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Monkeypox, an unusual disease

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Monkeypox, an unusual disease, is caused by the monkeypox virus, which has a structure related to that of the smallpox virus and causes a similar, but generally milder, illness.

Like the smallpox virus, monkeypox belongs to the group of Orthopox virus. Despite their name, non-human primates are not reservoirs for the monkeypox virus. Although the reservoir is unknown, possible candidates are small rodents (e.g., squirrels) that inhabit the tropical rainforests of Africa, especially in the western and central regions of that continent.

The disease appears sporadically in humans in Africa and sometimes causes epidemic outbreaks. The majority of reported cases occurred in the Democratic Republic of the Congo. Since 2016, confirmed cases have also been reported in Sierra Leone, Liberia, Central African Republic, Republic of the Congo and Nigeria, which has experienced the largest recent outbreak. A recent 20-fold increase in incidence is thought to be due to the cessation of smallpox vaccination in 1980; People who have received the smallpox vaccine, even > 25 years previously, have a reduced risk of monkeypox. Cases of monkeypox in Africa are also increasing because people are increasingly encroaching on the habitats of animals carrying the virus.

In the United States, an outbreak of monkeypox occurred in 2003, when infected rodents imported from Africa as pets spread the virus to prairie dogs, which then infected people in the western and central regions of that country. During the epidemic outbreak, 35 cases were confirmed, 13 were probable and 22 were suspected in 6 states, although there were no deaths.

Monkeypox is likely transmitted from animals through body fluids, including salivary or respiratory droplets or contact with wound exudate. Human-to-human transmission occurs inefficiently and is thought to occur primarily through large respiratory droplets during prolonged face-to-face contact. The overall secondary attack rate following contact with a documented human source is 3% and attack rates of 50% have been reported in people living with a monkeypox-infected patient (1). Intra-hospital transmission was also documented. Most patients are children. In Africa, the case fatality rate ranges between 4 and 22%. Monkeypox


Clinically, monkeypox is similar to smallpox; However, skin lesions usually manifest in outbreaks and lymphadenopathy is more common. Secondary bacterial infection of the skin and lungs may occur.

The clinical differentiation between smallpox of monkey, smallpox and chickenpox (a herpesvirus, not a poxvirus) can be difficult. Diagnosis of monkeypox is carried out with culture, polymerase chain reaction (PCR), immunohistochemistry, or electron microscopy, depending on the available tests.

There is no proven, safe treatment for monkeypox virus infection. Monkeypox treatment is supportive. Potentially useful drugs include

  • Antiviral drug tecovirimat (approved by the US Food and Drug Administration [FDA] for the treatment of smallpox)
  • The antiviral drugs cidofovir or brincidofovir (CMX001)

All of these drugs have activity against monkeypox in vitro and in experimental models. However, none of these drugs have been studied or used in endemic areas for the treatment of monkeypox.


  • 1. Nolen LD, Osadebe L, Katomba J, et al: Extended human-to-human transmission during a monkeypox outbreak in the Democratic Republic of the Congo. Emerg Infect Dis 22 (6):1014–1021, 2016. doi: 10.3201/eid2206.150579


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Yair Ramirez
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