Abstract
Feral pigeons, common wood pigeons and Eurasian collared doves are the most common representatives of the Columbidae family in Switzerland and are mostly present in highly populated, urban areas. Pigeons may carry various members of the obligate intracellular Chlamydiaceae family, particularly Chlamydia (C.) psittaci, a known zoonotic agent, and C. avium. The objective of the study was to identify the infection rates of common free-roaming pigeons for different Chlamydia species with the overall aim to assess the risk pigeons pose to public health. In this study, 431 pigeons (323 feral pigeons, 34 domestic pigeons, 39 Eurasian collared doves, 35 common wood pigeons) from several geographic locations in Switzerland were investigated for the presence of Chlamydiaceae. Samples consisted of pooled choanal-cloacal swabs (n = 174), liver samples (n = 52), and paired swab and liver samples from 205 pigeons (n = 410). All 636 samples were screened using a Chlamydiaceae family-specific 23S rRNA real-time PCR (qPCR). Subsequent species identification was performed by DNA-microarray assay, sequencing of a 16S rRNA gene fragment and a C. psittaci specific qPCR. In total, 73 of the 431 pigeons tested positive for Chlamydiaceae, of which 68 were positive for C. psittaci, four were C. avium-positive and one pigeon was co-infected with C. avium and C. psittaci. The highest infection rates were detected in feral (64/323) and domestic pigeons (5/34). Common wood pigeons (2/35) and Eurasian collared doves (2/39) revealed lower infection rates. Additionally, multilocus sequence typing of twelve selected C. psittaci-positive samples revealed closely related sequence types (ST) between and within different Swiss cities. Furthermore, liver and corresponding swab samples from the same bird were colonized by the same ST. Considering the high infection rates of C. psittaci in domestic and feral pigeons, close or frequent contact to these birds poses a human health risk.
Highlights
Members of the Chlamydiaceae family are gram negative, obligate intracellular bacteria with a biphasic developmental cycle
It can be expected that the C. psittaci strains infecting the pigeons of the different lofts express similar virulence, since samples taken from five feral pigeons originating from these three different lofts were all typed as ST55 by multilocus sequence typing (MLST) and outer membrane protein A (ompA) genotype B, the most common genotype found in pigeons [23, 40,41,42]
The present study revealed that C. psittaci is the predominant Chlamydia species identified in the three species of free-roaming Swiss pigeons with 68/73 Chlamydiaceae-positive pigeons positive for C. psittaci, 4/73 positive for C. avium, and 1/73 positive for both Chlamydia species
Summary
Members of the Chlamydiaceae family are gram negative, obligate intracellular bacteria with a biphasic developmental cycle. The single genus Chlamydia (C.) consists of thirteen species and three Candidatus species [1,2,3]. The most well-known chlamydial species harboured by birds is C. psittaci, which has been reported in at least 467 bird species belonging to 30 different orders [4]. This pathogen causes asymptomatic to severe systemic infections in several bird species, depending on susceptibility of the host species, immune status, infectious dose and virulence of the strain involved [5]. Bacterial shedding can be intermittently activated by stressful events such as breeding, migration or other illnesses, without presentation of clinical symptoms [5]
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