#16,815
Our understanding of the `classic' presentation and clinical course of Monkeypox is based, in large part, on cases detected in MKPV endemic nations like the DRC, Nigeria, and Cameroon and a smattering of exported cases.
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| Geographic Range of Monkeypox - Credit WHO |
At the same time, we know that surveillance and reporting from these nations is less than robust, which means we may be only seeing a subset of cases that match our expectations for what Monkeypox is supposed to look like (see IJID: Increased Outbreaks of Monkeypox Highlight Gaps in Actual Disease Burden in Sub-Saharan Africa).
This could help explain how this virus has managed to transmit, under the radar, around the world without raising alarm.
The CDC describes the `classic presentation' of Monkeypox as:
- After infection, there is an incubation period which lasts on average 7-14 days. The development of initial symptoms (e.g., fever, malaise, headache, weakness, etc.) marks the beginning of the prodromal period.
- A feature that distinguishes infection with monkeypox from that of smallpox is the development of swollen lymph nodes (lymphadenopathy). Swelling of the lymph nodes may be generalized (involving many different locations on the body) or localized to several areas (e.g., neck and armpit).
- Shortly after the prodrome, a rash appears. Lesions typically begin to develop simultaneously and evolve together on any given part of the body. The evolution of lesions progresses through four stages—macular, papular, vesicular, to pustular—before scabbing over and resolving.
But we continue to see reports of `atypical' - and often deceivingly mild - cases. Whether this is something new, or something entirely normal - but unrecognized until now - remains to be seen.
On June 7th the Lancet published the following comment which describes the atypical `. . . absence of prodromal symptoms, such as fever, malaise, and headache, and the presence of herald skin lesions at the point of sexual contact in some patients'.
Open Access Published:June 07, 2022
Yesterday the World Health Organization published their latest update (Link: Multi-country monkeypox outbreak: situation update), which includes the following:
To date, the clinical presentation of monkeypox cases associated with this outbreak has been variable. Many cases in this outbreak are not presenting with the classically described clinical picture for monkeypox (fever, swollen lymph nodes, followed by rash concentrated on the face and extremities).Atypical features described include:
- presentation of only a few lesions or even just a single lesion;
- lesions that begin in the genital or perineal/perianal area and do not spread further;
- lesions appearing at different (asynchronous) stages of development;
- and the appearance of lesions before the onset of swollen lymph nodes, fever, malaise or other symptoms.
The modes of transmission during sexual contact remain unknown; while it is known that close physical contact can lead to transmission, it is not clear what role sexual bodily fluids, including semen and vaginal fluids, play in the transmission of monkeypox.The situation is evolving and WHO expects that there will be more cases of monkeypox identified as surveillance expands in all regions and countries.
(Snip)
Any individual meeting the definition for a suspected case should be offered testing. The decision to test should be based on both clinical and epidemiological factors, linked to an assessment of the likelihood of infection. Due to the range of conditions that cause skin rashes and because clinical presentation may more often be atypical in this outbreak, it can be challenging to differentiate monkeypox solely based on the clinical presentation.
Two years ago, in the Bulletin of the World Health Organization's Modelling human-to-human transmission of monkeypox, the authors stated:
Monkeypox is not considered contagious during its incubation period and asymptomatic monkeypox infection has not been documented.
But yesterday's CDC update on the transmission of Monkeypox left that door open slightly (emphasis mine):
Unknown/Still learning: Contact with people who are infected with monkeypox but have no symptoms (We think people with symptoms are most likely associated with spread, but some people may have very mild illness and not know they are infected).
With Monkeypox - like with Ebola, COVID, Zika, and dozens of other outbreaks before it - we often know less about an emerging virus than we think we do.
Assumptions are often based on limited prior experience with an emerging virus, or with similar pathogens, and must be adjusted along the way.
- Ebola, we were told, was too virulent to spread effectively in an urban environment. Until it did.
- Arboviruses couldn't be transmitted through sexual contact. Until Zika proved it can happen.
- Arboviruses couldn't cause severe congenital birth defects. Again, Zika educated us.
- Since SARS didn't transmit asymptomatically, COVID-19 wouldn't either. Now we know better.
While some assumptions must be drawn - based on incomplete data - we will undoubtedly know far more about how Monkeypox transmits, and the spectrum of clinical (or subclinical) illness it can produce, a year from now.
Until then, we should remain humble enough to expect some surprises along the way.
