對目前流行的M痘病毒分支的分析，為了解該病毒如何在2022年傳播至全球，以及它可能如何再次傳播至全球提供了線索。

Max Kozlov / 2026年1月8日 / 新聞 / 自然

隨著M痘病毒持續在非洲以及世界其他地區引發局部疫情，研究人員正爭分奪秒地了解該病毒如何在2022年傳播至全球，以及它可能如何再次傳播。

去年12月發表的一項研究發現，導致2022年疫情爆發的病毒株在小鼠感染後數週仍存在於其睪丸中，並造成組織損傷¹，凸顯了該病毒可能影響男性生育能力的可能性。目前尚未在人體進行相關研究。

該研究已發佈在預印本伺服器bioRxiv上，尚未經過同行評審。與此同時，病毒仍在不斷變異。去年12月，衛生官員首次報告了一種混合了兩種現有病毒類型（或分支）基因的M痘病毒株。雖然M痘病毒等病毒的變異是正常的，但它們傳播的機會越多，最終逃避疫苗和治療的可能性就越大。

喬治亞州亞特蘭大埃默里大學傳染病醫生博古瑪·泰坦吉表示，綜合這些數據顯示，科學家們對現有毒株「仍有許多需要了解」，更不用說新毒株了。她補充說，M痘病毒屬於痘病毒科，該科還包括天花病毒，「因此，我們不應低估它一旦在人群中紮根並不斷適應環境所造成的危害」。

M痘病毒正在變異

M痘病毒感染會導致皮膚出現疼痛的充滿液體的病灶、發燒，嚴重時甚至會導致死亡。已知有四種痘病毒分支：Ia、Ib、IIa 和 IIb（請參閱「M痘病毒分支快速指南」）。

該病毒自 20 世紀 70 年代以來一直感染人類。歷史上，它很少廣泛傳播，但這種情況在 2010 年代後期發生了改變，當時一種 II 分支毒株在奈及利亞引發了大規模疫情。類似的 IIb 分支株引發了 2022 年的全球疫情，導致超過 10 萬人感染。疫情至今仍在持續。

M痘病毒分支快速指南

Ia 分支：自 1970 年首次發現該病毒可感染人類以來，該分支一直在中非傳播。大多數感染者是兒童，直到最近幾年，傳播途徑主要為動物傳人。

Ib分支：自2023年末發現以來，該分支已在中非地區造成病例激增。已知其可經由包括性接觸在內的多種途徑在人與人之間傳播。

IIa分支：研究最少的M痘分支。主要傳播於幾內亞、賴比瑞亞和象牙海岸。其傳播途徑尚未完全明確；目前尚無性傳播的記錄證據，但所有形式的密切接觸都可能促進其傳播。

IIb分支：導致2022年全球疫情持續蔓延的分支。已知其可經由包括性接觸在內的多種途徑在人與人之間傳播。受影響最嚴重的族群是男男性行為者。

2025年，I分支M痘感染病例大幅增加，該分支歷史上曾在中非農村地區引發零星但致命的疫情。一種名為 Ib 的新型 I 型M痘病毒亞型於 2023 年底開始在人口密集的城市地區傳播，可能透過性接觸傳播。 Titanji 表示，這種傳播令科學家擔憂，因為 Ib 型M痘病毒的突然出現與 II 型M痘病毒在全球蔓延之前的傳播軌跡相似。

M痘病毒正在迅速傳播。以下是研究人員正在爭分奪秒解答的問題

過去幾年，研究人員一直在努力了解新的M痘病毒亞型 Ib 和 IIb 與其前身有何不同。感染M痘病毒的囓齒動物的數據為一種理論提供了證據，該理論認為這些亞型致死率較低，但更容易在人與人之間傳播，因為它們引起的疾病症狀較輕微²。

研究人員發現，感染 Ib型M痘病毒的老鼠比感染 Ia 型痘病毒的老鼠存活率更高，但它們傳播的傳染性病毒數量卻相同。此外，Ib 型感染可見皮膚病變的出現時間也顯著延遲。

泰坦吉表示，這些發現有助於解釋為什麼這種病毒「可能透過性傳播非常有效」，因為人們可能在出現症狀之前就已經在不知不覺中傳播了病毒。

生育問題？

另一組科學家研究了IIb分支的M痘病毒如何感染小鼠¹。他們發現，感染後至少三週內，囓齒動物的睪丸中仍存在高水平的感染性病毒，這顯示雄性生殖道可能充當了病毒的儲存庫，並有助於解釋為什麼病毒能夠如此有效地通過性接觸傳播。

研究人員發現，這種感染會導致組織損傷，進而導致精子生成障礙。

「我們原本預期會看到一些發炎或組織紊亂，但沒想到這種感染竟然會影響男性生育能力，這著實令人震驚」，該研究的共同作者、加拿大卡加利大學的新興病毒專家艾莉森·凱爾文 (Alyson Kelvin) 說道。

泰坦吉 (Titanji) 表示，這項研究尤其重要，因為幾乎所有已記錄的 IIb 分支感染病例都發生在男男性行為者身上，因此，觀察小鼠的研究結果是否適用於成年男性至關重要。

活性病毒

旨在了解這些新分支的動物實驗目前才剛開始產生數據，但這種病毒仍在人類體內不斷進化。去年 12 月，英國衛生官員報告稱，一名患者感染了一種前所未見的病毒株，這是 Ib 和 IIb 分支的混合體。

這是由一種稱為重組的過程所造成的。當一個人同時感染同一種病毒的多個病毒株時，就會發生重組，病毒之間可以交換大量的遺傳密碼。

M痘病毒以其強大的重組能力而聞名，但通常情況下，重組產生的病毒適應性較差，因此無法複製或繼續傳播。然而，根據12月7日發佈在Virological.org論壇上的一項基因組分析，這是科學家首次從兩個分支中分離出一種具有活性的混合M痘病毒。

Titanji表示，這種毒株未必比其前身更危險，但它顯示重組事件可以產生一種具有活性的病毒。她補充說，還需要進一步的研究來確定它是否更危險、更具傳染性，或是否能夠逃避疫苗的保護。同時，她表示，衛生官員應該保持警惕，密切監測這種病毒株是否會開始廣泛傳播，因為這將是一個不祥之兆。

凱爾文表示，綜合來看，12月的研究結果顯示，M痘病毒「充滿變數」。 「M痘病毒在過去三年中引發了兩起公共衛生緊急事件，因此我們需要密切關注它。」

doi: https://doi.org/10.1038/d41586-025-04154-6

參考文獻

1. Swan, C. L. 等人，bioRxiv 預印本 https://www.biorxiv.org/content/10.64898/2025.12.16.694558v1 (2025).

2. Kaiser, F. K. 等人，bioRxiv 預印本 https://www.biorxiv.org/content/10.64898/2025.12.09.693236v1 (2025).

Will mpox go global again? Research shows it’s evolving in curious ways

Analyses of mpox clades currently in circulation provide clues to how the virus managed to spread worldwide in 2022 — and how it might go global again.

Max Kozlov / 08 January 2026 / news / nature

As mpox continues to spark localized outbreaks in Africa and, on occasion, in other parts of the world, researchers are racing to understand how the virus managed to spread globally in 2022 — and how it might do so again.

A study published in December found that the strain that caused the 2022 outbreak persisted in the testes of mice for weeks after infection and caused tissue damage1, highlighting the possibility that the virus could impact male fertility. This has not yet been studied in people.

The study was posted on the preprint server bioRxiv and has not yet been peer reviewed. Meanwhile, the virus continues to evolve. In December, health officials reported a strain of the mpox virus that combines genetic elements of two existing types, or clades, for the first time. Although it is normal for viruses such as mpox to evolve, the more opportunities they are given to spread, the more likely they are to eventually evade protection from vaccines and treatments.

Taken together, these data show that scientists “still have a lot to learn” about existing strains, let alone new strains, says Boghuma Titanji, an infectious-disease physician at Emory University in Atlanta, Georgia. Mpox belongs to the poxvirus family, which also includes smallpox, “so we should not underestimate what it can do if it’s allowed to become firmly entrenched in human populations and continue to adapt”, she adds.

Mpox is evolving

Mpox infections can cause painful, fluid-filled lesions on the skin, fever and, in severe cases, death. There are four known clades of the mpox virus: clades Ia, Ib, IIa and IIb (see ‘Quick guide to the clades of mpox virus’).

The virus has been infecting humans since the 1970s. Historically, it rarely spread widely, but this all changed in the late-2010s, when a clade II strain caused a large outbreak in Nigeria. A similar clade IIb strain sparked the 2022 global outbreak, in which more than 100,000 people were infected. It is still ongoing.

Quick guide to the clades of mpox virus

Clade Ia: this clade has been spreading in Central Africa since the virus was first discovered to infect humans in 1970. Most infections have been in children, and, until the past few years, transmission occurred mainly from animals to humans.

Clade Ib: this clade has caused a surge of cases in Central Africa since its discovery in late 2023. It is known to spread from person to person, through means including sexual contact.

Clade IIa: the least-studied mpox clade. It has spread mainly 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 clade responsible for the still-simmering 2022 global outbreak. It is known to spread from person to person, through means including sexual contact. The most-affected population has been men who have sex with men.

In 2025, there was a large increase in infections with clade I mpox, which historically caused sporadic but deadly outbreaks in rural parts of Central Africa. A new subtype of clade I, called Ib, began spreading between people in dense urban areas in late 2023, possibly through sexual contact. This spread has worried scientists because the sudden emergence of clade Ib mpox mirrors the trajectory of clade II before it went global, Titanji says.

Mpox is spreading rapidly. Here are the questions researchers are racing to answer

Over the past couple of years, researchers have been racing to understand how the new mpox clades, Ib and IIb, differ from their predecessors. Data from rodents infected with mpox offer evidence to support a theory that these clades are less lethal but more adept at spreading from one person to another because they cause milder illness2.

Rats infected with clade Ib mpox had higher survival rates than those infected with clade Ia, yet they transmitted just as much infectious virus. And the onset of visible skin lesions was significantly delayed in clade Ib infections, the researchers found.

These findings help to explain why the virus “might be quite efficient in spreading through sex”, as people could be unknowingly transmitting the virus before they are symptomatic, Titanji says.

Fertility issues?

Another group of scientists studied how clade IIb mpox infects mice1. They found high levels of infectious virus in the rodents’ testes for at least three weeks after infection, suggesting that the male reproductive tract might act as a reservoir for the virus, and helping to explain why the virus is so efficiently transmitted through sexual contact.

The infection caused tissue damage that led to the loss of sperm production, the researchers found.

“We were expecting to see some inflammation or disorganization, but to see that potentially this infection was affecting male fertility was shocking,” says study co-author Alyson Kelvin, an emerging-virus specialist at the University of Calgary in Canada.

Read the paper: Genomics reveals zoonotic and sustained human mpox spread in West Africa

This study is particularly important because nearly all documented clade IIb infections have been in men who have sex with men, so it will be important to see whether the findings in mice translate to adult men, Titanji says.

Viable virus

Experiments with animals aimed at understanding these new clades are only now yielding data, but the virus is continuing to evolve in humans. In December, health officials in the United Kingdom reported that a person had been infected with a never-before-seen strain that is a mashup of clades Ib and IIb.

This resulted from a process known as recombination, which occurs when a person is infected with more than one strain of the same virus at the same time, allowing the viruses to swap large chunks of their genetic code.

Poxviruses are notorious for their ability to recombine, but this typically yields viruses that are less fit, so they do not replicate or continue spreading. This is the first time scientists have isolated a viable mashup mpox virus between the two clades, however, according to a genomic analysis posted on the discussion forum Virological.org on 7 December.

This strain is not necessarily more dangerous than its predecessors, Titanji says, but it shows that recombination events can produce a viable virus. Further studies will be necessary to determine whether it is more dangerous or transmissible, or if it evades the protection offered by vaccines, she adds. In the meantime, she says, health officials should be vigilant, and monitor whether this strain starts to take off, which would be an ominous sign.

Taken together, December’s findings show that mpox is a “bag of surprises”, Kelvin says. “Mpox viruses have caused two public-health emergencies in the past three years, so we need to be paying attention to it.”

doi: https://doi.org/10.1038/d41586-025-04154-6

References

1. Swan, C. L. et al. Preprint at bioRxiv https://www.biorxiv.org/content/10.64898/2025.12.16.694558v1 (2025).
2. Kaiser, F. K. et al. Preprint at bioRxiv https://www.biorxiv.org/content/10.64898/2025.12.09.693236v1 (2025).