Monkey Pox Update

Monkeypox: An Imported Virus

Monkey pox is an uncommon viral disease that occurs mostly in central and western Africa. It is called "monkeypox" because it was first identified in laboratory monkeys (1958). Subsequently, other African animals, particularly rodents, were found to be susceptible to this virus. African Squirrels may be the reservoir for this infection.

Monkeypox in the United States

On June 13, 2003, the investigation of fifty-three suspected human monkeypox infections in Illinois, Indiana, and Wisconsin was reported in Mortality and Morbidity Weekly Reports (MMWR). (http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5223a1.htm) The earliest onset of illness was May 15. In an update published four weeks later, the number of suspected infections had increased to seventy-one and had been found in Kansas, Missouri, and Ohio. (http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5227a5.htm) However, only thirty-five infections had been laboratory confirmed.

FIGURE 1. Number of monkeypox cases)*, by date of illness onset — Illinois, Indiana, Kansas, Missouri, Ohio, and Wisconsin, 2003^†

* N = 69 of 71 cases with known date of illness onset.
^† As of July 8, 2003.

This is the first outbreak of this infection in the United States.

The Monkeypox Virus

The monkeypox virus is an orthopox virus, and is similar to other viruses in that group. Orthopox viruses include the smallpox virus (variola), the virus used in the smallpox vaccine (vaccinia), and the cowpox virus.

Signs and Symptoms of Monkeypox

In humans, the signs and symptoms of monkeypox are similar to those of smallpox, but are usually milder. A significant difference is that monkeypox causes lymphadenopathy. Seven to seventeen days after infection, individuals develop fever, headache, muscle aches, and backache; enlarged lymph nodes; and fatigue.

One to three days (or longer) after the onset of fever, a rash appears. The typical rash is vesicular and, like smallpox, all of the lesions tend to be in the same stage of development. It often starts on the face and spreads, but it can start on other parts of the body. It commonly involves the palms and soles. However, the rash can be macular, papular, vesicular, or pustular; generalized or localized; discrete or confluent.

The lesions go through several stages before they develop crusts and disappear. The illness usually lasts for two to four weeks. The CDC case definition criteria are available at http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5227a5.htm

Confirmation of Infection

Infections are confirmed by one of four laboratory studies:

• Isolation of monkeypox virus in culture;
• Demonstration of monkeypox virus DNA by polymerase chain reaction testing of a clinical specimen;
• Demonstration of virus morphologically consistent with an orthopox virus by electron microscopy in the absence of exposure to another orthopox virus;
• Demonstration of orthopox virus in tissue using immunohistochemical testing methods in the absence of exposure to another orthopox virus.

(One of the first infections to be recognized was identified by electron microscopy of a patient’s skin lesion, and by isolation of the virus from that tissue and from tissue from the patient’s pet prairie dog at the Marshfield Clinic in Marshfield, WI.)

Detailed instructions for collection and preparation of specimens for laboratory studies, including precautions and safety measures, are available at http://www.cdc.gov/ncidod/monkeypox/diagspecimens.htm

Mortality from Monkeypox

In Africa, monkeypox is associated with 1 to 10 percent mortality. The rate would be expected to be lower in the United States because nutrition and access to sophisticated medical care are better. None of the U. S. patients have died; only sixteen were hospitalized and some of those were hospitalized for isolation and not because the severity of their illness required such care.

Source of the Outbreak
Traceback investigations have determined that all thirty-five confirmed human cases of monkeypox were associated with prairie dogs obtained from a single Illinois animal distributor, or from animal distributors who purchased prairie dogs from that distributor. The prairie dogs appear to have been infected through contact with Gambian giant rats and dormice that originated in Ghana. Approximately 200 prairie dogs had been at the facility during April and May; an unspecified number overlapped with the arrival of the imported African rodents on April 21 and probably were exposed to monkeypox.

Ninety-three infected or potentially infected prairie dogs were traced from the Illinois distributor to six states; in addition, an unknown number of prairie dogs died or were reportedly sold as pets for sale or exchange at animal swap meets for which no records were available for tracing.
At CDC, laboratory testing of four prairie dogs originating from the Illinois distributor confirmed the presence of monkeypox virus by PCR and by immunohistochemistry.

Spread of the Virus

Individuals usually contract monkeypox from an infected animal. They may be bitten or come in contact with the animal’s blood, body fluids, or its rash.

In Africa 8 to 15 percent of the infections are spread from person to person through large respiratory droplets during long periods of face-to-face contact, or through contact with body fluids or bedding and clothing contaminated with the virus. No infections from these sources have been confirmed in the United States.

Treatment of Monkeypox Infection

No specific treatment for monkeypox infection is available. However, in Africa, people who have received smallpox vaccine in the past have a lower risk of monkeypox, and vaccination appears to provide protection for individuals who expect to be exposed to the virus. Vaccination after exposure lessens the severity of smallpox infections and may do the same for monkeypox.

The only contraindications to vaccination are immunodeficiency or severe allergy to latex or to the vaccine or one of its ingredients, which include polymyxin B, streptomycin, chlortetracycline, and neomycin.

Vaccinia immune globulin (VIG) and cidofovir have been considered for the treatment of monkeypox. VIG does not reduce the rate of complications in smallpox and would not be expected to be beneficial for monkeypox. Cidofovir has been demonstrated to have antimonkeypox properties in vitro and in animal studies, but has not been evaluated in humans.

The CDC guidelines for vaccination are available at http://www.cdc.gov/ncidod/monkeypox/treatmentguidelines.htm

Control of the Outbreak
On June 11, 2003, the Food and Drug Administration-CDC issued a joint order banning importation and prohibiting movement or release into the environment of the African rodents implicated in the spread of monkeypox: rope squirrels (Funiscuirus sp.), tree squirrels (Heliosciurus sp.), Gambian giant rats (Cricetomys sp.), brushtail porcupines (Atherurus sp.), dormice (Graphiurus sp.), and striped mice (Hybomys sp.). In addition, state-enacted measures to further restrict intra-state animal shipment and trade, quarantine of the premises where infected or potentially infected animals were housed, and euthanasia of such animals appear to have been effective in reducing exposure of humans to this infection, Few cases have been reported since implementation of these measures.

Additional control measures have included pre- and post-exposure vaccination of potentially exposed persons with smallpox vaccine.

Importing exotic animals and harvesting indigenous, wild animals for the commercial pet trade have been associated with outbreaks of infectious diseases in humans, including salmonella associated with reptiles and tularemia associated with prairie dogs. Infection of prairie dogs with other human pathogens such as plague also has been documented. CDC and other federal agencies, in collaboration with state and local health departments and professional organizations, are developing strategies to coordinate the control of importation, exportation, interstate trade, and intrastate sale of exotic and native wild animals.

1. Landyl ID, Siegler P, Kima A: A human infection caused by monkeypox virus in Basankusu Territory, Democratic Republic of the Congo (DRC) Bull WJO 1972;46:593-597.
2. Jezek ZM, Scczeniowski KM, Paluku M, Putombo M, Grab B: Human monkeypox: clinical features of 282 patients. J Infect Dis 1987;156:293-298.
3. Hutin Y, Williams RJ, Malfait P, et al: Outbreak of human monkeypox, Democratic Republic of Congo, 1996–1997. Emerg Infect Dis 2001;7:434-439.
    

Medical Editor, James A. Wilkerson, III, MD

Note: The information in this report was taken from CDC publications including its website. The graph and table of laboratory proven cases were copied from that site, which CDC explicitly permits for educational purposes. ed.