Hemorrhagic Fevers - Description

Hemorrhagic fevers are a growing concern throughout the world. They are not new diseases, but they are affecting much larger numbers of people every year.

The viruses that cause hemorrhagic fevers live in a great variety of animals, such as arthropods and mammals. Arthropods are insects, spiders, and other animals with hard external skeletons. These animals are called the natural reservoir for the disease. In many cases, these animals do not become ill when infected by the viruses. They do, however, carry the viruses in their body.

Viruses are transferred from these animals to humans by vectors. A vector is an organism that carries a disease from one animal to another. Mosquitoes are common vectors. When they bite an animal, they suck in some of its blood. If the animal is infected with a virus, the blood also contains that virus. When the vector bites a human, it leaves some of its saliva in the wound. Some of the virus may also be left behind. The human becomes infected with the virus.

Hemorrhagic fevers are often endemic. An endemic disease is one that affects many people in a given area over long periods of time. Dengue fever (pronounced DEN-gay) is an example. It affects about 100 million people annually. Most of these people live in southeast Asia. The area is very crowded. People often live in close contact with each other. The disease is transmitted easily from one person to another. In addition, the mosquito that carries dengue fever thrives in southeast Asia.

Disease reservoir:
A population of animals in which a virus lives without causing serious illness among the animals.
The widespread occurrence of a disease over a given area that lasts for an extended period of time.
Heavy or uncontrollable bleeding.
A drug used to treat viral infections.
An animal that transmits an infectious agent, such as a virus, from one animal to another animal.

Some hemorrhagic fevers are very rare. An example is Marburg hemorrhagic fever. It was first discovered in 1967. In the next thirty years after that, fewer than forty people were diagnosed with the disease.

The rate of fatalities (deaths) varies among the different forms of hemorrhagic fever. In the case of dengue fever, the death rate is about 1 to 5 percent. At the other extreme, ebola (pronounced ee-BO-la), an African hemorrhagic fever, kills 50 to 90 percent of those infected.

The onset (beginning) of hemorrhagic fevers may be sudden or gradual. They all have one characteristic in common, however. They all have the potential to result in hemorrhaging. The seriousness of the hemorrhaging also varies. In some cases, it involves no more than tiny pinpoints of bleeding under the skin. In other cases, the patient may bleed extensively from the mouth, nose, and other body openings.

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