This is a major means of transmission of several diseases of humans, shown in the table below. Several other diseases are acquired by inhaling particles from environmental sources rather than from an infected person. Droplets from air-conditioning systems, water storage tanks, etc., where the bacterium grows. Aspergillus fumigatus . Such a ball of hyphae growing saprotrophically in the lung is termed an aspergilloma .
Psittacosis is a serious disease acquired by handling birds or by inhaling dust from bird faeces.
It is caused by the bacterium Chlamydia psittaci , an obligate intracellular parasite. After entering the respiratory tract, the cells are transported to the liver and spleen, multiply there and then invade the lungs, causing inflammation, haemorrhage and pneumonia. Legionnaire's disease is a fairly common form of pneumonia in older or immunocompromised people. It is seldom transmitted directly from person to person. Infection occurs when people inhale aerosol droplets containing the bacteria.