Chlamydia are obligate intracellular, gram-negative pathogens. Extracellularly, chlamydia do not have their own metabolism and depend on the enzyme activity in the host cell.
Chlamydia relevant in veterinary medicine belong to the family Chlamydiaceae. Some years ago, this family was split into the two genera Chlamydia and Chlamydophila. However, based on recent genetic analyses, this classification is no longer considered justified. Because of this, the single term Chlamydia is used here.
In literature, only little data is available on chlamydia infections in dogs. Yet in general, its occurrence must be expected in Europe. Respiratory signs up to bronchopneumonia seem to be dominating here. At the onset of the disease, only progressive loss of condition may appear. High fever can develop. When the disease progresses, central nervous disorders are possible. Other manifestations of chlamydiosis in dogs are conjunctivitis and keratitis. Its involvement in keratitis superficialis chronica in German Shepherd dogs is being discussed.
Originally identified as the causative agent of “feline pneumonitis”, C. felis is rather associated with conjunctivitis in cats nowadays. The cardinal symptom is serous conjunctivitis which begins unilaterally and then spreads to the other eye after some days. Especially when there is a secondary bacterial infection, the discharge can become mucopurulent. Chemosis and blepharospasm may also be present. In severe cases, follicular hyperplasia develops or even keratoconjunctivitis with corneal ulcerations. Conjunctivitis can last for 8 weeks or more. Other acute symptoms include slight rhinitis and fever. Animals between 5 weeks and 9 months of age are most affected, though conjunctivitis neonatalis has also been described. In that case, kittens already suffer a severe conjunctivitis when opening their eyes, often due to a chlamydia infection acquired intrapartum. Transmission occurs directly through conjunctival secretions. Persistent infections are possible, and in some animals also respiratory symptoms may last for several weeks. When the immune system is weakened, the infection can be reactivated.
In our birds, infections with chlamydia are of particular significance. Infection rates of 10 to 40% may be prevalent in aviculture. As many birds have a carrier status, the disease can “suddenly” become clinically apparent under stress. Symptoms in birds are manifold and extremely non-specific. Ruffled feathers, apathy and lack of appetite must be mentioned. Basically, every “sick bird” could have a chlamydia infection. Respiratory symptoms with or without conjunctivitis are often seen, but central nervous disorders are also possible. The extent of clinical signs largely depends on the animals’ condition; the type of symptoms also varies from one bird species to another. Sudden deaths without prior illness might happen. It is therefore not possible to make a diagnosis based on clinical signs. To make a reliable diagnosis, the identification of the pathogen is always necessary. C. psittaci is a zoonotic agent. Infections in humans are normally airborne, resulting in a flu-like disease. In Germany, it is a notifiable disease.
Various species of chlamydia are regularly detected in reptiles and amphibians. In reptiles, they have been associated with granulomatous changes in different tissues as well as with pneumonia, enteritis, hepatitis and myocarditis. In amphibians, they were found in cases of systemic disease.
In Germany, chlamydiosis in cattle, sheep and goat, as well as in poultry is a notifiable disease.