Labelling it a “concern for global health security”, the US Centres for Disease Control and Prevention (CDC) have sounded the alarm about a surge in cases of a sometimes-fatal close relative of smallpox called monkeypox.
In its Morbidity and Mortality Weekly Report, the CDC notes a “recent apparent increase in human monkeypox cases across a wide geographic area”, and calls for urgent public health action and international collaboration to head off the threat of a pandemic.
Monkeypox is described by the World Health Organisation as being similar to smallpox. Primary infection is caused by contact with the bodily fluids of sick animals, but cases of human-to-human transmission have also been documented.
The disease presents in two phases. After an incubation period of up to three weeks, victims experience up to five days of intense fever, headache and muscle pain. This is followed by a rash, typically on the face, palms and soles of the feet, and sometimes across the entire body. The rash period lasts for around three weeks, after which recovery or death occurs.
Monkeypox is fatal in about 10% of cases.
The CDC warning targets several countries in Africa, many of which had not until recently reported a single case in decades. The Democratic Republic of Congo is experiencing more than 1000 cases a year, with, since 2016, additional cases reported in the Central African Republic (19), Liberia (two), Nigeria (more than 80), Republic of the Congo (88) and Sierra Leone (one).
There has also been an outbreak among captive chimpanzees in Cameroon.
Altogether, the CDC says, there have been monkeypox cases reported in more countries during the past decade than in the preceding 40 years. Describing the disease as an “emerging zoonosis”, the organisation flags multiple concerns, including the fact that many of the countries affected lack the knowledge, experience and facilities to respond quickly to outbreaks, thus increasing the likelihood that the virus will continue to spread.
In calling for an increase in resources to tackle the disease – a call echoed by WHO, which this year identified monkeypox as a developing threat – the CDC draws comparisons with smallpox.
While closely related, the two viruses differ in one crucial aspect. Smallpox is an entirely human disease, a crucial factor in its vaccine-led eradication. Monkeypox, however, is zoonotic – meaning that it exists outside humans in one or more animal species that serve as reservoirs.
These reservoirs have not been identified, meaning attempts at a smallpox-style eradication will be much harder, if not impossible. (A similar problem besets Ebola researchers. During the 2013 to 2016 West African outbreak, which killed over 11,000 people, the animal species reservoir was never conclusively identified. The search continues today, with candidates ranging from bats to snakes.)
There is, however, some good news. Although there is no specific treatment available for monkeypox, the smallpox vaccination offers cross-protection, meaning that, in theory at least, large-scale prevention is possible.
