Newman et al.
Infection by tickborne bacterium Candidatus Midichloria associated with first trimester pregnancy loss, Tennessee, USA Emerg. Infect Dis. 2025, in press, doi:10.3201/eid3102.240870
Candidatus Midichloria is a symbiotic bacterium commonly found in ticks, with a preference for female ticks. It was first identified in the ovaries of Ixodes ricinus ticks. The pathogenic potential of this genus remains unknown. Individuals bitten by ticks often develop antibodies against Candidatus Midichloria mitochondrii, but no pathogenic effects have been definitively established (see, e.g., Snapshot Week 36/2018).
Recently, a 26-year-old pregnant woman presented with a painful and pruritic rash on her torso, which appeared two weeks after she had been bitten by four ticks. Serologic testing was negative for several known tick-borne pathogens. However, two weeks and five days after her urgent care visit, the patient reported vaginal bleeding. A subsequent prenatal ultrasound confirmed intrauterine fetal demise.
Electron microscopy of the trophoblastic villi revealed intracellular bacterial organisms within cytoplasmic vacuoles, with morphology resembling Candidatus Midichloria mitochondrii. PCR analysis, followed by Sanger sequencing, identified the bacterium with over 95% nucleotide identity to two Ixodes ricinus-associated Candidatus Midichloria mitochondrii strains.
These findings suggest a tropism for human trophoblastic tissue and potential deleterious effects on the fetus. The authors propose that treatment with doxycycline should be considered for pregnant patients with tick bites, as the potential benefits may outweigh the risks.