Capillaria aerophila is the scientific name for the fox lungworm. Aelurostrongylus abstrusus, the most common lungworm of cats, is found in many parts of the world, including the USA, Europe, and Australia. They are small parasites (males 7 mm, females 10 mm), deeply embedded in the lung tissues.
The eggs are forced into alveolar ducts and adjacent alveoli, where they form small nodules and hatch. Once the larvae escape, they are coughed up, swallowed, and passed in the feces. The larvae seen in the feces of infected animals are tightly coiled, have an undulating tail with a spine, and are <400 μm long.