Monkey Business
January 15, 1998 3 minutes read
Monkey Business
ABSTRACT & COMMENTARY
Synopsis: The largest identified outbreak of human monkeypox infection is described. The discontinuation of smallpox vaccination may have increased susceptibility to monkeypox.
Source: Centers for Disease Control and Prevention. Human monkeypoxKasai Oriental, Democratic Republic of Congo. MMWR Morb Mortal Wkly Rep 1997;46:1168-1171.
The largest human outbreak of monkeypox infection ever recorded recently occurred in the Democratic Republic of Congo (the former Zaire), with a total of 511 cases having been identified in two zones. In an initial WHO and CDC investigation, 92 suspected cases were identified with onset during February 1996- February 1997. A second investigation, initiated in October 1997, identified 419 active or recent cases, 73% of which were probable monkeypox, while the remainder were identified as possible. The attack rate was 1.1 per 1000 population in the Katako-Kombe healthcare zone and 0.3 per 1000 in the Lodja zone. The attack rate in the village that was the epicenter of the initial outbreak was 113 per 1000 population. Eighty-five percent of cases occurred in persons less than 16 years of age. The case fatality rate in Katako-Kombe was 1.5%.
Twenty-two percent of cases identified during the second investigation were primary (i.e., there was no history of contact with another person with monkeypox), while the remainder were secondary.
COMMENT BY STAN DERESINSKI, MD, FACP
In August 1970, one year after the last proven case of smallpox had been detected in the area, a 9-month-old boy was admitted to Basankusu hospital in the Equateur province of Zaire. Investigations led to the conclusion that this represented the first known case of human monkeypox infection (Ladnyj ID, et al. Bull WHO 1972;46:593-597). Since that time, human monkeypox has been found repeatedly not only in Zaire, but also in additional African countries, including Côte d’Ivoire, Liberia, Nigeria, and Sierra Leone.
The clinical features of monkeypox are similar to those of smallpox. An evaluation of 282 patients with this infection found that fever, the initial manifestation in most, persisted for 1-3 days before the onset of skin eruption, usually peaking by the second day at temperatures between 38.5°C and 40.5°C (Jezek Z, et al. J Infect Dis 1987;156:293-298). The eruption most often began on the face, with the lesions developing contemporaneously and evolving together within the same body region through the stages of macules, papules, vesicles, and pustules with subsequent umbilication and drying. The number of skin lesions varied from a few to thousands, with fewer lesions being observed in those with smallpox vaccination scars than in those without. Lymphadenopathy was seen frequently early in illness, a finding that is uncommon in smallpox. Monkeypox may also be confused with varicella-zoster virus infection.
The outbreak of monkeypox infection discussed here, with human-to-human transmission continuing for at least two years, suggests a possible change in the relationship of humans to this virus. The virus may have altered in its ability to infect humans or, alternatively, humans may have become more susceptible to the virus. The latter seems a strong possibility, with an increase in the susceptible population occurring as the result of the discontinuation of smallpox vaccination, a vaccination that provides cross-protection against monkeypox infection. In an investigation of 91 cases of human monkeypox infection in northern Zaire in 1981-1985, the average annual primary attack rate was 0.04 per 10,000 for those with smallpox vaccination scars and 1.7 per 10,000 for those without. The secondary attack rates were, respectively, 0.7% and 4.3% (Jezek Z, et al. Trop Geogr Med 1988;40:73-83). The young age of the majority of monkeypox cases is consistent with this hypothesis, since it is this group who would never have received smallpox vaccine. If the outbreak continues, consideration will be given to the administration of smallpox vaccine to the local populations.
Since August 1970, human monkeypox infection has been found in:
a. Côte d’Ivoire.
b. Liberia and Zaire.
c. Sierra Leone.
d. Nigeria.
e. all of the above.
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