Mpox Surge Raises Fear Of Spread Before Patients Show Symptoms

(Bloomberg) -- Health authorities rushing to contain a fast-spreading mpox outbreak in the Democratic Republic of Congo are increasingly concerned that the disease may be spreading though people who aren’t yet showing symptoms.

Mpox, a typically less contagious and milder cousin of smallpox, has infected people in West and Central Africa with increasing frequency since the 1970s. Until the current outbreak, however, the variant endemic to the region never spread very efficiently between humans, nor had it been recorded as frequently mutating. 

While plenty remains unknown about the new subvariant driving this outbreak, the speed with which it is spreading is an unsettling development that may indicate risk for future pandemics.

The new mutated strain — related to a more virulent version called clade I — is responsible for many of the 17,794 cases and 535 deaths in Congo this year, according to the Africa Centres for Disease Control and Prevention. Of these fatal cases, more than 60% have been among children under the age of five. Unlike clade IIb, a milder strain that erupted in 2022 and spread primarily through men who have sex with men, the current variant is spreading through all kinds of sexual activity and other close physical contact. 

Given the difficulty in accessing health services in Congo, the true number of clade I cases is likely far higher than the official count. “We think that the severe cases are the tip of the iceberg,” said Helen Rees, founder of the Reproductive Health and HIV Institute in Johannesburg and chair of the World Health Organization’s African Regional Technical Advisory Group on Immunization.

Mpox has tended to present at first through fever, muscle aches, fatigue, headache, the swelling of lymph nodes and other flu-like symptoms. Within a few days of fever onset, some patients develop a rash that can produce lesions or fluid-containing pustules. 

Prior to 2022, it was largely assumed that transmission occurred mostly after such symptoms appeared, according to Adam Kucharski, a professor of infectious disease epidemiology at the London School of Hygiene & Tropical Medicine. 

However, Kucharski said, an analysis of a 2022 outbreak of mpox — also declared a global emergency — suggested that the majority of cases were transmitted before symptoms became visible.

“Even before a rash occurs” in patients with the new subvariant, Rees said, “we suspect that this can be spread.”

Transmission has likely been exacerbated by the outbreak’s location — Kamituga, a bustling mining hub in a mineral-rich area — along with conflict in the Congo that has displaced 4.2 million people in the region around the outbreak, leaving thousands in crowded, unsanitary refugee camps. Truckers and sex workers who move between Kamituga and the neighboring nations of Burundi and Rwanda are seen as potential transmitters, as are the thousands of small-scale miners who come to the city for short-term work. 

Children may be especially at risk as they’re less likely to have had previous exposure to the disease, and may be more vulnerable if they’re young and suffering from malnutrition, Rees said. 

The speed of the disease’s spread requires prompt action, Kucharski said. Research is needed to untangle the various strains of the virus to show the true scale of infection, while ensuring that vaccines and non-pharmaceutical measures are being used effectively.

So far, the clade I numbers in Congo have been the largest by far, but new cases have been reported in several African countries in the last month, as well as one in Sweden. Burundi has, since July, reported 100 cases of mpox caused by the subvariant in mutiple distcicts, according to the World Health Organization. Of those, 28% were children under five.

“In many ways, outbreaks like mpox can be thought of as a test for the next major pandemic,” Kucharski said. “Will the global response be effective and equitable? Or will it be late, disjointed and misdirected?”

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--With assistance from Ashleigh Furlong.

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