November 29-30, 2000
Ramada Inn
1775 Rockville Pike
Rockville, MD
Background
Otitis media is the most common cause for visits by children to physicians for acute illness, is the most common reason that antibiotics are prescribed to children, is the most common reason that children undergo surgery, and costs several billion dollars annually in the United States. Hearing loss that accompanies otitis media with effusion has been associated with delays in behavioral, educational, and language development. Current options for treatment, which rely heavily on the use of oral antibiotics, are being seriously hampered by the emergence of antibiotic-resistant organisms. Therefore, alternative strategies to deal with the problem of otitis media are needed urgently.
As a first step to address this urgent need for alternative approaches to the treatment of otitis media (OM), the NIDCD sponsored a workshop, entitled "Otitis Media: New Approaches for Analysis, Treatment, and Prevention," in November of 2000. Following a day of presentations, the 14 experts participating in the workshop made a series of recommendations for future areas of OM research, which are described below.
Discussion and Recommendations
The basic pathogenesis of OM often begins with viral infection of the upper respiratory tract. This viral infection elicits responses from the host that rapidly change the microenvironment of the upper respiratory tract, Eustachian tube, and middle ear. These micro-environmental changes result in bacteria of the nasopharynx invading and actively multiplying in the middle ear. Importantly, the bacterial phenotype is significantly altered in response to the inherent differences between the nasopharynx and the middle ear space. The host responds to the presence of dividing bacteria by releasing numerous extra- and intra-cellular signaling molecules. This complex series of events drives the pathogenesis, sequelae, and ultimately the resolution of otitis media.
Identification of New Targets for Treatment and Prevention
A series of "checkpoints" were envisioned where key molecules facilitate the process of bacterial colonization of the middle ear. The identification and study of these key molecules was considered a high priority to enable the development of novel approaches for intervention and prevention. One way in which these targets might be identified would be to take advantage of genomic technologies such as microarray analysis. Using microarray analysis and a suitable model system, host and pathogen gene expression could be followed throughout the entire disease process. This basic information could then be made available through a public database to allow multiple laboratories to analyze the data. The goal would be to identify specific genes or groups of genes showing expression patterns that would warrant further follow-up in the search for the proteins that appear to be essential for the initiation, continuation, or resolution of the disease process. Once identified, such gene products would represent new targets for the development of therapeutic agents that would block proteins essential to the disease process or augment proteins involved in resolving the infection and its sequelae. Examples of specific components of OM pathogenesis that might be targeted for therapeutic intervention include
- viral infection and alteration of the microenvironment of the upper respiratory tract, Eustachian tube, and middle ear
- bacterial invasion of the middle ear and rapid growth to a pathogenic density
- host response to the presence of dividing bacteria, which includes the release of numerous extra- and intra-cellular signaling molecules
- interaction of multiple adhesions and receptors for bacterial adherence
- viral, bacterial, and host cell induction and release of cytokines and other inflammatory mediators
- role of growth factors in hyperplasia and apoptosis as a mechanism for recovery of the middle ear mucosa
- host and pathogen intracellular signal transduction pathways that ultimately mediate the processes outlined above
- interactions between pathogenic and commensal bacteria in the nasopharynx
- formation of bacterial biofilms in the chronic forms of OM
Because complex interactions between host and pathogen are likely to be significantly influenced by experimental conditions, any results obtained in animal models should be confirmed for accuracy using human materials. Additionally, experiments using human cell lines should also be confirmed in freshly isolated human cells to determine whether in vitro handling/passaging of cells and pathogens has significant effects on experimental results.
Given that viral upper respiratory infection may be the first "checkpoint" in OM pathogenesis, the complete study of this process at the molecular, cellular, and population levels seems highly warranted. Studies should be aimed at identifying target molecules essential for upper respiratory infection (URI) pathogenesis. Additional research would include the development of tools to enable the comprehensive study of all of the viruses involved in URI such as the development of multiplex PCR assays to identify the 10-20 potential upper respiratory viruses that might be present in OM patients. Reliable assays to simultaneously identify all the viruses present in the nasopharynx would enable complete analysis at the individual and population levels. Such assays could determine the complete range of upper respiratory viruses most commonly found in specific populations of children. Additional critical information includes the frequency at which specific viruses are identified in children and, importantly, which viruses appear to be those that most often predispose an individual to subsequent OM.
Genetic Predisposition of the Host to OM
Another area of opportunity is the identification and study of host genetic predisposition to otitis media. Several heritability studies suggest that individuals carry genetic loci that confer susceptibility or resistance to otitis media. The identification of these loci and the study of the specific genes involved offers the possibility for screening individuals to predict OM susceptibility. In addition, the identification of susceptibility genes will provide valuable information on the mechanisms of OM pathogenesis and may suggest new therapeutic possibilities.
A complementary genetic approach includes the study of specific polymorphisms in genes known to be involved in host defense against infectious agents, such as cytokines and chemokines, which confer an increased susceptibility to infection. Whether these known polymorphisms correlate with increased susceptibility to OM is an important area that should be explored. The study of such marker polymorphisms, combined with the identification of specific genes that confer susceptibility to otitis media, could result in DNA-based identification of individuals with high or low OM susceptibility. The important outcome of these studies would be screening protocols that would assist physicians in determining which patients would most benefit from antibiotics and which patients are likely to have the condition resolve spontaneously without antibiotic treatment.
Development of Non-Invasive Diagnostics
An area that could have a significant impact on the decision of whether or not to treat with antibiotics is the development of non-invasive diagnostics for specific pathogens residing in the middle ear. State-of-the-art remote sensing strategies detecting specific signatures of middle ear pathogens must be developed including those that utilize light spectra, odors (aromatic profiles), or other emissions of middle ear fluids that would give a characteristic pattern for each specific pathogen. Technologies under development in other areas of infectious disease research must be applied to the problem of diagnosis in otitis media, the ultimate goal being the creation of an affordable device that could identify the pathogens present in the middle ear of OM patients. Such non-invasive, real time, "point-of-care" diagnostics, which could be used easily by pediatricians, would allow precise management of patients by physicians and reduce broad-based antibiotic use. Other bioengineering-based technologies might also be applied to the specific problems of OM. For example, technologies such as bactericidal nanoparticles and the use of electromagnetic fields to kill bacteria could offer novel approaches that could potentially replace oral antibiotics.
Animal models are an important tool for the study of any disease process. Current animal models of otitis media, such as the chinchilla, have been developed because of convenient access to the middle ear. Unfortunately, unlike the mouse, the chinchilla is not amenable to genetic studies or manipulations, a powerful type of analysis facilitated by the sequencing of the genomes of a number of organisms commonly used in research. A mouse model of OM could be used to identify the effects of genetic manipulations, such as transgene insertion, on OM pathogenesis. Knockout mice, lacking specific genes implicated in OM pathogenesis, could be crossed with a mouse OM model to study the effects of the knockout on the disease process.
Mouse models of OM have not been developed because existing mouse strains are generally resistant to middle ear infections. However, whole-genome random mutation strategies with chemicals such as ethyl-nitrosyl-urea (ENU) increase the feasibility of successful development of an OM mouse model. ENU mutagenesis followed by screening of mutant mice for susceptibility to OM pathogens would be one approach that has been successful for developing other mouse models of disease.
Immunology and Genomic Approaches to Vaccine Development
Genome-based technologies can now be used to comprehensively examine and identify potential bacterial epitopes that would result in vaccines with widespread pathogen coverage. Approaches include the examination of genomes from multiple clinical isolates from each bacterial pathogen to facilitate a multi-valent, broad coverage immunization strategy. Additional state-of-the-art vaccine approaches include
- utilization of genomics and proteomics to identify conserved epitopes
- improved understanding of the major histocompatibility complex (MHC) restriction of immune recognition
- application of computational immunology or "vaccinomics"
- utilization of tetramer technology to advance the study of immunological responsiveness to pathogens
In addition, a challenging but important long-term goal is the development of a single multi-epitope, multi-valent vaccine for the three major OM pathogens: Streptococcus pneumoniae, non-typeable Haemophilus influenzae, and Moraxella cattarhalis. This goal is based on the practical consideration that a complex vaccine regimen for OM, consisting of multiple injections for multiple pathogens, might not be tolerated by parents or adopted by physicians.
Regarding host immunology, a more complete understanding of the basic molecular mechanisms of mucosal immunity will be necessary for the development of vaccines aimed at blocking colonization. In addition, the detailed study of the immune systems of infants is a key area where much basic research is warranted. Stimulating the molecules of the innate immune system, such as the defensins, in an effort to neutralize OM pathogens is also an understudied, yet promising, area that could be especially effective in young children where acquired immunity has yet to mature.
Moraxella is the least studied of the three major otitis media pathogens and its occurrence in OM patients is increasing dramatically in some populations. Therefore, it is critical that the complete genomic sequence of Moraxella be obtained and made publicly available. Other essential tools for successful study of the pathogenesis of Moraxella in OM include the development of a shuttle vector that can be used in Moraxella, as well as the development of a relevant animal model of Moraxella cattarhalis-mediated OM.
Growth Factors and Signal Transduction Pathways
Because of their prominent role in the mucosal hyperplasia associated with OM, growth factors are a possible pharmacological target to down-regulate pathological growth conditions or enhance the return of the middle ear mucosa to a normal state. Also, the balance of mucosal cell growth and apoptosis is an area warranting significant basic investigation.
The study of the signal transduction pathways that mediate the receptor/ligand-based control of mucosal cell changes, including the pathogenic overproduction of mucin, also is a new fundamental area of research. Importantly, the study of the molecular mechanisms of carcinogenesis has resulted in the development of a number of compounds that can be used to inhibit and augment these intracellular pathways. The potential use of such compounds, to inhibit unwanted OM sequelae or to trigger/enhance the normal resolution of mucosal hyperplasia, is an area of investigation that could potentially result in new therapeutic approaches. Also, the identification of the specific bacterial and viral ligands and host cell receptors mediating these processes is also not well understood and should be investigated. Finally, the development of a mouse model specific for the mucoid form of OM could facilitate such studies and provide a model system to test potential therapeutics.
International OM research web site
Because there is significant OM research being undertaken in virtually all industrialized nations, an international OM research web site would serve to keep these investigators in constant communication. Such a web site could include links to a wide range of relevant sites with information on current literature, sequence data, microarray data, meetings of interest, funding opportunities, etc.
Conclusion
Otitis media is a formidable health problem in terms of dollars spent, childhood morbidity, and the alarming consequences of OM on the effectiveness of a limited arsenal of antibiotics. Therefore, the NIDCD determined that a panel of experts should be convened to report on the state of the art of otitis media research and to make recommendations regarding potential new approaches for OM analysis, intervention, and prevention. The resulting recommendations of the workshop participants included new avenues of research, applications of new technologies to OM research, and applications of existing tools and technologies that have yet to be fully applied to solving the problem of otitis media. These recommendations encompass a wide range of approaches with the potential to significantly impact otitis media research, diagnosis, and treatment.