Cutaneous Anthrax—Still a Reality in India

Introduction

Anthrax occupies an important place in the history of infectious diseases, as it is the first human disease to be attributed to a specific pathogen.^1,2 It is a zoonotic infection with Bacillus anthracis. The name anthrax comes from a Greek word for “coal,” a reference to black eschar that is eventually formed in cutaneous anthrax.

Human anthrax is of four clinical forms depending on the route of transmission: cutaneous (the most common form accounting for nearly 95% of all anthrax cases), inhalational, ingestion form, and injectional form.³

History

In 1876, Robert Koch (1843–1910) reproducibly transmitted anthrax to mice by inoculating them with blood from the cattle and subsequently, he then recovered the same rod-like bacteria from the sick mice as came from the cattle. He could pass the disease from one mouse to another by inoculating them with these pathogens. Based on his experiments, he proposed the “Henle–Koch postulates” for proof that a microorganism was the cause of an infectious disease.⁴

Robert Koch's landmark work on anthrax helped to establish the germ theory of disease, and an 1877 report on B. anthracis included the first published photomicrographs of any bacteria.³

B. anthracis is a large (1–5 micron), spore forming aerobic, or facultative anaerobic gram-positive rod, usually arranged in a box-car pattern.^1,5 When cultured on 5% sheep blood agar, 2 to 5 mm colonies have ground glass appearance with nonhemolytic, tenacious colonies (beaten egg-white appearance) after 15 to 24 hours. On India-ink staining, poly-D glutamic acid capsule can be visualized. On methylene blue staining, the bacterial cell is stained blue, whereas the surrounding capsule is pink. This is described as the M’Fadyean's reaction. Koch's postulates were proved on this organism for the first time.⁵

Epidemiology

Being a zoonotic infection anthrax is mainly linked to goat, sheep, cattle, antelope, kudu, pigs, horses, zebu, and other animals.⁶ Animals are infected by ingesting the spores from contaminated soil, feed, or even meat (in case of wild animals). It is transmitted to humans by meat, wool, hides, bones, and hairs and rarely from person to person.

Infection in animals commonly occurs due to ingestion of spores or inoculation into abraded perioral areas while grazing in contaminated area or eating contaminated feed or meat. Subsequent death of the animal causes recontamination of the environment.^6,7 After such multiple events, the area might become endemic. Other modes of spread in animals are fomites, by insects or legs of vultures.^6,7

Anthrax should be considered as possible cause of death in herbivorous animals that have died suddenly and unexpectedly, especially if hemorrhage from the nose, mouth, or anus has occurred.³ Failure of the blood to clot, the absence of rigor mortis, and the presence of splenomegaly are the most significant necropsy findings in such animals.^6,7

The disease has a global distribution but incidence in livestock and humans varies with local ecology, implementation of control strategies, and sociocultural practices that determine spillover from animals to humans. Although most developed countries report few sporadic cases in livestock and humans, the disease is still enzootic in parts of Africa (e.g., Zimbabwe and Chad), the Middle East, Central Asia, China, Pakistan, Bhutan, Bangladesh, and India.^1,2,6-15

The geographic distribution of anthrax is associated with certain ecological factors. In some ecosystems, outbreaks occur late in the hot–dry season, whereas in others, outbreaks are associated with the end of heavy rains, suggesting that weather extremes may be an important trigger of outbreaks.⁶

One of the largest outbreaks of anthrax occurred in Zimbabwe during 1979 to 1985 where approximately 10,000 cases of cutaneous anthrax were reported. Inhalational anthrax historically referred as “wool-sorters” disease because it occurred in industrial settings where spore contaminated wool or animal hides are handled.^5,16

Anthrax is also mentioned prominently as potential agent of biowarfare and bioterrorism. In the 1950s and 1960s, both the United States and former Soviet Union developed anthrax as a biological weapon, as have other countries.⁵

An epidemic of inhalation anthrax occurred among persons living in Sverdlovsk, Union of Soviet Socialist Republics, in April and May 1979 resulting in at least 96 cases and 66 deaths.^17-19 This outbreak also affected cattle within the city. It was concluded that this largest outbreak of human inhalation anthrax was due to an infectious aerosol emanating from the military facility. This outbreak raised considerable concern among scientists and policymakers about the potential for the use of aerosolized B. anthracis spores as an agent of biological terrorism. Indeed, these fears were confirmed in 2001 when an outbreak of 22 cases of anthrax (11 inhalational and 11 cutaneous) occurred in the United States from intentional contamination of the U.S. mail delivered to several persons by the U.S. Postal Service. Five deaths and 22 cases of anthrax occurred.^17-19

Since 2009, anthrax has emerged among heroin users in Europe, presenting a novel clinical manifestation, “injectional anthrax,” which has been attributed to contaminated heroin distributed throughout Europe; before 2009, only one case was reported.^20,21 During 2012 and 2013, new cases of injectional anthrax were diagnosed in Denmark, France, Germany, and the United Kingdom. Overall 70 confirmed cases were reported, with 26 fatalities (37% case fatality rate). The latest two confirmed cases occurred in March 2013.^20,21

Anthrax in India

A few sporadic cases and endemic outbreaks have been reported from India.^1,2 During the last two decades, 70 cases of human anthrax were encountered at the Christian Medical College at Vellore in Tamil Nadu of which 26 cases had cutaneous anthrax. A review of Indian literature in 1996 found 112 cases of anthrax (71 cutaneous anthrax cases) in places, other than Vellore. The authors have recorded 23 cases of cutaneous anthrax over a period of 3 years with a single mortality due to septicaemia.^1,2 Recently, outbreaks of cutaneous anthrax have been recorded from Andhra Pradesh (in the year 2005, 2009, and 2012), and West Bengal (2009).^22-25 These data confirm the endemicity of anthrax, besides in the state of West Bengal, in other three southern states of India, that is, Andhra Pradesh, Karnataka, and Tamil Nadu.