猴痘是如何傳播的？科學家知道那些呢
長期接觸，尤其是與人的皮膚損傷接觸，正在成為主要的傳播途徑。
資料來源：Max Kozlov / 新聞 /《自然》/ 2022 年 8 月 11 日 / 財團法人台灣紅絲帶基金會編譯
猴痘病毒顆粒（紅色）感染細胞（藍色），如透射電子顯微鏡的彩色圖像所示。圖片來源：NIAID/NIH/SPL
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隨著全球猴痘病例持續飆升，研究人員正更多地了解這種疾病的傳播方式。根據一系列新的研究，早期關於病毒主要透過人與人之間反復的皮膚接觸傳播的預測在很大程度上得到了證實。
「當你把所有這些研究放在一起時，我們發現各地的臨床表現都相似——但也令人驚訝」，西班牙巴塞羅那 Germans Trias i Pujol 大學醫院的傳染病研究員 Oriol Mitjà 說，他與同儕合作發表於最近的剌胳針醫學期刊的研究顯示。這是因為傳播的症狀和模式看起來不像過去研究人員在西非和中非觀察到的那樣，猴痘病毒已經在西非和中非造成了數十年的孤立式、持續的爆發。
非洲猴痘：世界忽視的科學
自 5 月初以來，猴痘已蔓延至 90 多個國家，並導致 32,000 多人感染，其中近三分之一的病例報告在美國。該病毒的迅速傳播導致世界衛生組織於 7 月 23 日發布了最高級別的公共衛生警報； 8 月 4 日，美國總統喬·拜登亦仿效，宣布美國進入公共衛生緊急狀態。
儘管自 5 月以來已經有一些婦女和兒童被感染，但迄今為止，大多數病例都發生在男男間性行為者 (MSM) 中，尤其是那些有多重性伴侶或有匿名性行為的人。 Mitjà 說，該病毒可能一直在利用 MSM 社區中密集的性網絡來有效傳播。病毒繼續傳播得越多，它感染其他種人群的機會就越大，也包括野生動物——科學家們警告說，這可能會建立病毒貯存窩，從而反復感染人類。
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「充滿病毒」
當一個人感染猴痘時，他們會出現流感樣症狀、淋巴結腫大和皮膚上獨特的充滿液體的病變。儘管一些研究人員認為猴痘病毒可以像 SARS-CoV-2 那樣透過呼吸道飛沫或空氣中的顆粒傳播，但 Mitjà 和他的同事報告說，在診斷時收集的皮膚損傷樣本中的病毒 DNA 比從喉嚨所採的多得多。沒有參與這項研究的喬治亞州亞特蘭大埃默里大學傳染病醫生 Boghuma Titanji 說，這些傷口病變中似乎相對「充滿了病毒」。
宣布猴痘為全球緊急狀態：它會幫助控制疫情嗎？
包括 Mitjà 在內的幾項研究顯示，很少有人會從沒有與受感染者發生性接觸的家庭成員身上感染這種疾病。 Titanji 說，這一發現與有關病毒載量的數據相結合，顯示呼吸道飛沫和空氣中的顆粒物可能不是主要的傳播途徑。她補充說，如果得到進一步研究的證實，可能會質疑人們是否應該在整個感染期間進行隔離，這可能很困難，因為這種疾病似乎需要長達一個月的時間才能痊癒。
紐約市哥倫比亞大學的傳染病醫生傑西卡·賈斯曼 (Jessica Justman) 說，仍然缺少關於一個人的病毒載量如何隨時間變化的詳細數據。她說，儘管 Mitjà 和他的同事在感染早期從人們的喉嚨中收集的樣本中沒有檢測到太多的病毒 DNA，但如果他們稍後——甚至更早地收集它們——病毒水平可能會更高。該團隊現在正在一項後續研究中收集這些數據，這將使公共衛生官員能夠為感染者提供更好的隔離和治療指導。
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談論性
猴痘是否是絕對意義上的性傳播——在性交過程中透過血液、精液或其他體液從一個人傳播給另一個人——目前還不清楚。但幾項研究發現，猴痘病毒的 DNA 會在人被感染後的數週內存在於精液中。一項研究還在症狀出現六天后從單一個人的精液中分離出傳染性病毒。
猴痘疫苗接種開始——全球疫情能否得到遏制？
即使病毒可以透過性傳播，與簡單地與人進行皮膚接觸或吸入他們的呼吸道顆粒（也發生在性行為期間）相比，這種傳播方式的作用有多大仍不清楚。如果其他研究在精液中發現傳染性病毒，了解它可以在體液中持續多長的時間將很重要。伊波拉病毒等病毒在感染後可以在精液中持續存在數月甚至數年，這使得預防爆發的努力變得複雜。在研究人員了解更多信息之前，英國衛生安全局建議人們在感染後八週內應繼續使用保險套。
Mitjà 和他的同事注意到，在他們所檢查的人中，口腔和喉嚨有更多的病變與口交有關，而肛門內和周圍有更多的病變與接受型肛交的性行為有關。鑑於所有這些發現，Titanji 表示，公共衛生官員在指導中不要迴避談論性相關問題並應明確說明可採用的保護類型，這一點至關重要。
Justman 說，來自嚴格設計研究的更多數據來得不夠快。鑑於疫苗庫存不足、抗病毒治療無法獲得以及檢測不足的消息，一些研究人員已經擔心疫情業已超過了控制範圍。她說，與 COVID-19 相比，研究猴痘的資金和動力是有限的。她補充說：「我們沒有＜曲速行動＞，就像美國在大流行期間加快疫苗開發那樣。
doi：https://doi.org/10.1038/d41586-022-02178-w
How does monkeypox spread? What scientists know
Prolonged contact, especially with a person’s skin lesions, is emerging as the top transmission route.
•Max Kozlov / NEWS / 11 August 2022
Monkeypox virus particles (red) infect a cell (blue), as shown in this coloured image from a transmission electron microscope.Credit: NIAID/NIH/SPL
As global monkeypox cases continue to soar, researchers are learning more about how the disease is spreading. Early predictions that the virus transmits primarily through repeated skin-to-skin contact between people have largely borne out, according to a tranche of new studies.
“When you put all these studies together, we see that the clinical presentation everywhere is similar — but also surprising,” says Oriol Mitjà, an infectious-disease researcher at Germans Trias i Pujol University Hospital in Barcelona, Spain, who co-authored one of the recent studies in The Lancet. That’s because the symptoms and pattern of spread don’t look like what researchers had observed in West and Central Africa, where the monkeypox virus has caused isolated, persistent outbreaks for decades.
Monkeypox in Africa: the science the world ignored
Since early May, monkeypox has spread to more than 90 countries and led to more than 32,000 infections, with nearly one-third of cases reported in the United States. The virus’s quick spread led the World Health Organization to issue its highest-level public-health alert on 23 July; US President Joe Biden followed suit on 4 August by declaring a US public-health emergency.
Although some women and children have been infected since May, most cases have so far occurred in men who have sex with men (MSM), especially those with multiple sexual partners or who have anonymous sex. The virus has probably been taking advantage of dense sexual networks in the MSM community to spread efficiently, Mitjà says. The more the virus continues to spread, the more opportunities it will have to infect other populations, including wild animals — which scientists have warned might establish viral reservoirs that could infect humans repeatedly.
‘Teeming with virus’
When a person contracts monkeypox, they can develop flu-like symptoms, enlarged lymph nodes and distinctive fluid-filled lesions on their skin. Although some researchers have suggested that the monkeypox virus could spread through respiratory droplets or airborne particles, as SARS-CoV-2 does, Mitjà and his colleagues report that samples from skin lesions, collected at the time of diagnosis, contain much more viral DNA than do those from the throat. The lesions seem to be comparatively “teeming with virus”, says Boghuma Titanji, an infectious-disease physician at Emory University in Atlanta, Georgia, who was not involved with the study.
Monkeypox declared a global emergency: will it help contain the outbreaks?
Several studies, including Mitjà’s, show that few people contract the disease from an infected household member with whom they didn’t have sexual contact. This finding, paired with the data about viral load, suggests that respiratory droplets and airborne particles probably aren’t the primary transmission route, Titanji says. If corroborated by further research, it could call into question whether people should isolate for the entire duration of infection, which might be difficult because the illness seems to take up to a month to resolve, she adds.
Still missing are detailed data about how a person’s viral load changes over time, says Jessica Justman, an infectious-disease physician at Columbia University in New York City. Although Mitjà and his colleagues didn’t detect much viral DNA in samples that they collected from people’s throats early during infection, it’s possible that if they had collected them later — or even earlier — viral levels could have been higher, she says. Such data, which the team is now collecting in a follow-up study, would allow public-health officials to offer better isolation and treatment guidance to infected people.
Talking about sex
Whether monkeypox is sexually transmitted in absolute terms — passed from one person to another through blood, semen or other bodily fluids during sex — is still unclear. But several studies have found that DNA from the monkeypox virus is present in a person’s semen for weeks after they become infected. One study also isolated infectious virus from a single individual’s semen six days after their symptoms appeared.
Monkeypox vaccination begins — can the global outbreaks be contained?
Even if the virus can be sexually transmitted, it’s unclear how large of a role this mode of transmission has, compared with simply being in close, skin-to-skin contact with a person or inhaling their respiratory particles — which also occur during sex. If other studies find infectious virus in semen, understanding how long it can persist in that bodily fluid will be important. Viruses such as Ebola can persist in semen for months, if not years, after infection, which has complicated efforts to prevent outbreaks. Until researchers know more, the UK Health Security Agency recommends that people should continue to use condoms for eight weeks after infection.
Mitjà and his colleagues noticed that, in the people they examined, having a larger number of lesions in the mouth and throat was linked to oral sex, and having more lesions in and around the anus was linked to anal-receptive sex. Given all these findings, Titanji says it’s crucial that public-health officials don’t shy away from talking about sex in their guidance and are explicit about the types of protection available.
More data from rigorously designed studies can’t come fast enough, Justman says. Some researchers already worry that the outbreak is past the point of being contained, given news of inadequate vaccine stockpiles and inaccessible antiviral treatments, as well as insufficient testing. Funding and motivation to study monkeypox are limited compared with COVID-19, she says. “We don’t have an ‘Operation Warp Speed’,” like there was to rev up US vaccine development during the pandemic, she adds.
doi: https://doi.org/10.1038/d41586-022-02178-w
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