The strain circulating here is milder and less transmissible than the one in Africa, but that could arrive here soon.
Western Australia and Victoria both issued health alerts this week over cases of mpox. WA has seen two cases, while Victoria has recorded 125 cases so far this year. New South Wales, which has had 135 cases, also published a public health notice on mpox this month.
Around the country, 306 cases have been recorded so far in 2024 – 198 of those since the beginning of July. By comparison, there were 144 cases for all of 2022, and 26 in 2023.
The mpox cases in Australia are a different type to those spreading in Africa which prompted the World Health Organization (WHO) to declare a public health emergency of international concern last week.
Fortunately, people infected in Australia have a milder strain of the virus. But it’s still important to know what to look out for.
A look back
Mpox, formerly called monkeypox, is a disease caused by the monkeypox virus. It comes from the same family as smallpox. Symptoms include fever and a rash, which tend to affect the anal and genital areas, chest and back, face and head, and hands and feet.
Until relatively recently, mpox was almost always found in western and central Africa. There have been outbreaks outside this area, such as one in the United States in 2003. But in May 2022, there was a major outbreak of mpox that spread rapidly to many countries, including some where mpox is not typically found, such as Australia.
As a result, in July 2022, the WHO declared the outbreak to be a public health emergency of international concern.
The emergency classification was lifted in May 2023, because there was a significant decline in cases after countries increased control measures, such as surveillance and vaccination.
So the declaration of a public health emergency last week is actually WHO’s second for mpox. But it relates to a different strain of the virus.
Clades and subclades
The mpox virus can be divided into two variants or “clades”: clade I and clade II. Clade I, found mainly in central Africa, is a much more severe disease with a death rate up to 10%. Clade II is found mainly in western Africa and is much milder, with a death rate below 1%.
Clade II can be further divided into clade IIa and clade IIb. It’s clade IIb mpox, which caused the major outbreak in 2022, that we’re currently seeing in Australia.
In the latter half of 2023, a new subclade of clade I was discovered in the Democratic Republic of Congo (DRC). Clade Ib has primarily affected the DRC, with around 70% of suspected cases there in children under the age of 15. The outbreak has also spread to neighbouring East African countries, including Burundi, Kenya, Rwanda and Uganda.
The death rate from the clade Ib outbreak is still being worked out. But in the DRC, 7,851 cases and 384 deaths were reported up to late May. This suggests a fatality rate of about 5%.
Outside Africa, cases have recently been found in Sweden and Thailand.
Due to the rapid spread of clade Ib cases in Africa, and the potential for it to spread more widely, the WHO declared this outbreak a public health emergency of international concern on August 14.
Clade I versus clade II
In line with the higher mortality rates, clade I infections tend to be more severe overall. They’re said to be associated with higher rates of complications such as encephalitis (inflammation of the brain), pneumonia, respiratory distress and secondary bacterial infections. Patients often experience more intense skin rashes, larger lesions and more swollen lymph glands.
In the laboratory, the different clades are distinguished using real-time polymerase chain reaction (PCR), a similar technique to that used to test for COVID.
As for mode of spread, clade I has a higher rate of person-to-person transmission, especially through respiratory droplets and close contact.
Clade II has a lower rate of person-to-person transmission. It’s mostly sexually transmitted, primarily affecting men who have sex with men. All but one of the 476 cases of mpox recorded in Australia since 2022 have been in men.
Should we be worried?
Clade IIb mpox, which first hit us in 2022, is on the rise in Australia again, but public health authorities should be able to bring it under control. The more severe clade Ib is likely to hit Australia in the next few months. It could spread into the heterosexual community, or children, but the risk appears low. And fortunately, mpox is far less transmissible than COVID.
Australia’s public health system is strong and forged excellent relationships with the LGBTQ+ community during HIV. With testing at-risk groups (including sex workers), good contact tracing and vaccination, we were able to control the 2022 outbreak. There’s no reason a similar response won’t work should we see an outbreak of clade Ib mpox in Australia.
An effective vaccine is available against smallpox and all variants of mpox. Although there appears to be a worldwide shortage of mpox vaccines, we do currently have supplies in Australia.
Here the vaccine is recommended for groups at risk of exposure to the virus, including sexually active gay, bisexual or other men who have sex with men, and sex workers.
The most prominent feature of mpox is the rash, which could include fluid-filled blisters, a small raised area on the skin that contains pus, pimples, ulcers or lesions. Other symptoms may be similar to a COVID or a flu infection. If you’re unwell and have potentially been exposed to mpox, consult your GP.
This article was originally published by The Conversation.
Adrian Esterman is a professor of biostatistics and epidemiology at the University of South Australia.
