Monkeypox, chickenpox or shingles? Infectious diseases experts explain the difference

We’ve yet to get over the COVID-19 pandemic (good thing the current wave of cases is not severe) and we've got another health concern on hand: Monkeypox.

The virus has made its way to our shores in the form of the first local case detected in Singapore. The man is not linked to the imported case that culminated in 13 close contacts identified so far. The previous run-in Singapore had with monkeypox was in 2019.

As of Jun 22, the World Health Organization (WHO) recorded more than 3,400 laboratory-confirmed cases and one death globally – that’s 1,310 more new cases and eight new countries added to the list since the WHO’s report on Jun 17, which also noted that 86 per cent of the cases are detected in Europe.

With so many diseases to keep an eye on, you might be feeling overwhelmed. For instance, how do you tell if the fluid-filled blisters you’ve developed are signs of monkeypox or chickenpox? If you’ve had chickenpox before, do you still need to get vaccinated? (You still might.) And how protected are you against monkeypox? (Yes, you just might be.)

CNA Lifestyle checks in with the infectious disease specialists for the rundown:

ARE MONKEYPOX AND CHICKENPOX CAUSED BY THE SAME VIRUSES?

Despite the physical similarities between monkeypox and chickenpox – rashes that turn into blisters that scab and fall off – including the names, they are not caused by the same virus. The monkeypox virus belongs to the Orthopoxvirus genus, which also includes the virus that causes smallpox.

Chickenpox, on the other hand, is caused by the varicella zoster virus (VZV), which can reactivate after you’ve recovered. The fever, chills, body aches and rashes that arise are just part of the primary infection.

“This is when the virus first enters the body, then manifests as chickenpox,” said Dr Nares Smitasin, a senior consultant with National University Hospital’s Department of Medicine, Division of Infectious Diseases. “After the immune system clears the virus, the virus will stay dormant in the nervous system.”

And there the VZV remains until your immune system weakens. As for predicting when and which part of the body may get affected when the virus reactivates, it depends on how immunosuppressed you are and which nerve root the virus is lying dormant in, said Dr Shawn Vasoo, the clinical director of the National Centre for Infectious Diseases.

For instance, an individual who is very immunosuppressed may develop shingles in various parts of the body, whereas someone who has a stronger immune system may just get it in one patch, he said. “If the virus is lying dormant in a nerve in the face, you may develop Ramsay Hunt syndrome. You might get ear pain and facial paralysis.” (Read this for more on shingles and Ramsay Hunt syndrome.)

HOW ARE BOTH DISEASES SPREAD?

The incubation periods for both viruses are about the same, said Dr Vasoo, which can last up to 21 days. The difference, though, is their modus operandi: Chickenpox is largely spread via aerosols (the virus is airborne), while monkeypox is spread mostly through close or direct contact such as sex.

“Specifically, for monkeypox, in the unprecedented 2022 multi-country outbreak, scientists are investigating whether beyond close contact, reproductive fluids (for example, semen) can transmit the virus. That’s something we are still needing more research and data on,” said Dr Vasoo.

HOW DO YOU TELL IF IT’S MONKEYPOX OR CHICKENPOX?

One of the distinct characteristics of monkeypox are the blisters that are concentrated on the face, hands and feet, said Dr Smitasin. “In the recent outbreak, there are many reports of rashes starting in the genital area,” he said.

According to him, they first appear as rashes or red dots, and evolve uniformly to become tense, fluid-filled blisters. The final stage is when they become scabs that eventually fall off in about one to two weeks. Sounds familiar? For those who have had chickenpox before, that might have formed a big part of your recollection.

But there are differences. For chickenpox, you may experience fever, tiredness and sore throat first. According to Dr Vasoo, a rash typically starts on the trunk and face before spreading all over the entire body. The rash then develops into itchy, fluid-filled blisters and “typically evolves in different stages” and “erupts in several ‘crops’ on different parts of the body”. It can take about one week for the blisters to scab over, he said.

“While both illnesses may cause fever and rash, swollen lymph nodes are one distinguishing feature of the prodomal period (when symptoms such as fever begin before the rash appears) of the monkeypox disease, which is not seen typically in chickenpox,” said Dr Vasoo.

Here’s a summary from Dr Smitasin on how monkeypox and chickenpox compare:

WHAT ARE YOUR CHANCES OF CATCHING EITHER VIRUS?

As recent as the 1970s, the world was still battling the highly contagious smallpox, which had a high mortality rate and those who survived were often disfigured for life.

In Singapore, vaccination against smallpox was mandatory at that time. It was only in 1980 that the Health Organization (WHO) declared smallpox eradicated. Two years later, Singapore took its cue from the WHO and ended the legal vaccination requirement.

This would mean that those above age 38 would have been vaccinated against smallpox decades ago. Now, this gets interesting as smallpox and monkeypox are from the same Orthopoxvirus genus. “There is some expected cross-protection if one has had smallpox vaccination before,” said Dr Vasoo.

Dr Vasoo added: “We have data that immune responses from previous smallpox vaccination may last decades. However, this may be somewhat variable between people, so while there may be some residual immunity which confers some protection, it may be hard to predict just based on a history of vaccination decades ago if one may be completely protected.”

Dr Smitasin agreed that “the immunity wanes over time, so there is still a chance of getting monkeypox even with prior smallpox vaccination”. Still, in one study, distant smallpox vaccination has the efficacy of approximately 81 per cent, he said.

As for the monkeypox vaccine, the Ministry of Health is evaluating the pros and cons of offering monkeypox vaccination to workers at high risk such as some healthcare and laboratory workers. However, the ministry is not recommending inoculation for the general population.

In the parliamentary sitting on Jul 5, Senior Minister of State for Health Janil Puthucheary explained that monkeypox is typically a “self-limiting illness”. Moreover, data from the current multi-country outbreak indicated that 99 per cent of the cases were spread through sex. 

“Given that sexual contact with infected individuals appeared to be the main driver of the current monkeypox outbreak, and that transmission requires close physical or prolonged contact, the risk to the general public remains low,” said Dr Puthucheary.

DO YOU STILL NEED TO BE VACCINATED IF YOU’VE HAD CHICKENPOX BEFORE?

Remember, the VZV can be dormant in your body after you’ve recovered from chickenpox – and reactivates to cause shingles. The most common complication is postherpetic neuralgia, which causes shingles pain for a long time after your blisters have cleared.

There are two types of shingles vaccines to consider: A live vaccine called Zostavax (contains a weakened version of the actual virus), and a recombinant vaccine (contains no live virus) called Shingrix. Zostavax is given as a singular injection, while Shingrix requires two shots about two to six months apart. In studies, it is found that Shingrix is better at preventing shingles than Zostavax (97.2 per cent versus 51 per cent respectively).

“For those with compromised immune systems, Shingrix may be considered and they should discuss with their doctors as to the optimal time to get vaccinated if they are undergoing immunosuppressive treatment,” said Dr Vasoo.

DO ADULTS NEED THE CHICKENPOX VACCINATION IF THEY HAVEN'T CONTRACTED THE VIRUS BEFORE?

There is a good reason for getting the varicella jabs (two doses, four to eight weeks apart) if you weren't already vaccinated as a baby as part of the Singapore National Childhood Immunisation Schedule: About 90 per cent of unvaccinated household contacts of an infected person will catch chickenpox. Yes, the VZV is that contagious.

Also, consider this: Adults are 25 times more likely to die from chickenpox than children. This is because the risk of hospitalisation, from complications such as pneumonia and rarely, encephalitis (brain inflammation), is higher in adults. Even if you dodge the complications, adults may have stronger reactions to chickenpox than children, according to Healthline.