Date Posted: 29-Apr-2005

Growing awareness of the threat of biological terrorism has spurred funding, initiatives and research into new drugs and vaccines for some of the potentially lethal diseases that could be spread by deliberate release.

In February, Cambridge Biostability, based in the UK, announced progress in developing a vaccine for botulism, a muscle-paralysing disease that occurs as a result of infection by the bacterium Clostridium botulinum following the ingestion of toxin-contaminated food or through an inadequately dressed wound. It is also technically possible to create an aerosol that could spread the bacteria through the air enabling the toxin - the most toxic known natural substance - to be inhaled, thereby causing rapid injury to large numbers of people. The estimated oral lethal dose is 70 mcg, the lethal inhalation dose is 0.70 mcg.

Previous examples of botulism being tried as a weapon include three aerosol-released toxin attempts from 1990 to 1995 by the Japanese Aum Shinrikyo cult. During the 1991 Gulf war, Iraqi forces loaded 19,000 litres of botulinum toxin onto short-range missiles.

Botulism vaccine in development

Botulism is currently treated by an anti-toxin antidote, which is only effective in saving lives and reducing the severity of symptoms if administered early in the course of the disease... a time when only ordinary, non-lethal food poisoning may be suspected. Botulism can take between 12 and 36 hours for symptoms to develop. The anti-toxin can prevent patients from deteriorating, but recovery, where possible, still takes weeks of supportive care and subsequent months of intensive physiotherapy.

The main problem in developing a vaccine against botulism poisoning is that seven different toxins cause botulism. Vaccines do exist, but they are not effective against all toxin types and it has not been possible to mix the seven vaccines into a single injection. Therefore, a vaccination programme involves multiple injections and booster shots. In the event of an attack a patient would possibly need to be given as many as 21 injections. Most vaccines are created by turning the specific poison into a toxoid (a weaker non-toxic version that triggers an immune response in the body). Each toxin has different isoelectric points that require different buffer systems for stability, so that the toxoids - the essential ingredients of the vaccine - cannot be mixed together without inactivating some components. Also, some of the toxins are inherently unstable in solution and require storage at low temperatures.

Cambridge BioStability’s work is based on developing completely stable and instantly injectable liquid vaccines. The new technology uses stabilised vaccines isolated in glass microspheres and suspended in an inert injectable liquid. This means that the components of different vaccines in the different microspheres cannot interact with each other. Each vaccine can be dried in the stabilising microspheres under its own optimal conditions and is only rehydrated in body water after injection. The final product of the research programme is intended as a complete vaccine against all seven serotypes - administered as a one-shot vaccine (in a single injection) against botulism, which requires no booster injections. Mass vaccination of the entire population would be feasible, in a similar programme as is carried out for tetanus.

The liquid stable technology to be used is based on the process of desiccation undergone by some plants and animals, which can remain in a desiccated state for long periods by reducing the water content of their bodily fluids. Water within the cells is replaced with a sugar solution, which thickens when water is excluded, to the point of vitrification. When rehydrated the organism regains normal functioning. In the new vaccines, sugar is hardened to form a non-crystalline glass. The vaccine is first spray-dried using the sugar syrup to form microscopic glass spheres. The dry vaccine is then suspended in an approved inert liquid, which can be injected into muscle where bodily fluids reactivate the vaccine.

In the event of an attack the vaccine would be readily available as it can be stockpiled in widely dispersed sites such as fire stations and other emergency points without the need for refrigeration. Final deployment of stable vaccines into dispersed stockpiles will therefore eliminate the current logistical problems of storage and delivery of unstable refrigerated vaccines.

Cambridge Biostability is to collaborate with a US company, Dynport Vaccine Company (DVC), of Maryland, which has the sole licence to provide new vaccines for the US forces and which has obtained funding from the US Biodefense Initiative to develop the botulism vaccine.

New anthrax vaccines

The US anthrax mail attacks, which claimed the lives of five people in 2001, and subsequent attempts at disseminating anthrax at postal facilities in the US have spurred many companies to try to develop more effective vaccines and new antidotes. In May 2004, early-stage trials of a new and potentially more effective anthrax vaccine were initiated on people in 12 US cities. Developed by the US company VaxGen and the US Army Medical Research Institute of Infectious Diseases (USAMRIID) at Fort Detrick, the vaccine is designed to last longer and have fewer side-effects than the existing vaccine, which was developed in the 1950s and is used to vaccinate military personnel or people who have contact with animals that harbour anthrax. However, it has a record of adverse effects and requires six injections over 18 months before it becomes fully effective and annual booster shots are also needed.

VaxGen's rPA102 vaccine is composed of a purified protein - recombinant protective antigen (rPA) - and an aluminium salt routinely used in many vaccines. rPA induces antibodies shown to neutralise anthrax toxins but cannot cause infection and requires no more than three doses. VaxGen has been awarded the first contract under Project BioShield, the US government initiative introduced in 2004 to stimulate research into treatments for bioterrorism-related diseases. Some 75 million doses of the rPA102 vaccine will be supplied within three years for civilian protection against inhalation anthrax, the most deadly form of the disease and the one most likely to be used in bioterrorism.

Another new anthrax vaccine is being manufactured at the Defence Science and Technology Laboratory (DSTL) at Porton Down, Wiltshire, UK for the UK Health Protection Agency. A two-shot vaccine that must be administered shortly after exposure, it has entered clinical trials that are being carried out in the US on 115 volunteers. Unlike the current vaccine, which requires the handling of live anthrax bacteria, the new vaccine is based on a purified anthrax protein. DSTL has developed the vaccine with a British biotechnology company, Avecia, which has been awarded a contract by the US government to manufacture an initial supply of three million doses with the possibility of Avecia providing a further 75 million doses. The ultimate aim is to have it licensed in Europe within five years.

The development of widely available new vaccines that could be easily administered is seen as a major deterrent to would-be bioterrorists. However, vaccines for anthrax, a non-infectious disease, - and botulism, a non-infectious form of poisoning, botulism - may be just the beginning of the offensive against the many other infectious diseases that could break out as a result of a deliberate release.

Plague vaccine

A new vaccine against bubonic plague, which killed millions in Europe in past centuries and could be a choice of weapon for bioterrorists, is under development at Porton Down. A team led by Prof Rick Titball recently carried out safety tests of the vaccine in humans. Having shown no side-effects, the vaccine has gone into larger-scale trials with a view to it being licensed in 2006. The vaccine is produced by a genetic engineering technique widely used in civilian microbiology laboratories and is based on two harmless antigens known as F1 and V on the surface of the plague bacterium, Y.pestis, which are capable of triggering an immune response against the disease.

Research began on a plague vaccine after the 1991 Gulf War, when it emerged that Iraq had been developing stocks of plague bacteria. A killed whole cell plague vaccine has been used in the past, but recent studies in animals have shown that this vaccine offers poor protection against pneumonic disease. A live attenuated vaccine is also available. While this vaccine is effective, it retains some virulence and in most countries is not considered to be suitable for use in humans. It is therefore reserved for use only in high-risk cases, such as those working in plague research.