Disease Outbreak News

Monkeypox - United States of America

25 November 2021
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Description of the situation

On 16 November 2021, the IHR National Focal Point of the United States of America (USA) notified PAHO/WHO of an imported case of human monkeypox in Maryland, USA. The patient is an adult, resident of the USA, with recent travel history to Nigeria.

The individual was in Lagos, Nigeria when they developed a rash. On 6 November, they travelled from Lagos, Nigeria to Istanbul, Turkey and, on 7 November, from Istanbul to Washington, D.C, USA. The patient has not been vaccinated against smallpox in the past and is currently in isolation in Maryland.

Samples of skin lesions were positive on 13 November by real-time polymerase chain reaction (RT-PCR) assays for orthopoxvirus-generic and non-variola orthopoxvirus at the Maryland laboratory of the Laboratory Response Network (LRN). On 16 November, the USA Centers for Disease Control and Prevention (US CDC) confirmed the diagnosis on the same two lesion specimens by PCR assays for monkeypox, and also, specifically for the West African clade of monkeypox, the strain that re-emerged in Nigeria since 2017.

At this time, while the patient had remained in Lagos throughout the stay in Nigeria, the source of infection for this case is unknown.

This is the second time that an imported human monkeypox case has been detected in a traveler to the USA. The first imported human case in a traveler from Nigeria was reported on 15 July 2021 (for more information on the first case, please see the Disease Outbreak News published on 27 July 2021). In addition to these two cases, since 2018, six importations of human cases of monkeypox have been reported in non-endemic countries in travelers from Nigeria to Israel (one case), Singapore (one case) and the United Kingdom of Great Britain and Northern Ireland (four cases). The frequency of global travel indicates that further exported cases may be expected among travelers from endemic areas / countries. Additionally, there may be cases that are undetected, misdiagnosed, or not reported.

Public health response

The USA CDC is working with their international health counterparts, state, and local health officials to assess potential risks and to contact airline passengers and others who may have had contact with the patient on flights from Nigeria to Turkey and onwards to the USA, in transit, or after arrival in the USA. Travelers on these flights were required to wear masks due to the ongoing COVID-19 pandemic, the risk of spread of monkeypox via respiratory droplets to others on these flights is therefore considered low.

Public health measures are being taken, including isolation and continued monitoring of the patient’s clinical recovery. Possible contacts are being notified for assessment and monitoring by their local or state health department. Post-exposure vaccination with a smallpox vaccine within 14 days of the last contact with the case may be recommended for cases who are at intermediate and high risk.

Healthcare providers have been advised to be vigilant to poxvirus-like lesions, particularly among travelers returning from Nigeria. Because of the public health risks associated with a single case of monkeypox, clinicians should report suspected cases immediately to state or local public health authorities regardless of whether they are also exploring other potential diagnoses. 

WHO risk assessment

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 (MPXV) that belongs to the Orthopoxvirus family. Genomic sequencing shows there are two monkeypox clades – Congo Basin and West African and there have been observed differences in human pathogenicity and mortality in the two geographic areas. Both clades can be transmitted by contact and droplet exposure via exhaled large droplets or contact with fomites such as bedding; infection can be fatal in humans.

The incubation period for monkeypox is usually from 6 to 13 days but can range from 5 to 21 days. The disease is often self-limiting with signs and symptoms usually resolving spontaneously within two to four weeks. Signs and symptoms can be mild or severe, and lesions can be painful. Immune deficiency, young age, and pregnancy appear to be risk factors for severe disease. The case fatality ratio (CFR) for the West African clade has been reported to be around 1%. The recent outbreak in Nigeria recorded a higher CFR related to underlying conditions which may lead to immunodeficiency. A case fatality ratio of up to 11% (in individuals without prior smallpox vaccination) has been reported for the Congo basin clade.

Since 2017, a monkeypox outbreak has been occurring in Nigeria with 218 cases confirmed to date. In addition to Nigeria, outbreaks have also been reported in nine other countries in central and western Africa since 1970. These include Cameroon, Central African Republic, Cote d'Ivoire, Democratic Republic of the Congo, Gabon, Liberia, Republic of Congo, Sierra Leone, and Sudan. Sporadic small outbreaks continue to occur in some of these countries including Cameroon and the Central African Republic. However, the vast majority of cases continue to be reported in the Democratic Republic of the Congo, with 2780 cases and 72 deaths (CFR 2.6%) reported between 1 January through 31 October 2021.

While a new vaccine has been approved for the prevention of monkeypox, and traditional smallpox vaccine has been demonstrated to provide protection, these vaccines are not widely available. Increased susceptibility of humans to monkeypox is thought to be related to waning immunity due to cessation of smallpox immunization. Contact with live and dead animals through hunting and consumption of wild game or use of animal-derived products are presumed sources of human infection. Milder cases of monkeypox in adults could go undetected, misdiagnosed, or unreported and represent a risk of human-to-human transmission.

There is likely to be little immunity to infection in those exposed as endemic disease is geographically limited to West and Central Africa and populations worldwide under the age of 40 or 50 years no longer benefit from the protection afforded by prior smallpox vaccination programmes. There is no specific treatment for monkeypox disease, and care is symptom-based optimal care. In some circumstances, treatment approved for smallpox may be offered on a compassionate or emergency use basis.

WHO advice

Any illness during travel in an endemic area or upon return should be reported to a health professional, including information about all recent travel and immunization history. Residents and travelers to endemic countries should avoid contact with sick, dead, or live animals that could harbor monkeypox virus (mammals including rodents, primates) and should refrain from eating or handling wild game or use of products derived from animals. The importance of hand hygiene using soap and water, or alcohol-based sanitizer should be emphasized.

A patient with monkeypox should be isolated during the infectious period, just prior to and including the rash stage of the infection and until all lesions have crusted and fallen off. Timely contact tracing, surveillance measures and raising awareness of endemic and imported emerging diseases among health care providers are essential parts of preventing secondary cases and effective management of monkeypox outbreaks.

Treatment for monkeypox is optimal care based on the patient’s symptoms and clinical condition.

Health care workers caring for patients with suspected or confirmed monkeypox should implement standard, contact and droplet infection control precautions. Samples taken from people and animals with suspected monkeypox virus infection should be handled by trained staff working in suitably equipped laboratories.

WHO does not recommend any restriction for travel to or trade with Nigeria, Turkey or the USA based on available information at this point in time.

Further information