Tuesday, February 15, 2022

PLoS NTD: The Changing Epidemiology of Human Monkeypox—A potential threat?

Geographic Range of Monkeypox - Credit WHO


Beyond avian and swine flu, and now zoonotic coronaviruses, there are a number of emerging infectious diseases that we pay particular attention to, including Nipah (and Hendra)Viral Hemorrhagic Fevers, and Monkeypox. 

Monkeypox, which is endemic in parts of West and Central Africa, has been on the ascendent for the past couple of decades, as immunity from long-discontinued smallpox vaccinations has waned. 

In recent years we've seen sporadic exported cases - and even rarer secondary transmissions - reported in the UK, Singapore, Israel and the United States

Although the primary animal reservoir for Monkeypox remains unknown, humans can become infected in the wild from an animal bite or direct contact with the infected animal’s blood, body fluids, or lesions, but consumption of under cooked bushmeat is also suspected as an infection risk. 

Human-to-human transmission is also possible. This from the CDC’s Factsheet on Monkeypox:

The disease also can be spread from person to person, but it is much less infectious than smallpox. The virus is thought to be transmitted by large respiratory droplets during direct and prolonged face-to-face contact. In addition, monkeypox can be spread by direct contact with body fluids of an infected person or with virus-contaminated objects, such as bedding or clothing.
According to the CDC there are two distinct genetic groups (clades) of monkeypox virus—Central African and West African. West African monkeypox - such as has been spreading recently in Nigeria - is associated with milder disease, fewer deaths, and limited human-to-human transmission.

Research over the past few years suggests that Monkeypox outbreaks are becoming more frequent, and getting larger, potentially increasing its threat to public health. A few recent reports include:

WHO Update & Risk Assessment On Monkeypox In The DRC

WHO: Modelling Human-to-Human Transmission of Monkeypox

All of which brings us to a new Open Access systemic review in PLoS Neglected Tropical Diseases, which examines recent trends in the spread and epidemiology of Monkeypox, and finds the threat is growing. 

Follow the link to read the full review, as I've only included a few excerpts.

The changing epidemiology of human monkeypox—A potential threat? A systematic review

Eveline M. Bunge, Bernard Hoet, Liddy Chen, Florian Lienert, Heinz Weidenthaler, Lorraine R. Baer, Robert Steffen

Published: February 11, 2022



Monkeypox, a zoonotic disease caused by an orthopoxvirus, results in a smallpox-like disease in humans. Since monkeypox in humans was initially diagnosed in 1970 in the Democratic Republic of the Congo (DRC), it has spread to other regions of Africa (primarily West and Central), and cases outside Africa have emerged in recent years.

We conducted a systematic review of peer-reviewed and grey literature on how monkeypox epidemiology has evolved, with particular emphasis on the number of confirmed, probable, and/or possible cases, age at presentation, mortality, and geographical spread. The review is registered with PROSPERO (CRD42020208269). We identified 48 peer-reviewed articles and 18 grey literature sources for data extraction.

The number of human monkeypox cases has been on the rise since the 1970s, with the most dramatic increases occurring in the DRC. The median age at presentation has increased from 4 (1970s) to 21 years (2010–2019). There was an overall case fatality rate of 8.7%, with a significant difference between clades—Central African 10.6% (95% CI: 8.4%– 13.3%) vs. West African 3.6% (95% CI: 1.7%– 6.8%).

Since 2003, import- and travel-related spread outside of Africa has occasionally resulted in outbreaks. Interactions/activities with infected animals or individuals are risk behaviors associated with acquiring monkeypox.

Our review shows an escalation of monkeypox cases, especially in the highly endemic DRC, a spread to other countries, and a growing median age from young children to young adults. These findings may be related to the cessation of smallpox vaccination, which provided some cross-protection against monkeypox, leading to increased human-to-human transmission. The appearance of outbreaks beyond Africa highlights the global relevance of the disease. Increased surveillance and detection of monkeypox cases are essential tools for understanding the continuously changing epidemiology of this resurging disease.

Author summary

Monkeypox, a zoonotic disease caused by an orthopoxvirus, results in a smallpox-like disease in humans. We conducted a systematic review to assess how monkeypox epidemiology has evolved since it was first diagnosed in 1970 in the Democratic Republic of the Congo. In total, human monkeypox has now appeared in 10 African countries and 4 countries elsewhere. Examples include Nigeria, where the disease re-emerged in the last decade after a 40-year hiatus, and the United States, where an outbreak occurred in 2003.

The number of cases has increased at a minimum of 10-fold and median age at presentation has evolved from young children (4 years old) in the 1970s to young adults (21 years old) in 2010–2019. This may be related to the cessation of smallpox vaccinations, which provided some cross-protection against monkeypox. The case fatality rate for the Central African clade was 10.6% versus 3.6% for the West African clade.

Overall, monkeypox is gradually evolving to become of global relevance. Surveillance and detection programs are essential tools for understanding the continuously changing epidemiology of this resurging disease.