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Last Updated: Monday, 27 June, 2005, 23:04 GMT 00:04 UK
Lassa fever vaccine shows promise
Lassa virus particles
Lassa virus can cause deafness
Scientists have developed a promising vaccine for the potentially lethal disease Lassa fever.

A joint US and Canadian team found a single jab was enough to protect macaque monkeys against a potentially deadly dose.

Lassa fever is endemic in West Africa, where hundreds of thousands of people are infected each year. Isolated cases have been seen in Europe and the US.

Details are published in the journal PLoS Medicine.

Lassa causes several thousand deaths in Africa every year
Dr Thomas Geisbert

The virus that causes Lassa fever is related to others which result in haemorrhagic fever, such as Ebola and Marburg.

Eight out of 10 people infected with the virus develop either mild symptoms, or no symptoms at all.

However, about 20% of cases have severe illness, and up to 2% of people die.

Death rates are particularly high for women in the final months of pregnancy, and for the babies they are carrying.

The most common complication of Lassa fever is deafness.

The virus is transmitted to humans from rodents that harbour the virus.

As rodents are ubiquitous in the endemic areas, the only realistic hope for control of the disease is a vaccine.

Lassa vaccine initiatives have suffered from a lack of funding in the past.

But bioterrorism and recent importation of the disease to the US and Europe have brought new resources to Lassa virus science.

Key protein

The new vaccine has been developed by a team from the US Army Medical Research Institute for Infectious Diseases and the Public Health Agency of Canada.

It contains a protein produced by the Lass virus.

This is wrapped up in a different type of virus which has been rendered harmless.

Once injected into the body, the presence of the Lassa protein stimulates a response from the immune system.

Four macaques given the vaccine were protected against a dose of the virus which was big enough to kill two unvaccinated animals.

The researchers said larger studies were needed to assess whether the vaccine is safe for humans, and for how long it works.

Another crucial question will be how quickly vaccinated individuals acquire protection, and thus whether the vaccine would be suitable for creating a ring of vaccination around an outbreak zone.

Lead researcher Dr Thomas Geisbert told the BBC News website no previous attempts at developing a Lassa vaccine had succeeded in completely protecting non-human primates.

He said: "Lassa causes several thousand deaths in Africa every year - more than Ebola and Marburg, which get a lot more press."

Dr Diana Lockwood, an expert in tropical medicine at the London School of Hygiene and Tropical Medicine, said: "It looks like a very effective and promising vaccine that uses a neat technology."

Dr Lockwood said a Lassa fever posed a "very significant" public health burden in West Africa, where as many as half of all people admitted to hospital showed signs of having been exposed to the virus.


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