Since the disease due to Chlamydia involves many organs/systems, system-wise descriptions of clinical signs is described as under:
Genital infections and abortions: The incidence depends mostly upon the status of the animal and flock. The most characteristic feature of the organism to produce pathological changes in uterus and resulted into abortions. In general chlamydaemia is necessary for infection of placenta and fetus. Enzootic abortion in sheep has been reported from many parts of the world and this syndrome has also been identified in other livestock. Infection of pregnant animals may result in abortions, stillbirths or delivery of weak offspring. Enzootic abortions occur suddenly without any clinical evidence. Placenta is commonly retained and metritis usually results.Ascites, hepato and/or splenomegaly and enlarged and edematous lymph nodes along with petechiae over mucosa, conjunctiva, subcutis, salivary gland, thymus and lymph nodes are the characteristic features in abortion cases or the animals died during 72 hrs. after the birth. Fibrinous placentitis with edema is predominantly the characteristic lesions in such cases with smooth surface towards foetal side and granularity with hemorrhages and pinkish-yellow coloration at maternal side. Accumulation of clay coloured exudates between inter-cotyledonary areas are other features of this infection. Elementary bodies or inclusions may be demonstrated in the smears of infected placenta, fluid and foetal organs. Genital infections in males are reported but the role of venereal transmission is unexplored, though sporadic cases of this infection were also reported.
Enteritis: Organism was isolated from the faeces of normal animals. The organisms have been isolated after intratracheal inoculation and abortion after parental infection. Adult animals rarely develop enteric disease due to intestinal infections. Chlamydial enteritis has been reported in new born in less than 10 days. The shift in host parasite balance in favour of the organism may be secondary to deficient local immunity in the gut. The disease is caused experimentally in colostrum-deprived animals. Mucoid, watery and bloody diarrhoea are also recorded.Catarrhal enteritis and occasionally fibrinous peritonitis are observed. Histologically, the lesions are characterized by dilation of crypts, desquamation and denudation of epithelium and leucocytic infiltrations which are of course not specific but chlamydial inclusions can be demonstrated in special stained sections and on FAT in the cytoplasm of the mucosal epithelial cells of ileum and jejunum and inflammatory cells.
Pneumonia: Organisms have been isolated from the cases of clinical pneumonia and have also been experimentally reproduced. Most of the cases are moderate to severe and are characterized by fever, mucoid or mucopurulent nasal discharge, coughing and depression. Concurrent presence of stress associated with bacteria/virus is necessary to experimentally cause the disease. Infection occurs by inhalation of infected nasal droppings or faecal dust. Exudative broncho-pneumonia with interstitial epithelization and typical interstitial leucocytic infiltration were the main lesions encountered in such cases. Bacterial contaminations are reported frequently where chlamydia has been incriminated as predisposing factor.
Polyarthritis: Chlamydia following oral infection may result in subsequent localization of organisms in joints but the mortality is very less. The disease is characterized by fever, stiffness, lameness, anorexia and frequently conjunctivitis. Enlargement of joints is not usually apparent except in long standing cases. Chlamydial inclusions may be found in special stained sections and synovial smears and also by FAT. Isolation of organism may be carried out from joint fluid or synovia in early cases.
Encephalitis: It was first recognized in Iowa, which was due to generalize chlamydial infection, and in India such manifestations in lambs and kids were reported with the lesions of hyperemia, oedema and gliosis. Glial nodules along with mononuclear cells infiltrations and presence of elementary bodies were also demonstrated in special stained sections.
Ocular infections: Chlamydial agents have been associated with eye infections-kerato conjunctivitis and follicular conjunctivitis. These infections are frequently associated with poly arthritis and pneumonia. The disease is transmissible by contact, probably by aerosol. Latent infection occurs in some recovered animals, leading to enzootic infections. Typical inclusions can be demonstrated in the conjunctival scraping. It has been suggested that the rodents may act as reservoirs for the organisms in areas where epizootic in domestic animals occur sporadically.
Disease in birds: The affected birds appear sleepy, may show fits, shivering, ruffled plumage, nasal discharge, watery greenish diarrhea with pasting around the vent region and market wasting of pectoral muscles. The mortality may be high-large number of birds dying in short period. In pigeons there may be acute respiratory distress along with other symptoms described for other birds. The common lesions are atrophy of pectoral muscles, hepatitis and necrosis of liver, enlargement of spleen ad fibrino- purulent inflammation of respiratory and peritoneal surfaces along with fibrinous pericarditis. Orchitis and epididymitis are also observed.