Monkeypox Technical Background and Outbreak Implications for Bioterrorism Preparedness
CRS Report for Congress
Monkeypox: Technical Background and
Outbreak Implications for Bioterrorism
Dana A. Shea and Frank Gottron
Analysts in Science and Technology Policy
Resources, Science, and Industry Division
Specialist in Social Legislation
Domestic Social Policy Division
Monkeypox, a viral disease related to smallpox, has appeared in humans in the
Midwest. Though monkeypox usually has a fatality rate of 1 to 10%, no fatalities have
occurred in the outbreak, which has been linked to pet rodents. Although officials do
not believe that this outbreak is bioterrorism, the delay between the initial presentation
of an unusual disease and the notification to the federal government has raised concerns
regarding the state of bioterrorism preparedness. The Centers for Disease Control and
Prevention (CDC) have provided guidance to local communities regarding handling of
ill patients and animals, treatment regimens, and sample protocols. The CDC have
recommended and released smallpox vaccine as prophylaxis against monkeypox
infection. The CDC and the Food and Drug Administration banned interstate commerce
in prairie dogs and certain other rodents and the CDC suspended import of all rodents
from Africa. Possible issues related to this outbreak include the regulatory process that
allowed import of diseased animals; how efficient the public health system response has
been in alerting the government to potential health emergencies; and whether the
monkeypox outbreak provides an opportunity to evaluate recent efforts to increase
public health preparedness and the state of bioterrorism preparedness. This report will
be updated as events warrant.
An outbreak of monkeypox, a disease caused by a virus closely related to smallpox
virus, began in May 2003 in Wisconsin. As of this writing, 79 suspected and diagnosed
Congressional Research Service ˜ The Library of Congress
cases have been identified in multiple states.1 Most of the afflicted individuals were
infected by ill, pet prairie dogs. Officials do not believe that the current outbreak was
caused by an act of terrorism.2 This report describes previous human outbreaks,
symptoms, and treatments of monkeypox; the government response to the current
outbreak; and implications this outbreak may have in evaluating the public health system
response to biological terrorism.
What Is Monkeypox?
Monkeypox’s causative agent is an Orthopox virus in the Poxviridae family. In the
wild, rodents, predominantly squirrels in central and western Africa, are the reservoir for
this virus. Monkeypox is a zoonotic disease, meaning that humans can catch the disease
from infected animals. Human monkeypox outbreaks occur infrequently and generally
in rural, African rainforest villages. The largest recent confirmed outbreak occurred in
the Democratic Republic of Congo in 1996–1997, with 88 cases over a 12-month period.3
Between January 2000 and March 2002, 22 cases of monkeypox worldwide were reported
to the World Health Organization.4 Monkeypox is not native to North America and has
not previously been diagnosed in the United States.
Human monkeypox symptoms are similar to those of smallpox. Initial symptoms
include fever, aches, and malaise. Unlike smallpox, monkeypox often causes swollen
lymph nodes. These symptoms are followed by a rash which converts into blisters. An
incubation period of up to 2 weeks is possible, and symptoms may last for 2 to 4 weeks.5
There is no known, proven cure for monkeypox. Monkeypox victims are treated
with supportive care. There are indications that some antivirals, namely cidofovir and
ribavirin, may be effective. Cidofovir has been recommended for treating monkeypox
during this outbreak, but only in life-threatening cases, due to its significant side effects.6
Because monkeypox is closely related to smallpox, the smallpox vaccine (vaccinia) is an
effective prophylactic. Vaccination with vaccinia is estimated to provide greater than
85% protection against monkeypox.7 Vaccinia may reduce the severity of a monkeypox
infection if the victim is vaccinated a few days after exposure to monkeypox, generally
before symptoms appear.
1 Daily updates of the number and location of suspected monkeypox cases are provided by the
CDC online at [http://www.cdc.gov/od/oc/media/monkeypx.htm].
2 Linda Spice, “13 Sick After Prairie Dog Contact; Milwaukee Pet Store Employee, Two Others
Remain Hospitalized,” Milwaukee Journal Sentinel, June 6, 2003.
3 Y.J.F. Hutin, R.J. Williams, P. Malfait, et al., “Outbreak of Human Monkeypox, Democratic
Republic of Congo, 1996 to 1997,” Emerging Infectious Diseases, 7(3) May–June 2001.
4 J.G. Breman, I. Arita, and F. Fenner, “Preventing the Return of Smallpox,” New England
Journal of Medicine, 348(5), 463-466, January 30, 2003.
5 CDC, “What You Should Know About Monkeypox - Fact Sheet,” June 12, 2003.
6 CDC, “Interim Guidance for Use of Smallpox Vaccine, Cidofovir, & VIG for Prevention and
Treatment in the Setting of Outbreak of Monkeypox Infections,” June 12, 2003, available online
Monkeypox is less contagious than smallpox. Studies of African outbreaks suggest
that 8-15% of those in household settings with a victim may become infected.8
Transmission experiments indicate that it is possible to infect others via aerosol, for
example through coughing or sneezing.9 The human fatality rate for monkeypox is lower
than that for smallpox. In documented cases in Africa, the fatality rate has ranged from
1% to 10% in unvaccinated individuals. The comparable fatality rate for smallpox is
approximately 30%.10 The fatality rate in the United States may be lower than that
observed in Africa because of better nutrition and health-care access.11
Current Monkeypox Outbreak
The current monkeypox outbreak began in May 2003, with the onset of illnesses in
Wisconsin. All cases to date have involved contact between an infected animal and the
victim. The CDC investigation suggests that monkeypox entered the United States via
import of infected African rodents for use as exotic pets. These rodents apparently
infected nearby captive prairie dogs in a pet store. The infected prairie dogs were
distributed and sold over three states. There are not any reports of wild animals in the
United States becoming infected with monkeypox, although this remains a risk.
The CDC recommends that doctors follow a standard protocol when diagnosing a
disease with acute, generalized rash in order to rule out smallpox,.12 If smallpox remains
a possibility, physicians should alert their local and state health departments. The health
departments, working with the Laboratory Response Network, can further test specimens
taken from suspected cases. The health departments may then notify the CDC, which will
begin an investigation and may help test the samples. In the May outbreak, physicians
reportedly ruled out smallpox at an early stage because of the apparent link of the cases
to ill animals.13 This assumption reportedly led to a 13-day delay before the local or state
health departments were notified.14 Identification of the disease as monkeypox was
announced by the CDC on June 7, 2003, following preliminary serologic testing and DNA
analysis.15 Suspected cases of monkeypox continue to be investigated. While person-to-
person transmission of the disease is possible, all diagnosed cases so far in this outbreak
have been linked to animal-human transmission.
9 G.M. Zaucha, et al., “The Pathology of Experimental Aerosolized Monkeypox Virus Infection
in Cynomolgus Monkeys (Macaca fascicularis),” Lab. Invest., 81, pp. 1581-1600 (2001).
10 CDC, “Basic Information About Monkeypox - Fact Sheet,” June 12, 2003.
11 CDC, “What You Should Know About Monkeypox ...”
12 “The Acute, Generalized Vesicular or Pustular Rash Illness Protocol,” CDC, available online
13 Linda Spice, “13 Sick After ...”
14 Steve Mitchell, “Monkeypox Shows Gap in Bioterror Readiness,” UPI International, June 12,
15 CDC, “Preliminary Report: Multistate Outbreak of Monkeypox in Persons Exposed to Pet
Prairie Dogs,” June 9, 2003.
In response to the outbreak, several states have banned the importation, display and
sale of prairie dogs. Some state and local governments have quarantined animals or
seized and destroyed them.16 Other state efforts have focused on identifying those who
have been exposed to the infected animals; monitoring those who provide care for ill
persons; alerting physicians to look for suspected monkeypox cases; and tracking down
all of the potentially infected animals.
The CDC has banned import of all African rodents.17 The CDC and the Food and
Drug Administration have prohibited the transportation, sale, distribution or release of
prairie dogs and the following rodents from Africa: tree squirrels, rope squirrels, dormice,
Gambian giant pouched rats, brush-tailed porcupines, and striped mice.18 The CDC
suggests that states may also choose to prohibit the importation, display, and sale of other
species that may carry monkeypox, such as rabbits, gerbils, or hamsters.
The CDC has issued guidelines for treatment and isolation of suspected monkeypox
cases19 and guidelines for the use of smallpox vaccine to protect against monkeypox.20
Smallpox vaccine is recommended for people who have had close contact with a
monkeypox case. Household contacts of monkeypox cases and those who may have
handled sick prairie dogs are also advised to be vaccinated. Vaccination is recommended
for health care workers who are caring for known or suspected monkeypox cases or will
be in the near future. All vaccinations should be done within 4 days of initial direct
contact, though it may be considered for anyone with exposure within the previous 2
weeks. The CDC have recommended Vaccinia Immune Globulin (VIG), and cidofovir
to counteract some of the serious side effects of the smallpox vaccine.21
Congress has expressed interest in assuring that federal, state, and local public health
organizations are held accountable for making effective use of recent funding increases
to improve public health preparedness. Some policymakers have suggested that
evaluating the public health response to unusual disease outbreaks may be a valuable tool
for assessing improvements in public health preparedness. Others argue that unless an
outbreak is categorized as a suspected bioterrorism event, it is not a true test of the
nation’s bioterrorism response plans. Even where a comprehensive assessment of
16 Dan Rozek and Art Golab, “Monkeypox Cases ‘Will Go Up’; Dozens of Prairie Dogs Linked
to Virus Can't Be Found,” Chicago Sun-Times, June 11, 2003.
17 Authority is granted by the Public Health Service Act, 42 U.S.C. 264, see also 42 CFR
18 Authority is granted by the Public Health Service Act, 42 U.S.C. 264, see also 42 CFR 70.2 and
19 Available online at [http://www.cdc.gov/ncidod/monkeypox/infectioncontrol.htm].
20 CDC, “Interim Guidance for Use of Smallpox Vaccine ...”
21 For more information about the side effects of the smallpox vaccine see CRS Report RL31694
Smallpox Vaccine Stockpile and Vaccination Policy, by Judith A. Johnson.
bioterrorism preparedness is not possible, certain aspects of public health response are
similar whether a disease outbreak occurs naturally or through an intentional act. An
effective public health response includes: performing appropriate laboratory tests using
protocols established through the Laboratory Response Network to rule out and/or
identify the pathogenic agent; timely, accurate reporting to appropriate public health
officials; rapidly disseminating accurate and consistent information to public health
officials, health care providers, the media, and the public; using epidemiologic
information to determine and control potential transmission vectors; and assuring
appropriate medical care by rapidly providing guidelines for treatment and diagnosis.
Public health experts have favorably compared the public health system response to
both SARS and monkeypox to the confused public health reaction during the anthrax
attacks.22 However, some have claimed that there may still be areas for improvement, as
gaps and weaknesses remain in some state and local public health communication and
surveillance capabilities.23 Development of a systematic method for using disease
outbreak response to evaluate public health system preparedness could assist in
identifying areas for improvement in the system and a metric for measuring improvement.
Many federal agencies regulate animal import. The regulatory situation that allows
importation of diseased animals is similar to that allowing importation of invasive
species.24 Since many diseases are zoonotic, ill-animal importation may have bioterror
implications. Such imports might be used in an agroterrorism attack by using a lightly
regulated animal to introduce a disease for a different animal, causing economic harm.
Another possibility might be intentionally importing and releasing ill animals to increase
the number of naturally occurring fatal diseases in humans. The monkeypox outbreak is
likely to increase scrutiny of these regulations and may result in new legislative proposals
to modify them.
The CDC reportedly expressed concern over the delay between the occurrence of the
initial case and notification of the agency.25 However, in other statements, the CDC has
praised the response of state officials.26 Critics state that the delay between presentation
and public health response suggests the notification system needs improvement.27 They
assert that a comparable delay in the case of smallpox would lead to a sizeable epidemic.
Furthermore, simply identifying the disease as monkeypox might not rule out
bioterrorism. In the early stages of this outbreak, the fact that monkeypox had never been
22 David McGlinchey, “Monkeypox Outbreak Tests Bioterrorism Response Systems,” Global
Security Newswire, June 12, 2003.
23 General Accounting Office, Bioterrorism: Preparedness Varied Across State and Local
Jurisdictions, GAO-03-373, April 2003.
24 For a thorough review of agencies responsible for regulating importation of animals and the
regulatory gaps, see CRS Report RL30123, Invasive Non-Native Species: Background and Issues
for Congress, by M. Lynne Corn, Eugene H. Buck, Jean Rawson, Alex Segarra, and Eric Fischer.
25 Chris Logan, “Feds Didn’t Hear about Monkeypox for Weeks, Officials Say,” CQ Homeland
Security, June 9, 2003.
26 Marilynn Marchione, “U.S. Bans Sale of Prairie Dogs; CDC Urges Smallpox Shots, But State
Officials Reluctant to Comply,” Milwaukee Journal Sentinel, June 12, 2003.
27 Steve Mitchell, “Monkeypox Shows Gap ...”
previously diagnosed in the United States and had been reportedly developed as a
weapon28 may have raised concerns that the outbreak was not of natural origin. Following
CDC notification and epidemiological investigation, the discovery of infected rodent
imports from an area known to have endemic monkeypox strongly supports a natural
Some observers have defended the delay as reasonable, since smallpox was ruled out
quickly because it cannot infect animals, and there was an apparent link between the
human cases and diseased animals. On the other hand, many of the diseases that have
been the targets of weapons programs in the past are transferable from animal to man,
such as plague, tularemia, and hantavirus.29 It is conceivable that a terrorist group with
access to these agents, but lacking advanced dissemination technology, would choose to
use animal vectors. A documented case is the Japanese use of fleas to cause plague
outbreaks in China in the 1930s.30 Some critics suggest that since such links do not
preclude a bioterrorism event, healthcare providers should err towards potential over-
Whether the current monkeypox outbreak tests the nation’s bioterror preparedness
is an open question. Some claim that the early classification of this outbreak as not
related to bioterrorism means that this is not a true test of the nation’s bioterrorism
response plans. Since this is a public health concern, the Department of Health and
Human Services is the lead agency for federal response, unlike in a terror event, where
the Department of Homeland Security would assume responsibility. Others claim that an
outbreak of a new disease, no matter the vector, magnitude, or source, should be treated
as a potential bioterror event until proven otherwise, and they suggest a need for a more
rapid and coordinated response.32 Congress may consider whether to further address
when and how the federal bioterror response should be engaged.
28 Ken Alibek, Biohazard: the Chilling True Story of the Largest Covert Biological Weapons
Program in the World – Told From Inside by the Man Who Ran It (New York: Random House,
29 Center for Non-proliferation Studies, Monterey Institute of International Studies, Chemical and
Biological Weapons Resource page at [http://cns.miis.edu/research/cbw/possess.htm].
30 Peter Williams and David Wallace, Unit 731: Japan’s Secret Biological Warfare in World War
II (New York: Free Press, 1989), p. 27.
31 Steve Mitchell, “Monkeypox Shows Gap ...”