Last week, UK health authorities confirmed the diagnosis of 2 cases of monkeypox. Both patients, who are thought to be unrelated, traveled to the UK from Nigeria, which experienced a reemergence of the disease nearly a year ago. Though sporadic cases of monkeypox in Nigeria have been reported since the larger outbreak began to decline in the fall of 2017, UK health authorities said that the diagnosis of 2 imported cases so close together is unusual and warrants additional investigation. Nigeria Centre for Disease Control is collaborating with health authorities in the UK to investigate the source of these recent infections. In light of these recent case reports, this week’s Outbreak Thursday will provide an update on the larger outbreak that has been ongoing in Nigeria and discuss the prospects for control given the country’s recent experience with Lassa fever.

Monkeypox in the UK

Monkeypox is a zoonotic infection caused by a virus in the Orthopoxvirus genus, the same genus to which the now-eradicated smallpox belongs. Symptoms of monkeypox are similar to smallpox (eg, vesicular rash) but are much more mild, with a case fatality between 1 and 10%. Though rare, sporadic cases of monkeypox are reported, mostly in west and central African countries. Following the eradication of smallpox, international surveillance efforts have placed more attention on the diagnosis of monkeypox, given the similarity of symptoms between the two diseases and the need to ensure that smallpox no longer circulates.

Public Health England (PHE) reports that the first monkeypox patient—the first case ever diagnosed in the UK—was a naval officer from Nigeria who was participating in a training exercise at the Royal Naval base in Cornwall, England. The second patient was diagnosed in Blackpool, England, the opposite side of the country. UK health authorities believe that both patients were infected in Nigeria prior to their arrival in the UK, but they have not identified an epidemiological link between the two patients. PHE officials said that, as a precautionary measure, they are working with the UK’s National Health Service to identify and contact people who may have had close contact with these two cases, including healthcare providers and passengers who “travelled in close proximity” to the patients on their flights to the UK. Nigeria CDC is collaborating with state health departments to identify and monitor any contacts that the cases had in Nigeria for a period of 2 weeks before they departed for the UK.

Nigeria’s Monkeypox Outbreak

As previously covered by the Outbreak Observatory, Nigeria experienced a reemergence of monkeypox in September 2017. Before last year, only 3 cases had ever been reported by the country; however, Nigeria CDC reports that a total of 262 suspected cases with seven deaths have occurred through August 2018. Cases have been identified in 26 states, with the highest number of reports from the South-South region of the country.

Considering the lack of specific medical countermeasures to treat or prevent monkeypox infection, the principal strategy for limiting transmission is reducing individuals’ risk of exposure to the virus. Since monkeypox may be transmitted to humans via contact with wild animals, possibly through consumption of improperly cooked meat from infected animals, and through human-to-human transmission, the WHO recommends proper infection control practices when caring for infected patients and avoiding contact with rodents and primates.

Prospects for Control

Though a few family clusters have been identified, most of the monkeypox cases investigated in Nigeria have had no known epidemiological linkage. This suggests that the outbreak may be fueled by multiple sources of exposure rather than by person-to-person transmission. While the absence of human-to-human transmission is often good news for outbreaks, the lack of a single source of exposure will likely make the outbreak difficult to control.

As has been demonstrated in another recent outbreak in Nigeria, Lassa fever, controlling transmission from wild animals is quite challenging. The Lassa outbreak, which began early this year, is the largest ever recorded in Nigeria. From January to September 2018, a total of 504 confirmed and 10 probable cases have been reported, with 132 deaths (case fatality= 26.2%). As with the current monkeypox outbreak, the majority of Lassa infections likely occurred from exposure to infected wild animals (eg, rodents), and control efforts have focused in part on educational campaigns encouraging the public to limit their exposure to rodents and other potential animal sources of infection. Nigeria CDC deployed risk communication and community engagement teams to 3 of the most affected states. Additionally, rodent control efforts can be challenging, as evidenced by a household study of rodent contact, which found that rodents had been observed in 49 of 50 surveyed households in Nigeria. Even Nigeria’s President Muhammadu Buhari was forced to work from home in August 2017 due to a rodent infestation in his office. Further complicating response efforts, rodents can be an important source of protein to some populations in West Africa, and educational campaigns aimed at discouraging rodent hunting and consumption have had mixed results.


Though challenging, efforts to limit transmission from wild animals are important for controlling monkeypox and other zoonotic diseases such as Lassa. These efforts will become increasingly important in the months to come, when, as infectious disease experts explain, seasonal cycles in food availability cause the rodent populations to surge and increase their contact with humans. As Nigeria likely gears up to increase control efforts, other countries should also be on the lookout for possible cases.

Photo courtesy of Pixabay.

Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly to allow others to learn from these experiences in order to improve global outbreak response capabilities.