Table 7. Initial infection region of microorganisms (Baskerville, 1981).

Microorganism	Animal	Infection region
Bordetella bronchiseptica	Pig	URT
Haemophilus spp.	Pig	URT
Pasteurella spp.	Pig	URT
	Cattle	URT
	Sheep	URT
Mycoplasma	Poultry	URT
	Pig	URT
	Cattle	URT
Bovine herpesvirus-1	Cattle	URT
Parainfluenza-3	Cattle	URT
	Sheep	URT
Infectious laryngo-tracheitis virus	Poultry	URT
Infectious bronchitis virus	Poultry	URT
Aujeszky's disease virus	Pig	URT
Aspergillus fumigatus and other fungi	Poultry	LRT
Respiratory syncytial virus	Cattle	LRT
Adenoviruses	Cattle	LRT

Note. URT = upper respiratory tract (including nose, pharynx, and tonsil); LRT = lower respiratory tract (including trachea, bronchi and bronchioles, and alveoli).