Swine Flu Increases Risk of a Person Developing Parkinson’s, Study in Mice Suggests

A strain of influenza commonly known as swine flu could trigger the development of Parkinson’s disease, according to a study in mice.

Mice infected with the H1N1 strain lost a lot of their brain neurons, even long after the virus struck. Neuron loss is a hallmark of Parkinson’s. Importantly, vaccination against the virus, or antiviral medications such as Tamiflu, prevented neuron loss, researchers said.

The research, “Synergistic effects of influenza and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can be eliminated by the use of influenza therapeutics: experimental evidence for multi-hit hypothesis,” appeared in the journal npj Parkinson’s Disease.

Dr. Richard J. Smeyne of St. Jude Children’s Research Hospital in Memphis led the study.

In addition to respiratory problems, flu can cause brain inflammation, which makes a person more susceptible to developing other health problems.

In a previous study, the researchers discovered that the H5N1 strain of influenza — the so-called bird flu — could kill neurons in an area of the brain called the substantia nigra pars compacta. The research showed that the strain traveled from the nerve cells of mice to their brains, where it caused inflammation that could lead to neuron death.

Scientists have linked sustained brain inflammation, such as that caused by a head injury, to the development of Parkinson’s.

Bird flu kills about 60 percent of the people it infects, so Smeyne’s team decided to study the association between a less lethal strain of flu and Parkinson’s. The H1N1 strain, or swine flu, also can trigger brain inflammation, although it does not infect neurons. The inflammation it generates stems from the pro-inflammatory molecules that immune cells unleash when they fight the virus.

Researchers first created a mouse model of Parkinson’s, then exposed the mice to the H1N1 virus.  The animals developed the kind of neuron loss seen in Parkinson’s disease. Meanwhile, healthy mice that the team used as controls did not develop neuron loss when exposed to the virus.

The team concluded that the virus made the mice that were susceptible to developing Parkinson’s even more susceptible.

Vaccinating mice against the virus, or giving them antiviral medications such as Tamiflu when they were exposed to it, made them less susceptible to developing neuron loss, the researchers said.

“This study has provided more evidence to support the idea that environmental factors, including influenza, may be involved” in the development of Parkinson’s, Smeyne said in a press release. The study further shows that “even mice who fully recover from the H1N1 influenza virus” are more susceptible to toxins that trigger Parkinson’s in a lab, he said.

The findings are particularly relevant because the H1N1 virus “belongs to the family of Type A influenzas, which we are exposed to on a yearly basis,” Smeyne said.

Although scientists need to confirm the results in humans, he said the results in mice provide  “good reason to investigate this relationship further in light of the simple and potentially powerful impact that seasonal flu vaccination could have on long-term brain health.”