Antibiotics Use Exacerbate Effects of Viral Diseases
Antibiotic consumption in humans continues to increase with greater than 800 courses of Abs prescribed annually per 1,000 people in outpatient populations in the United States alone. A new study from Washington University School of Medicine in St. Louis now suggests taking antibiotics increases susceptibility to subsequent viral infection, at least in mice.
Flaviviruses including West Nile (WNV), Dengue (DENV), and Zika (ZIKV) viruses account for approximately 400 million infections annually, with billions at risk and no specific therapy available. Now, the team of scientists have observed increased susceptibility of mice to severe West Nile (WNV), Dengue, and Zika virus infections after treatment with oral antibiotics (Abx) that depleted the gut microbiota.
Antibiotics kill off members of the normal bacterial community and allow some potentially harmful ones to overgrow. Since a healthy immune system depends on a healthy gut microbiome, they reasoned, antibiotics may be hobbling the immune system, leaving the body unprepared to fight off a subsequent viral infection.
“The immune system is activated differently if the gut does not have a healthy microbiome,” said senior author Michael S. Diamond, MD, PhD, the Herbert S. Gasser Professor of Medicine. “If someone is sick with a bacterial infection, they absolutely should take antibiotics. But it is important to remember that there may be collateral effects. You might be affecting your immune response to certain viral infections.
”In the course of their investigation, the team infected mice with the flaviviruses- all three viruses were more harmful to the mice who had received antibiotics prior to infection than to the mice that didn’t receive antibiotics, the researchers found.
The researchers then examined West Nile virus in greater detail- they gave mice either a placebo or a cocktail of four antibiotics — vancomycin, neomycin, ampicillin and metronidazole — for two weeks before infecting them with the virus. About 80 percent of the mice that received no antibiotics survived the infection, while only 20 percent of the antibiotic-treated mice did.
Different antibiotic treatments administered separately or in combinations led to different changes in the bacterial community in the mouse gut, and these changes correlated with vulnerability to the viral infection in the study. For example, treatment with ampicillin or vancomycin alone made the mice more likely to die from West Nile infection. Metronidazole had no effect alone, but it amplified the effect of ampicillin or vancomycin.
“Once you put a dent in a microbial community, unexpected things happen,” lead study author Larissa Thackray, an assistant professor of medicine also at Washington University School of Medicine in St. Louis, said in a statement. “Some groups of bacteria are depleted, and different species grow out. It’s likely that antibiotic use could increase susceptibility to any virus that is controlled by T-cell immunity, and that’s many of them.”
Diamond, Thackray, and others still need to confirm the connection between the immune system, antibiotics, and the gut microbiome in humans. For now, the study’s findings support the idea that overuse of antibiotics can have dangerous consequences.
“There’s are number of people who get sick, some more than others, for reasons we don’t understand,” said Diamond, who is also a professor of molecular microbiology, and of pathology and immunology. “If your immune system doesn’t get activated because your microbiome is perturbed by antibiotics or anything else – diet, other infections, underlying medical conditions – you may be at higher risk of severe viral disease.”
