Monkeypox 2003: Tracing the Path of Exotic Pets
Abstract & Commentary
Synopsis: The recent monkeypox outbreak in 6 midwestern states has been associated with exposure to sick pet prairie dogs that were infected through contact with imported Gambian giant rats and dormice at an Illinois animal facility.
Source: CDC Update: Multistate outbreak of monkeypox—Illinois, Indiana, Kansas, Missouri, Ohio, and Wisconsin, 2003. MMWR Morb Mortal Wkly Rep. 2003;52(27):642-646.
As of july 8, 2003, a total of 71 cases of monkeypox were reported to the CDC of which 35 cases (49%) were laboratory confirmed. One additional case has been added from Illinois bringing the final count to 72 cases. Some cases reported in earlier CDC updates were later excluded when they met the exclusion criteria of the updated monkeypox case definition.
On April 9, 2003, a Texas animal distributor received a shipment of approximately 800 small mammals from Ghana. That shipment contained 762 African rodents including rope squirrels, tree squirrels, Gambian giant rats, brushtail porcupines, dormice, and striped mice. The CDC has since confirmed the presence of monkeypox by PCR or virus isolation in 1 Gambian rat, 3 dormice, and 2 rope squirrels from that shipment. From Texas, some of the Gambian giant rats and dormice were sent to an animal distributor in Iowa, who in turn sold them to another animal distributor in Illinois. At the Illinois facility, approximately 200 prairie dogs overlapped with the arrival of the African rodents and hence were exposed to monkeypox. The exposed prairie dogs were then sent out to 5 other states causing a wave of monkeypox illness in persons exposed to these prairie dogs.
Wisconsin reported 39 human monkeypox cases of which 17 were confirmed (CF) and 22 probable (P). Indiana reported 16 cases (7 CF, 9 P), Illinois reported 13 cases (9 CF, 4 P), and Missouri reported 2 cases (CF). Ohio had 1 probable case and Kansas had 1 confirmed case. Only 93 of the original 200 infected or potentially infected prairie dogs were able to be traced. The others may have either died or were sold at "swap meets" (gatherings of animal traders, exhibitors and buyers); therefore, further tracing could not be done.
Clinical information was available for 69 of the human monkeypox patients. Eighteen patients (26%) were hospitalized, some for isolation precautions only. No deaths occurred, but 2 children had serious clinical illness. One child with severe monkeypox-associated encephalitis was hospitalized for 14 days but recovered. Another child had diffuse pox lesions and profound cervical and tonsillar adenopathy. Despite difficulty breathing, the child did not require mechanical ventilation. Affected patients were either exposed to prairie dogs, exposed while in premises where prairie dogs were kept, or exposed to persons with monkeypox. No cases of monkeypox that could be attributed exclusively to person-to-person contact have been confirmed.
Comment by Mary-Louise Scully, MD
The recent monkeypox outbreak appears to have ended with no new cases reported since mid June. The last issue of TMA Update reported the initial early data on the outbreak, as well as historical background and clinical features of monkeypox.1 Highlights to recall are that the rash of monkeypox may not be distinguishable from smallpox often, but not always, showing synchronous progression through vesicular, pustular, umbilicated, and crusted stages. This could differ from the rash of chickenpox where lesions are often found at different stages of development. In contrast to smallpox, monkeypox patients often develop either localized or, more often, generalized lymphadenopathy. The nodes can be firm and often tender, appearing shortly after the prodromal fever, rarely 1-2 days after the onset of the rash. The rate of person-to-person transmission of monkeypox is much lower than smallpox, with secondary attack rates of about 10% in unvaccinated persons.2 This lower rate of transmission, coupled with much lower reported case fatality rates (2-10%), make monkeypox a less likely candidate than smallpox for biological terrorism.
On June 11, 2003, the CDC and Food and Drug Administration (FDA) jointly issued an order prohibiting the further importation of African rodents to the United States and also banned the sale, transport between states, or release into the environment of prairie dogs or any of the 6 genera of rodents in the original April 9 shipment from Ghana. Important information and guidelines can be accessed on the CDC monkeypox web site including advice for health care and community exposures, exposures of veterinarians and pet owners, and quarantine and euthanasia of exposed or infected animals (www.cdc.gov/ncidod/monkeypox/index/htm). These guidelines remind pet owners not to release their sick or exposed prairie dogs or African rodents out into local environments. Also, any remains of infected deceased or exposed animals should be incinerated and not simply buried in the environment to prevent monkeypox from becoming established and maintained in native wildlife.
Smallpox vaccination has been shown to reduce the risk of monkeypox if given pre-exposure (> 85% effective), and it is believed that it may prevent or ameliorate disease if given postexposure as well. Since June 13, 2003, smallpox vaccine has been administered to 30 persons in 6 states to prevent monkeypox. The vaccine was given pre-exposure to 7 persons and post-exposure to 23 persons. One of the 30 persons given smallpox vaccine developed a rash that was confirmed as monkeypox. No serious adverse events have been reported in those receiving smallpox vaccinations to prevent monkeypox.
Rapid response, detailed epidemiologic tracing, and vigorous quarantine and euthanasia of infected animals appear to have halted this outbreak of monkeypox. The outbreak has heightened awareness of the need for more stringent rules governing importation of exotic wildlife for private ownership. Currently, both state and federal legislation oversee the importation of wild animals. The federal responsibility is divided between the Customs and Border Protection Service (part of the Department of Homeland Security), the CDC, the Department of Agriculture, and the Fish and Wildlife Service. A permit is required from the Fish and Wildlife Service to import wildlife, and imported animals must then enter through a designated port. A recent editorial in the Lancet Infectious Disease notes that since 800,000 iguanas are imported to the United States for pet trade every year, it seems unlikely that these permits are difficult to obtain.3 New regulations and restrictions in exotic pet trade are needed and will no doubt be forthcoming, to better protect against diseases from zoonotic pathogens.
Dr. Scully, Seattle, WA.
References
1. Barry M. Monkeypox in Wisconsin. Travel Medicine Advisor Update. 2003;13(3):22-23.
2. Jezek Z, et al. Human monkeypox: Secondary attack rates. Bull World Health Organ. 1988;66:465-470.
3. Trade in wild Animals: A disaster ignored. Lancet Infect Dis. 2003;3(7):391.
The recent monkeypox outbreak in 6 midwestern states has been associated with exposure to sick pet prairie dogs that were infected through contact with imported Gambian giant rats and dormice at an Illinois animal facility.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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