June 12 (UPI) -- Scientists have identified a protein on the outside of the bacteria that causes syphilis and has shown promise in early research as a potential vaccine target against the sexually transmitted infection.
With rates of the STI rising worldwide, University of Connecticut researchers plan to use the protein discovery to test immunization of rabbits against syphilis and prove it could work as a vaccine. Their findings were published Tuesday in the journal mBio.
Syphilis is a sexually transmitted infection that can have serious complications -- including stillbirth and miscarriage, stroke, dementia and other neurological diseases -- when left untreated. The World Health Organization estimates there are 5.6 million new syphilis cases each year, and that number is growing in developing nations among women sex workers and their clients.
In the United States, after once being nearly eliminated, rates of the infection are increasing, especially among men who have sex with men, according to the Centers for Disease Control and Prevention.
Besides treating patients with syphilis, health agencies attempt to track down their recent sex partners, though people are often slow to share their sex history.
"Syphilis is the great imitator; it can look like hyper pigmentation, or other conditions," Dr. Juan C. Salazar, chairman of pediatrics at UConn Health and physician-in-chief at Connecticut Children's Medical Center, said in a press release.
About 15 years ago, Salazar began collaborating with CIDEIM, an infectious disease research institute in Cali, Colombia, where he was born. In Cali, about 7 percent of young, sexually active people have evidence of syphilis.
UConn Health microbiologists began analyzing the genetics of the syphilis bacteria from patients in Colombia and samples from collaborators in San Francisco and the Czech Republic. They noticed strains were from different places yet similar.
The team then went back through T. pallidum's genetic code for genes that code for proteins in the outer membrane and never change.
Although T. pallidum, which has only about 1,000 genes, was first identified in 1905, no one had identified proteins on its outer membrane until now.
"They're mutating to avoid the immune system," UConn Health microbiologists Justin Radolf said.
Because they suspected these mutating genes coded for the sought-after proteins, they tested them using a computer modeling program. They wanted to see if those proteins were barrel-shaped and used by the bacteria on its outer membrane. Indeed, many possessed these attributes.
The bacteria that causes the infection, T. pallidum, is also delicate and often breaks open and spills its guts, making it impossible to determine which proteins are supposed to be on its outside.
Syphilis is hard to study because it cannot be grown in a lab dish or in mice. Rabbits are the only animals susceptible to the infection, and their bodies clear it quickly, requiring them to be infected regularly in order to be useful.
The researchers made the proteins and tested to see if they folded into that barrel shape. Then, they made antibodies for the proteins and attached them to the exteriors of intact T. pallidum bacteria finding that the correct proteins were present.
"You want the best candidate outer membrane protein for a vaccine, the one that varies the least," UConn microbiologist Melissa Caimano said.
The next step, the researchers say, will be working with others at the University of North Carolina, and to enroll patients in China and Malawi, for a test to see if the syphilis they've studied is representative enough of the infection worldwide. And then they'll get to testing it with groups of people.