New Study Shows Why Pneumococcal Infections Affect Humans

Presidential candidate Hillary Clinton’s health recently made the news when her doctor diagnosed her with pneumonia, sidelining her with a prolonged cough during an important stretch of the campaign. Nearly 900,000 people in the United States get pneumococcal pneumonia each year, resulting in about 400,000 hospitalizations annually. Researchers behind a new study have made an important discovery on how the bacterium behind these infections works to target humans, which may offer new insight on how to develop vaccines to fight it.

The new research comes out of the Karolinska Institutet and the Karolinska University Hospital in Stockholm, Sweden and was published in the journal Cell Host & Microbe. The study’s authors looked at intranasal infections with the Streptococcus pneumoniae (S. pneumoniae) bacterium to understand why pneumococcal disease is more prevalent in humans than in other animals, and found that the answer may be inside our nasal mucous.

About 5-7% of those in the United States infected with pneumococcal pneumonia lung infections die each year. According to the Centers for Disease Control and Prevention (CDC), the bacteria pneumococcus can cause several types of deadly infections other than pneumonia. While the bacteria can cause sinus infections and middle ear infections in children, it can also invade parts of the body typically free of germs and cause higher risk invasive infections such as meningitis in the brain and spinal cord and bacteremia in the blood. In 2013, nearly 3,700 deaths in the United States were the result of pneumococcal meningitis and bacteremia, most of those in adults.

S. pneumoniae appears to thrive in humans in ways it cannot in other mammals, though researchers in the past have not understood why. In their paper, the research team in Stockholm notes that human nasal mucous contains a distinct sugar molecule called sialic acid. Pneumococcal bacteria encounter terminally sialylated glycoconjugates and free sialic acid in human airways, and the sialic acid essentially serves as a carbon source for the bacteria. The bacteria use an enzyme to release this acid and then take it into the bacterial cells to convert into energy. This component of human nasal mucous essentially creates a breeding ground for S. pneumoniae bacteria, helping them grow, get stronger, and survive the human immune response.

To test this process, the research team in Stockholm studied the disease progression of S. pneumoniae in vivo in mice. They studied an experimental group of mice with a mutation to produce sialic acid against a control group of mice without the mutation, and found that the experimental group were more prone to develop severe pneumococcal infections than the control group. With this finding, the medical community has a new insight into the pathogenesis of pneumonia and other pneumococcal infections, and may help researchers develop new and better vaccines to protect humans from the diseases caused by the bacteria.

The World Health Organization considers pneumococcal diseases to be a major global public health problem, and stresses the importance of vaccines in controlling and preventing the spread of pneumococcal disease. There are currently two kinds of vaccines given to protect humans from pneumococcus—pneumococcal conjugate vaccine and pneumococcal polysaccharide vaccine. These vaccines are primarily given to young children and adults 65 years or older, as they are at greater risk for pneumococcal disease. Non-invasive infections such as ear and sinus infections are typically treated with antibiotics, though these infections have become increasingly drug resistant. For invasive pneumococcal infections, early diagnosis and treatment is key, so the CDC advises individuals to visit their doctor if they experience any of the common symptoms.