Serious illness occurs mainly under conditions of crowding and stress both in the wild and in captivity. Shedding of the agent occurs after a latent or carrier infection is reactivated - through feather dust and fecal contamination. The organism appears in the droppings 10 days prior to the bird becoming ill, and intermittent shedding can occur for months with no illness. Dogs, cats, horses, humans, cattle, sheep, frogs and goats all are susceptible to infection. Psittacosis can exist as a completely asymptomatic condition or acute, systemic fatal disease.
Different strains vary in virulence.
The shortest incubation time is 42 days up to 1.5 years or longer. The clinical illness is caused primarily by a toxin that affects the liver and kidneys. The bird is lethargic, dehydrated, hypothermic, anoretic and puffed. Droppings appear watery and yellowish-green with the urates and feces intermixed. Central nervous system signs such as tremors, convulsions, paralysis and twisted neck can occur.