Infection and Disease Epidemiology

Abstract

Chlamydiae cause a wide variety of diseases. In their natural hosts, chlamydial infections usually cause relatively mild diseases characterized by persistent infections with relatively poor immunity, so that recurrent infections can occur. C. psittaci is an extraordinarily common organism among avian species. While infections in the wild may affect only a small fraction of the birds at any given time, the agents are highly infectious and often cause enteric and respiratory infection. The chapter first talks about C. psittaci infections. Many cases of human psittacosis go undiagnosed because it requires a high index of suspicion on the part of a clinician to test cases of atypical pneumonia or unusual febrile diseases for psittacosis. Control of psittacosis depends on control of the avian sources of infection. Despite the wide host range of C. psittaci, infection of humans from nonavian animals is rare. Next, the chapter discusses C. trachomatis infection. C. trachomatis is passed from eye to eye by direct contact. The epidemiology of trachoma continues to provide hope for those trying to produce an effective vaccine for trachoma. Finally, the chapter focuses on C. pneumoniae infections. C. pneumoniae is recognized as an important cause of respiratory disease in young adults and may cause serious respiratory disease in older debilitated individuals. There are no gold standards for diagnosis of C. pneumoniae infection. Tetracycline and erythromycin are effective against C. pneumoniae in vitro. C. pneumoniae has also been associated with a bewildering array of chronic diseases.