PDF: Infectious Disease
THREAT: Infectious Disease
Globalization and freedom of air travel allow a communicable human disease to travel from anywhere to anywhere else within 24 hours. Short of blood tests and lengthy quarantine of travelers there is little that can be done to prevent a carrier of a highly communicable, highly lethal disease walking the streets of a large population centre today. The use of disease as a new asymmetric tactic would make explosives seem primitive. Walking the path to martyrdom through densely populated cities infected with a well-chosen disease, a “dead man walking” could bring havoc – and fear. But if the “terrorists” don’t do it, diseases assisted only by ignorance and negligence may get there first. Broadly speaking, diseases have three sources:
Protozoa – the tiniest of animals typically inhabiting water and other animals as parasites; the commonest example is malaria, threatening one-twelfth of the human population, caused by protozoans in the bite of an infected female Anopheles mosquito. Such diseases can be prevented by physical interdiction (DDT, mosquito nets) and medication treating or repairing the effects.
Bacteria – microscopic single celled organisms; life would not exist without bacteria in animal digestion, the nitrogen cycle and other essential processes. But some bacteria turn to the dark side – tuberculosis readily treatable if diagnosed early is caused by Mycobacterium tuberculosis; Bacillus anthracis can form hardy air-borne spores and cause highly lethal anthrax. Common treatments are killing the bacteria before it infects or the use of the appropriate antibiotic after infection.
Viruses, the ultimate in simplicity and masters of self-preservation, are simply a nucleic acid (DNA or RNA) instruction-set covered by a protein sheath. They reproduce only by penetrating cells and using the cell’s reproductive mechanism to replicate themselves. Variations in copying the code produces mutations of the virus. Examples are highly contagious, high lethality Ebola caused by an airborne virus spores and H5N1 (avian influenza) that is highly communicable among some animals but non-communicable (or weakly communicable) to humans. Such infections are commonly prevented or attenuated by injecting a vaccine, small doses of crippled or dead versions of the target virus, that teaches the body’s immune system what to kill on sight.
That’s the good news. DDT remains the most effective interdiction against malaria but it is banned in most developed nations because of the devastating persistent effect on the environment. Use of the wrong antibiotic, or misuse, or over-use creates – by natural selection – strains of bacteria that are resistant to many or all antibiotics. Mutation of viruses means that the vaccine administered today after three months development may be useless against a mutant version of the virus that appeared in the infected subject yesterday. Simple changes in the protein sheath will render it invisible to an immune system trained by a vaccine to recognise other characteristics. The worst case is when a virus attacks the cells of the immune system itself – as with HIV/AIDS.
These “second generation” dangers of infectious diseases are not just theoretical. A new strain of tuberculosis identified recently in South Africa is quickly fatal in HIV/AIDS patients and a disease once thought beaten may spread around the world anew. A mutation in the H5N1 virus is theoretically possible any day and would make it highly communicable to humans. A range of vaccine-preventable diseases thought to be eliminated in developed countries such as measles, mumps, whooping cough, and poliomyelitis are making a reappearance – complacency has led to a drop-off in vaccination and many doctors have “forgotten” to look for these diseases in patients. Neglect of these vaccination programs poses the hazard of self-inflicted epidemics. The over-use and misuse of antibiotics over decades, particularly in the US, is acknowledged as a major contributor to new more dangerous strains of pathogens such as some Staphylococci that are found only in hospitals.
Apart from these dangers to ourselves, miscreants using asymmetric tactics can bring immense harm to populations by transporting uncommon but highly contagious pathogens to highly populated areas. Whether a pathogen is weaponisable is a buzz-word in this field; that is, can it be produced, packaged, transported and effectively deployed in potent, dispersed form. Anthrax in spore form is well-suited to this but a range of other pathogens can be presented in a matrix of lethality and deployability. There is little confidence that health infrastructures could cope beyond a few days or weeks against even a small but effective pathogen attack in a large population centre — the health services themselves will be the first victim, followed possibly by public order. Mortality will be a mere detail.
There is every indication that a public health investment would yield worthwhile benefits in doing the easily do-able — education of doctors and the population about vaccination, misuse of antibiotics, and early detection and treatment of diseases such as tuberculosis. Meanwhile, the security community should continue to inventory the hazards from various pathogens – lethality vs. communicability vs. availability vs. deployability vs. treatments vs. likelihood. A careful study may show that anthrax (and VX) is the least of worries.
The abilities of the biological sciences around the world is as good as scientific discovery allows. The weakest link by far is government coordination in the mitigation of avoidable endemic diseases, fore-knowledge of the logically possible types of pathogen attacks by miscreants, and planning for response in the event of such attacks. Planning and exercises around the world prompted by the perceived H5N1 threat are encouraging but exercises and resource planning should accommodate a range of incubation periods and infection rates. Many variations will provide very bleak results.
Control of airspace, liquids on aircraft, quick temperature measurement of incoming travelers and other measures all mitigate against some forms of biological attack. One scenario worthy of exploring is a highly contagious, highly lethal (or debilitating) disease with a long incubation period and long period of contagion. Concealing a weapon of mass destruction in the cells of the body is simple, cheap, effective, and un-detectable until vast numbers of people have been infected. Generally, the actors in this scenario need to be prepared to die but that might not be an impediment.