Testimony

Statement by
Stephen Ostroff, M.D., M.P.H.
Deputy Director, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Dept. of Health and Human Services
on
CDC's Role in Zoonotic Disease Outbreaks
before the
The Committee on Environment and Public Works, United States Senate

July 17, 2003

Introduction

Good morning, Mister Chairman and other Members of the Committee. I am Dr. Stephen Ostroff, Deputy Director of the National Center for Infectious Diseases, Centers for Disease Control and Prevention. I would like to thank you for the invitation to participate in this hearing on the important public health issues raised by exotic animal importation and distribution in the United States. Today I will discuss the role of zoonotic diseases in public health and CDC's involvement in the investigation and control of the recent outbreak of monkeypox infections in the Midwest which prompted this hearing.

As highlighted in a report released by the Institute of Medicine earlier this year entitled Microbial Threats to Health: Emergence, Detection, and Response (copy provided), at the beginning of the 21st century, we live in an era of emerging infectious diseases. Over the last several decades, dozens of newly recognized infectious diseases have been identified, many of which pose significant threats to public health and safety. In only the last year, we have seen three major emerging infectious disease threats. Last summer's West Nile virus outbreak was unprecedented in scale and scope, with more than 4,000 human illnesses in 44 states and Washington D.C. Earlier this year, severe acute respiratory syndrome, or SARS, rapidly spread throughout the world from an initial focus in southern China with extraordinary public health, economic, and political consequences. And now for the first time, we have seen the emergence of monkeypox infections outside of the natural range of the virus in rural areas of west and central Africa.

More than half of these newly recognized emerging infectious diseases have their origins in animals, either via direct transfer from animals to humans (known as zoonotic diseases) or through an intermediate vector (known as vectorborne diseases). Examples of the former include hantavirus pulmonary syndrome from domestic rodents, human immunodeficiency virus from non-human primates, salmonellosis from reptiles, variant Creutzfeldt Jacob disease (or human BSE) from cattle, and probably the SARS coronavirus. Examples of the latter are Lyme disease (from deer via ticks) and West Nile virus (from birds via mosquitoes). The emergence of a number of these diseases has been facilitated by the ever increasing global movement of people, products, and animals. West Nile virus was unknown in North America before 1999, and although we do not know how it was introduced into New York City, the leading hypothesis remains via an infected bird, either imported or migratory. These phenomena highlight the fact that U.S. health and global health are inextricably linked and that fulfilling CDC's domestic mission to protect the health of the U.S. population- requires global awareness and collaboration with domestic and international partners to prevent the emergence and spread of infectious diseases.

The Outbreak

In early June, CDC received reports from several Midwestern states of persons with fever and rash illness who had recently had close contact with prairie dogs. The Marshfield Clinic in Wisconsin identified a virus that was consistent with a poxvirus in tissue samples from a patient and an ill prairie dog. Additional testing at CDC indicated that the causative agent was monkeypox, a virus first identified in the 1950s that belongs to the family of orthopox viruses which also includes smallpox. Monkeypox and smallpox share many clinical features, but monkeypox has a known animal reservoir in rodents, is less transmissible in humans, and is less virulent than smallpox.

In response, CDC initiated extensive investigations (many of which continue today) to determine the scope and scale or the outbreak in humans and animals, and initiated prevention and control measures to limit the impact of the disease on the public's health and welfare.

As of July 15th, a total of 72 human cases of monkeypox have been reported to CDC from Wisconsin, Illinois, Indiana, Missouri, Kansas, and Ohio. In 37 of these cases the diagnosis of monkeypox has been laboratory confirmed, while the remainder are considered suspected or probable cases. Eighteen of these persons were hospitalized, and two children were severely ill but are now recovering. Fortunately, there have been no fatalities associated with this outbreak.

The Traceback

In partnership with our other federal, state, and local partners, traceback investigations were conducted to identify how monkeypox virus was introduced into the United States. Results of this traceback effort are summarized in graphic A and in CDC's Morbidity and Mortality Weekly Report (MMWR) of July 11th, 2003. The prairie dog associated with the index patient in Wisconsin was obtained from a Milwaukee-area distributor (distributor A) that had obtained the animals from a vender in suburban Chicago (distributor B). At distributor B, the prairie dogs had been housed with Gambian giant rats, a rodent species found in areas of Africa known to be endemic for monkeypox virus. So far, all confirmed cases of human monkeypox are associated with prairie dogs that are known or suspected to have come from distributor B.

Further investigation revealed the Gambian giant rats had been legally imported from Ghana into Texas in early April, sold to an Iowa distributor, who then sold them to the Chicago distributor. These animals were part of a larger shipment of approximately 800 animals of nine different species, including six genera of African rodents which could serve as potential hosts for monkeypox (graphic B). These animals were then widely distributed within the United States and some were even re-exported to Japan. Subsequent testing of some of these animals at CDC has identified monkeypox virus in a Gambian giant rat in addition to dormice and rope squirrels.

Prevention and Control Measures

In addition to issuing guidance on infection control, therapeutics, and use of smallpox vaccine for pre- or post-exposure prophylaxis, on June 11, 2003, the Director of CDC and the Commissioner of Food and Drugs, pursuant to 42 CFR 70.2 and 21 CFR 1240.30, respectively, issued a joint order prohibiting, until further notice, the transportation or offering for transportation in interstate commerce, or the sale, offering for sale, or offering for any other type of commercial or public distribution, including release into the environment, of prairie dogs, tree squirrels, rope squirrels, dormice, Gambian giant pouched rats, brush-tailed porcupines, and striped mice.

The June 11, 2003, order did not apply to the transport of listed animals to veterinarians or animal control officials or other entities pursuant to guidance or instructions issued by federal, State, or local government authorities. In addition, pursuant to 42 CFR 71.32(b), CDC implemented an immediate embargo on the importation of all rodents from Africa (order Rodentia). These actions have been enhanced by recommendations regarding euthanasia of prairie dogs linked to the Illinois distributor and the rodents from the original shipment, and quarantine of other mammals in contact with the implicated animals.

Animal Importation and Human Health

Introduction of exotic species, such as rodents from Africa, can pose a significant threat to human public health, to domesticated animals and agriculture, and to indigenous wildlife through the introduction of non-native pathogens. As noted in last week's MMWR and in a recent editorial in Lancet Infectious Diseases (copy provided), importation of exotic animals and the movement in commerce of indigenous, wild animals harvested for the commercial pet trade have been associated with previous outbreaks of infectious diseases in humans. Examples include salmonellosis associated with reptiles and tularemia associated with prairie dogs. West Nile virus may be another such example. Prairie dogs are also known to harbor the bacterium responsible for plague. In the monkeypox outbreak, the rapid and widespread distribution of infected and potentially infected wild animals to distributors and potential buyers in numerous settings enabled the spread of this virus through multiple states before the problem was even recognized and effective interventions could be implemented. Fortunately, the June 11th joint order appears to have been highly effective in reducing further transmission, as few human illnesses have been recognized due to exposures that occurred since that time.

The development of long-term strategies is needed to coordinate and control the importation, exportation, re-exportation, interstate trade, and intrastate sale and distribution of exotic and native wild animals. However, there are a number of complex issues and questions which must be addressed regarding the sale and trade of exotic and native wild animals. Such a position was recently adopted by the Council of State and Terroritorial Epidemiologists and the National Association of State Public Health Veterinarians (position statement provided). Accredited zoological parks and bona fide research facilities mandate specialized training for handlers and enforce strict protocols concerning prevention of zoonotic diseases and injury hazards with captive animals. In contrast, well intentioned pet dealers, breeders, and private owners often lack the expertise and resources to maintain exotic and native wildlife safely.

In conclusion, the recent experience with monkeypox highlights the continued threat of emerging infectious diseases and the importance of global disease surveillance, to have prompt disease reporting, and to strengthen the linkages and interactions between human and veterinary clinical and public health practitioners. While we have made progress in building domestic and global capacity to address intentional and naturally-occurring threats to human public health, our job is far from complete and much more remains to be done. CDC looks forward to working with Congress, and our federal, state, local, public, and private partners, to address the infectious disease threats of the present and the future.

Thank you for allowing us to participate in today's hearing. I would be happy to answer any questions that you may have.

Last Revised: July 17, 2003