剛果民主共和國發生的一系列MPOX病例引發了人們對更大範圍疫情爆發的擔憂。馬克斯‧科茲洛夫 / 2024 年 4 月 23 日 / 新聞 / 自然 / 財團法人台灣紅絲帶基金會編譯
Mpox病毒顆粒（人工著色）。圖片來源：英國健康安全局/科學圖片庫
新數據顯示，猴痘病毒的一種強毒株已經能夠透過性接觸傳播。 這引起了研究人員的警惕，他們擔心 2022 年世界各地的 MPOX 疫情會再次爆發。
過去爆發的證據顯示，這種被稱為分支 I 的病毒株比引發 2022 年疫情分別的另一病毒株更具致命性。 數十年來，第I 型分支一直在中非引發小規模疫情，通常僅限於少數家庭內或社區的傳播。 去年之前從未曾有報導過透過性行為而獲得第 I 型分支病毒株造成的感染。
但從 2023 年底開始，一種似乎透過性接觸傳播的第 I 型病毒株在中非剛果民主共和國 (DRC) 衝突地區引發了一系列感染。 4 月 15 日發布的期刊預印本報告稱，有241 例疑似感染和 108 例確診感染與此波疫情有關，且因檢測能力有限，因此可能還有更多病例，有 近 30% 的確診感染者是性工作者。
除了挑戰之外，該地區還面臨人道危機，剛果民主共和國正在應對霍亂等其他疾病的嚴重蔓延。 加州大學洛杉磯分校的流行病學家 Anne Rimoin 自 2002 年以來一直致力於剛果民主共和國的 MPOX 疫情研究，她表示，這兩種情況意味著「疫情爆發升級到當前地區以外的地區存在巨大風險」。
被忽視的警訊
猴痘病毒會導致皮膚出現疼痛、充滿液體的病變，嚴重時會導致死亡。 （儘管該疾病在2022 年被重新命名為mpox，但該病毒仍被稱為猴痘病毒。）該病毒在包括剛果民主共和國在內的幾個非洲國家的野生動物中持續存在，偶爾也會傳染給人類。
首次通報的大規模人傳人疫情於2017 年在奈及利亞爆發，由一種名為 Clade II 的病毒株引起，該毒株的毒性低於 Clade I； 此次疫情造成確診病例200餘例，疑似病例500例。當時，研究人員警告說，Clade II 菌株可能已經適應了透過性接觸傳播。他們的警告沒有被理睬； 2022 年，一場部分由性接觸引發的全球疫情促使世界衛生組織 (WHO) 宣布為公共衛生緊急事件。 此次疫情仍在持續，由第 II 分支病毒株引起，已感染 95,000 多人，並導致 180 多人死亡。
儘管自 2022 年以來，全球 MPOX 感染人數有所減少，但剛果民主共和國的感染人數卻呈上升趨勢：去年，該國報告了超過 14,600 例疑似感染病例和超過 650 例死亡病例。 9月，剛果民主共和國南基伍省出現了新的疑似I型分支感染群。 這群人尤其令研究人員擔憂，因為許多感染者是性工作者，這顯示病毒已經適應了輕易地透過性接觸傳播。
位於亞的斯亞貝巴的非洲疾病管制與預防中心的病毒學家 Nicaise Ndembi 表示，這可能會導致更快速的人際傳播，而且潛在地可能僅有少數症狀。 「剛果民主共和國被其他九個國家包圍——我們在這裡玩火，」他說道。
衛生官員非常擔心，剛果民主共和國和 11 個週邊國家的代表於本月稍早舉行了會議，計畫應對措施並承諾加強病毒監測。 由於檢測能力有限，去年剛果民主共和國僅約 10% 的疑似 MPOX 病例接受了檢測。 恩登比說，衛生官員「無法全面地了解正在發生事情的情況」。
對導致這次疫情爆發的病毒進行基因分析，發現了突變，例如病毒基因組的大部分缺失，研究人員已證明這是病毒適應的跡象。 這使得該研究的作者為該省流行的病毒株起了一個新名稱：clade Ib。
更令人擔憂的是，南基伍省與盧安達和蒲隆地共和國接壤，該地區正在努力應對「衝突、流離失所、糧食不安全和提供充足人道主義援助方面的挑戰」，世界衛生組織去年警告說，這「可能成為Mpox進一步傳播的沃土」。
需要疫苗和治療
2022 年，許多富裕國家向感染MPOX的高危險群提供了天花疫苗，這種疫苗也能預防 MPOX。 但非洲國家的疫苗劑量很少，這些國家的疾病死亡人數歷來最高。
雖然剛果民主共和國正在考慮監管部門批准這些疫苗，世界衛生組織的 MPOX 技術負責人羅莎蒙德‧劉易斯 (Rosamund Lewis) 表示，美國已承諾向剛果民主共和國提供足以供 25,000 人接種劑量的疫苗，日本也承諾將提供疫苗。但剛果民主共和國的疫苗接種活動需要數十萬甚至數百萬劑疫苗才能為每個感染高風險的人接種，她說道。
目前尚不清楚這些疫苗能對mpox I分支提供多少保護，位於喬治亞州亞特蘭大的美國疾病管制與預防中心的痘病毒流行病學家麥科勒姆（ Andrea McCollum ）表示，來自動物研究的數據很有希望。 研究人員還在剛果民主共和國進行了 tecovirimat 的試驗，這是一種被認為對猴痘病毒有效的抗病毒藥物。 麥科勒姆說，預計明年會有結果。劉易斯說，世界衛生組織和美國疾病預防和控制中心幫助採購了設備，以便在剛果民主共和國，特別是農村地區更快速地診斷該疾病。 她補充說，非洲衛生官員的迅速動員給她帶來了希望，在 Ib 分支病毒株開始在其他地方傳播之前能夠控制疫情。
Monkeypox virus: dangerous strain gains ability to spread through sex, new data suggest
A cluster of mpox cases in the Democratic Republic of the Congo sparks worries of a wider outbreak.
Max Kozlov / 23 April 2024 / NEWS / Nature
Monkeypox virus particles (artificially coloured).Credit: UK Health Security Agency/Science Photo Library
A virulent strain of the monkeypox virus has gained the ability to spread through sexual contact, new data suggest. This has alarmed researchers, who fear a reprise of the worldwide mpox outbreak in 2022.
Evidence from past outbreaks indicates that this strain, called clade I, is more lethal than the separate strain that sparked the 2022 outbreak. Clade I has for decades caused small outbreaks, often limited to a few households or communities, in Central Africa. Sexually acquired clade I infections had not been reported before last year.
But starting in late 2023, a clade I strain that seems to spread through sexual contact has caused a cluster of infections in a conflict-ridden region of the Democratic Republic of the Congo (DRC), in Central Africa. A preprint1 posted on 15 April reports that 241 suspected and 108 confirmed infections are connected to this outbreak — and testing capacity is limited, so there are probably many more cases. Almost 30% of the confirmed infections were in sex workers.
Adding to the challenges, the region is facing a humanitarian crisis, and the DRC is contending with the aggressive spread of other diseases, such as cholera. The combination means there is a “substantial risk of outbreak escalation beyond the current area”, says Anne Rimoin, an epidemiologist at the University of California, Los Angeles, who has worked on mpox outbreaks in the DRC since 2002.
Unheeded warnings
The monkeypox virus can cause painful, fluid-filled lesions on the skin and, in severe cases, death. (Although the disease was renamed mpox in 2022, the virus is still called monkeypox virus.) The virus persists in wild animals in several African countries, including the DRC, and occasionally spills into people.
The first large reported outbreak with human-to-human transmission occurred in 2017 in Nigeria and was caused by a strain called Clade II, which is less virulent than Clade I. The outbreak caused more than 200 confirmed and 500 suspected cases. At the time, researchers cautioned that the Clade II strain might have adapted to spread through sexual contact.
Their warnings were not heeded; in 2022, a global outbreak driven in part by sexual contact prompted the World Health Organization (WHO) to declare it a public-health emergency. The outbreak, which is still ongoing, is caused by a clade II strain and has infected more than 95,000 people and killed more than 180.
Although mpox infections have waned globally since 2022, they have been trending upwards in the DRC: last year, the country reported more than 14,600 suspected infections and more than 650 deaths. In September, a new cluster of suspected clade I infections arose in the DRC’s South Kivu province. This cluster especially concerns researchers because many infections were in sex workers, suggesting that the virus has adapted to transmit readily through sexual contact.
This could lead to faster human-to-human spread, potentially with few symptoms, says Nicaise Ndembi, a virologist at the Africa Centres for Disease Control and Prevention, who is based in Addis Ababa. “The DRC is surrounded by nine other countries — we’re playing with fire here,” he says.
Health officials are so concerned that representatives of the DRC and 11 nearby countries met earlier this month to plan a response and to commit to stepping up virus surveillance. Only about 10% of the DRC’s suspected mpox cases last year were tested, owing to limited testing capacity. Health officials “don’t have a full picture of what’s going on”, Ndembi says.
Genetic analyses of the virus responsible for the outbreak uncovered mutations such as the absence of a large chunk of the virus’s genome, which researchers have shown is a sign of adaptation in the virus. This has led the study’s authors to give a new name to the strain circulating in the province: clade Ib.
Making matters more fraught, South Kivu borders Rwanda and Burundi and is grappling with “conflict, displacement, food insecurity and challenges in providing adequate humanitarian assistance”, which “might represent fertile ground for further spread of mpox”, the WHO warned last year.
Vaccines and treatment needed
In 2022, many wealthy countries offered vaccines against smallpox, which also protect against mpox, to individuals at high risk of contracting the disease. But few vaccine doses have reached African countries, where the disease’s toll has historically been highest.
While the DRC weighs regulatory approval for these vaccines, the United States has committed to providing the DRC with enough doses to inoculate 25,000 people, and Japan has said it will also provide vaccines, says Rosamund Lewis, technical lead for mpox at the WHO. But a vaccination drive in the DRC would require hundreds of thousands — if not millions — of doses to inoculate every individual at high risk of infection, she says.
It’s not clear how much protection these vaccines will provide against clade I mpox, but Andrea McCollum, a poxvirus epidemiologist at the US Centers for Disease Control and Prevention in Atlanta, Georgia, says that data from animal studies are promising. Researchers are also conducting a trial in the DRC of tecovirimat, an antiviral that is thought to be effective against the monkeypox virus. Results are expected in the next year, McCollum says.
The WHO and the CDC have helped to procure equipment that will allow for more rapid diagnosis of the disease in the DRC, especially in rural areas, Lewis says. She adds that the rapid mobilization of African health officials gives her hope that the outbreak can be controlled before the clade Ib strain starts spreading elsewhere.
doi: https://doi.org/10.1038/d41586-024-01167-5
References
- Vakaniaki, E. H. et al. Preprint at medRxiv https://doi.org/10.1101/2024.04.12.24305195 (2024).
Monzón, S. et al.Nature Commun.15, 3059 (2024).