Adebayo O.1 and Owoeye D. 2

  1. Department of Medicine, University College Hospital, Ibadan, Nigeria
  2. Infection Prevention and Control Directorate, Jazan, Kingdom of Saudi Arabia

Monkeypox is a rare zoonotic disease that occurs sporadically in Sub Saharan Africa and known to cause clinically indistinguishable disease from other pox diseases especially smallpox.1,2

The disease was first discovered in 1958 among sick monkeys (Macaca cynomolgus) originating from Singapore and isolated at the State Serum Institute in Copenhagen, Denmark; however, the first human case was discovered in 1970 in a child in Equateur region of Republic of Congo (formerly Zaire).3-7 It has largely been believed its epidemiology was masked by smallpox transmission and the eradication of smallpox in 1977 brought the disease to prominence.1,8 It is also expected that as the immunity for small pox virus wane in the population, the risk for monkeypox virus will increase.9 The virus has potential of being used as a bioterrorism agent.

The disease’s burden is largely concentrated in rural & near tropical rain forest of Central and Western Africa, although outbreaks have been reported in other part of the world especially United States.5 The affected communities are also noted to be impoverished and generally have a high prevalence background of parasitic infections, malnutrition, and other significant heath-compromising conditions.10 There is no racial or gender predilection.

The disease is endemic in Democratic Republic of the Congo (DRC) (also Zaire) while it occurs sporadically in other part.5 Crude incidence rate of 5.53 per 10,000 people have been reported in DRC with most of the affected people below 15years.5,11 Some other countries where the disease has been reported include Cameroon, Central African Republic, Liberia, Nigeria, and Sierra Leone.5,10

The most likely reservoir of the disease is the rodent. 1,9 Other possible sources of the infection include squirrels – Funiscuirus spp., sooty mangabey – Cercocebus spp., sun squirrels – Heliosciurus spp., giant pouched rats – Cricetomys spp., brush-tailed porcupines – Atherurus spp., African dormice – Graphiurus spp., and West African Hybomys or temminck’s striped Mouse-Hybomys spp., rope squirrels, tree squirrels, Gambian rats, striped mice and pet prairie dogs (Cynomys species).5

The minority of cases occur through human-to-human transmission and rarely beyond two generations. As much as 80% of cases occur through animal to human transmission.5,12

Monkeypox virus (MPV) belong to genus orthopoxvirus of Poxviridae family (subfamily- Chordopoxvirinae).6 Other members of orthopoxvirus include Cowpox virus and Variola virus which causes cowpox and small pox diseases respectively. Monkeypox virus (MPV) is closely related to Variola virus (about 90% genome homology).11

It is a single molecule of double stranded DNA and have two major genetic clades of the virus; the lesser virulent clade occurring in West Africa and the other in Central Africa.10