Scientists have found that mpox, formerly known as monkeypox, causes severe, fatal disease progression in people with untreated or advanced HIV.

The study, published in the journal The Lancet, found that in immunosuppressed people with HIV, mpox infection is seen to be deadly in about 15% of cases.

“The virus appears to be behaving completely differently in these individuals,” Prof Chloe Orkin, at the Queen Mary University of London and Barts Health NHS Trust, said, The Guardian reported. “Normally, the disease affects the area around the site of entry, but in this case, it is disseminated all over the body and causing these massive destructive ulcerating skin lesions. It is also causing lung disease. It is horrific.”

As per the outlet, about 85,000 mpox cases and 93 deaths have been reported from 110 countries across the globe since May 2022. A majority of these cases have been observed in men who have sex with men, of which 38-50% of them have both mpox and HIV.

Scientists also want mpox to be added to the World Health Organization’s list of severe infections that make people with advanced HIV more susceptible. This they hope will provide access to better financial and medical support for those at risk.

“Everyone with mpox should be tested for HIV, and if someone has HIV and gets mpox, their CD4 status must be measured,” Orkin advised. “Things have changed. We have a disease which is now circulating at low levels in humans, which is potentially lethal for people with HIV, and they die within a month.”

Low CD4 cell count signals the severity to which HIV has weakened the immune system.

“If you know someone who is vacillating about getting a test, encourage them,” Orkin added.

In the study, researchers analyzed 382 cases of people with advanced HIV disease and mpox. This included 27 who had died of mpox during the recent outbreak.

Following analysis, it was found mpox appeared to be fatal in 15% of people with advanced HIV and immunosuppression. However, the figure could be as high as 27% in individuals with the lowest CD4 cell counts.

It should be noted not everyone with HIV is at risk of getting this severe form of mpox. Patients getting antiretroviral treatment for HIV and those who have a healthy CD4 count show the same prognosis as a normal person when infected with mpox.

“It is an unpleasant disease – I wouldn’t wish it on anyone – but it is self-limiting,” Orkin said.

“Although mpox is rarely severe for those of us whose HIV is controlled with treatment, the rates of serious illness and mortality as a result of mpox for people with untreated or unsuppressed HIV are worrying,” Matthew Hodson, executive director of the HIV charity NAM aidsmap, said.