Monkeypox travels from Africa to America

April 8, 2022

As reported by the Centers for Disease Control and Prevention (CDC), a traveler returning to Dallas, Texas, from Nigeria in July, 2021, tested positive for Monkeypox.

Monkeypox is a rare, sometimes life-threatening zoonotic infection that occurs in west and central Africa. It is caused by Monkeypox virus, an orthopoxvirus similar to Variola virus (the causative agent of smallpox) and Vaccinia virus (the live virus component of orthopoxvirus vaccines) and can spread to humans. After 39 years without detection of human disease in Nigeria, an outbreak involving 118 confirmed cases was identified during 2017–2018; sporadic cases continue to occur. During September 2018–May 2021, six unrelated persons traveling from Nigeria received diagnoses of monkeypox in non-African countries: four in the United Kingdom and one each in Israel and Singapore. In July 2021, a man who traveled from Lagos, Nigeria, to Dallas, Texas, became the seventh traveler to a non-African country with diagnosed monkeypox. Among 194 monitored contacts, 144 (74%) were flight contacts. The patient received tecovirimat, an antiviral for treatment of orthopoxvirus infections, and his home required large-scale decontamination. Whole genome sequencing showed that the virus was consistent with a strain of Monkeypox virus known to circulate in Nigeria, but the specific source of the patient’s infection was not identified. No epidemiologically linked cases were reported in Nigeria; no contact received postexposure prophylaxis (PEP) with the orthopoxvirus vaccine ACAM2000.

On July 13, 2021, an emergency department (ED) physician in Dallas evaluated an early middle-aged man with a 2-week history of fever, cough, and fatigue, followed by onset of a diffuse rash. Less than 1 week earlier, the patient had been in Nigeria for a large social gathering. Because of the extensive pustular rash on his face, hospital staff members immediately placed the patient in an airborne isolation room, where he was managed with airborne and contact precautions plus eye protection. After reviewing CDC’s Travelers’ Health destination webpage for Nigeria, the ED physician suspected monkeypox, and public health authorities were immediately notified. The following day, the Dallas County Health and Human Services Laboratory Response Network laboratory confirmed, by real-time polymerase chain reaction (PCR), the presence of nonvariola orthopoxvirus DNA from lesion swabs. Subsequent testing by species-specific real-time PCR at CDC confirmed West African clade Monkeypox virus.

Interviews revealed that the patient had arrived in Nigeria on June 25 and stayed in three urban centers during his trip (Figure). By June 30, he began experiencing diarrhea, vomiting, cough, subjective fever, and fatigue, all characteristic signs and symptoms of the monkeypox prodrome, which also mark the onset of transmissibility of the virus to others (e.g., through infected body fluids or respiratory droplets). On July 8, 1 day before boarding the first of two return flights, the patient developed a purulent rash confined to a covered part of his body. After a brief layover in the Atlanta airport, he took a domestic flight to Dallas, and then a ride-share vehicle to his residence, where he lives alone. The next day, the rash had worsened and was visible on his face, prompting a friend to drive him to the hospital on July 13. Like many persons his age, the patient had never received the smallpox vaccine, which would have provided cross-protection against monkeypox but has not been routinely administered following the eradication of smallpox in 1980.

This was the first travel-associated monkeypox case in the United States, and the seventh such case worldwide, since a large 2017 outbreak in Nigeria. Case recognition launched a large public health response involving extrapolation of limited data about monkeypox to develop a framework for managing potentially exposed persons and preventing additional cases.

The reservoir for Monkeypox virus has not been identified but is suspected to be a rodent or other small mammal or mammals. Before the 2017 Nigeria outbreak, most human monkeypox cases occurred in rural, forested areas of Africa; however, in Nigeria, monkeypox cases have occurred in urban areas, suggesting novel risk factors. Two distinct clades of Monkeypox virus circulate in Africa: the West African clade, which is endemic in west Africa, and the Congo Basin clade, which occurs in central Africa. Complicating the public health response, cases in Nigeria, although confirmed to be caused by the West African clade, have clinically been distinct: the West African Clade is historically believed to cause milder human disease, few deaths, and limited human-to-human transmission. However, some cases in Nigeria have been severe, even resulting in death, most commonly in persons with HIV infection. In addition, epidemiologic and genomic analyses have shown multiple human-to-human transmission events in Nigeria, including within households and a prison; secondary cases occurred in a healthcare provider and in family members of one patient whose illness was diagnosed in the United Kingdom.

Fortuitously, mask use during the ongoing COVID-19 pandemic ensured that contacts, including fellow airline passengers and crew members, community contacts, and healthcare providers, were at reduced risk for being infected with Monkeypox virus from this patient. Sparse data on Monkeypox virus epidemiology, increasing numbers of immunocompromised persons in the United States (e.g., from chemotherapy and other therapeutics), and waning of immunity to orthopoxviruses since the eradication of smallpox and cessation of routine smallpox vaccination led investigators in this situation to take a cautious approach. Clinical laboratory personnel are typically not at risk for exposure to Monkeypox virus; however, use of specific laboratory instruments near persons not wearing adequate personal protective equipment caused investigators to be concerned about exposure to aerosols. The possible presence of Monkeypox virus on the patient’s covered body during lavatory use similarly prompted a guarded approach; passengers who used that lavatory were monitored in the “low/uncertain” risk group. Most exposures occurred during airline flights that, relative to the time the patient was in the community and admitted to the hospital, were brief.

Four months after this case, an eighth travel-associated monkeypox case in a traveler from Nigeria occurred, also in the United States, prompting CDC to issue a Level 1 Travel Health Notice for travel to Nigeria. Multiple reasons have been proposed for continued human cases in Nigeria, including population growth, increased human interaction with Monkeypox virus reservoirs because of deforestation and climate change, accumulation of unvaccinated cohorts, and declining smallpox vaccine immunity. The Nigerian Federal Ministry of Health continues to work to prevent, detect, and investigate monkeypox cases in Nigeria, but as cases continue to occur, U.S. public health and hospital authorities might consider developing local strategies for responding to future imported cases. Early clinical suspicion facilitated by elicitation of a complete travel history, use of appropriate infection control precautions, and timely identification of activities performed during the period of infectivity were among the most critical actions taken. Understanding the types of exposures that are most concerning for Monkeypox virus transmission, knowing contaminated surfaces need to be quickly identified and decontaminated, and anticipating potentially long hospitalizations and contact monitoring periods might also aid in planning for future cases.

CDC release