Chapter 3Infectious Diseases Related To Travel
Smallpox & Other Orthopoxvirus-Associated Infections
Mary G. Reynolds
Smallpox is caused by variola virus, a member of the Poxvirus family, genus Orthopoxvirus. Other members of this genus known to cause infection in humans are vaccinia virus, monkeypox virus, and cowpox virus. In 1980, the World Health Organization declared that smallpox had been eradicated globally. As a result, smallpox is not considered a risk for international travelers. International travelers may, however, be at risk for contracting other orthopoxvirus infections, including vaccinia, monkeypox, and cowpox.
MODE OF TRANSMISSION
During the smallpox era, disease transmission from person to person occurred principally through face-to-face contact, via respiratory routes. Respiratory droplets produced during the first 3–7 days of illness in a person suffering from smallpox are heavily laden with virus and can efficiently establish infection in a susceptible person who is exposed. Less commonly, new infections were the result of a person’s inhaling or having mucus membrane exposure to virus-containing material shed from skin lesions or scabs.
Monkeypox virus infection can occur after contact with infected animals or from people who are ill with monkeypox. Person-to-person transmission is thought to occur by way of large respiratory droplets and, less commonly, through contact with lesions or objects contaminated with lesion material (fluid, scab). Multiple species of African rodents and primates have been observed to harbor the virus, and could transmit infection to humans, but the precise reservoir host for monkeypox virus remains unknown.
Vaccinia virus causes a localized infection of the skin that is typically confined to the portal of entry, often a freshly abraded (scratched) area. Vaccinia virus is the live virus component of contemporary smallpox vaccines. Rarely, social contacts of people recently vaccinated for smallpox develop infections with vaccinia virus. These infections occur either when a susceptible person’s skin comes into direct contact with fluid from the inoculation lesion of a recent smallpox vaccinee, or when a person is exposed to objects (towels, clothing) contaminated with lesion material. Zoonotic infections with vaccinialike viruses have been reported in Brazil and India.
Cowpox virus also causes localized infections of the skin that occur at the portal of entry, typically a freshly abraded (scratched) area. Human infections with cowpox virus stem from contact with infected animals; transmission of the virus between humans has not been observed. Rodents, predators of rodents (cats), and occasionally exotic animal species in zoos can become infected with cowpox virus. Infected animals typically demonstrate signs of illness, including skin lesions.
The last reported case of endemic smallpox occurred in Somalia in 1977, and the last reported case of laboratory-acquired smallpox occurred in the United Kingdom in 1978.
Monkeypox virus is endemic in tropical forested regions of West and Central Africa, notably the Congo Basin. Hundreds of monkeypox virus infections are reported to health authorities annually in the Democratic Republic of the Congo. Rodents imported from West Africa were the source of an outbreak of human monkeypox that occurred in the United States in 2003. Travelers should avoid contact with forest-dwelling animals that appear sick or that have been found dead.
Infections with wild vaccinialike viruses have been reported among cattle and buffalo herders in India and among dairy workers in southern Brazil.
Human infections with cowpox virus have been reported in Europe.
Monkeypox virus infection causes an illness clinically identical to smallpox, with fever and widespread vesiculopustular rash involving the palms and soles. One feature distinctive to monkeypox is marked lymphadenopathy. The case-fatality ratio for monkeypox is estimated to be 10%.
Vaccinia and Cowpox
Human infections with vaccinia, wild vaccinialike viruses, and cowpox virus are most often self-limited, characterized by localized pustular (occasionally ulcerative) lesions. Fever and other constitutional symptoms may occur briefly after lesions first appear. Lesions can be painful and can persist for weeks. Orthopoxvirus infections in humans are rare. People who are immunocompromised or who have exfoliative skin conditions (such as eczema or atopic dermatitis) are at substantially higher risk of severe illness or fatal outcomes.
Orthopoxvirus infection is confirmed by PCR or virus isolation. Physicians can refer to CDC smallpox website (emergency.cdc.gov/agent/smallpox/diagnosis) for guidance in the application of a clinical algorithm designed to aid in distinguishing smallpox from other disseminated rash illnesses, namely chickenpox.
Treatment of human orthopoxvirus infection is mainly supportive, to include hydration, nutritional supplementation, and prevention of secondary infections. Vaccinia lesions should remain covered by bandage, gauze, or clothing until the scab detaches, in order to diminish chances of inadvertent inoculation of the virus to other parts of the body or transmission to another person. To prevent person-to-person transmission of smallpox and monkeypox, patients should be isolated and cared for by someone who has received the smallpox vaccine. Physicians managing orthopoxvirus infection in a patient who is at high risk for severe outcome (such as a patient who is immunocompromised or has an underlying skin condition) should consult with CDC to explore investigational treatment options; contact the CDC Emergency Operations Center at 770-488-7100.
PREVENTIVE MEASURES FOR TRAVELERS
Smallpox vaccine is not recommended for international travelers. Live vaccinia virus is the main component of the smallpox vaccine. Because of the elimination of smallpox, routine smallpox vaccination ceased worldwide in 1980. Smallpox vaccination is recommended only for laboratory workers who handle variola virus (the agent of smallpox) or viruses closely related to variola virus and health care and public health officials who would be designated first responders in the event of an intentional release of variola virus. In addition, members of the US military may be required to receive the vaccine.
There are no preventive vaccines for other orthopoxvirus infections. No drugs for preventing or treating orthopoxvirus infection are licensed. Travelers are advised to avoid contact with rodents and sick or dead animals, including pets and domestic ruminants (cattle, buffalo). For more information about monkeypox and other orthopoxviruses, contact the CDC Poxvirus Inquiry Line (404-639-4129).
- Baxby D, Bennett M, Getty B. Human cowpox 1969–93: a review based on 54 cases. Br J Dermatol. 1994 Nov;131(5):598–607.
- Campe H, Zimmermann P, Glos K, Bayer M, Bergemann H, Dreweck C, et al. Cowpox virus transmission from pet rats to humans, Germany. Emerg Infect Dis. 2009 May;15(5):777–80.
- CDC. Human monkeypox—Kasai Oriental, Democratic Republic of Congo, February 1996–October 1997. MMWR Morb Mortal Wkly Rep. 1997 Dec 12;46(49):1168–71.
- Damon IK, Roth CE, Chowdhary V. Discovery of monkeypox in Sudan. N Engl J Med. 2006 Aug 31;355(9):962–3.
- de Souza Trindade G, Drumond BP, Guedes MI, Leite JA, Mota BE, Campos MA, et al. Zoonotic vaccinia virus infection in Brazil: clinical description and implications for health professionals. J Clin Microbiol. 2007 Apr;45(4):1370–2.
- Learned LA, Reynolds MG, Wassa DW, Li Y, Olson VA, Karem K, et al. Extended interhuman transmission of monkeypox in a hospital community in the Republic of the Congo, 2003. Am J Trop Med Hyg. 2005 Aug;73(2):428–34.
- Levine RS, Peterson AT, Yorita KL, Carroll D, Damon IK, Reynolds MG. Ecological niche and geographic distribution of human monkeypox in Africa. PLoS One. 2007;2(1):e176.
- Reynolds MG, Davidson WB, Curns AT, Conover CS, Huhn G, Davis JP, et al. Spectrum of infection and risk factors for human monkeypox, United States, 2003. Emerg Infect Dis. 2007 Sep;13(9):1332–9.
- Rotz LD, Dotson DA, Damon IK, Becher JA. Vaccinia (smallpox) vaccine: recommendations of the Advisory Committee on Immunization Practices (ACIP), 2001. MMWR Recomm Rep. 2001 Jun 22;50 (RR-10):1–25.
- Trindade GS, Guedes MI, Drumond BP, Mota BE, Abrahao JS, Lobato ZI, et al. Zoonotic vaccinia virus: clinical and immunological characteristics in a naturally infected patient. Clin Infect Dis. 2009 Feb 1; 48(3):e37–40.
- Centers for Disease Control and Prevention
1600 Clifton Rd
Atlanta, GA 30333
TTY: (888) 232-6348
- Contact CDC-INFO
- Travel Notices
- Find a Clinic
- Disease Directory
- Information Centers
- For Travelers
- Common Travel Health Topics
- Adventure Travel
- Bug Bites
- Business Travel
- Counterfeit Drugs
- Cruise Ship Travel
- Cold Climates
- Deep Vein Thrombosis
- Food and Water
- Health Care Abroad
- High Altitudes
- Hot Climates
- Humanitarian Aid Workers
- Jet Lag
- Last-Minute Travel
- Long-Term Travel
- Mass Gatherings
- Medical Tourism
- Mental Health
- Motion Sickness
- Natural Disasters
- Pregnant Travelers
- Road Safety
- Senior Citizens
- Sex Tourism
- Sick After Travel
- Study Abroad
- Sun Exposure
- Swimming and Diving
- Travelers' Diarrhea
- Travelers with Chronic Illnesses
- Travelers with Weakened Immune Systems
- Traveling with a Disability
- Traveling with Your Pet
- Visiting Friends or Relatives
- Water Disinfection
- Traveler Survival Guide
- CDC-TV Videos
- Common Travel Health Topics
- For Clinicians
- Travel Industry
- For Travelers
- Yellow Book
- RSS Feeds
Before you travel make sure you speak with your doctor.