Differences in the US Mpox Outbreaks of 2003 and 2022: A Review


Objectives: This research aims to focus on the differences in mpox outbreaks that occurred in 2003 and 2022 in the United States. Methods: We searched the following databases Medline, Google Scholar, Gayle Power Search, PubMed, and Springerlink using the following search terms “mpox virus”, “MPX”, “mpox in the US”, “US mpox virus 2003”, “US mpox virus 2022”, “US mpox outbreak 2003” and US mpox outbreak 2022”. The only articles selected were those written between 2003 and 2022. Results: Findings showed more Mpox research was conducted during the first US Mpox outbreak in 2003 compared to the US Mpox outbreak in 2022. Findings also indicated that the mpox outbreak of 2003 consisted of more animal-to-human transmissions acquired from sick prairie dogs compared to more human-to-human from an infected international traveler from Nigeria to the US. Conclusion: Major differences in the mpox outbreaks in the US include the number, location of lesions, and transmission type. We recommend further research to increase awareness of the human-to-human transmission of mpox via sexual contact to assist healthcare professionals and public health leaders in providing prevention and wellness in US communities.

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Henley, S. and Woods-Crawford, S. (2023) Differences in the US Mpox Outbreaks of 2003 and 2022: A Review. Advances in Infectious Diseases, 13, 1-11. doi: 10.4236/aid.2023.131001.

1. Introduction

The Mpox virus (MPXV) is a poxvirus disease of the Genus Orthopoxvirus that can produce disease in animals and Humans [1]. Monkeys housed in a Denmark research lab during the late 1950s became infected with a pox-type illness while engaged in poliovirus vaccine research [2]. More than a decade later in 1970, it was noted that the first animal-to-human case occurred in the Democratic Republic of Congo (DRC) in a child less than one year of age [2]. Since the first presentation of the pox-like illness occurred in monkeys, the virus was named “mpox” [3]. Recent literature indicates mpox is prevalent in Central and Western Africa and the reservoir of the mpox virus remains unknown [4]. The mpox virus stems from the West African clade and the Congo Basin African clade [4]. The West African clade consists of mpox virus cultures isolated from infected individuals from Nigeria, and Liberia along with ones spread from Ghana to the United States [5]. In contrast, the Congo Basin African clade consists of mpox virus cultures isolated from individuals in Cameroon, the Republic of the Congo, Gabon, and the DRC [5]. Research indicates that the West African clade mpox is milder than the DRC clade and is responsible for the mpox outbreak in the US [6].

Rope squirrels, tree squirrels, Gambian pouched rats, and dormice are noted to be hosts for the double-stranded DNA mpox virus according to researchers [7]. Transmission during the 2003 outbreak transpired by contact with animal body fluids, bites, or lesions compared to transmission by intimate skin-to-skin contact with human body fluids, and lesions [8].

2. Methods

Data Collection

The following databases were searched: Medline, Google Scholar, Gayle Power Search, PubMed, and SpringerLink using the following search terms “mpox virus”, “MPX”, “mpox in the US”, “mpox virus 2003” and “mpox virus 2022”. Information extracted from each article included author name, publication title, publication year, publication type, clade, transmission type, and lesion location. Additionally, we obtained information from the websites of leading health experts such as the Centers for Disease Control and Prevention and the World Health Organization.

Following the identification of every article collected from the five databases, we removed duplicates and all articles about mpox outbreaks in other countries and animal studies to focus only on articles referring to the mpox outbreak in the US among human subjects. Other exclusions included articles that focused on smallpox and data unrelated to the topics of interest. Only articles written between 2003 and 2022 were selected. Article types appropriate for extraction consisted of research articles, non-research articles, case reports, review articles, reports, opinions, views, perspective articles, editorials, letters to the editor, and commentaries.

3. Results

The thorough review of literature collected from PubMed, Medline, Google Scholar, Springerlink, and Gayle Power Search, resulted in 54 out of 69 articles, respectively. This review includes 4 opinion, view, and perspective articles, 6 case reports, 6 three letters to the editor, 1 editorial, 6 commentaries, 7 reports, 13 research, 7 review articles, and 4 non-research articles (See Figure 1 below).

As suspected, more mpox research was conducted during the 2003 outbreak compared to the amount of research conducted for the 2022 mpox outbreak in the US. Article types published during the 2003 mpox outbreak consisted of research and review articles whereas during the 2022 mpox outbreak, most of the information came from reports, commentaries, opinions, viewpoints, and perspective articles and letters to the editor. The 2022 mpox has disseminated very little research literature compared to 2003 (see Table 1).

Figure 1. Number of US mpox peer reviewed articles from 2003-2022.

Table 1. US Mpox outbreak 2003 and 2022 articles.

4. The U.S. Mpox Outbreak, 2003

The mpox virus initially surfaced in 1958 by way of animal-to-animal transmission and resurfaced in the Democratic Republic of Congo (DRC) via animal-to-human transmission in 1970 [9]. Studies show that the occurrence of human-to-human transmission was endemic to only DRC [10]. The mpox virus of 2003 consisted of no human-to-human infections, and only animal-to-human transmissions were reported at that time [10] [11] [12]. Before 2003, the mpox virus did not reach the United States until after a sick prairie dog from Ghana infected a small child in the Midwest [13]. Exotic animals such as prairie dogs, tree squirrels, rope squirrels, dormice, Gambian giant pouched rats, brush-tailed porcupines, and striped mice from Africa were being transported to the US and sold as pets [13]. More specifically, the parents of a small child purchased a prairie dog from a flea market, and shortly after being in the home; the dog became sick and died [13]. The child in turn developed a rash covering her face, chest upper, and lower extremities, and bottom of her feet along with swollen lymph nodes, and problems swallowing and breathing [13]. Another animal-to-human transmission during the 2003 mpox outbreak involved a Milwaukee, Wisconsin veterinarian who presented to the emergency room complaining of swollen lymph nodes and a skin lesion after exposure to a sick prairie dog [14]. Lesions associated with the 2003 US mpox outbreak tended to start in the face followed by the arms/hands, legs/feet, head/neck, chest/abdomen, back, palms, groin/buttocks, soles, and mucosa [15]. Another characteristic of the lesions associated with the 2003 mpox outbreak involved determining the “rash burden” developed by the World Health Organization [15]. A “moderate” rash consisted of 26 - 100, a “grave” rash consisted of 101 - 250 lesions and a “plus grave” rash consisted of greater than 250 lesions [15] (See Table 2).

Table 2. 2003 US mpox outbreak.

5. The U.S. Mpox Outbreak, 2022

There had not been any mpox globally since the 2003 outbreak until it resurfaced in the United Kingdom in 2022 [16]. Literature indicates that a British traveler contracted the virus after returning from Nigeria and through contact tracing, more individuals were identified as having had contact with the same British traveler [16] and that all the individuals were gay or bisexual. In May 2022, a Massachusetts male contracted the mpox virus after engaging in unprotected sexual intercourse with males while in Canada [16]. Another person encountered the same British traveler in Florida where he and his husband engaged in unprotected sexual intercourse with an unknown number of men resulting in the contraction of the mpox virus [17].

In the current mpox outbreak, the virus was primarily contracted by men having unprotected sex with other men, who had the human immunodeficiency virus (HIV), syphilis, and other sexually transmitted diseases [17] [18]. Most all the individuals infected had smaller manifestations of the anogenital lesions in the 2022 outbreak compared to greater than one hundred lesions covering the upper and lower extremities, face, soles of feet, and palms of hands during the 2003 outbreak [19] (See Table 3).

6. Discussion

Viral Zoonosis consists of viruses that are transmitted from animals to humans such as Monkepox, a viral zoonosis that comes from the Orthopoxvirus genus of the Poxviridae group [20]. The Mpox virus erupted initially in the Congo basin of central Africa in the 1970s [20] and presented again in the United Kingdom, Singapore, Israel and again in the United States 2018 to 2022 [20]. Zoonotic transmission, also referred to as animal-to-human transmission results from close contact with blood or body fluids from an infected animal to an human [20]. This review indicates that the first mpox outbreak in the US involved animal-to-human transmission with the suspected host being infected prairie dogs imported from West Africa and the second mpox outbreak involved human-to-human transmission among men having sex with men initiated by an individual that traveled from Nigerian to the US [20]. The literature notes that although the mpox virus is contracted by skin-to-skin contact, there remains no definitive data on the virus being sexually transmitted currently [20]. There are several differences between the two US out-breaks. The first difference involves the number and location of lesions. For example, in 2003, lesions were numerous at greater than 100, starting in the face, covering the whole body, and progressing to the palms of the hands and soles of the feet which are characteristic of mpox [20]. In the current mpox outbreak, the lesions are localized to the mouth, anus, and genitalia and are less numerous, and appear before other symptoms [20]. Another distinguishing characteristic of mpox compared to other “pox-like” disorders is Lymphadenopathy which is uncharacteristic of smallpox and chickenpox [20]. This research aims to focus on the differences in

Table 3. 2022 US mpox outbreak.

mpox outbreaks that occurred in 2003 and 2022 in the United States. This study also reviewed the number of research papers compared to commentaries, reports, and case reports written about the US mpox out-break in 2003 and 2022 to gain more insight into these differences and their impact on population health in the US.

7. Limitations

This review has identified limitations beginning with the limited amount of research conducted about the 2022 mpox outbreak in the United States. Therefore, there were not enough research articles to choose for inclusion. Next, several studies were excluded because they consisted of animal research, and genetic research or was conducted outside of the US. The authors underestimated the limitations of Mpox articles and research. Therefore, due to identified gaps in the literature, more research is recommended to further determine the clinical, social, and psychological impact of the mpox virus globally.

8. Conclusions

In this study, we reviewed various types of articles written during both the 2003 and 2022 mpox outbreaks. We compared the two outbreaks and found that more research was conducted during the first US mpox outbreak compared to the current outbreak.

Major differences in the mpox outbreaks include differences in the number and location of lesions and transmission type. More research is recommended to increase awareness of the human-to-human transmission of mpox via sexual contact to assist healthcare professionals and public health leaders in providing prevention and wellness in US communities.


No funds or grants from the public, commercial, or any other funding agency were received by the authors of this manuscript. This manuscript has not been published nor is it under consideration for publication by any other journal.

Credit Authorship Contribution Statement

The manuscript was conceptualized and written by Sandra Henley, and Stephanie Woods-Crawford provided the final review and critique.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.


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