Monkeypox Virus Infections and Blood and Plasma Donors


In early June 2003, CDC reported monkeypox virus as the cause of illness among some residents in the U.S. after coming in contact with sick prairie dogs. Monkeypox virus is an orthopoxvirus related to smallpox, and also related to the virus used in the smallpox vaccine (vaccinia). Monkeypox causes a human disease that resembles smallpox but has a lower person-to-person transmission rate. Monkeypox infections occur naturally in Africa, and the current U.S. infections appear to have originated from imported animals. However, domestic prairie dogs and rabbits can transmit this disease to people. Additional current information about monkeypox is available from the CDC at

On June 11, 2003, CDC recommended smallpox vaccination under a CDC-sponsored Investigational New Drug Application (IND) for people exposed to monkeypox ( and FDA has recommended temporary blood and plasma donor deferrals after smallpox vaccination (

Signs and Symptoms of Monkeypox Infection

In humans, the symptoms of monkeypox are similar to those of smallpox, except that more swelling of lymph nodes is associated with monkeypox. About 12 days after exposure, the illness begins with fever, headache, muscle aches, backache, swollen lymph nodes, a general feeling of discomfort, and exhaustion. Within 1 to 3 days (sometimes longer) after onset of fever, the patient develops a papular rash (i.e., raised bumps), often first on the face but sometimes initially on other parts of the body. The lesions usually develop through several stages before crusting and falling off. The illness typically lasts for 2 to 4 weeks. In Africa, monkeypox has been reported to be fatal in as many as 10% of people who get the disease. However, although over 50 suspected or confirmed cases have occurred in the U.S. to date, there have been no deaths, and the disease appears to be following a mild to moderate course of severity. In contrast, the case fatality ratio for smallpox was about 30% before the disease was eradicated.

Case definition of Monkeypox Infection

An interim case definition for human cases of monkeypox has been published by CDC (

Mode of transmission of monkeypox in humans

People can get monkeypox from an infected animal through a bite or direct contact with the infected animal's blood, body fluids, or rash. The disease also can be spread from person to person, but it is much less infectious than smallpox. The virus is thought to be transmitted by large respiratory droplets during direct and prolonged face-to-face contact. In addition, monkeypox can be spread by direct contact with body fluids of an infected person or with virus-contaminated objects, such as bedding or clothing.

Risk for Transmission by Blood or Plasma

There have been no reports of transmissions of any poxvirus, including monkeypox, through transfusion. However, the risk of monkeypox transmission by blood or plasma is not known, and a viremic phase and resultant risk of transmission by transfusion could potentially exist. Since people with monkeypox infection usually have fevers, rash, and other signs of illness, they would ordinarily be deferred from donation based on answers to donor questions about current health.

CDC is working to identify all people with monkeypox infection, and their close contacts. CDC has recommended that pet owners, health care workers, and others who may have been exposed to monkeypox be vaccinated with the smallpox vaccine under a CDC-sponsored IND which is in effect (

CDC has recommended that asymptomatic close contacts of infected people or animals be placed under fever surveillance for 21 days (

  • Donors who have been exposed to monkeypox, and have fever and/or rash, may have monkeypox, and be at risk of viremia.
  • Donors undergoing fever surveillance may be incubating monkeypox virus, and may be at risk of viremia.
  • CDC is offering smallpox vaccination under IND to people who may have been exposed to monkeypox, or who are likely to become exposed. This may result in increased use of the smallpox vaccine. In our existing guidance on smallpox vaccination, we recommend blood and plasma donor deferrals for people who have recently received the smallpox vaccine (
  • If you suspect a case of unreported monkeypox, CDC recommends that you contact your state or local health department (
  • If you have questions about blood or plasma donors, please contact the Division of Blood Applications, Office of Blood Research and Review FDA at (301- 827-3543).
Updated: June 13, 2003