Confluent Smallpox (Bramwell 1892)
Confluent smallpox1

Vaccination against smallpox ended some 40 years ago. As the vaccinated population gets smaller and the susceptible population gets larger, at least one poxvirus is re-exploring the human population. Not smallpox, of course, but monkeypox, which is becoming dramatically more common in humans than it used to be.2

Monkeypox (which is actually primarily a rodent disease — the monkeys it’s named after were also hapless aberrant hosts, like humans) is closely related to smallpox, and causes a very similar disease in humans — clinically virtually identical, they say (I haven’t seen either myself, and hope I never will), though with a somwhat lower mortality rate. Of course, having a lower mortality rate than smallpox is not exactly high praise: Monkeypox is quite bad enough, with mortality rates of up to 10%.3

Vaccination against smallpox used (and still uses — I just got re-vaccinated a couple weeks ago) live vaccinia virus, which is yet another poxvirus that is similar enough to both smallpox and to monkeypox that it provides excellent protection against infection with either. People who were vaccinated against smallpox are still resistant to infection with monkeypox; but a large and growing population are too young to have received vaccinia, and those people are at least five times more likely to be infected with monkeypox.4 As a result, there’s been a 20-fold increase in monkeypox infections in the Democratic Republic of Congo, and there has been at least one well-publicized case where the disease was shipped into the US in pet rodents.5

Smallpox in california, 1919
Smallpox in California, 1919 (click for larger version)6

A recent paper, looking for animal models of monkeypox that accurately reflect the human situation (so that different vaccines and treatments can be tested) finds that cynomologous macaques [a species of monkey] are susceptible and have similar symptoms as humans:

Animals started to show clinical signs of disease, including decreased appetite and activity, by day 3. … By 6–8 days post-exposure, macules began to form in all animals and macaques were also inactive, somnolent, and exhibited depressed posture. … Lesions progressed to papules by day 10 and evolved to vesicular and pustular stages by 12–14 days post-exposure. … Two non-survivors had too many lesions to count (>2000).3

The lesions they talk about here (macules, papules, vesicles and pustules) are, of course, the titular small pox. Not many people today still remember the pox, so I’ve included some pictures from the good old days.  You’re welcome!

Smallpox vaccination poster
“Hei, siudy, divchata, zhyvo!” (Poster advising vaccination against smallpox, ca. 1920)


  1. Byrom Bramwell
    Atlas of Clinical Medicine v.I, pl.XXIII, p.169
    Edinburgh, Constable, 1892[]
  2. Rimoin, A., Mulembakani, P., Johnston, S., Lloyd Smith, J., Kisalu, N., Kinkela, T., Blumberg, S., Thomassen, H., Pike, B., Fair, J., Wolfe, N., Shongo, R., Graham, B., Formenty, P., Okitolonda, E., Hensley, L., Meyer, H., Wright, L., & Muyembe, J. (2010). Major increase in human monkeypox incidence 30 years after smallpox vaccination campaigns cease in the Democratic Republic of Congo Proceedings of the National Academy of Sciences, 107 (37), 16262-16267 DOI: 10.1073/pnas.1005769107
    and
    Pierre Formenty, Mohammed O. Muntasir, Inger Damon, Vipul Chowdhary, Martin L. Opoka, Charlotte Monimart, Elmangory M. Mutasim, Jean-Claude Manuguerra, Whitni B. Davidson, Kevin L. Karem, Jeanne Cabeza, Sharlenna Wang, Mamunur R. Malik, Thierry Durand, Abdalhalim Khalid, Thomas Rioton, Andrea Kuong-Ruay, Alimagboul A. Babiker, Mubarak E.M. Karsani, & Magdi S. Abdalla (2010). Human Monkeypox Outbreak Caused by Novel Virus Belonging to Congo Basin Clade, Sudan, 2005 Emerging Infectious Diseases, 16 (10) : 10.3201/eid1610.100713[]
  3. Nalca, A., Livingston, V., Garza, N., Zumbrun, E., Frick, O., Chapman, J., & Hartings, J. (2010). Experimental Infection of Cynomolgus Macaques (Macaca fascicularis) with Aerosolized Monkeypox Virus PLoS ONE, 5 (9) DOI: 10.1371/journal.pone.0012880[][]
  4. Rimoin, A., Mulembakani, P., Johnston, S., Lloyd Smith, J., Kisalu, N., Kinkela, T., Blumberg, S., Thomassen, H., Pike, B., Fair, J., Wolfe, N., Shongo, R., Graham, B., Formenty, P., Okitolonda, E., Hensley, L., Meyer, H., Wright, L., & Muyembe, J. (2010). Major increase in human monkeypox incidence 30 years after smallpox vaccination campaigns cease in the Democratic Republic of Congo Proceedings of the National Academy of Sciences, 107 (37), 16262-16267 DOI: 10.1073/pnas.1005769107[]
  5. Hutson CL, Lee KN, Abel J, Carroll DS, Montgomery JM, Olson VA, Li Y, Davidson W, Hughes C, Dillon M, Spurlock P, Kazmierczak JJ, Austin C, Miser L, Sorhage FE, Howell J, Davis JP, Reynolds MG, Braden Z, Karem KL, Damon IK, & Regnery RL (2007). Monkeypox zoonotic associations: insights from laboratory evaluation of animals associated with the multi-state US outbreak. The American journal of tropical medicine and hygiene, 76 (4), 757-68 PMID: 17426184[]
  6. Public health reports, Volume 36, Part 1, Issues 1-25 (January-June, 1921)
    U.S. Public Health Service
    Washington
    Government Printing Office[]