Monkeypox: A Terrorist Weapon?

 On July 11, 2003, the Centers for Disease Control and Prevention reported that there were 71 cases of confirmed or suspected human monkeypox in the United States.

 On July 11, 2003, the Centers for Disease Control and Prevention reported that there were 71 cases of confirmed or suspected human monkeypox in the United States. The cases occurred in Illinois, Indiana, Kansas, Missouri, Ohio, and Wisconsin. There have been no previously recognized cases of human monkeypox in the United States. It is believed that the infected persons acquired the disease from sick prairie dogs.  The disease was spread among prairie dogs after an exotic animal distributor in Texas housed several of the prairie dogs in the same cage with an infected Gambian giant rat and subsequently shipped the infected prairie dogs to an animal distributor in Illinois.  The Gambian giant rat was part of a shipment containing 762 African rodents imported on April 9 from Ghana to Texas. 

In 1970 the World Health Organization (WHO) reported the first case of human monkeypox in a nine-month old boy in the Democratic Republic of the Congo (formerly Zaire) -- one year after the last reported case of smallpox in that region. In 1980, the WHO designated monkeypox to be, like smallpox, an important Orthopoxvirus infection. Indeed, the WHO considers monkeypox to be the most serious Orthopoxvirus infection in the post-smallpox era. Since 1980 there have been several outbreaks of human monkeypox in rural villages in the rainforest regions of west and central Africa but fewer than a thousand confirmed or suspected infections. The fact that smallpox vaccine has not been routinely administered for over two decades has increased concern that outbreaks of monkeypox could be more serious given the absence of widespread immunity against monkeypox that was previously conferred by routine smallpox immunization.

Monkeypox is a zoonotic viral disease which infects rodents, especially prairie dogs, tree squirrels, rope squirrels, Gambian giant rats, brush-tail porcupines, and striped mice. The term "zoonotic" refers to a disease which can be transmitted from animals to people.

Monkeypox transmission also occurs from animal-to-animal.  The virus can spread from person-to-person but only if there is very close contact, especially through respiratory droplets, body fluids, and virus-contaminated objects, such as bedding or clothing. Infected persons present with fever, rash, respiratory symptoms, lymphadenopathy, and sore throat.  The pustular skin lesions are similar to those of smallpox and just as disfiguring.  The mortality rate in the African outbreaks of monkeypox has ranged from one to ten percent.  In the recent cases in the United States there were no deaths. All infected persons reported contact with animals, mostly prairie dogs, although one person was infected after contact with a Gambian giant rat and another after contact with a pet rabbit that had been exposed to an infected prairie dog at a veterinary clinic.

There is no specific vaccine for monkeypox.  There is evidence, however, that smallpox vaccination is at least 85 percent effective in preventing or ameliorating the disease, even if administered after exposure.  This is, however, of small consolation since, seven months after the Bush Administration called for the vaccination of 400,000 to 500,000 members of the health community -- so-called "first responders" -- only about 40,000 had been vaccinated as of July 2003.  Furthermore, there is a shortage of vaccine and little "surge capacity" in the event of a terrorist attack employing the smallpox virus.  Virtually no persons born in the last 35 years have been vaccinated and older persons, vaccinated many years ago, may no longer have protective immunity from the disease.

Since the 9/11 terrorist attacks there has been much concern about biological warfare.  Anthrax is considered to be an especially horrendous weapon, with the potential to kill hundreds of thousands.  Smallpox also has received much attention, especially since it is known that the former Soviet Union had weaponized smallpox and the world population is now largely defenseless against a smallpox attack.           

Given these concerns, it is not surprising that the outbreak of monkeypox has led to speculation that it too, since it is so similar, though much less deadly than smallpox, could become a terrorist weapon.  Deliberate spread of monkeypox is made feasible by the fact that the virus can maintain infectivity for months at room temperature and perhaps almost indefinitely at cold temperatures. Hence it would be possible for terrorists to acquire the virus from infected animals and introduce it into the U.S. animal population.  Of course bringing in already infected animals, such as prairie dogs, and releasing them into the wild would be a more effective method.  This suggests the importance of strict border control as the best defense against monkeypox.

In early June 2003, the Centers for Disease Control and Prevention and the Food and Drug Administration issued a joint order announcing an immediate embargo on the importation of all rodents from Africa.  Other agencies charged with the responsibility to contain a monkeypox outbreak are the Animal and Plant Health Inspection Service of the Department of Agriculture, Customs and Border Protection, the Department of Homeland Security, the Fish and Wildlife Service of the Department of the Interior, and state and local health authorities.  First responders, in this case veterinarians and other animal handlers, should receive smallpox vaccine.