Chlamydial infections occupy a significant place in human pathology. They settle inside the cell, thus avoiding the immune system’s attempts to eliminate them. Relapses and reinfections are often present, because the antibodies do not persist for a long time, and the microorganism manages to exist in a latent form, being reactivated under suitable conditions. Often the infection takes place in a subclinical form, thus the partner can be infected, in cases where it concerns the urogenital tract, since there are no symptoms to indicate a problem. The application of treatment – if it is delayed or in an insufficient dose, can suppress the clinical manifestations, but the infection remains without being eliminated. This requires that the therapy for chlamydial infection be long enough and with selected specific antibiotics to which the causative agent has shown sensitivity. Therefore, even after treatment, it is necessary to carry out a re-examination to see if the infection has had an effect and has been completely cleared. Even if the infection primarily affects the lungs and the clinical picture begins with symptoms from the upper respiratory tract, it often affects the joints – arthralgias (pains), myalgias – pain in the muscles, reactive arthritis. In pregnant women engaged in animal husbandry, abortions can be observed in the late months of pregnancy – 6-7, as a result of damage to the placenta, reduced amount of platelets and affecting the function of the kidneys and liver. Working in a pet shop where birds infected with strains of chlamydia are kept also poses a risk. In recent years, a specific type of chlamydia – Chlamydia pneumoniae – has been linked to chronic obstructive pulmonary disease, as well as lung carcinoma and asthma. Often, in chlamydial pneumonia, leukocytes are normal, and ESR (erythrocyte sedimentation rate) is slightly increased. In case of persistent fatigue and cough, it is appropriate to apply a second course of antibiotics. Heart involvement can develop as complications – pericarditis, myocarditis. Specialists in the field of chlamydial pathology also state the hypothesis of the connection of chlamydia as a trigger mechanism for atherosclerotic changes in the vessels and, accordingly, with the heart attack. The basis for this theory is the isolation of chlamydia strains from sclerotic plaques on vessels. Chlamydia trahomatis is widespread in the human population, and the clinical course can be highly variable. Mild asymptomatic forms are very common, but when the urogenital tract is affected in women, the clinical picture can be expressed. Transmission is by contact-household route, which is facilitated in poor hygiene conditions and lack of water. Tests for this strain are recommended in women with vaginal discharge for which no causative agent is found in microbiological examination, in frequent cystitis and vaginitis,as well as in persons with already established several sexually transmitted pathogens – for example, gonorrhea, syphilis, trichomoniasis. Last but not least are newborns who after birth have prolonged conjunctivitis and cough due to infection during the passage through the birth canal. In men, the main cause of urethritis is Chlamydia trahomatis, which can be mild or asymptomatic. But in most cases there is discomfort, burning. Complaints occur 1-2 weeks after risky intercourse. Common complications after a past chlamydial infection are prostatitis, epididymitis, as well as involvement of the rectum – proctitis. A number of cases with mixed infection are also known – often together with gonorrhea as well as mycoplasmas. In women, chlamydial infection occupies an important place in the development of pelvic inflammatory disease. The fallopian tubes are also affected to a great extent, which in turn has an important effect on sterility. Regarding joint diseases, it is important to note Reiter’s syndrome, which occurs with the triad – conjunctivitis, arthritis and urethritis. Chlamydial-induced urethritis is considered part of sexually acquired arthritis. References: Art. Dundarov et al., Clinical Virology, Sofia, 2006.