A human case of Q fever associated with cat in China: a neglected risk factor of Q fever

Abstract

Q fever is a globally distributed zoonosis caused by Coxiella burnetii, which is mainly harbored by farm ruminants. Although some studies have reported the presence of C. burnetii in cats, cat-associated Q fever is very rare. In this study, we report the case of a 30-year-old man who was diagnosed with Q fever in May 2024. The diagnosis was based on the results of next-generation sequencing and confirmed by nested PCR. Epidemiological investigations suggest that he had not come into contact with any infection sources other than two cats, one of which was a parturient cat. The blood samples of the cats were collected and tested by nested PCR and immunofluorescence assay. The results showed that the serum of the parturient cat was positive for both phase I and phase II Q fever antigens, suggesting that it had been infected with C. burnetii. This is a rare human case of Q fever transmitted by a domestic cat in China. Importantly, it shows that the pet cat may be a neglected risk factor of Q fever in China.

Supplementary information

The online version contains supplementary material available at 10.1186/s42522-025-00189-x.

Introduction

Q fever is a globally distributed zoonotic infection caused by Coxiella burnetii (genus Coxiella, family Coxiellaceae, order Legionellales). It can cause either acute (manifested as high fever, pneumonia, etc) or chronic disease (manifested as endocarditis, hepatitis, osteomyelitis, fibrosis, etc) [1]. Some household genes, such as dnaK and rpoB, are used for the detection and phylogenetic analysis of C. burnetii; however, the atypical symptoms and low level of bacteremia make the diagnosis of Q fever difficult [2, 3]. Coxiella burnetii is an environmentally stable bacterium with an extremely high level of infectivity; this makes it a potential bioweapon. Farm ruminants such as cattle, sheep, and goats, are the most frequent reservoirs associated with human infections. In addition, domestic cats can also get asymptomatically infected with C. burnetii and occasionally transmit the pathogen to humans [4]. However, such cases have rarely been reported in the last 30 years, with the exception of a human outbreak of Q fever at an animal refuge described by Malo et al. in Australia in 2018 [5]. In China, as well as in Asia, Q fever transmitted through cats has never been reported. This makes the present case of cat-transmitted Q fever the first such one to be reported in both China and Asia.

Case presentation

On May 11, 2024, a 30-year-old man living in Guilin City in Southwest China presented to the hospital after four days of fever (highest temperature, 40.6℃). He also complained of chillness, dizziness, headache, muscle soreness, malaise, asthenia, anorexia, and occasional nausea. He reported that he had been scratched by a cat before onset of the symptoms. On admission, blood tests showed elevated C-reaction protein (CRP) (136.40 mg/L) and procalcitonin levels (1.74 ng/mL), liver dysfunction (alanine transferase: 197.0 IU/L, aspartate transferase: 136.5 IU/L, lactate dehydrogenase: 506 IU/L), coagulopathy (D-dimer: 6.21 μg/mL), and kidney dysfunction (Table S1). Based on these symptoms, he was initially diagnosed with infectious fever and received an intravenous infusion of moxifloxacin hydrochloride and sodium chloride injection (250 mL per day for five days, 11^th May to 15^th May) as anti-infection therapy. On the third day (13th May), he still presented with fever (39.5℃), chills, and dizziness. Moreover, the laboratory tests still showed elevated CRP levels (114.05 mg/L), liver dysfunction (alanine transferase: 157.4 IU/L, aspartate transferase: 93.5 IU/L), and kidney dysfunction. Because the causative agent was still unclear, oseltamivir phosphate was tentatively administered orally (75 mg, twice a day) for the treatment of the possible viral infection for six days (13th May to 18th May). From 14th May to 24th May, cefepime was additionally administered as an anti-infection agent. On the fifth day (15th May), the possibility of rickettsial infection was considered because the symptoms were still not alleviated. Accordingly, moxifloxacin hydrochloride was replaced with intravenous infusion of doxycycline hydrochloride (0.1 g per 12 h) for 13 days (15^th May to 27^th May).

The patient’s blood sample was subjected to next-generation sequencing (NGS) for accurate diagnosis. Subsequently, 82 sequences of C. burnetii were identified on the sixth day. For confirmation, DNA was extracted from the blood sample, and nested PCR was performed to amplify the rpoB and DnaK genes of C. burnetii (primers shown in Reference [6] and Table S2). The DNA of C. burnetii isolated from Hyalomma asiaticum ticks was used as the positive control. Both the rpoB (512 bp) and DnaK (558 bp) sequences were successfully amplified (GenBank Numbers: PP993553, PP993554) from the patient’s blood, and they exhibited 100% identity to most other C. burnetii strains. Phylogenetic analysis based on Maximum Likelihood (ML) method in the GTR model using PhyML v3.0 showed that it was in the same clade as most C. burnetii strains worldwide (Fig. 1).

Fig. 1.

Phylogenetic tree based on the rpoB (512 bp) and dnaK (558 bp) sequences of the Coxiella burnetiid strain

After the diagnosis of Q fever, the therapy was not changed and the application of Doxycycline hydrochloride injection continued. On the seventh day (17^th May), the body temperature was still high, and blood test results still showed high CRP levels, liver dysfunction, and kidney dysfunction (Table S1). Therefore, levofloxacin sodium chloride injection (0.5 g per day) was additionally administered from 17^th May to 27^th May. His liver and kidney functions became normal on the thirteenth day (23^rd May), and his CRP level showed a continuous decrease. He was discharged from the hospital on the seventeenth day (27^th May). Throughout therapy, ibuprofen oral suspension was used to control body temperature.

Epidemiological investigation

To clarify the source of infection, an epidemiological investigation was carried out after the diagnosis of Q fever. The investigation revealed that the patient neither had contact with livestock nor had been bitten by ticks during the past few months. He also denied contact with raw meat or raw milk. However, he mentioned that he had two pet cats, one of which had scratched him a few days before the onset of his symptoms. The female cat had just given birth to kittens approximately a week before the onset of his symptoms (Fig. S1). Whole blood and serum samples of the female cat were collected, and a whole blood sample of the other cat (male cat) was also collected. Although nested PCR detected no DNA sequences of C. burnetii, an immunofluorescence assay (IFA) using Q Fever Substrate Slides (catalogue number: IF0200G, Focus, USA), performed according to the manufacture’s manual, revealed that the serum of the female cat was positive for both phase I and phase II antigens (IgG titers ≥ 1:16) (Fig. S2). Based on these results, it is believed that the patient was infected through contact with the parturient cat. The patient’s family declared that the cats were bought from market when they were kittens. Moreover, they had been fed commercial cat food and had never eaten raw meat. No ectoparasites (ticks, fleas, etc) were found on physical examination. Thus, the source of infection of the cat was unclear.

Discussion

Farm ruminants such as cattle, goats, and sheep, are the main reservoirs and infection sources of C. burnetii [7, 8]. Although numerous studies have revealed the presence of C. burnetii in cats [9–11], they are still a neglected source of Q fever infection. Apparently healthy cats can shed huge numbers of C. burnetii bacteria into the environment during parturition and humans can easily get infected on inhalation of contaminated aerosols [4]. Since the 1980s, several outbreaks of Q fever associated with parturient cats have been reported in the USA, Canada, and Australia [5, 12–14]. This is a rarely reported cat transmitted case of Q fever in China and highlights the risk of cat-transmitted Q fever in China. Due to the unspecific symptoms of Q fever (which presents with typical flu-like respiratory symptoms), it is possible that some cat-associated human cases may have been misdiagnosed.

Cats are popular pets, with over 40 million pet cats recorded in China until 2022 [15]. However, the infection rate of C. burnetii in cats is almost completely unknown. To date, only one study has investigated the presence of C. burnetii in 140 cats in China, but no cases were detected [16]. Notably, cats infected with C. burnetii are usually asymptomatic, which makes it difficult to identify infected cats [4]. Considering the huge number of pet cats in China and their close interactions with their owners, the risk of Q fever exposure may not be restricted to suburban areas but may also spread to county towns and big cities. Therefore, cat owners should be aware of the risk of transmission of this pathogen via parturient cats and undertake strict hygiene measures to prevent Q fever infection.

A couple of limitations need to be mentioned here. Due to the low level of bacteremia in cats, we did not recover the DNA of C. burnetii from blood samples of the cats. Further, if available, the uterus, postpartum lochia, or vaginal swab after parturition would be preferable sample choices for detection of C. burnetii DNA.

Conclusions

Q fever is considered a One Health problem. The observations from the present case imply that pet cats may be a neglected risk factor for Q fever. Given the large number of pet cats in China and the asymptomatic presentation in cats, the actual rate of infection among cats (and the risk of human transmission) might be enormously higher that what is currently recorded. With the development of laboratory testing methods and strengthening of surveillance, more such cases may be discovered in the future. Our results also emphasize the need for public awareness of this risk factor and the adoption of hygiene measures to prevent cat transmitted Q fever.

Electronic supplementary material

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Author contributions

Miao Lu: Conceptualization, Methodology, Writing — review & editing. Dongsheng Zhou, Yun Lin, Huoying Chen, Lina Gong, Siyan Xie: Resources, Writing — review & editing. Haijian Zhou, Wenping Guo, Hai Jiang, Kun Li: Conceptualization, Supervision, Visualization, Writing — review & editing. Jinyong Qin, Bao Lu, Hui Huang, Guorong Tang, Yi Quan: Investigation.

Funding

This work was funded by Platform project of Datong City (2022082), Guangxi Medical and Health Key Discipline Construction Project, Guangxi Medical and Health Key Cultivation Discipline Construction Project, Guangxi Clinical Key Specialty Construction Project, Guangxi Clinical Key Specialty Construction (Cultivation) Project, and National Nature Science Foundation of China (82361148725).

Data availability

The DNA sequences obtained in this study have been uploaded to the GenBank Database (GenBank Accession Numbers: PP993553, PP993554).

Declartions

Ethics approval

The Ethics Committee of the Second Affiliated Hospital of Guilin Medical University and the National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, approved the study on the patient (Approval No.: ICDC-LPJ-2004002). The Ethics Committee of Chengde Medical University approved the study on the cats (Approval No.: 202,004).

Consent to publish declaration

Not applicable.

Competing interests

The authors declare no competing interests.