Microbe that lives in salt shows promise for salmonella vaccine
University of Maryland researcher says platform has potential to help variety of diseases, especially in poor countries
Shiladitya Dassarma, professor of microbiology and immunology at the University of Maryland School of Medicine, is developing salt crystals containing microbes that can be used as a cheap and self-stable carrier of vaccines for diseases such as salmonella or typhoid. (Kenneth K. Lam, Baltimore Sun / June 1, 2012)
It's a bit more complicated than ordinary table salt, though the crystals have the same origins. The salt forms around an ancient microbe that has been genetically manipulated to act as a vaccine for salmonella, responsible for hundreds of thousands of deaths a year globally.
Discovered decades ago and the subject of intense research by many scientists, the microbe, called Haloarchaea, turns out to be such a good platform for vaccines that it could be employed against a variety of afflictions in poor and rich countries alike, said Shiladitya DasSarma, professor of microbiology and immunology in Maryland's School of Medicine.
"We have a designer vaccine system which can be used for many different diseases," DasSarma said. "Salmonella is a very serious problem affecting kids. If we give them a vaccine, we eliminate the problem because they never get sick."
DasSarma targeted salmonella after receiving a $100,000 grant from the Bill & Melinda Gates Foundation for the research. Eradicating infectious disease in poor countries is one of the foundation's primary goals.
Researchers still need to test the vaccine and determine the appropriate dosage, said DasSarma and his wife, Priya, manager of the lab inside Maryland's Institute for Marine and Environmental Technology where they are leading the studies. In the end, the salt vaccine will likely be a pill to be swallowed rather than crystals to be shaken on food.
The vaccine would be the culmination of years of work by DasSarma that began in graduate school in Massachusetts on Haloarchaea, which occurs naturally in very salty water and is what gives the Great Salt Lake its pink hue.
The labor has been personal for DasSarma. His father almost died when he was a young child in India of salmonella-caused typhoid disease. (The salmonella that causes typhoid is a different strain from the one that causes intestinal problems in the United States.) As the father of two, he also wanted to pick off a disease that sickens so many young people.
If the vaccine proves safe and effective, it could solve one of the biggest problems of global vaccine distribution, because salt doesn't need refrigeration, as most vaccines do. The vaccine would also be cheap to make, easy to store and safe because Haloarchaea doesn't cause any diseases itself.
The vaccine could go a long way in stamping out the form of salmonella that causes typhoid fever, a major contributor to infectious-disease deaths in poor countries, said Dr. Robert Black, chairman of the Department of International Health at the Johns Hopkins' Bloomberg School of Public Health.
Black's latest research shows that 64 percent of deaths among children under 5 globally in 2010 were from infectious causes. And there is no effective vaccine to prevent typhoid caused by salmonella in children younger than 2.
There were about 27 million typhoid cases in 2010 among adults and children worldwide, with at least 1 percent of cases ending in death when antibiotics weren't accessible or were ineffective, he said.
"Typhoid fever is quite a substantial problem, and I think a vaccine approach would be very wise," Black said. "A vaccine that does not require refrigeration and is taken orally would be quite attractive."
Typhoid is seen in every part of the world, Black said, but far more so in African and Asian countries where sanitation is a problem. And a vaccine will be needed for typhoid and other infectious diseases until environmental advances can make food and water safe, Black said.
Haloarchaea works as a delivery device for the vaccine because its properties naturally promote the same immune response of vaccines, DasSarma said.
To make the vaccine, DasSarma had to find the right spot among the 2,500 genes that make up the Haloarchaea genome and splice in salmonella protein antigens.
The antigens are placed on the surface of gas bubbles inside the Haloarchaea, and then the bubbles or whole microbes are enveloped in salt crystals. People swallow the salt for inoculation.
Scientists expect to be able to swap in other antigens to make new vaccines with the salt.
That potential innovation attracted the grant from the Grand Challenges Explorations initiative of the Gates Foundation.