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East Coast fever kills hundreds of thousands of cattle in eastern and central Africa every year. The animals become infected when they get bitten by ticks carrying the parasite that causes the disease. A parasite is an organism that feeds on other organisms.

Donald Knowles directs the animal disease research unit in the Agricultural Research Service, part of the United States Department of Agriculture. The service is working with the International Livestock Research Institute in Kenya to find better ways to prevent parasitic diseases in cattle. Dr. Knowles is also a professor at Washington State University.

He points out that East Coast fever is not a contagious disease, so animals cannot give it to each other.

DONALD KNOWLES: "You need a tick to transmit from one infected cow to the other. They won't transmit just by standing next to each other. You need a tick to move it between them."

Farmers in parts of Africa use a vaccination method against East Coast fever known as infect and treat. First they infect animals with live parasites. Then they treat them with drugs to help them recover.

That way, explains Dr. Knowles, the animal becomes immunized or vaccinated against a full case of the deadly fever. But there are problems with this method of vaccination. Uninfected ticks that bite the vaccinated animal can still get infected and spread the parasite to other animals.

DONALD KNOWLES: "Once a cow is infected with this parasite, all the data indicates that the cow stays infected for life. And the consequences of that, the big deal about that is, that means that cow, even a cow that has been vaccinated, now it's protected against the disease, but it can still transmit. See it's infected for life. And so that animal is still a source of transmission."

And that is not the only problem with this method of vaccination.

DONALD KNOWLES: "One of the things in using live vaccines is that they usually require cold storage. And that adds to the cost of it, and also adds to the difficulty of using it in places like Africa."

For more than four years, American and Kenyan scientists have studied diseases carried by ticks. The scientists in the United States centered their work on the parasite that causes Texas cattle fever. This fever is common to the Americas.

This year, the scientists began a new study in Africa. The study is aimed at developing a new vaccine for the East Coast fever parasite. Dr. Knowles says their goal is a vaccine that does not require infecting and treating animals or the need for cold storage.

内容解析：

1. DONALD KNOWLES: "Once a cow is infected with this parasite, all the data indicates that the cow stays infected for life. And the consequences of that, the big deal about that is, that means that cow, even a cow that has been vaccinated, now it's protected against the disease, but it can still transmit. See it's infected for life. And so that animal is still a source of transmission."

protect against 使免受，保护

The plants should be protected from the cold.

应该保护这些植物使之不受冻。

Such guards also protect against fraying by roe deer.

这种保护措施还可防止獐鹿摩擦损伤。

2. This year, the scientists began a new study in Africa. The study is aimed at developing a new vaccine for the East Coast fever parasite. Dr. Knowles says their goal is a vaccine that does not require infecting and treating animals or the need for cold storage.

aim at以...为目的

What are you aiming at?

你的用意何在?

译文：

每年，非洲东中部数十万牲畜死于海岸热，动物一旦被携带致病寄生虫的壁虱叮咬，就会感染此病。寄生虫是以其他生物为食的生物。

Donald Knowles是农业服务研究院动物疾病研究所的主任，该研究院隶属美国农业部，目前正与肯尼亚国际家畜研究所合作，寻找预防牲畜感染寄生病的更好办法。Knowles博士也是华盛顿州立大学的教授。

他说，海岸热不是一种感染病，无法在动物间传染。

Donald Knowles：“疾病从一个动物传染到另一个动物需要有壁虱，动物贴近站立是不会传染的，必须有壁虱来传递疾病。”

一些非洲农场主使用一种叫“感染和治疗”的预防法来对付海岸热，先是用活寄生虫感染动物，再用药物帮助他们康复。

Knowles博士解释说，这种方法可使动物对各种致命发热都有免疫力，不过这种方法也有问题，未受感染的壁虱一旦叮咬了接种动物，仍能将寄生虫传给其他动物。

Donald Knowles：“一旦牛感染了这种寄生虫，所有数据显示，这头牛将终生受感染。所以最大的问题是，甚至是接过种的牛，能够预防这种疾病，但仍能传播疾病，而且终生受感染，因此它仍是感染源。”

这还不是这种免疫法的唯一问题。

Donald Knowles：“使用活性疫苗的问题之一就是，需要有冷藏设备，这就增加了成本，对于非洲这样的地区来说，就增加了使用的难度。”

四年多来，美国和肯尼亚科学家一直在研究壁虱携带的疾病，美国科学家将研究重点放在引发德州牛发热的寄生虫上，这种热病在美国很常见。

今年，科学家在非洲开始一项新研究，目的是开发一种预防海岸热寄生虫的疫苗，Knowles博士称，他们的目标是研制出一种不需要先感染再治疗、也不需要冷藏的疫苗。