Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: TUESDAY, November 2, 1993 TAG: 9311020013
SECTION: NATIONAL/INTERNATIONAL PAGE: A-1 EDITION: METRO
SOURCE: Associated Press
DATELINE: ST. LOUIS LENGTH: Medium
The vaccine causes a harmless, temporary infection in the intestine that triggers antibodies against genetic components of sperm that have been spliced into the bacteria, said Roy Curtiss of Washington University in St. Louis.
Unaltered salmonella bacteria cause 4 million cases of food poisoning each year in the United States and are a major source of diarrhea worldwide, Curtiss said.
Curtiss is using the genetically engineered forms to produce vaccines against hepatitis B and malaria. Human trials of the hepatitis B vaccine have begun, and the Army plans to begin tests of the malaria vaccine this winter, Curtiss said.
Tests of the contraceptive vaccine have been done only in mice so far. But the results suggest that a single dose of the vaccine might prevent conception for several months or longer, and the effect would be reversible, Curtiss said.
"The idea now would be you don't get your booster, and within a year or so you can conceive again," he said at a meeting of the Council for the Advancement of Science Writing.
The method also might be used to produce a male version of the vaccine, intended to disarm sperm and make the man temporarily infertile, Curtiss said.
Paul Primakoff, a biologist at the University of Connecticut who is working on a more conventional injectable birth-control vaccine, said Curtiss's approach was promising, but that considerably more research is needed.
"We're trying something simpler, and if what we try doesn't work, maybe we would take an approach like his," Primakoff said.
Curtiss expressed some concern about what he said was the potential for abuse of the salmonella birth-control vaccine.
"You could put it in the milk or water and immunize everybody," he said. "You could think of government or some other entity misusing that," perhaps by secretly sterilizing an entire population.
Because of the temporary nature of the vaccine, however, "this is something someone might be able to undo," he said.
The salmonella vaccines might prove especially useful in developing countries and rural areas, because they don't require refrigeration and are cheaper to produce than the bottles that would contain them, Curtiss said.
Similar vaccines also are being tested to prevent the salmonella infections in chickens and pigs that can lead to food poisoning, he said.
The human vaccines are produced from salmonella bacteria that have been altered in two ways: Parts of the bacteria that cause disease have been removed, and genetic codes from sperm - or hepatitis B virus or malaria parasites - have been inserted.
These altered bacteria cause an infection lasting perhaps two weeks. The foreign genetic components trick the bacteria into producing proteins normally found only in sperm or hepatitis B virus or malaria parasites, as the case may be.
The body then mounts an immune response to whatever proteins have been inserted into the bacteria, bolstering immune defenses against an infection or against sperm.
A further advantage of the salmonella vaccines compared to other vaccines is that they lead to production of immune defenses in mucus. That provides enhanced protection in places where infectious organisms enter the body, such as the mouth and vagina, Curtiss said.
by CNB