Ravi Kaul and Wanda M. Wenman

Department of Pediatrics, Section of Infectious Diseases, 403 Neurosciences Building, School of Medicine, 1515 Newton Court, University of California, Davis, CA 95616

Received 2/16/ 98 Accepted 2/20/98

2. INTRODUCTION

Chlamydiae are obligate intracellular parasites which have evolved within host eukaryotic cells. Once classified as viruses, they are now considered specialized bacteria that possess discrete cell walls and contain both DNA and RNA. Chlamydiae differ from conventional bacteria in their intracellular nature, small size, longer generation time and a requirement for an exogenous energy supply (1). The order Chlamydiales consists of one family, Chlamydiaceae, and one genus Chlamydia, containing three species - Chlamydia trachomatis, C. psittaci and C. pneumoniae. C. trachomatis has been recognized for centuries as the agent of trachoma which remains the leading preventable cause of blindness worldwide (2). However, in both developing and industralized countries C. trachomatis is a major agent of sexually transmitted disease, estimated to cause more than 4 million new cases each year in North America (3, 4). The major sequelae of chlamydial genital tract infections occur in women, and include salpingitis, ectopic pregnancy and infertility (5). Maternal carriage rates have a profound effect on neonatal health since conjunctivitis and pneumonia are seen in up to 50% and 20% respectively of infants born to infected mothers (6). C. psittaci is a heterogeneous species and primarily an animal pathogen that rarely causes human disease. C. pneumoniae is a relatively new species containing the TWAR strains, and is thought to be an important cause of community acquired pneumonia (7).