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Monkeypox in UK, apparently from Nigeria: extensive contact tracing in Britain

Monkeypox can be transmitted by contact and droplet exposure via exhaled large droplets

On 7 May 2022, WHO was informed of a confirmed case of monkeypox in an individual who travelled from the United Kingdom to Nigeria. The case developed a rash on 29 April 2022 and returned to the United Kingdom on 4 May. Monkeypox was suspected and the case was immediately isolated.

As of 11 May, extensive contact tracing has been undertaken to identify exposed contacts in healthcare settings, the community and the international flight. These individuals are being followed up for 21 days from the date of last exposure with the case. None has reported compatible symptoms so far.

Since the case was immediately isolated and contact tracing was performed, the risk of onward transmission related to this case in the United Kingdom is minimal. However, as the source of infection in Nigeria is not known, there remains a risk of ongoing transmission in this country.

Epidemiology of the disease

Monkeypox is a sylvatic zoonosis with incidental human infections that usually occur sporadically in forested parts of Central and West Africa. It is caused by the monkeypox virus which belongs to the orthopoxvirus family. Monkeypox can be transmitted by contact and droplet exposure via exhaled large droplets. The incubation period of monkeypox is usually from 6 to 13 days but can range from 5 to 21 days. The disease is often self-limiting with symptoms usually resolving spontaneously within 14 to 21 days. Symptoms can be mild or severe, and lesions can be very itchy or painful. The animal reservoir remains unknown, although is likely to be among rodents. Contact with live and dead animals through hunting and consumption of wild game or bush meat are known risk factors.

There are two clades of monkeypox virus, the West African clade and Congo Basin (Central African) clade. Although the West African clade of monkeypox virus infection sometimes leads to severe illness in some individuals, disease is usually self-limiting. The case fatality ratio for the West African clade has been documented to be around 1%, whereas for the Congo Basin clade, it may be as high as 10%. Children are also at higher risk, and monkeypox during pregnancy may lead to complications, congenital monkeypox or stillbirth.

Milder cases of monkeypox may go undetected and represent a risk of person-to-person transmission. There is likely to be little immunity to the infection in those travelling and exposed as endemic disease is geographically limited to parts of West and Central Africa. While a vaccine has been approved for prevention of monkeypox, and traditional smallpox vaccine also provides protection, these vaccines are not widely available and populations worldwide under the age of 40 or 50 years no longer benefit from the protection afforded by prior smallpox vaccination programmes.

Public health response

• Health authorities in the United Kingdom have set up an incident management team to coordinate identification and management of contacts.

• As of 11 May, extensive contact tracing has identified exposed contacts in the community, the healthcare setting and on the international flight. None has reported compatible symptoms so far.

• All identified contacts have been assessed and classified based on their exposure to the case and are being followed up accordingly through either active or passive surveillance for 21 days after their last exposure to the case. Post-exposure prophylaxis with vaccination is being offered to the higher risk contacts.

• Nigerian authorities were informed about this case and travel history in Nigeria on 7 May. The case did not report contact with anyone with a rash illness or known monkeypox in Nigeria. Details of travel and contacts within Nigeria have been shared with authorities in Nigeria for follow up as necessary.

In the United Kingdom, there have been seven cases of monkeypox previously reported; all importations were related to a travel history to or from Nigeria. In 2021, there were also two separate human monkeypox cases imported from Nigeria reported by the United States of America.

Since September 2017, Nigeria has continued to report cases of monkeypox. From September 2017 to 30 April 2022, a total of 558 suspected cases have been reported from 32 states in the country