# Waddlia chondrophila: from a bovine abortigenic agent to a potential cause of human adverse pregnancy outcomes

## TL;DR

Waddlia chondrophila, originally found in bovine abortions, is now linked to human pregnancy complications and respiratory infections, but its transmission route and prevalence remain unclear.

## Contribution

This paper reviews Waddlia chondrophila's role in adverse human pregnancy outcomes and highlights the need for systematic diagnostic testing.

## Key findings

- Waddlia chondrophila is associated with miscarriage and infertility in humans.
- High prevalence of anti-Waddlia antibodies is found in infertile couples.
- The bacterium's transmission route to humans remains unclear.

## Abstract

Waddlia chondrophila is an obligate intracellular bacterium that was first isolated from an aborted bovine foetus, but since then, it has been primarily found in different aquatic environments, including wells and hot water systems. In amoebae and other eukaryotic host cells, it has a biphasic developmental cycle, with an infectious extracellular form (elementary body) and a replicative intracellular form (reticulate body). W. chondrophila is a prevalent abortigenic agent in African cattle and is associated, in humans, with adverse pregnancy outcomes and respiratory infections. Its reservoir is probably mammals or amoebae, but the mode of transmission to humans remains unclear. It could be zoonotic (from companion animals or livestock, especially cattle), vector-borne (through arthropods) or water-borne (via infected amoebae).

Waddlia chondrophila is a strict intracellular bacterium belonging to the Chlamydiales order, which also encompasses important human and animal pathogens, including Chlamydia trachomatis and Chlamydia psittaci. Like all other members of the order, W. chondrophila displays a biphasic developmental cycle, alternating between infectious extracellular and replicative intracellular forms.

First isolated from a bovine aborted foetus, W. chondrophila was later demonstrated to be associated, in women, with adverse pregnancy outcomes, such as miscarriage. Furthermore, recent studies have demonstrated a high prevalence of anti-W. chondrophila antibodies in asymptomatic women who consulted doctors regarding infertility problems, and in the male patients of infertile couples. Additionally, a role for this bacterium in respiratory tract infections has been suggested, as it has also been recovered from respiratory samples.

Although the cause of miscarriage is not identified in ∼50% of cases, nowadays, no systematic diagnostic testing for the presence of W. chondrophila is routinely performed. Implementing large-scale testing in women with reproductive health issues would undoubtedly increase our knowledge of W. chondrophila prevalence and its implications for disease outcomes.