THURSDAY, Sept. 22 (HealthDayNews) -- Researchers say they've decoded the genome of the bacterium that causes Legionnaire's disease and are hunting for genes that can explain its occasional virulence and provide targets for better treatments.
Legionnaire's disease is a respiratory infection that is so named because it was first described after a 1976 outbreak at a convention of former servicemen in Philadelphia. The U.S. Centers for Disease Control and Prevention estimates there are between 8,000 and 18,000 cases in the United States each year, and that it is fatal in from 5 percent to 30 percent of those cases. It can also occur in a milder form called Pontiac disease.
Having the complete genome of the bacterium could help explain why the infection is severe in some patients and mild in others, said James J. Russo, a research scientist at Columbia University's Genome Center, and lead author of a report on the discovery in the Sept. 24 issue of Science.
"At the moment, some genetic factors are known to be involved in the development of the infection," Russo said. "Knowing the full gene set of the bacterium and being able to distinguish between more severely pathogenic and less pathogenic strains could provide a fuller explanation and give targets for drugs or a vaccine."
Despite the relatively low number of cases of the disease, a vaccine might be useful because Legionnaire's is a constant danger for persons whose immune defenses are depressed, such as those with AIDS, patients awaiting an organ transplant or older hospitalized individuals, Russo said.
Erythromycin is the antibiotic of choice for treatment of the disease, with rifampin sometimes used in severe cases. For better treatments, "we want to know which of these genes is turned off or on in an infection," Russo said.
One unusual aspect of the genome is that it includes "a huge number of transporters and exporters of drugs" that can purge antibiotics from an infected cell, he said. "If we take a better look at some of these exporters, we can get an idea of which antibiotics might be most effective."
Medical applications are being pursued by Howard A. Shuman and Sergey Kalachikov, two other research scientists at the Columbia Genome Center. They are using a system devised by Shuman that allows them to monitor the workings of genes in infected cells.
"The most intriguing part is that these bacteria can infect macrophages, immune system cells that are designed to kill bacteria," Kalachikov said. "They somehow manage to survive inside these immune system cells."
Shuman's system enables the researchers to follow the course of infection of macrophages in cell cultures, Kalachikov said.
"We can look at the macrophages at different stages of the infectious cycle," he said. "In this way, we hope to isolate the crucial subset of genes that promotes the survival of the bacteria."
More information
Facts and figures about Legionnaire's disease are given by the U.S. Centers for Disease Control and Prevention. |
