbreak in Zimba bwe caused 10,000 human cases2.Even in de veloped nations anthrax has continued to cause problems.Between 1944 and 1994, the USA reported 224 cases, of which 18 were inhalational3.Occasional cases have surfaced elsewehere in the developed West, for instance in 1976 fatal pulmonary anthrax was contracted from bone meal fertiliser in the UK4.Cutane ous anthrax occurred in a casual labourer in Lon don in 19965, and a Norwegian who skin-popped heroin in 2000 6.The annual total for cases worldwide is estimated at 20,000-100,000 2.

The anthrax bacillus as a bioterrorist weapon
The use of anthrax as a bioterrorist weapon was extensively reviewed only 2 years before the 2001 outbreak by Inglesby in the Journal of the American Medical Association 1.There has been interest in anthrax as a weapon of war for many years.During WWII British scientists conducted experiments on Gruinard Island off the West coast of Scotland and several decades elapsed before it was successfully decontaminated.Aum Shinrikyo terrorists in Japan made at least eight unsuccessful attempts to release aerosols of an thrax spores before their more tragically ef fective release of sarin nerve gas in a Tokyo sub way in 1995.After the Gulf War, Iraq admitted producing and deploying weaponized anthrax in missiles, lending weight to the view that a clear threat remained, a threat which has now become all too obvious1.
A few litres of standard broth culture prepared in a kitchen can produce sufficient spores to in fect a few people if sent through the post.Lyophilising cultures into powder requires sim ple equipment, but ultra refining spores is nec essary if more extensive bioterrorism is planned.Particles need to be between 1-5 um 1 and elec trostatically neutral in order to avoid clumping M .This is probably beyond the ability of small groups and it has been estimated that for an at tack on an urban population of 5 million, the aerial discharge of 50 kg of highly refined sporecontaining powder would be needed to cause 250,000 cases 2.
The major experience with anthrax in bioterrorist form comes from Russia.In 1979 accidental discharge into the atmosphere oc curred at a biological warfare research establish ment at Sverdlovsk.Precise figures are not avail able but it is thought that 100 inhalational cases may have occurred of which 66 were fatal, all aged over 24 years *.Cases in humans occurred up to 4 km and in animals up to 50 km from the factory site '.On the basis of experiments in primates the dose in humans causing 50% lethality is between 2500 and 55,000 spores 1 and this amount is not visible to the naked eye.
The strain of anthrax used in bioterrorism in late 2001 in the USA was a derivative of Ames strain used worldwide by researchers, and first isolated from a dead animal in Ames, Iowa in the 1950s.Preliminary analysis suggested the presence of constitutive and inducible beta lactamases and for this reason treatment with penicillin, ampicillin or amoxicillin was not rec ommended 2. The CDC website does not give a clear total for the number of human cases asso ciated with this outbreak at the point of writing this paper in May 2002 but by 28th November 2001 23 cases had been identified of which 11 were inhalational and 12 cutaneous 1.

Principal clinical m anifestations
Cutaneous anthrax (Figures 1-4) This occurs as the result of direct contact with viable organisms invading through a skin break.Person to person spread does occur but very rarely and has been documented as a result of sharing scrubbing brushes used during bathing-1.The cutaneous form is referred to as a malignant pustule, but this is a misnomer since there is no pus unless secondary bacterial infection occurs.The incubation period is 1-7 days, following which a pimple grows rapidly over 2-4 days.The initial itchy painless vesicle is 1-2cm in diam eter and filled with clear or serosanguinous fluid.As the vesicle enlarges satellite vesicles develop with impressive surrounding oedema.When the vesicle ruptures it forms an ulcer covered by a black eschar by day 4-5.Without the use of an tibiotics resolution occurs after 10 days and in 80-90% of cases healing occurs without scar ring.Ulceration may still occur after antibiotic use and total resolution may take 2-6 weeks.

Gastro-intestinal anthrax
This occurs as a result of eating infected meat and comprises 95% of cases with a mortality of only 1%.The incubation period is 1-7 days af ter ingestion, during which an eschar develops on the intestinal mucosa, usually in the terminal ileum or caecum but it may occur anywhere from the oropharynx downwards 3. Gross mesenteric lymphadenitis follows and perforation of the in testine may occur at the site of the eschar.Gastro intestinal anthrax is usually undiagnosed until too late.The clinical features are sudden onset of severe diffuse abdominal pain, nausea and vomiting and variably, watery or bloody diar rhoea may be present.On physical examination there will usually be fever, rebound tenderness, shock, and collapse, and ascites may be present after 2-4 days.Death occurs in a few hours or recovery may occur after 10-14 days.

Pseudomonas aeroginosa
Rat bite fever

Staphylococcus aureus
Cutaneous TB

Mycobacterium ulcerans
Spider bite

Pulmonary anthrax
Pulmonary anthrax occurs as a result of the in halation of spore-laden dust.The incubation period is 1 -6 days.Prior to the 1960s in the USA, workers in goat hair mills were exposed to high concentrations of viable spores but there were few cases of inhalational anthrax.However when dispersed in the air as an aerosol anthrax spores can present a real hazard even long dis tances downwind, as demonstrated by the Sverdlovsk outbreak in 1979.Modal incubation is 10 days, but in the Sverdlovsk outbreak some cases occurred up to 6 weeks after accidental discharge.Longer incubation times probably occur with smaller inocula.During the first few days patients have no symptoms or 'flu' for a few days and then there is abrupt onset of chills, a strident cough, blood stained vomit due to haematogenous spread to the gut.dyspnoea and cya nosis, and on examination moist chest sounds and signs of systemic collapse.The spleen and Figure 5. Tick typhus lesion in visitor to Tenaxillary lymph nodes may be enlarged.A chest erife (Rickettsia conorii) X-ray may show widened mediastinum, and blood culture becom es positive within 2-3 days o f the onset o f sym ptom s (sam ple chest X-rays can be dow n loaded from the CD C w ebsite).Death usually occurs in 2-3 days but m ilder cases occur with bronchitic sym ptom s.Varying advice is given for acutely ill cases in current textbooks, but initially benzyl penicillin should be given in a dose o f 2.4 G 4-6 hourly, initially iv for three to five days.Cutaneous sores becom e sterile in one to tw o days.P lasm aphoresed serum from a vaccinated person 'm ay be life sa v in g ' '.

Treatment of anthrax bio-terrorism
The Russians are reported to have bio-engineered an anthrax strain resistant to tetracyclines and penicillin1, but there is, as yet.no evidence o f engineered quinolone resistance.The concerns already m entioned o f delayed germ ination o f spores carried after exposure to the prim ary aero sol m ean s th at sh o rt c o u rs e s o f a n tib io tic may be insufficient.Initial treatm ent is ciprofloxacin 400mg iv 12 hourly, although in sensitive strains optimal treatment is with ben zyl penicillin as above iv.The antibiotic may be administered orally when the patient's clinical condition improves.The total duration of therapy should be 60 days.
Supportive therapy if oedema is extensive may include corticosteroids.Other general measures include the prevention of septic shock and main tenance of fluid and electrolyte balance.

Anthrax post-exposure prophylaxis
The agent of choice is ciprofloxacin 500mg twice daily for 60 days.Alternatives are doxycycline lOOmg twice daily for 60 days or amoxycillin 500mg three times daily for 60 days.Hart and Beeching have cautioned that such prophylactic treatment should be given only to those who re ally need it, since ciprofloxacin in prolonged courses may induce resistance in commensal organisms, and these in turn may transmit re sistance to pathogenic organisms'.

Vaccination
An anthrax vaccine consisting of an attenuated strain has been given to members of the US armed forces since 1998.Six injections are given over 18 months, the first three in the first month and aerosol challenge studies in monkeys sug gest complete protection at 8 weeks and 88% protection at 100 weeksSw artz.No serious adverse events have been reported but vaccine supplies are extremely limited.In the UK advice on the use of the vaccine must be obtained from the Public Health Laboratory Service14.

Figure 2 .
Figure 2. Facial 'malignant pustule ' with ery thema and oedema spreading down onto the an terior chest wall.The patient was hypotensive and febrile.
Above: Figure 3a.Marked oedema in cutane ous anthrax affecting the thigh.No clear malig nant pustule is seen.A BCG scar is present in the centre o f the photograph.Below: Figure 3b.Ulceration in the same p a tient during convalescence.Above: Figure 4 One o f fou r patients admitted to Kilimanjaro Christian Medical Centre, Tanzania in 1977.They had found a dead zebra, carried it to their village and cooked it over an open fire.The three patients who had eaten zebra meat developed severe abdominal symptoms suggestive o f an intra-abdominal catastrophe and died in the sur gical department.This patient had marked cu taneous invasion o f spores as a result o f having carried the zebra on his right shoulder.He has oedema o f the anterior chest wall, visible as nip ple oedema, and was severely hypotensive.He died fou r hours later.

Figure 6 .Figure 7 .
Figure 6.Tick typhus lesion in visitor to K ruger G am e reserve (Rickettsia africae)

Table 1 :
Differential Diagnosis of Cutaneous Anthrax