IVF Treatment The respiratory illnesses are frequent, that is why studying this problem is especially relevant nowadays. The main reason for respiratory system illness progression among people is the presence of pathogens. They are viruses, bacteria, fungus and, in less incident cases, parasites. Besides the listed problems, another important factor that incites the respiratory illnesses is allergens. This case observes indoor allergens such as dust and domestic mites that often cause bronchial asthma.