News
Avian Chlamydia abortus variant leads to respiratory infections in humans
Research shows that avian Chlamydia abortus can cause pneumonia in humans. An unknown phenomena until now. Wageningen Bioveterinary Research (WBVR, part of Wageningen University & Research) was able to culture this Chlamydia from patient material and determined its DNA sequence. ‘We are the only laboratory in the Netherlands that has expertise in culturing this type of Chlamydia,’ said WBVR researchers Marloes Heijne and Jeroen Koomen.
The study on avian Chlamydia abortus in humans is the result of collaboration between Zuyderland MC, St Antonius Hospital in Nieuwegein, GGD Utrecht, NVWA, RIVM and WBVR. The investigation was prompted by the hospitalisation of a family cluster of four people, three of whom were hospitalised with pneumonia. One patient even ended up in intensive care. Initially, an infection with C. psittaci was suspected, but further investigation revealed an infection with a variant of the bacterium C. abortus. This variant had not been detected in humans before.
Background
C. abortus is best known as a pathogen that induces abortion in sheep and goats. However, a number of variants have been described in 2021 that are genetically different from strains found in sheep and goats. These variants are classified as ‘avian C. abortus’ and have genetic similarities with C. psittaci, a known cause of pneumonia in humans. The naming ‘avian’ C. abortus indicates that these variants have so far only been described in birds.
Genetic analysis
Material for culture of Chlamydia could be collected from three of the four patients. All three isolates were typed using genetic analysis, so-called whole genome sequencing, and compared with known Chlamydia strains. The isolates found in the patients were found to be carrying a plasmid. ‘This plasmid is not known to occur in C. abortus isolates derived from sheep and goats,’ says researcher Jeroen Koomen. In addition, a cytotoxin gene was found that may contribute to its pathogenic potential. This gene does not occur in sheep and goat isolates known so far, but it does in the zoonotic C. psittaci.
Retrospective study
Research on material from the ‘national surveillance programme psittacosis’ enabled the identification of avian C. abortus infection in 10 more patients. This showed that this type had been seen in the Netherlands since 2010. The 10 patients were hospitalised, at least five of them developed pneumonia, one patient died.
Source investigation
A source of the infection could not be identified. The investigators suspect that faeces from wild birds may have been the possible source for the infection of the first (index) patient. For two family members, human-to-human transmission was plausible, but could not be proven. Until now, it has always been assumed that human-to-human transmission of zoonotic Chlamydia infections is not possible. In recent years, an increasing number of publications have appeared, showing that in exceptional situations, human-to-human transmission is plausible.
Importance
Without targeted diagnostics, these types of infections do not come to light as Chlamydia cannot be detected by standard culture methods. Targeted PCR diagnostics are needed to detect Chlamydia species. If patients themselves do not report having been in contact with birds or animals, a zoonotic Chlamydia infection may not be considered. Human-to-human transmission should also be kept in mind in patient clusters such as the one in this research. ‘This is why it is important to share the results of our study,’ said Marloes Heijne, who makes a strong plea for further research. ‘As a veterinarian and researcher, I would like to know in which birds in the Netherlands this Chlamydia variant occurs, as the source of these infections remains unknown at present.’