Mpox Emergence: A Review of the 2022-2023 Outbreak

Monkeypox under a microscope.

(Adobe Stock, anon)

In May 2022, the first reports of the mpox (formerly “monkeypox”**) virus circulating the European continent began to surface. Since the start of the 2022 mpox outbreak, there have been 85,922 global cases reported. Of those total confirmed global cases, 30,193 cases have been confirmed in the United States, with 32 total deaths. During the current outbreak, most people have been infected during sexual activity from contact with mpox lesions on the skin or mucosal surfaces. Other cases have resulted from injury with a contaminated sharp or through skin piercing and tattooing. The 2022-2023 mpox outbreak was the first time many mpox cases and clusters had been reported concurrently in nonendemic and endemic countries in widely disparate geographical areas. A total of 110 countries have reported cases. According to the World Health Organization (WHO), the confirmation of 1 mpox case in a country is considered an outbreak.

“The clinical and epidemiological presentation of mpox has changed,” Kevin Kavanagh, MD, a member of the Infection Control Today® Editorial Advisory Board, explains. “Although not typically considered a sexual disease, there is evidence that the virus can be present in semen early in the disease, possibly during an asymptomatic period. Although spread by this route has not been firmly established, epidemiological data and the clinical presentation of lesions support the contention that this can be a major route of spread. Initial outbreaks were associated with gay and bisexual men. In general, these communities had experience with the HIV epidemics and had high acceptance of public health measures, including vaccines. Working together with public health officials, the mpox pandemic was brought under control. Unfortunately, during the COVID-19 pandemic, the adoption of public health measures was not uniformly embraced throughout our society. The response and results achieved by the gay and bisexual communities to mpox should be emulated by others when dealing with COVID-19."

According to the CDC, it is predicted that the mpox virus has been circulating silently and undetected for about 2 decades in multiple non-mpox-endemic countries outside of Africa. This conclusion was determined from mpox virus genome sequencing. Phylogenetic analysis of mpox virus genomes revealed that the virus from the 2022-2023 outbreak belonged to 2 clades that can be traced back to the previous 2017-2018 outbreak. In 2017, Nigeria experienced a large outbreak of human mpox. The virus reemerged after 39 years after the last reported case in Nigeria. Over 200 cases were associated with this outbreak in Nigeria.

The unexpected appearance of mpox and the broad geographic spread of cases indicate that the virus has been circulating unnoticeably.

Increased susceptibility of humans to mpox is thought to be related to waning immunity due to the cessation of smallpox immunization. In recent years, only a small number of individuals have been vaccinated against the virus, primarily military personnel, frontline health professionals, and laboratory workers. The current global outbreak could also be driven by the relaxation of COVID-19 prevention measures, international travel, and sexual interactions associated with large gatherings. These risk factors suggest changes in human behavior and aspects of the virus.

The clinical presentation of cases associated with the 2022-2023 human mpox is also atypical. Most cases do not present with the infection's characteristic symptoms, such as fever, swollen lymph nodes, and a centrifugal rash. Rather, patients present with the absence of skin lesions or the presence of only 1 or a few, lesions in genital or perineal areas that do not spread further, lesions at different stages of development, and the absence of the prodromal period in the infection.

The unexpected appearance of mpox and the broad geographic spread of cases indicate that the virus has been circulating unnoticeably. Surveillance systems could not detect low levels of the virus and small but sustained human-to-human transmission. The definite number of confirmed cases is likely to be underestimated. This underestimation is due to a lack of early clinical recognition of infection and limited surveillance systems, according to the WHO. Surveillance systems were restricted for human mpox because this disease remained ‘unknown’ for most health systems since most cases occurred in Africa.

Mpox was first identified in 1958 when a colony of monkeys kept for research in a Danish laboratory experienced an outbreak of pox-like disease. Despite its name, the source of the infection remains unknown. The first human case of mpox was identified in 1970 in a child in the Democratic Republic of the Congo.

According to the WHO, all countries should be alert for mpox and remember that individuals may present with atypical symptoms in the 2022-2023 outbreak.

**As of November 2022, the WHO has also recommended a new name for the disease to reduce stigma and other issues identified with prior terminology. Mpox will become the new preferred term replacing monkeypox. The term mpox can also be used in other languages.