Anthrax

Anthrax

V DE VOS AND P C B TURNBULL

Introduction

Anthrax is a peracute, acute or subacute, highly contagious disease of domestic and wild animals and humans caused by the bacterium Bacillus anthracis. In most species of animals it is characterized terminally by the development of a rapidly fatal septicaemia, resulting in sudden death. The principal lesions are those of widespread oedema, haemorrhage and necrosis.

The first record indicative of anthrax is considered to be that in the Bible (Exodus, Chapters 7 to 9) which refers to the fifth and sixth plagues of Egypt — believed to be systemic and cutaneous anthrax, respectively — which occurred in about 1491 BC. 74, 136, 145, 146, 232, 298 Virgil (70 to 19 BC) not only described major periodic outbreaks of anthrax in animals and humans in ancient Rome, but also associated the occurrence of anthrax in humans with the consumption ofmeat or contact with hair or hides of animals that had died of the disease.67 Reference is also made to anthrax in the ‘Hippokratika’, a collection of veterinary documents dating from the tenth century.136 The more recent history of anthrax is intimately associated with the history of microbiology and infectious diseases.136, 152, 232, 263, 299 Anthrax appears to be the first disease of humans and animals that was shown to be caused by a microorganism. Barthelémy in 1823 demonstrated its transmissibility by inoculation, and Rayer and Davaine in 1850 observed filiform bodies in the blood of animals that had died of the disease. This organism, referred to as Bacterium by Davaine in 1864, was named Bacillus anthracis by Cohn in 1875.40, 299 Final proof of its causative role was furnished by Koch in 1876143 who, in a classic masterpiece, subsequently referred to as ‘Koch’s postulates’, described not only the organism, its ability to form resistant spores and its cultivation in vitro, but also the reproduction of the disease by injection of pure cultures, and the recovery of the organism at necropsy from animals that had died as a result of experimental infection.143Anthrax was also the first disease against which avirulent strains of the causative organism were used as immunizing agents in vaccines.

In spite of the fact that Pasteur’s 1881 vaccine against anthrax199 has long been credited with being history’s first bacterial vaccine, it has since been pointed out that Greenfield prepared an effective vaccine against anthrax and described his results some months before Pasteur’s experiments were conducted.259

The pathogenesis of anthrax was extensively studied during the first half of the twentieth century,263 but interest in it has fluctuated since then. The development of Sterne’s effective livestock vaccine in 1937,246, 247 and the successful application of penicillin therapy140, 187 lessened the concern about the disease, but the threat of B. anthracis being used as an agent in biological warfare during and after World War II reawakened interest in it.39, 41, 173, 245 After the signing of the 1972 Biological Weapons Convention, interest in B. anthracis waned to the extent that the subsequent period, albeit short, has been referred to as a ‘dark age’ for research into anthrax.263 However, since then an epidemic of anthrax in humans occurred near Sverdlovsk in Russia in April 1979, a facility suspected of being utilized for the production of materials for use in biological warfare.11, 95, 178, 211, 274, 281 This caused international concern and appeared to violate the 1972 Biological Weapons Convention.95 Subsequent threats to use B. anthracis as an agent for biological warfare have been made as recently as 1990 during the Gulf War and afterwards as tension between Iraq, neighbouring countries and the United Nations’ forces continued.75 Bioterrorism is also considered another potential area of misuse for anthrax.127 It was calculated that the economic impact of such an act in the USA could amount to $26,2 billion per 100 000 persons exposed.127 Biological warfare/terrorism, involving anthrax, and possible means to combat it, will therefore remain a nightmare for the international community in the foreseeable future and has rekindled interest in the disease from the standpoints of detection, protection and treatment.

Earlier writings pointed to the probable origin of anthrax being in erstwhile Mesopotamia and northern Africa,136, 145, 146, 232,while the Nile valley is the locality where the disease was first recorded.

Its further spread was thought to be associated with the process of domestication of wild ungulates and the dispersion of domestic cattle into the rest of Africa,76, 89, 204 and subsequently into areas such as Eurasia,146 the USA,105, 239, 298 and Australia.217 It is, however, also possible that the native tribes and their domesticated animals, during their southern migrations through Africa, encountered anthrax along the way, where it already existed endemically and indigenously among free-living wild animals. The recent works of Keim et al. 129 and Smith et al.,225, 226 allowing for the genotypic grouping of anthrax isolates, supports this hypothesis and suggests that the geographic origin of B. anthracis may be the subSaharan African continent. In the Kruger National Park in South Africa an intricate ecological pattern, with anthrax an integral part of it, has also been identified. It suggests a...

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