Chlamydia psittaci is a Gram-negative obligate intracellular bacterium causing respiratory disease and mortality in birds. The pathogen is a biosafety risk level 3 and bioterrorism category B organism. The infection often occurs in Psittaciformes (parrots, parakeets, cockatiels and lories) and they are most frequently infected with the highly virulent genotype A. Tetracyclines are the drugs of choice. However, development of resistant strains of C psittaci is a concern for avian patients. Chlamydia can be transmitted (airborne) from birds to humans and in humans the disease is called psittacosis. Most psittacosis cases are genotype A infections due to contact with Psittaciformes, resulting in severe atypical pneumonia and systemic disease, which can be lethal in untreated patients. There is no C. psittaci vaccine for birds. Humoral and cellular immune responses are required for protection. Vaccine studies in companion birds are challenging as we have no detailed information on the immune system of pet birds and this is largely due to the fact that pet bird-specific leukocyte markers are unavailable. Synthetic biology will be used for engineering a self-amplifying mRNA vaccine for Psittaciformes against the underestimated respiratory zoonotic pathogen Chlamydia psittaci. To study the immune response against the vaccine, a parakeet-specific immunological toolbox will be developed. Next, the efficacy of the vaccine will be tested in an established parakeet model of infection.