許多熱帶疾病由寄生物傳播。但沙眼是由一種衣原體病菌引起的傳染病，並有可能導致患者失明。

沙眼是通過人與人，尤其是兒童之間或母嬰之間的眼鼻分泌物傳播。飛蠅也可攜帶病菌。在缺少清潔水源和衛生設施的地方，沙眼細菌甚至可以由臟衣服或被褥傳染。

但是，通過每年一次服用抗生素，可以大幅度減少感染沙眼。一個以此為目的的全球行動已經拉開序幕。

在美國國際發展署（U.S. Agency for International Development）、世界衛生組織（World Health Organization）以及一些基金會和合作夥伴——其中包括美國輝瑞製藥公司（Pfizer）的支持下，每年有千百萬人服用免費抗生素，包括輝瑞公司捐助的強力抗生素希舒美（Zithromax，普通名稱阿奇黴素）。自1999年以來，輝瑞公司已捐贈（英文）7.6億劑希舒美。

沙眼威脅著全球41個國家，其中大多數在非洲，也有一些在亞洲和拉丁美洲。全球因患沙眼而失明或視力受損的人有將近200萬。

世界衛生組織最近宣布，迦納（Ghana）和尼泊爾（Nepal）已經消除了沙眼對公共衛生健康的威脅，分別成為世界上第六個和第七個實現了這一目標的國家。前幾個國家是柬埔寨、寮國、墨西哥、摩洛哥和阿曼。有更多國家正在接近達到目標。

一個衛生醫療隊在迦納農村為患者作沙眼檢查。(USAID)

但是，原定在2020年以前根除沙眼威脅的目標不太可能實現。世衛組織駐剛果共和國布拉柴維爾（Brazzaville）的致力於消滅被忽視的熱帶疾病的特別項目辦事處負責人、西班牙公共健康醫務工作者瑪麗亞·雷沃略·波羅（Maria Rebollo Polo）醫生說，「我們顯然落後於時間表。」

不過，這仍然不失為一個由美國資金和公司引路的政府與民間的成功合作。雷沃略說，「美國納稅人是對全球受忽視的熱帶疾病項目的最大投資者」。

美國國際發展署的羅布·亨利（Rob Henry）說，美國國際發展署每年拿出1億美元，每位納稅人提供醫藥捐助26美元。

據世界衛生組織介紹，受到病菌感染的兒童和成人的眼睛可能會反覆發炎，最後導致上眼瞼內翻，摩擦眼球，形成疼痛結痂，最後造成無法逆轉的失明。2016年，有25萬人接受了矯正眼瞼手術，8500萬人得到了抗生素治療。

發放抗生素成為一項通過國家衛生部門和社區衛生工作者開展的年度行動。雷沃略說，「這些葯非常安全，可以由經過培訓的志願人員發放使用」。醫療工作隊還強調必須保持面部清潔和養成其他衛生習慣。

一位醫務工作者在尼泊爾納爾艾斯沃村（Nareswor）為患者作檢查。 (Nabin Baral/RTI International/USAID)

雷沃略說，有些熱帶疾病可以被根除，但沙眼病菌會自然生髮，因此總會有一些沙眼病例出現。世界衛生組織的標準是，如果兒童眼瞼感染率在5%以下，成年人的沙眼患病率為千分之一，就可被視為消除了沙眼對公共健康的威脅。

輝瑞製藥公司的抗生素也被用於治療其他病菌感染。《新英格蘭醫學雜誌》（New England Journal of Medicine）的一項研究發現，每年服用兩次抗生素在尼日、坦尚尼亞和馬拉維大幅度降低了各種因素導致的兒童死亡率（英文）。

另一家美國製藥龍頭公司默克（Merck）也為消滅熱帶疾病發揮了重大作用。默克公司在30年前開始捐贈它研製的抗寄生蟲葯Mectizan，用於防治河盲症和淋巴絲蟲病。2017年默克公司提供了3.68億份治療劑。

Progress in curbing trachoma, a blinding, infectious disease

Trained community health specialists are on the front lines of stopping trachoma. This specialist examines the eyes of a patient in Nepal"s Nareswor village. (Nabin Baral/RTI International/USAID)

Many tropical diseases are spread by parasites. Trachoma is different. It』s an infectious disease caused by a form of chlamydia bacteria that can blind its victims.

It spreads from person to person and especially child to child or mother to infant through discharges from the eye and nose. Flies also can carry it. The infection can even spread on soiled clothing or bedding where families dwell without adequate clean water and sanitation.

But it can be stopped or sharply curtailed with yearly administration of antibiotics. A global campaign is making headway in doing that.

Each year free antibiotics are given to ten of millions of people thanks to the U.S. Agency for International Development (USAID), the World Health Organization (WHO), foundations and other partners, including the American pharmaceutical company Pfizer, which donates its powerful antibiotic Zithromax (generic name azithromycin). Pfizer has donated 760 million doses since 1999.

Trachoma is a problem in 41 countries, mostly in Africa but also in Asia and Latin America. It』s blamed for the blindness or visual impairment of almost 2 million people.

Recently the WHO declared that Ghana and Nepal have eliminated trachoma as a public health problem, becoming the sixth and seven countries to do so. The others are Cambodia, Laos, Mexico, Morocco and Oman. More are closing in on that goal.

A medical team screens a patient for trachoma in a rural village in Ghana. (USAID)

The original goal of eliminating the threat by 2020 is unlikely. 「Clearly we are behind schedule,」 said Dr. Maria Rebollo Polo, who heads a WHO special project office in Brazzaville, Republic of Congo, working to eliminate neglected tropical diseases.

But it is still a triumph for public-private partnerships, with U.S. dollars and companies leading the way. 「The American taxpayer has been the biggest investor in neglected tropical disease programs in the world,」 said Rebollo, a public health physician from Spain.

USAID puts up $100 million a year and every taxpayer dollar leverages $26 in pharmaceutical donations, said the agency』s Rob Henry.

Some children and adults fight off repeated eye inflammations caused by exposure to the bacteria. But the cumulative effect of many such episodes can cause the upper eyelid to turn inward, scratch the eyeball, leave painful scarring and lead to irreversible blindness, the WHO says. In 2016 surgeons operated on a quarter-million people to correct the eyelid problem and 85 million were given antibiotics.

Working through national health ministries and community health workers, the antibiotics are administered in yearly campaigns. 「These drugs are so safe that trained volunteers can administer them,」 Rebollo said. The health teams emphasize the importance of facial cleanliness and other sanitary practices.

A health worker checks the eyes of a patient in in Nepal』s Nareswor village. (Nabin Baral/RTI International/USAID)

Some tropical diseases can be eradicated, but there will always be some trachoma cases because the bacteria occur naturally, Rebollo said. WHO considers trachoma』s threat to public health eliminated if fewer than 5 percent of children have inflamed eyelids and only one adult in 1,000 has the disease.

The Pfizer antibiotic is also used to treat other bacterial infections. A recent New England Journal of Medicine study found giving it twice a year sharply reduced child mortality from all causes in Niger, Tanzania and Malawi.

Another U.S. pharmaceutical giant, Merck, also plays a big role in the fight against tropical diseases. Merck began donating Mectizan, its drug for river blindness and lymphatic filariasis, 30 years ago. It provided 368 million treatments in 2017.

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