Intranasal inoculation of chickens with encapsulated or nonencapsulated variants of Haemophilus paragallinarum: electron microscopic evaluation of the nasal mucosa.

Chickens were inoculated intranasally with encapsulated or nonencapsulated strains of Haemophilus paragallinarum. The nasal mucosa of the chickens were examined, using scanning and transmission electron microscopy. In chickens given the encapsulated variant, marked loss of cilia and microvilli, infiltration of leukocytes, and deposition of a mucopurulent substance were seen on the surface of the nasal mucosa; the number of microvillous cells were markedly increased, and infiltration of mast cells into the lamina propria of the mucous membrane was observed. Numerous encapsulated organisms were found near cilia and on microvillous cells, and the capsule surrounding the organisms appeared to mediate attachment of the organisms to the cilia. In contrast, the nasal mucosa of the chickens given the nonencapsulated variants changed little morphologically. A few nonencapsulated organisms were found near cilia. Colonization of the nasal mucosa by encapsulated organisms probably was essential to induce the morphologic changes seen in the nasal mucosa.