INTRODUCTION

Members of the family Chlamydiaceae cause multi- syndromic disease in a wide range of species of mammals and birds, both wild and domesticated. These are, within the genus Chlamydophila, the species Chlamydophila abortus, Chlamydophila caviae, Chlamydophila felis, Chlamydophila pecorum, Chlamydophila psittaci, Chlamy- dophila pneumoniae, and within the genus Chlamydia, the species Chlamydia muridarum and Chlamydia suis.

Two different developmental stages can be identified during the cycle of infection and replication of chlamy- diae. The ‘elementary body’ (EB) is a small, electron-dense, spherical body of 0.2—0.6 μm in diameter, and is adapted to survive in the external environment. It is the infectious form of the organism, which binds on receptors of suscep­tible target cells and is internalized by endocytosis and/or phagocytosis. Chlamydia inhibit the fusion of the endo­some and the lysosome; hence the whole life cycle of chlamydiae occurs within the endosome. Within the host cell endosome the EB transforms into the ‘reticulate body’ (RB). RB (up to 1.5 μm in diameter) are metabolically active and pass through multiple rounds of binary fission. Some days after infection of the host cell, RB transform back into metabolically inactive, infectious EB that are released through the endosome, and host cell rupture or the inclusion is extruded by reverse endocytosis. Interme­diary forms between EB and RB exist. Many chlamydiae co- exist in a subclinical state within specific vertebrates.

In production agriculture, diseases due to C. psittaci, C. abortus, C. pecorum and C. suis are of main relevance. Chlamydophila psittaci is the zoonotic agent of psittacosis/ ornithosis and affects principally birds. Chlamydophila abortus primarily infects ruminants, principally sheep and goats and in some European countries is the most signifi­cant cause of infectious abortion in these species (e.g. epizootic/enzootic abortion in sheep). Strains of C. pecorum cause a number of disease syndromes in ruminants, koalas (Phascolarctos cinereus) and pigs. Chlamydophila suis causes respiratory disease, enteritis and conjunctivitis in swine.

Infectious Diseases of Wild Mammals and Birds in Europe, First Edition. Edited by Dolores Gavier-Widen, J. Paul Duff, and Anna Meredith. © 2012 Blackwell Publishing Ltd. Published 2012 by Blackwell Publishing Ltd. Material authored by Paul Duff remains Crown Copyright.

Diseases caused by chlamydia also occur in reptiles, amphibians and fish. Chlamydial infection of mammals and birds may result in systemic disease, pneumonia, abor­tion, rhinitis, conjunctivitis, arthritis, enteritis, or no apparent disease.

PSITTACOSIS/ORNITHOSIS

Avian chlamydiosis (psittacosis or ornithosis) is a conta­gious, often systemic disease, caused by the bacterium Chlamydophilapsittaci (previously Chlamydiapsittaci). The organism causes a variety of clinical syndromes in a wide range of domesticated and wild animals and birds. Orni­thosis refers to disease in, or transmitted from, domestic and wild birds, as opposed to disease in psittacines.

AETIOLOGY

Chlamydophila psittaci is an obligate intracellular bacte­rium that uses the host cell for energy. It occurs in the cytoplasm of eukaryote cells, forming membrane- bound cytoplasmic inclusions (endosomes).