Thailand confirms first mpox case; experts say disease presents hard-to-weigh risks

PARIS - An mpox case reported in Thailand this week has been confirmed as being the clade Ib strain of the virus – the first in the country – a disease control official said on Aug 22.

“This man is likely infected from an endemic country,” Mr Thongchai Keeratihattayakorn, director-general of the Department of Disease Control, told Reuters.

He added that no other local infections had been detected through contact tracing.

Thailand on Aug 21 said the case was a 66-year-old European man who had arrived from an African country where the disease is spreading.

As fears mount globally about mpox, apparently simple questions such as its danger and differences between variants do not have clear and simple answers.

The World Health Organisation in July

declared an international health emergency

over the spread of mpox, which first appeared in humans around 1970 in the Democratic Republic of Congo (DRC).

For decades, the illness long known as “monkeypox” was restricted to a few African countries, with estimates of its mortality rate ranging from 1 per cent to 10 per cent of people infected.

That uncertainty grew from 2022, when mpox spread elsewhere in the world, especially to Western countries.

Cases in these newly infected states had very low mortality rates of around 0.2 per cent.

Such differences likely stem from several variables.

First, someone living in the US or Europe is much more likely to receive swift, appropriate medical treatment than patients in most African nations.

The danger mpox presents “strongly depends on the quality of basic care”, said Dr Antoine Gessain, a virologist specialising in the disease.

The mortality rate measured in the current outbreak – around 3.6 per cent – would therefore likely be much lower were it not limited mostly to the DRC.

Child malnutrition

Other factors weighing on the mortality rate include those that make some patients more vulnerable than others.

The vast majority of the deaths recorded in the DRC – over 500 out of more than 15,000 mpox cases – have been children, many of whom are affected by malnutrition in the country.

In contrast, in the DRC’s 2022 to 2023 epidemic, the very small number of people who died – around 200 out of 100,000 cases – were mostly adults whose immune systems were already weakened by human immunodeficiency virus (HIV) infection.

Different mortality outcomes can also be explained by the way the disease is spread.

In 2022 to 2023, most transmission was via sex between homosexual or bisexual men.

Another factor adding complexity is the clade, or family, to which the specific virus causing an mpox outbreak belongs.

Scientists are struggling to determine the differences between clades when it comes to health risks and transmission.

Tricky comparisons

The 2022 to 2023 mpox epidemic was caused by clade II mpox, which is present mostly in western Africa, but also found in South Africa.

DRC’s deadly current outbreak stems from clade I mpox, mostly found in the continent’s central areas. But a distinct second epidemic hitting mostly adults in the same country is linked to variant Ib, a derivative of clade I that has appeared only recently.

Confusion in the media has led some outlets to call variant Ib more dangerous than previously existing mpox varieties.

“There are rather big claims in the popular media for which evidence is limited, both about severity and about transmissibility of the new sub-lineage Ib,” Dutch virologist Marion Koopmans told the UK-based Science Media Centre. “What we do know is that clade I is associated with more severe disease than clade II.”

Clade I outbreaks have been associated with higher mortality rates than clade II.

But researchers call for caution before drawing conclusions, even with apparently clear-cut figures.

The urgency of establishing the facts about mpox variants is all the greater, as

clade I was detected in Sweden in mid-July

– for the first time outside Africa.

“It’s very difficult to compare” between different clades “given that the context and the type of at-risk population are so important”, Dr Gessain said.

“How can you compare children suffering from malnutrition and HIV-positive adults?” he asked. AFP, REUTERS