Wednesday, December 7, 2011

Ebola vaccine

Ebola vaccine

Ebola vaccine, New vaccine targets Ebola virus. Scientists have developed a vaccine they say could protect against a deadly form of the Ebola virus. A test of the vaccine found that it protected 80 percent of those with the virus. Researchers say the next step is to test it on a strain of Ebola closer to the one that infects humans.

SYDNEY: Ebola, a viral disease that kills as many as 90% of infected humans, may be one step closer to a cure.

Researchers at government institutions in the U.S. have created a vaccine that successfully immunises monkeys against the two most lethal strains of the disease, and have found that it also protects against a newer strain not represented in the vaccine.

There are presently five known strains of Ebola. The deadly disease was discovered in 1976, and the newest strain in 2007.

Deadly pathogen

Since its discovery, Ebola has killed about 1,200 reported victims, according to the World Heath Organisation. There is currently no treatment or cure for the Ebola virus.

“An ideal Ebola vaccine would stimulate broad immunity so that we wouldn’t have to scramble to create entirely new vaccines whenever new virus species are identified,” said Nancy Sullivan of the U.S. National Institute of Allergy and Infectious Disease (NIAID), lead researcher of the study.

Incubation of the Ebola virus in humans can take between two and 21 days. Death usually follows within two weeks of the first symptoms of Ebola Hemorrhagic Fever (EHF) - which include vomiting, external bleeding and diarrhoea- and is generally the result of massive blood loss.

Previous vaccines

The primary mode of person-to-person transmission of Ebola is through contact with infected blood.

Previous vaccines have been discovered for Ebola, but none that prevent against multiple strains, or show promise to prevent against emerging strains.

Ebola also affects non-human primates such as gorillas, chimpanzees and monkeys, some species of forest antelope and even porcupines. According to the WHO, humans can contract the disease through contact with infected host animals.

However these animals are not thought to be the source of the disease, and the source is still highly contested. Some bats experimentally infected with Ebola have shown resistance, raising speculation that they may “play a role in maintaining the virus,” according to the WHO’s website.

No symptoms

Four cynomolgus macaques, monkeys whose symptoms of Ebola are similar to humans, were vaccinated with a prime dose followed by a boost, one year later.

Four unvaccinated macaques were exposed to the newest strain of Ebola, not included in the vaccine, and three of them died. All of the four vaccinated animals showed no symptoms of Ebola following exposure to the newest strain.

The prime contained a piece of genetic material that coded for surface proteins of both the Sudan (50% survival rate in humans) and Zaire forms (10% survival rate in humans) of Ebola virus. The boost contained a weakened cold virus that delivered the surface protein of the Zaire virus.

The prime and the boost strategy create immunity through the stimulation of T-cells, which create a strong immune response in the body.

Immunity against several species

Because the vaccine strategy does not rely on antibodies, which can only target exact genetic matches and thus only one species of the virus, the vaccine is able to provide immunity against several species of the Ebola virus.

T-cells, on the other hand, can target viruses that share only small amounts of genetic material, and so, the vaccine may even hold promise in the defence against yet-unknown species of the virus.

“The vaccine tested to provide cross protective immunity Is a strategy that generates high magnitude immune responses,” said Sullivan.

These findings provide hopeful insight for an effective and broad-reaching Ebola vaccine for human use.

“This finding will guide future vaccine design and may open an avenue for developing a single vaccine that works against both known and emerging Ebola virus species,” said NIAID director Anthony S. Fauci, in a press release.

Although this study represents an important first step in developing a human vaccine, this may still be many years in the future. All Ebola vaccines must be tested in formal human clinical trials to determine the safety, efficacy and proper dosage for humans
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