Monkeypox Incubation Period Varies Depending on Type of Exposure

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Definition

Monkeypox

Monkeypox is a zoonotic pox virus infection that can occur in both humans and some other animals. Monkeypox in humans and animals is caused by infection with the monkeypox virus - a double-stranded DNA virus in the genus Orthopoxvirus, family Poxviridae. Two recognized distinct types are described as the Congo Basin clade and the milder West African clade.

Main Digest

During the currently evolving outbreak of monkeypox cases worldwide, 31 cases have been confirmed in the Netherlands up to 31 May 2022. Efforts to stop the spread of infection focus on active case finding, contact tracing of close contacts, and their isolation or quarantine. Related recommendations from public health bodies on the need for active monitoring and isolation for a minimum of 21 days after the last day of exposure are based on the known monkeypox incubation period (up to 21 days).

Observed Incubation Periods Vary Depending on Type of Exposure

Miura et al. [1] analyzed data of 18 cases confirmed in the Netherlands who reported the date of onset of symptoms and the most likely date of exposure. Depending on the transmission route, the typical duration of the incubation period for monkeypox varies from 9 days following complex and invasive exposure, e.g., contact with broken skin, to around 13 days after non-invasive exposure such as droplet transmission or contact with intact skin.

In their rapid communication published in Eurosurveillance, the authors argue that "given the particular types of exposures and differences in route of transmission, the incubation period for monkeypox in the current outbreaks may also have a different duration."

All 31 laboratory-confirmed monkeypox cases detected in the Netherlands until the end of May 2022 were among men between 23-64 years old who self-identified as men who have sex with men. Miura et al. analyzed the distribution of the incubation periods based on the information about symptom onset and exposure histories for monkeypox among 18 of them. They used a likelihood-based approach, which allows for exposure to be a single time point or a time interval.

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Mean Incubation Period Estimated at 8.5 Days

Among the analyzed cases in this outbreak and using this best-fitting (lognormal) distribution, the mean incubation period of monkeypox was estimated to be 8.5 days (95% credible intervals: 6.6-10.9 days), with the 5th percentile of 4.2 days and the 95th percentile of 17.3 days.

This means the incubation period is in line with the typical timeline for so-called complex invasive exposure, and "direct contact between respective broken skin or mucous membranes during sexual activity might be the most likely route of transmission among cases reported" in the Netherlands.

Based on this, Miura et al. estimate that the percentage of people with monkeypox that would develop symptoms only after 21 days is approximately two percent, thus supporting the current use of 21 days for quarantining or other approaches to avoid infectious contacts.

The authors note that:

"More epidemiological information on details of possible exposure routes is required to establish whether the results of the current study are generalizable to other men who have sex with men cases in the current outbreak and to what extent the incubation period differs between alternative transmission routes."

References:

[1] Miura Fuminari, van Ewijk Catharina Else, Backer Jantien A., Xiridou Maria, Franz Eelco, Op de Coul Eline, Brandwagt Diederik, van Cleef Brigitte, van Rijckevorsel Gini, Swaan Corien, van den Hof Susan, Wallinga Jacco. The estimated incubation period for monkeypox cases was confirmed in the Netherlands in May 2022. Euro Surveill. 2022;27(24).

[2] Monkeypox is a zoonotic disease, i.e., it can be transmitted between animals and humans via direct or indirect contact. Following the eradication of smallpox and the end of universal smallpox vaccination, monkeypox is currently the most prevalent human orthopoxvirus infection. See: European Centre for Disease Prevention and Control. Monkeypox multi-country outbreak - 23 May 2022. ECDC: Stockholm; 2022.

Attribution/Source(s):

This peer reviewed informative article relating to our Monkeypox Virus section was selected for publishing by the editors of Disabled World due to its likely interest to our disability community readers. Though the content may have been edited for style, clarity, or length, the article "Monkeypox Incubation Period Varies Depending on Type of Exposure" was originally written by European Centre for Disease Prevention and Control (ECDC), and published by Disabled-World.com on 2022/06/16 (Updated: 2023/09/21). Should you require further information or clarification, European Centre for Disease Prevention and Control (ECDC) can be contacted at ecdc.europa.eu/en. Disabled World makes no warranties or representations in connection therewith.

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