CDC expert answers questions about monkeypox

CDC expert answers questions about monkeypox
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Monkeypox, a disease that rarely appears outside of a belt of countries across West and Central Africa, has exploded into the news recently, with reported cases in the UK, Spain, Portugal, USA, Sweden, Italy and probably Canada.

At this stage, cases are mainly detected by clinics that treat sexually transmitted diseases and are seen in men who have sex with men. But the World Health Organization and the Centers for Disease Control and Prevention have warned that assuming the virus is only circulating in a single subset of the population risks missing cases that may occur in other people.

Monkeypox causes an array of flu-like symptoms, but also comes with a distinctive rash; a telltale sign is the fact that lesions often appear on the palms of the hands. Cases so far appear to be caused by viruses from the West African clade, which trigger a milder disease than the other family of viruses, called the Congo Basin clade. All monkeypox viruses are cousins ​​to the one that caused smallpox, the only human virus to have been eradicated.


STAT had many questions about monkeypox. Fortunately, Andrea McCollum, head of the poxvirus epidemiology team in the CDC’s Division of High Consequence Pathogens and Conditions, had many answers.

Portions of the conversation have been lightly edited for clarity and length.


Do we know how good the monkeypox virus is at spreading from person to person?

Monkeypox is truly transmissible from the onset of signs or symptoms throughout the course of the disease. And the definition of “disease progression” is until all lesions have healed, the scabs have separated, and a new layer of skin has formed. It can be quite a long period. This may take several weeks.

To what extent it is transmissible is a slightly trickier question. We don’t have very good contemporary R-naught estimates. [R-naught is the figure that estimates how many people an infected person, on average, will infect.] We don’t really have any R-naught estimates for the West African clade. Most of our estimates come from the Congo Basin. And most of these estimates are less than 1. But I remind you that you can have an R-naught less than one and the agent can still be transmitted from person to person.

I think we can learn a lot from what we know about monkeypox in the Congo Basin and West Africa. Even though human-to-human transmission is documented, it is usually documented among very close contacts. So the members of the family, the people who take care of the sick. Or health care providers.

About the CDCs website, it indicates that transmission can occur via respiratory droplets. But do we really think that most of the transmission actually takes place through skin-to-skin contact?

I don’t think we really know if most are respiratory or skin-to-skin. I think from historical literature and certainly learning about smallpox, which was a closely related virus, we knew that respiratory droplet transmission, especially in the early stages of transmission, contributed significantly to this. And we believe this is largely due to the lesions that often develop in the oral cavity. These lesions are teeming with viruses and of course you can imagine that with saliva they spread easily.

We know that the lesions themselves, including those on the surface of the skin, are loaded with viruses. They are therefore contagious. If a patient has been in bed, then the lesions have exudate and pus and that ends up on the sheets and the virus is in that material.

Are the lesions so distinct that people will go to a doctor to have them examined? Or could they think it was hives or something?

It depends on the person and the extent of the rash. I think if people have a very diffuse, very diffuse rash on multiple parts of the body and it is very noticeable and obvious, it may prompt someone to see a doctor. If it is more confined to a single body site or a few body sites that can easily be covered by clothing, they may be less susceptible.

The monkeypox patients I have spoken with often speak of a rather long illness with a sort of flu-like syndrome with respiratory involvement. They talk about a lot of discomfort, aches. They are tired. And the lesions themselves are often described as very painful, regardless of where they occur on the body.

That’s what we usually hear from patients, that because of these kinds of signs or symptoms, they knew they were really sick.

Do these lesions heal in the same way as smallpox? Or chickenpox, for that matter?

Yes, they can lead to hypo or hyperpigmentation and scarring, yes. People with darker skin may experience post-healing hypopigmentation, lighter areas where the lesions used to be.

How many lesions do people usually have?

There is a range of lesions that people present, ranging from a handful to several hundred. It can be quite serious.

Do they itch like chickenpox?

No. One of the clinical signs that we ask clinicians to address is that, usually up to the crusting stage, orthopoxvirus lesions are usually painful and chicken pox is itchy. It is only during this healing phase [with monkeypox] when there are crusts and the skin regenerates a little, patients mention itching.

Is it one of those conditions where the older you are when you get it, the more severe the disease?

I think it’s something we don’t really know.

There are a few aspects with age. One could certainly worry about underlying immunosuppression simply due to the nature of age and other underlying health conditions. But people who have already been vaccinated against smallpox have some degree of protection against monkeypox. So we would expect these people to potentially have a milder form of the disease. But again, that’s something we really didn’t find in people who were vaccinated 50 years ago, 60 years ago. [The United States stopped vaccinating against smallpox in 1971.]

A number of cases involve men who have sex with men, raising the issue of sexual transmission. But is it really sexual transmission? It is transmitted by skin-to-skin contact or the exchange of saliva if there are lesions in the mouth. Is it correct?

We have no data on the virus in semen or vaginal secretions. But what we do know is that it requires close contact. And that is certainly what happens during intimate contact. So I think for us it’s not entirely different from what we already know about monkeypox in terms of close contact.

Now, there may be things we learn later as we learn more about these cases. And if there’s an important component of intimate contact that we can try to untangle, then that may present that opportunity. But at this point, everything we hear and see is consistent with what we know about monkeypox, which is that it requires close contact.

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