许多热带疾病由寄生物传播。但沙眼是由一种衣原体病菌引起的传染病，并有可能导致患者失明。

沙眼是通过人与人，尤其是儿童之间或母婴之间的眼鼻分泌物传播。飞蝇也可携带病菌。在缺少清洁水源和卫生设施的地方，沙眼细菌甚至可以由脏衣服或被褥传染。

但是，通过每年一次服用抗生素，可以大幅度减少感染沙眼。一个以此为目的的全球行动已经拉开序幕。

在美国国际发展署（U.S. Agency for International Development）、世界卫生组织（World Health Organization）以及一些基金会和合作伙伴——其中包括美国辉瑞制药公司（Pfizer）的支持下，每年有千百万人服用免费抗生素，包括辉瑞公司捐助的强力抗生素希舒美（Zithromax，普通名称阿奇霉素）。自1999年以来，辉瑞公司已捐赠（英文）7.6亿剂希舒美。

沙眼威胁着全球41个国家，其中大多数在非洲，也有一些在亚洲和拉丁美洲。全球因患沙眼而失明或视力受损的人有将近200万。

世界卫生组织最近宣布，加纳（Ghana）和尼泊尔（Nepal）已经消除了沙眼对公共卫生健康的威胁，分别成为世界上第六个和第七个实现了这一目标的国家。前几个国家是柬埔寨、老挝、墨西哥、摩洛哥和阿曼。有更多国家正在接近达到目标。

但是，原定在2020年以前根除沙眼威胁的目标不太可能实现。世卫组织驻刚果共和国布拉柴维尔（Brazzaville）的致力于消灭被忽视的热带疾病的特别项目办事处负责人、西班牙公共健康医务工作者玛丽亚·雷沃略·波罗（Maria Rebollo Polo）医生说，“我们显然落后于时间表。”

不过，这仍然不失为一个由美国资金和公司引路的政府与民间的成功合作。雷沃略说，“美国纳税人是对全球受忽视的热带疾病项目的最大投资者”。

美国国际发展署的罗布·亨利（Rob Henry）说，美国国际发展署每年拿出1亿美元，每位纳税人提供医药捐助26美元。

据世界卫生组织介绍，受到病菌感染的儿童和成人的眼睛可能会反复发炎，最后导致上眼睑内翻，摩擦眼球，形成疼痛结痂，最后造成无法逆转的失明。2016年，有25万人接受了矫正眼睑手术，8500万人得到了抗生素治疗。

发放抗生素成为一项通过国家卫生部门和社区卫生工作者开展的年度行动。雷沃略说，“这些药非常安全，可以由经过培训的志愿人员发放使用”。医疗工作队还强调必须保持面部清洁和养成其他卫生习惯。

雷沃略说，有些热带疾病可以被根除，但沙眼病菌会自然生发，因此总会有一些沙眼病例出现。世界卫生组织的标准是，如果儿童眼睑感染率在5%以下，成年人的沙眼患病率为千分之一，就可被视为消除了沙眼对公共健康的威胁。

辉瑞制药公司的抗生素也被用于治疗其他病菌感染。《新英格兰医学杂志》（New England Journal of Medicine）的一项研究发现，每年服用两次抗生素在尼日尔、坦桑尼亚和马拉维大幅度降低了各种因素导致的儿童死亡率（英文）。

另一家美国制药龙头公司默克（Merck）也为消灭热带疾病发挥了重大作用。默克公司在30年前开始捐赠它研制的抗寄生虫药Mectizan，用于防治河盲症和淋巴丝虫病。2017年默克公司提供了3.68亿份治疗剂。

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.

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.

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.