How to Keep Your Child Safe Amid the 'Tripledemic'
The Virus That Causes Mpox Keeps Getting Better At Spreading In People
November 1, 2024
5 min read
The Virus That Causes Mpox Keeps Getting Better at Spreading in People
Analysis of a strain of the virus circulating in Central Africa shows genetic mutations indicative of sustained human-to-human spread
Colorized transmission electron micrograph of monkeypox virus particles (pink and yellow) found within an infected cell, cultured in the laboratory.
NIH-NIAID/IMAGE POINT FR/BSIP/Universal Images Group via Getty Images
Yet another strain of the virus that causes mpox might be readily spreading from person to person, according to an analysis of the pathogen's genome. This development could further complicate efforts to halt the spread of the disease in Central Africa, which has seen a surge in infections over the past year. And it has left researchers scratching their heads over what is currently driving this surge.
The findings hint that the strain, called clade Ia, is spreading in a sustained fashion between people — possibly through sexual contact — in an outbreak in Kinshasa, the capital of the Democratic Republic of the Congo (DRC). Previously, the viral variant was known to transmit predominantly from animals to humans in Central Africa.
"We know that viruses evolve — we have seen it with Ebola, we have seen it with COVID and we expected to see it with mpox as well," says Placide Mbala, head of epidemiology and global health at the National Institute of Biomedical Research in Kinshasa, who co-led the analysis. "We don't know how far these adaptations can go, and we are gathering data to understand how this evolution is occurring."
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The preliminary results, which have not yet been peer-reviewed, were posted on 22 October to the genomic-epidemiology discussion forum Virological.
Mpox diversifiesThere are four known variants of the monkeypox virus: clades Ia, Ib, IIa and IIb (see 'Quick guide to the strains of monkeypox virus'). Historically, clade I viruses have appeared mostly in Central Africa, and clade II viruses have cropped up in West Africa.
This all changed in the mid-2010s, when a clade II strain sparked an outbreak in Nigeria. At the time, some researchers suggested that the variant might be capable of transmission through sexual contact. Their insights proved prescient: a similar clade II strain, called IIb, sparked a global outbreak of mpox in 2022 that has infected more than 90,000 people and continues today.
Meanwhile, clade I viruses have caused sporadic infections in people for more than 50 years — largely in rural regions of Central Africa. But in late 2023, researchers identified a rapidly growing outbreak in more densely populated, urban areas in eastern regions of the DRC that disproportionately affected sex workers, suggesting that this strain of the virus could, like IIb, spread readily between people.
Genomic sequencing confirmed that the variant causing this outbreak contained several key differences from other clade I viruses, leading researchers to name it Ib. This strain has been detected in the United Kingdom, Sweden, Thailand, India, Germany and six African countries that had never reported mpox infections before. The DRC has been hit particularly hard: the country has reported nearly 36,000 suspected infections and more than 1,000 deaths from mpox in 2024.
But now — about one year after researchers detected an outbreak of clade Ib in eastern DRC — clade Ia is worrying health officials, too. The strain has also been on the rise in western regions of the DRC and in Kinshasa. In particular, having both Ia and Ib circulating in the capital city threatens the 17 million people living there and raises the possibility of clade I spreading internationally, given that Kinshasa is a travel hub.
Quick guide to the strains of monkeypox virusClade Ia: a strain that has been spreading in Central Africa since the virus was first discovered to infect humans in 1970. Most infections have been in children, and it was known to mainly transmit from animal to human — until recently.
Clade Ib: the strain that has caused a surge of cases in Central Africa since its discovery in late 2023. Known to spread from person to person, including through sexual contact.
Clade IIa: the least-studied mpox strain. It has mainly spread in Guinea, Liberia and Côte d'Ivoire. Modes of transmission are not fully understood; there is no documented evidence of sexual transmission, but it is likely that all forms of close contact contribute to its spread.
Clade IIb: the strain responsible for the still-simmering 2022 global outbreak. Known to spread from person to person, including through sexual contact. Most affected population has been men who have sex with men.
Health officials have been using genomic-sequencing tools to track the outbreak. As part of the effort, Mbala and his colleagues sequenced virus samples from infections in Kinshasa. In samples of both the clade Ia and Ib virus, they found a specific pattern of single-letter genetic mutations indicative of the ongoing battle between the human immune system and the virus — a pattern that would be unlikely to appear unless there was sustained human-to-human spread.
However, the pattern did not show up in a report posted to a preprint server in August. In that study, a team sequenced clade Ia virus samples collected between 2018 and 2024. That the researchers didn't spot the pattern suggests that it might be a recent development. "We didn't pick up on strong signs of evolution" in the more rural and endemic regions of the DRC, says Jason Kindrachuk, a virologist at the University of Manitoba in Winnipeg, Canada, who collaborates with Mbala and co-authored the August preprint as well as the Virological one. "But in Kinshasa, it seems that there is something unique going on."
Clade Ia might also have the ability to spread through sexual contact: researchers reported the first probable case of sexually transmitted clade I mpox last year, and another such publication is forthcoming, Kindrachuk says.
Given that clade I has been circulating between animals and people in the DRC since 1970, Kindrachuk adds that it will be important to investigate why clade Ib suddenly emerged in 2023, and why Ia has caused a surge in the number of detected infections in the past two years. "Is it because we're better at surveillance, or because we're more conscious of mpox at the community level? Is it because people have been moving around more after the [COVID-19] pandemic, or because there's been a greater reliance on contact with wildlife?" he asks.
For now, plans to roll out the continent's first doses of mpox vaccines are unlikely to change in light of these findings, says Nicaise Ndembi, a virologist at the Africa Centres for Disease Control and Prevention in Addis Ababa. Health officials have already been allocating doses to regions that have a higher number of infections, regardless of the specific strain found in the area, he says.
This article is reproduced with permission and was first published on October 30, 2024.
Marburg Virus Kills 11 In Rwanda. What To Know About The Ebola-like Outbreak And Symptoms
Eleven people have died in Rwanda from the highly contagious Marburg virus, and 36 cases have been confirmed, the country's health ministry reported Tuesday, just days after the country declared an outbreak of the deadly hemorrhagic fever that has no authorized vaccine or treatment.
"Marburg is a rare disease," health minister Sabin Nsanzimana said Sunday. "We are intensifying contact tracing and testing to help stop the spread."
He said the source of the disease has not been determined yet.
Previous Marburg cases and outbreaks have been recorded in Tanzania, Equatorial Guinea, Angola, Congo, Kenya, South Africa, Uganda and Ghana, according to the World Health Organization.
Here's what else to know about the disease.
What causes Marburg virus?Like Ebola, the Marburg virus originates in fruit bats. It can spread between people through close contact with the bodily fluids of infected individuals or with surfaces, such as contaminated bed sheets, clothing, needles or medical equipment.
The World Health Organization notes that Marburg virus does not spread through the air.
The rare virus was first identified in 1967 after it caused simultaneous outbreaks of disease in laboratories in Marburg, Germany, and Belgrade, Serbia. Seven people died who were exposed to the virus while conducting research on monkeys.
Marburg virus symptomsAccording to the Centers for Disease Control and Prevention, symptoms of Marburg virus include:
"In later stages of the disease, bleeding from various sites such as the gums, nose and anus can occur. Patients can suffer shock, delirium and organ failure," WHO says.
Without treatment, Marburg can be fatal in up to 88% of people who fall ill with the disease. There are currently no approved vaccines or treatments specifically for this virus.
A person infected with the virus can take between three days and three weeks to show symptoms, Nsanzimana added.
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U.S. Death From Lassa Fever, An Ebola-like Virus, Is Reported In Iowa
A person from Iowa who recently returned to the United States from West Africa has died after contracting Lassa fever, a virus that can cause Ebola-like illness in some patients. State health officials reported the case on Monday.
"I want to assure Iowans that the risk of transmission is incredibly low in our state. We continue to investigate and monitor this situation and are implementing the necessary public health protocols," Robert Kruse, state medical director of the Iowa Department of Health and Human Services, said in a statement posted to the department's website.
The unnamed person was described as a middle-aged individual from eastern Iowa. The statement said the person had been cared for at University of Iowa Health Care. It did not indicate how long he or she had been in care or if the individual had sought care anywhere else before being admitted to the hospital.
That is important because while person-to-person spread of the Lassa virus is rare, transmission can occur in health care settings, especially if health workers don't realize they are dealing with a patient who has the disease and don't take adequate precautions. Testing conducted on Monday by the Nebraska Laboratory Response Network indicated the person had Lassa fever; confirmatory testing will be done by the Centers for Disease Control and Prevention.
No details were released about when the person developed symptoms or even when he or she returned to the United States. The CDC said in a statement, however, that the individual was not sick while traveling, so "the risk to fellow airline passengers is extremely low."
Although there have been previous Lassa fever cases imported to the United States, they are not common occurrences. The statement said there have been eight known imported cases, including the new one, in the past 55 years.
There was a case in May 2015, in a New Jersey resident who had traveled to Liberia and another in a New Jersey resident in 2004. Both those people died. Minnesota reported a case in 2014; that person recovered.
Africa CDC faults U.S. Government over Marburg-related travel advisory to RwandaLassa fever is endemic to a number of countries in West Africa, including Nigeria, Ghana, Guinea, Sierra Leone, and Liberia. In these countries, the virus causes several hundred thousand infections and about 5,000 deaths every year.
The main source of the virus is a rodent called the multimammate rat. People contract the virus either by handling or eating infected rodents, or as a result of having the rodents in their homes. Food or household items that have been contaminated with urine or feces from infected rodents can transmit the disease.
Though severe Lassa fever causes symptoms like those seen with Ebola infection, it does not trigger large chains of human cases, as can occur during Ebola outbreaks, said Armand Sprecher, a viral hemorrhagic fever expert who works for Doctors Without Borders.
"You don't see a lot of human-to-human transmission," Sprecher told STAT. "Most people get it from the source, the reservoir."
The World Health Organization says that about eight of 10 people who contract the virus have no or only mild symptoms, which include headache, fatigue, and low-grade fever.
In those that go on to develop severe illness, symptoms can include bleeding, difficulty breathing, vomiting, and shock, according to the CDC. The WHO suggests that about 15% of people who develop severe Lassa disease die from the condition.
The death rate can be much higher in some places, said Robert Garry, a professor at Tulane Medical School in New Orleans who has been studying Lassa fever for the past couple of decades. In Sierra Leone, where Garry has research projects, the fatality rate among severe cases can be as high as 70%, he said. Good supportive care — for instance replenishment of fluids — can increase the chances of survival, he said.
He agreed that most cases are people who are infected by an animal source, but said some person-to-person transmission can occur, especially in hospitals. "It happens in West Africa, even in places where they're very aware of the possibility [of Lassa cases]. So, yeah, if you were not expecting a disease like that to show up in your hospital, it could happen."
That said, Garry said he doesn't expect to see transmission here. "There's very little chance that this is going to spread beyond that hospital setting. But they have to do the case contacts [investigations] and all that to make sure."
Of the diseases that cause viral hemorrhagic fevers — things like Ebola and Marburg fever — Lassa is probably the one that is most commonly imported to non-endemic countries, Garry said.
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