Causes
Otitis media is most commonly caused by infection with viral, bacterial, or fungal pathogens. The most common bacterial pathogen is Streptococcus pneumoniae. Others include Pseudomonas aeruginosa, nontypeable Haemophilus influenzae, and Moraxella catarrhalis. Among older adolescents and young adults, the most common cause of ear infections is Haemophilus influenzae. Viruses such as respiratory syncytial virus (RSV) and those that cause the common cold may also result in otitis media by damaging the normal defenses of the epithelial cells in the upper respiratory tract.
A major risk factor for developing otitis media is Eustachian tube dysfunction, which leads to the ineffective clearing of bacteria from the middle ear.
The bacterial infections are caused by Trimeric Autotransporter Adhesins (TAA). The UspA1 protein domain is a TAA found in the bacteria Moraxella catarrhalis which causes middle ear infections in humans. TAAs are virulence factors or in other words, an infective agent that infects the host cell by attaching to them and secreting the virulence factor by a secretion pathway.
The role of the anti-H. influenzae vaccine that children are regularly given is to prevent invasive disease such as meningitis and pneumonia. This vaccine is active only against strains of serotype b, which has been found to cause meningitis and pneumonia in children under five years, with children between 4 and 18 months the most susceptible. Isolates of serotype b rarely cause otitis media.
Susceptibility is heritable, though the specific genetic markers are still under investigation. Casselbrant et al. found in 2009 that the "best-supported linkage regions may contain susceptibility genes that influence the risk for recurrent/persistent OM. Plausible candidates in 17q12 include AP2B1, CCL5, and a cluster of other CCL genes, and in 10q22.3, SFTPA2."
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