Monkeypox Outbreak in Nigeria-2017 to 2019

Since September 2017, Nigeria has experienced the largest outbreak of monkeypox in the country's history. This is the largest outbreak caused by the West African clade of monkeypox virus (MPXV) after more than 30 years of no reported cases. And the virus spread by travelers from Nigeria to the rest of the world in 2018 and 2019, respectively.

Situation of the Monkeypox Outbreak in Nigeria-2017 to 2019

During September to November 2017, Nigeria experienced the most severe outbreak of West African clade of human monkeypox up to that time. The first case was an 11-year-old boy, and since then there have been confirmed cases of MPXV infection recorded involving 18 states. In 2017, Nigeria reported approximately 100 cases of monkeypox. Then by early 2018, cases declined rapidly. As of 2019, a total of approximately 200 cases were reported. The characteristics of the 2017-2019 outbreak suggest that strains MPXV in West Africa can be identified as an epidemic.

Fig. 1 Total number of MPXV cases by state in Nigeria in 2017 (left) and 2019 (right).¹

Fig. 2 All human MPXV cases in Nigeria over the years.¹

On the face of it, Nigeria appears to have successfully contained the virus, as the situation of all previous monkeypox outbreaks. In fact, the monkeypox epidemic in Nigeria never stopped. The virus spread underground in Nigeria for many years. Re-emergence of it is not only a public health problem in Nigeria, but leads to global health implications. This outbreak has spread to other parts of the world.

Possible Factors for Re-Emergence

The outbreak of human monkeypox in Nigeria is somewhat unexpected and suggests a change in the epidemiological dynamics of MPXV in West Africa. Determining the cause of human monkeypox emergence in Nigeria is critical, which may include changes in the distribution of animal hosts and human behavior.

• Encroachment of wildlife habitat
• Increased trade in wildlife species
• Rainfall and flooding
• Infection by other viruses
• Younger populations

Phylogeny and Evolution of MPXV in Nigeria

Later virological studies proved that the West African clade MPXV is the cause of the outbreak. The following tools were used at that time to confirm that the pathogen was human monkeypox.

• The Nigerian isolates all belong to the West African clade.
• The Nigerian isolates form a subgroup that is distinct from isolates from other regions.
• There is genomic similarity between the MPXV-Nigeria isolates from 1971, that of 1978, and the 2017 virus strains, but also at a greater genetic distance.

Nigeria MPXV Spread in 2018-2019

There was the first report of MPXV brought out of Africa by a human in 2018, which includes 2 unrelated cases of human monkeypox in the United Kingdom who returned from travel to Nigeria, and 1 case in Israel, of a staff member permanently stationed in Nigeria.

In 2019, 1 imported case of a male from Nigeria was reported in Singapore. 1 human case of monkeypox imported from Nigeria was reported in the UK.