2 Deliberate release of zoonotic agents

Since 9/11 2001, international attention has once again focused on the risks to human and animal health from the deliberate release of infectious or toxic chemical agents. In theory any agent could be used by terrorists and disaffected people, but the most serious risk for infectious agents are mainly zoonotic (Franz et al. 1997). Three modes of exposure may be anticipated, inhalation of powder or spray or dust from explosives, direct contact or inoculation from an explosion, and ingestion. Centers for Disease Control (CDC) list 19 bioterrorism agents or groups of agents of which 14 are zoonotic (http://emergency.cdc.gov/bioterrorism). In Category A are 6 agents which can be easily disseminated or transmitted from person to person, that result in high mortality rates and have the potential for major public health impact, which might cause public panic and social disruption and which require special action from public health preparedness. Of these 6, four are zoonoses—Anthrax, Plague, Tularaemia and Viral Haemorrhagic Fevers. In Category B, are 12 groups of agents, which are moderately easy to disseminate and cause moderate morbidity. Of these 12 groups, 8 contain zoonoses:

In the twentieth century the main concern was biological warfare perpetrated by states. In the twenty-first century the concern is non-state deliberate release by disaffected groups. Leintenberg (2001) has published a comprehensive review of biological weapons in the twentieth century. In World War I, Germany targeted draft animals (horses and mules) with anthrax and glanders, but apparently without much effect. Following World War I several countries developed biological weapons, including France, USSR, UK, USA, Japan, Germany, Italy, Hungary and Canada. It is reported that only Japan actually used biological weapons, in China in the 1930s, and these included plague, typhoid, cholera and anthrax. The Japanese allegedly experimented with biological agents on at least 3,000 prisoners of war. The USA-UK-Canadian BW programme in which anthrax featured heavily was cancelled before the end of the war. However the USA did manage to develop small particle size aerosol dissemination of wet or dry precipitations of pathogens. Effective delivery of an aerosol requires particle sizes of 1–10 micros in order to reach alveoli.

Following the Second World War, the USSR/Russia, USA, Iraq, UK and South Africa appear to have continued biological weapons programmes. The USA programme up to 1969 produced weaponized Anthrax, Tularaemia, Borreliosis, Q fever, Yellow fever, and Venezualan Equine Encephalitis. The USSR programme was the most extensive and included weaponization of Tularaemia, Anthrax, Brucellosis, Marburg, Smallpox, Plague, Anthrax and Venezualan Equine Encephalitis and included research on Ebola, Bolivian and Argentinian Haemorrhagic Fever, Lassa Fever, Japanese and Russian Spring-Summer Encephalitis. In 1979 an epidemic of anthrax affected people and animals in a narrow 4 km zone downwind of a USSR military bio-weapons facility at Sverdlovsk. 77 cases were identified with certainty and 66 died. The weight of spores released as an aerosol appear to have been less than a gram (Henderson 1998).

In 1992 the United Nations (UN) set up the Biological and Toxic Weapons Convention but several countries mainly in the Middle East and South East Asia are believed to have still sought to acquire biological weapons. Stockpiles of agents will exist in many laboratories throughout the world and more recent concern has focused on the role of states that might sponsor terrorism.

Databases have been compiled of non-state groups using or threatening to use biological weapons, and Leitenberg summarizes these as containing nearly 1,000 events, although real events were extremely rare.

The potential destructive power of infectious agents is clear. The World Health Organization (WHO) has estimated that a release of 50 kg of anthrax in a population of 5 million people could produce 100, 000 deaths, of plague 36, 000 deaths, and of tularaemia 19, 000 deaths. Preparedness for such eventualities is challenging. Two scenarios are usually considered—an overt release which will initially be difficult to distinguish from hoaxes and false alarms, and covert release which will only become manifest once health care staff make the diagnosis. The delay in recognition is a major impediment to effective control, and therefore attention has focussed on developing surveillance systems that collect data on syndromes rather than just confirmed diagnosis. The WHO Global Outbreak Alert and Response Network links more than 70 separate information and diagnostic networks around the world. An important aspect of this system is the use of informal sources to both alert and verify information. Rumours of outbreaks and scanned and early warning of for example Ebola in Uganda in 2009, and yellow fever in West Africa in 2010 were picked up early. The GLEWS for animal disease and zoonoses is a complementary surveillance and early warning network. Ryan (2008) has argued for the use of animal disease as an early warning of bioterrorism attack and integration of veterinary and human health surveillance, a constant theme of this book.

Complacency is discouraged by the fact that there have been notable episodes of malicious release of zoonotic agents. The Aum Shinrikyo Group in Japan who released Sarin in Tokoyo in 1995 also attempted but failed to produce Botulism toxin and anthrax. However, a more successful venture was perpetrated in October 2001 in the USA when letters carrying anthrax spores and mailed through the USA postal system caused 18 cases of anthrax over 8 weeks. The public health response monitored by the USA was unprecedented. Chemoprophylaxis was given to 32, 000 potentially exposed people, and those considered at higher risk were on 60 day courses. 120, 000 environmental and chemical samples were processed during the acute phase.

International contamination of food was perpetuated by members of a religious cult in the USA in September 1984. Salmonella typhimurium was sprinkled on salad bars and 751 people developed illness (Tovok et al. 1997). Sobel, Khan and Sverdlow (2002) identify episodes of deliberate contamination of food by Shigella dysentiae and Ascaris Suis which caused severe pulmonary disease. Clearly all food supplies are vulnerable, as is proven by the frequent accidental contamination incidents of ‘normal’ food-borne diseases. Detection of a covert attack would be challenging since outbreaks are common. In the Dallas, Oregon, Salmonella Outbreak it was the size and nature of the outbreak that led to an crucial investigation in which a vial of the outbreak strain of salmonella was discovered in the cult’s laboratory. The restaurants affected by the same strain of salmonella did not have common food suppliers and epidemiologic analyses of food consumption revealed multiple food vehicles.

Dembek et al. (2006) suggest eleven clues to detecting an unnatural outbreak:

In addition to these clues, Dembek et al. (2007) draw attention to Grunow and Finke’s (2002) procedure for differentiating between the unnatural release of agents and natural outbreaks.

Effective to deliberate release will require effective response routine diagnostic and surveillance systems, capacity for rapid and expert field epidemiological investigation and good public health communication systems. It is generally recognized that the best way to deal with deliberate release is to use well tried and tested public health systems that are applied to naturally occurring infectious diseases. For some infections, stockpiles of antibiotics/antitoxins and vaccines are appropriate. However, it is clear that most public health systems, especially in conflict areas, are under resourced and could not reasonably be expected to cope with early detection of deliberate release. The field epidemiological skills required to investigate and interpret findings with the precision required in applying Grunow and Finke’s (2002) procedure would challenge even the best public health units. Continued investment in ‘One Health’ surveillance and field investigation should be a priority for all countries.