Influenza virus seen as possible bioterrorism weapon

Jul 8, 2003 (CIDRAP News) – An influenza virus—especially one genetically manipulated for increased virulence—would be an attractive weapon for bioterrorists, according to physicians writing in the Journal of the Royal Society of Medicine.

As a potential biological weapon, influenza has several advantages over smallpox, including ready accessibility, write Mohammad Madjid, MD, and three colleagues. The authors are affiliated with the University of Texas–Houston Health Center and two heart institutes in Houston.

"The possibility for genetic engineering and aerosol transmission suggests an enormous potential for bioterrorism," they assert.

The Spanish flu epidemic of 1918 killed between 20 million and 40 million people. The "usual estimate" of the annual influenza death toll in the United States is 20,000, but recent studies of all-cause mortality suggest it is closer to 90,000, the authors state. They also cite recent evidence that influenza may be a risk factor for sudden cardiac death and stroke.

Since the terrorist attacks of 2001, "We must . . . consider the possibility of malicious genetic engineering to create more virulent strains" of influenza, they continue. "Sequencing of the genome of the 1918 Spanish influenza virus is nearly complete; once it is published, unscrupulous scientists could presumably utilize candidate virulence sequences."

Influenza is usually transmitted by direct contact, but aerosol transmission also occurs and requires "27,000 times fewer virions to induce equivalent disease," the article says.

Influenza virus is far more accessible than smallpox virus, known stocks of which are held only in secure facilities in the United States and Russia, the authors note. They contend that influenza has other advantages over smallpox as a potential weapon:

• Since influenza occurs naturally, an epidemic would have more time to spread before triggering a major public health response.
• Postexposure immunization is ineffective for influenza because of its short incubation period (1 to 4 days), which is not the case with smallpox.
• Influenza is harder to eradicate because it has animal and avian reservoirs.

The authors propose several steps to address the threat of influenza as a terrorist weapon, including the following:

• The Centers for Disease Control and Prevention should classify influenza virus as a "critical agent" for bioterrorism.
• Immunization should be expanded, possibly by requiring it for all medical personnel.
• Laboratories that work with influenza virus should strengthen their security.
• Antiviral drugs should be stockpiled and vaccine-making capacity should be increased.
• The government should consider a gene-sequencing and vaccine development program.
• Surveillance efforts should be increased and should include incentives for reporting of clinical cases.
• The fitting of ventilation systems with virus detection and inactivation devices should be considered.

Madjid M, Lillibridge S, Parsa M, et al. Influenza as a bioweapon. J R Soc Med 2003;96(July):345-6