The symptoms of monkeypox may not always be obvious

The symptoms of monkeypox may not always be obvious

A recent article in the magazine JAMA Medical News & Perspectives has found that some monkeypox infections can be asymptomatic or very mildly symptomatic and therefore can easily go unnoticed. This statement was made based on two recent case reports from Europe. Medical News & Perspectives – Reports of asymptomatic monkeypox suggest that at least some infections go unnoticed. Photo credit: NIAID

Monkeypox outbreaks

Recent monkeypox virus outbreaks since May 2022 have caused nearly 48,000 infections in over 99 countries around the world. This estimate was released by the US Centers for Disease Control and Prevention (CDC), which is believed to be the largest documented outbreak in largely non-endemic countries.

The majority of recent monkeypox infections have been observed in men who have sex with men (MSM). This has led scientists and doctors to consider sexual contact as the primary route of virus transmission during recent outbreaks.

Two recent case reports from Belgium and France have highlighted that monkeypox infection can be asymptomatic.

In the Belgian study, four MSM tested positive for monkeypox infection during routine sexually transmitted infection screening. Of four patients, three were asymptomatic at the time of testing and remained symptom-free for approximately three months after diagnosis.

In the French study, monkeypox infection was detected in 13 asymptomatic patients. Only two later developed symptoms and visited the clinic to receive medical attention.

Marjan Van Esbroeck, a clinical microbiologist at the Institute of Tropical Medicine, Belgium, explained: "These studies suggest that, contrary to what is known about monkeypox in Africa, not all patients show symptoms."

Are these infections asymptomatic or subtle?

The researchers noted that although patients were asymptomatic during the study period, there was a possibility of unrecognized symptoms.

Given that patients were not physically examined at the time of sample collection, Van Esbroeck said, "We cannot rule out that smaller lesions were missed or that people did not remember general symptoms such as mild fever or malaise."

Evidence shows that the monkeypox virus circulated undetected in non-endemic countries for some time before the first case was discovered in the UK in May 2022.

Overall, these observations suggest that patients with monkeypox infection can develop very subtle symptoms that often go unrecognized by physicians and patients. This raises the question of whether patients with subtle symptoms can infect others.

Is asymptomatic transmission possible?

Studies investigating the possibility of asymptomatic transmission of monkeypox virus identified asymptomatic patients with high viral loads during recent monkeypox outbreaks in Europe. In addition, the Belgian study detected replication-competent monkeypox viruses in anogenital swabs from asymptomatic patients.

These observations highlight the risk of inadvertent viral transmission from asymptomatic patients. In this context, Van Esbroeck mentioned: "The difference between completely asymptomatic patients and patients with unrecognized minor symptoms is theoretical. Both will result in people not isolating themselves and may continue to engage in risky behavior."

As Boghuma Kabisen Titanji, assistant professor of medicine at Emory University, noted, in many patients with monkeypox infection, the only noticeable symptom is pain when swallowing, which can easily be overlooked as a symptom of monkeypox infection.

In some patients, lesions are not present on the skin but may be found by doctors in the larynx or rectum. She specifically mentioned that monkeypox infections “can look and sound like many things we see in clinical practice” and that “monkeypox is an incredible mimic.”

According to the expert, both doctors and patients should be aware of the spectrum of clinical symptoms associated with monkeypox infection. This helps to quickly detect even a very subtle symptom, which is crucial for the timely detection and therapeutic treatment of monkeypox infection.

Measures to identify asymptomatic infection

Due to the high cost of testing, not all patients with high-risk behaviors can be tested for monkeypox.

Given the sharp rise in monkeypox cases during recent outbreaks, Abraar Karan, an infectious disease doctor at Stanford University, predicted that shedding of infectious viruses from asymptomatic or mildly symptomatic patients is very likely.

To better understand the potency of asymptomatic infections to spread the virus, frequent physical examinations and testing of exposed individuals are needed to monitor the clinical evolution of the infection.

As suggested by Abraar Karan, population-level serological testing could be effective in understanding the extent of unrecognized infections. However, this is currently not possible as there are no monkeypox-specific serological tests available on the market.

Douek, chief of the Division of Human Immunology at NIAID's Vaccine Research Center, is currently developing a monkeypox-specific assay in collaboration with smallpox virus experts at the CDC.

Douek said: "Presumably we will catch all cases of asymptomatic monkeypox infection because there may be people who have antibodies to monkeypox but no recorded symptomatic history of an actual known infection."

The successful development of this assay will help monitor the dynamics of monkeypox transmission in high-risk populations, including MSM, sex workers and people living in endemic countries.

Reference:

• Abbasi J. 2022. Berichte über asymptomatische Affenpocken deuten darauf hin, dass zumindest einige Infektionen unbemerkt bleiben. JAMA. https://jamanetwork.com/journals/jama/fullarticle/2796003

.