There is a growing epidemic of monkeypox—a close cousin to smallpox—in Africa during the past two years. More than 1,000 cases of monkeypox have been confirmed among people in the Democratic Republic of the Congo (DRC) since 2016, followed by 88 confirmed cases in the Republic of the Congo, over 80 cases in Nigeria, 19 in the Central African Republic, 16 in Cameroon, two in Liberia, and one in Sierra Leone.1 2 3 4 5
According to the World Health Organization (WHO), the monkeypox virus is a rare “viral zoonosis,” which means that it can be transmitted from animals to humans. Like smallpox, monkeypox is an orthopoxvirus and symptoms are similar to those of smallpox, although milder. Monkeypox can be fatal in 1-10 percent of cases, while smallpox can be fatal in three out of 10 cases.6
The incubation period for monkeypox disease—from the time of infection to the onset of symptoms—is usually from six to 16 days but has also been known to range from five to 21 days.7
The first five days of monkeypox infection are characterized by fever, severe headache, swelling of lymph nodes (lymphadenopathy), back pain, muscle aches (myalgia), and an intense lack of energy (asthenia). Within one to three days after the onset of fever, people with monkeypox will experience rashes on their skin, usually beginning on the face, then spreading to the palms of the hands and soles of the feet, and elsewhere. The rashes will turn into maculopapules (flat lesions) and subsequently into vesicles (small fluid-filled blisters), pustules, and finally crusts or scabs.7 8
One major difference is that monkeypox causes lymphadenopathy and smallpox does not.7 There is also a difference in the viral protein structure of the two orthopoxvirus infections.9 10 The viral protein structure is where the genetic material of a virus is stored.11 Otherwise, in terms of symptoms, there is little difference between monkeypox and smallpox.
The first warning that monkeypox was becoming a problem in the Republic of Congo was signaled in 2010, when an article in a medical journal published by the US National Academy of Sciences reported that there had been a 20-fold increase in human monkeypox incidence in that country since the 1980s. Researchers suggested that there might be a link between the cessation of smallpox vaccination 30 years earlier and the numbers of people who are “immunologically naïve” to orthopoxviruses.”12
Recently, the Centers for Disease Control and Prevention (CDC) has referred to the monkeypox epidemic in Africa as a “global health security concern.”13
In 2014, the National Vaccine Information Center (NVIC) published a report, The Emerging Risks of Live Virus and Virus Vectored Vaccines: Vaccine Strain Infection, Shedding and Transmission, which noted that, in addition to cases of monkeypox in Africa, there were reported cases of other types of orthopoxvirus infections in humans, such as cowpox in Europe and areas of Asia among children and young adults born after smallpox vaccine campaigns ended in the 1970s.14 By 2014, CDC researchers were already talking about developing new new smallpox vaccines warning that, “Possible smallpox reemergence drives research for third-generation vaccines that effectively neutralize variola virus.”
There is no treatment for monkeypox but human infection with one type of orthopoxvirus is considered to be cross protective with other types.15 Recent media reports have noted that smallpox vaccination offers “cross-protection,” suggesting that the smallpox vaccine could be used to combat monkeypox.5
2 Herriman R. Monkeypox confirmed in Liberia. Outbreak News Today Apr. 11, 2018.
3 FPA Reporter. Two Confirmed Cases of Monkey Pox in Liberia since 1970 (Not Four As Reported). Front Page Africa Apr. 18, 2018.
4 Guest Author. Monkeypox outbreak spreads to five regions in Cameroon. Outbreak News Today June 4, 2018
5 Masterson A. Health authorities issue warning on monkeypox outbreak. Cosmos Mar. 19, 2018.
6 Centers for Disease Control and Prevention. What is Smallpox? CDC.gov June 7, 2016.
7 World Health Organization. Monkeypox. WHO.int June 6, 2018.
8 CDC. Monkeypox. CDC.gov.
9 Gaublomme K. Has smallpox really disappeared from the earth? The International Vaccination Newsletter December 1997.
10 Shchelkunov SN, et. al. Human monkeypox and smallpox viruses: genomic comparison. FEBS Letters 509 (1); 66-70 Nov. 30, 2001.
11 Viral protein. Wikipedia.
12 Rimoin AW, Mulembakani PM et al. Major increase in human monkeypox incidence 30 years after smallpox vaccination campaigns cease in the Democratic Republic of Congo. Proc Natl Acad Sci 2010; 107(37).
13 CDC. Emergence of Monkeypox — West and Central Africa, 1970–2017. Morbidity and Mortality Weekly Report 67(10); 306–310 Mar. 16, 2018.
14 Fisher BL. Smallpox (Variola) and Live Attenuated Vaccinia Virus (pp. 16-21). The Emerging Risks of Live Virus and Virus Vectored Vaccines: Vaccine Strain Virus Infection, Shedding and Transmission. NVIC.org November 2014.
15 Shchelkunov SN. An Increasing Danger of Orthopoxvirus Infections. PLOS Pathogens 2013; 9(12).
16 Cáceres M. The Smallpox Vaccine Was No Silver Bullet. The Vaccine Reaction June 6, 2017.
17 New York State Department of Health. Smallpox Questions and Answers: The Disease and the Vaccine. Health.ny.gov.