23, February 2010
By Bhargavi Kerur
Madhumati SM, a 27–year–old HR executive, recently underwent an abortion, fearing that the foetus might have been affected by Salmonella bacteria that caused her to be unwell with a typhoid fever in the early stages of her pregnancy. There were no vaccines that would protect the foetus from the bacteria, and abortion was seen as the best recourse.
That state of affairs is set to change. Scientists at the Indian Institute of Science (IISc) are developing the world’s first vaccine against Salmonella bacteria, the cause of typhoid (Salmonella typhi). The vaccine would not only protect the unborn child, it could also immunise the general population against bio–terrorism. Salmonella typhi has been listed by the World Health Organisation (WHO) as the third most deadly weapon of bioterrorism.
Researchers Dipshikha Chakravortty, Vidya Devi Negi, Arvindhan G and Nagarajan of the centre for infectious disease research at the department of microbiology and cell biology at the IISc published a research paper in a peer–reviewed science journal this month, after conducting research on the vaccine by experimenting on mice for five years.
“The immunity of pregnant women is weak, and they are highly susceptible to all kinds of infection. One of the deadlier ones is the Salmonella bacteria, which causes typhoid that induces abortion when the bacteria infect the foetus, which may be ejected in a dead form. If delivered, the infected baby may suffer brain damage. The existing vaccines for the bacteria are harsh, and not able to protect the unborn baby,” said Chakravortty.
The researchers came across literature about Salmonella–induced abortion in cattle. Cases were also reported of women losing their unborn babies as the disease proved highly infectious. “This was when we hit upon the idea of doing research to design a safe vaccine,” Chakravortty said.
Chakravortty and her team used mice for the experiments. About 25 mice, about five to six weeks old, were administered the DV–STM–07 vaccine strain, which was followed by two booster doses on days seven and 14 after the initial dose. The research team also observed mice which were not vaccinated, for purposes of comparison.
“The net result of vaccination of the mice was protection of the pregnant mice against the disease. The vaccine strain, DV–STM–07, was able to achieve protective immunity without triggering abortion because of its high degree of attenuation and also its ability to not induce inflammation,” the study said. The vaccination was able to reduce the bacterial load significantly in mice that were challenged with Salmonella.
There are two other vaccines available to treat typhoid fever. The effect of those does not last long, and it has to be injected repeatedly, in high doses. “The harsh medicines induce harmful side–effects in pregnant women,” said Chakravortty.