Some protozoa such as L blattarum and Spirotrichonympha live in anaerobic environments. While they are mainly endosymbionts living in the hindgut of certain insects such as termites and cockroaches, L blattarum and Spirotrichonympha have also been observed in human respiratory secretions under light microscopy.4 An interesting question is whether these parabasalids inhabiting in the intestines of termites and cockroaches are associated with lung diseases. Through their feces, termites and cockroaches can eject the parabasalids into unfavorable environmental conditions, in which the parabasalids can form protective cysts. The protozoal cysts may be easily spread through the air or by soil, and inhalation of protozoal cysts by humans is possible. Under favorable conditions in the respiratory system, especially anaerobic status caused by hypoxic inspissated mucopurulent secretions, flagellate protozoa may be released from the cysts through excystation (Fig 1). Based on the interaction between certain protozoal proteases and the respiratory epithelial cells, a number of mechanisms for how protozoa cause lung diseases have been proposed. Proteolytic enzymes secreted by protozoa can destroy bonds such as the tight junctions between bronchial epithelial cells, causing structural damage of the respiratory epithelium. In addition, synthesis of protozoal proteases may activate the protease-activated receptors, causing airway inflammation through a number of inflammatory mediators such as IL-6 and IL-8. More interestingly, these uncommon multiflagellated protozoa were identified in respiratory secretions and were associated with unusual inflammatory responses characterized by a marked increase of monocytes rather than other types of leukocytes.5 In summary, the role of pathogenic parabasalids in respiratory infections should be recognized and highlighted.