Abstract
Background:
Brucella microti is a pathogen of rodents and wild mammals. Here, we report the first probable infection with B. microti in a mammalogist.
Materials and Methods:
In the study, we provided complete clinical description as well as laboratory analysis of probable human infection caused by B. microti.
Results:
Considering the clinical course of the infection, the obvious epidemiological link (a bite by an infected rodent), the isolation of a pathogen from a sick vole that was affected by clinical infection with B. microti, and the specific serological response (slow agglutination test) in human patient, we can conclude that the human disease described here was probably caused by B. microti, an emerging bacterial pathogen transmitted by rodents.
Conclusion:
Rodents and other wildlife need to be monitored not only for established zoonotic agents such as hantaviruses, lymphocytic choriomeningitis virus, Leptospira spp., Francisella tularensis, but also for Brucella microti and other atypical rodent-borne brucellae.
Introduction
During a zoological survey of a population of the common vole (Microtus arvalis) affected by brucellosis in South Moravia (Czech Republic), a mammalogist capturing rodents in live traps was bitten in the fourth left finger (a bleeding wound appeared) by an adult (50 g) male common vole that revealed typical signs of the disease including colliquating abscesses on August 31, 2000.
The vole, labeled as #4005, was euthanized the same day, and from its visceral organs (liver and kidneys), Brucella microti (although originally misidentified as Ochrobactrum intermedium when using commercial biochemical test kits) was isolated as described in another article (Hubálek et al., 2007)—the strain has been deposited in the Czech Collection of Microorganisms in Brno under accession number CCM 4915, and it is now the type strain of B. microti (Scholz et al., 2008b).
Materials and Methods
Clinical description
In the mammologist (a 50-year-old woman), a high fever (39.5°C) with chills; total weakness; and head, leg, joint, and back aches appeared on September 21, 2000. A tiny ulcer was seen on her wounded finger, several left axillar lymph nodes were enlarged (3–4 cm) and moderately painful. On September 26, she visited a specialist who found that the lymphadenopathy also appeared in her inguinal areas. These symptoms were combined with edema of both feet—especially at tarsus and around ankles (the fingers remained unaffected), with a mild pain.
Moderate proteinuria was detected, bacteria and debris were also present in urine, but urinary infection was not confirmed by repeated examinations. In the blood sample, leucocyte concentration was 4.5 × 109/L; that of thrombocytes was 64 × 109/L (slight thrombocytopenia), hemoglobin 147 g/L (normal), C-reactive protein was increased (45 mg/L); liver enzymes were slightly elevated (alanine aminotransferase [ALT] 1.30, aspartate transaminase [AST] 1.37, glutamyl transferase [GMT] 1.22), whereas urea, creatinine, sodium, potassium, calcium, magnesium, chloride, and bilirubin levels were all normal; erythrocyte sedimentation rate was normal (8/18 mm after 1/2 h—Westergren); blood pressure 120/70; ECG normal, and no meningeal irritation was observed.
Empirical therapy with peroral deoxymykoin (200 mg daily) was started on September 27 and prolonged until October 4 when the symptoms retreated. However, on October 6, the disease relapsed: subfebrilia (37.5°C) and an expanding feet edema (especially pronounced on October 8–9) occurred again. The patient was oriented, afebrile, without efflorescences or other changes on skin; the slightly increased left axillar lymph node persisted. The leg edema was bilateral, perimalleolar, and partially also crural. Monoarthritis of left talocrural joint was also present. No bleeding or thromboses were found.
Epigastric pressures and pain appeared, and small volume of pleural effusion close to the liver as well as peritoneal exudate (at the bottom of pelvis) was detected by ultrasonography; diffuse hepatopathy was also detected although liver enzymes were only slightly elevated (ALT 1.46, AST 0.96, GMT 1.66, lactate dehydrogenase 7.47); no icterus was observed and only a mild hepatomegaly was palpable. In the blood, the concentration of cells was leucocytes 5.35 × 109/L (lymphocytes 32%, monocytes 8.5%, neutrophiles 55%, eosinophiles 1.4%, basophiles 2.6%), thrombocytes 203 × 109/L, hemoglobin 115 g/L (a slight anemia), erythrocyte sedimentation rate increased 25/50; urine was normal (no leucocytes, erythrocytes or bacteria observed). Radiography of the lungs and heart was negative, ECG normal, breathing normal, no cough was present.
Therapy with deoxymykoin (200 mg daily) was started again (for 10 days), and the patient was admitted in the 2nd Internal Haemato-Oncological Department of the Faculty Hospital in Brno-Bohunice from October 9 to 13, 2000, after she was released in a good health status. At the release, the disease was described by physicians as a “febrile illness of unknown aetiology, probably starting after a bite of an ill vole, followed by regional and afterwards a generalized lymphadenopathy, feet oedema, talocrural monoarthritis, accompanied with pleural and peritoneal exudate.”
The patient's health status was then checked at outpatient clinic consecutively on October 16 and 23, and November 3, 8, and 22, 2000. On November 22, no pathological signs were observed or detected (pleural and peritoneal exudate absent, no feet edema), and no subjective symptoms were reported by the patient. She has remained without sequelae thereafter.
Laboratory analysis
Repeated hemocultures were negative, whereas Escherichia coli (>105 cells/mL) was present in the urine. PCR for cytomegalovirus was negative. Serological tests for antibodies: hepatitis A IgG was positive but IgM negative, hepatitis B and C were negative, Toxoplasma gondii IgG was positive but IgM was negative, Chlamydia pneumoniae was positive (complement-fixation test, 1:64), whereas Coxiella burnetii, Leptospira spp., Listeria monocytogenes, Francisella tularensis, and Brucella abortus (slow agglutination test [SAT]) were all negative.
Also repeated serology in the human patient (sample collected on November 3, 2000) with SAT in tubes with commercial B. abortus antigen was again negative. In contrast, a home-made antigen prepared from the centrifuged culture of B. microti agglutinated moderately in SAT with the serum dilution of 1:80. Late convalescent serum collected on June 5, 2008, gave negative SAT results with B. abortus as well as with B. microti. In our opinion, it is possible that the early antibiotic treatment of the patient inhibited the formation of specific agglutinating antibodies to a higher titer.
Results and Discussion
Retrospectively, the disease of the mammalogist seems to have been caused by the novel species B. microti (the agent was unknown at the time of her illness), which occurred massively in the affected vole population at that locality and time. Certain similarities in the clinical signs of the human and vole patients are very suggestive for this conclusion, that is, lymphadenopathy, edema of feet, and presence of exudate in pleural and peritoneal cavities.
It has been proved experimentally that B. microti has a good zoonotic potential in that the bacterium is capable of replication inside not only murine but also human macrophage-like cells similarly as the other Brucella spp. pathogenic for humans (Jiménez de Bagüés et al., 2010). Moreover, B. microti exhibits a high pathogenicity in experimental infection of laboratory mouse (Hubálek et al., 2007; Jiménez de Bagüés et al., 2010).
Later on, B. microti was isolated from soil in the Czech enzootic focus (Scholz et al., 2008b) and also from mandibular lymph nodes of red fox (Vulpes vulpes) in Austria (Scholz et al., 2009) and wild boar (Sus scrofa) in Hungary (Rónai et al., 2015). Recently, B. microti-like strains were found in the native moor frog (Pelophylax ridibundus) from a French farm (Jaÿ et al., 2020; Jaÿ et al., 2018). Based on the case of human infection with B. microti already described, there is a possibility that some cases of B. microti may go unnoticed in the general population (or the agent might be easily misidentified as Ochrobactrum anthropi or O. intermedium in standard biochemical tests: Hubálek et al., 2007; Scholz et al., 2008b).
Certain public health measures should be taken among people such as hunters, farmers, forestry workers, zoologists, and veterinarians who come into contact with rodents and their environment (Rouzic et al., 2021). We note that rodents and other wildlife need to be monitored not only for established zoonotic agents such as hantaviruses, lymphocytic choriomeningitis virus, Leptospira spp., and F. tularensis, but also for B. microti and other atypical rodent-borne brucellae.
Conclusion
Considering the clinical course of the infection, the obvious epidemiological link (a bite by an infected rodent), the isolation of a pathogen from a sick vole that was affected by clinical infection with B. microti, and the specific serological response in human patient, we can conclude that the human disease described here was probably caused by B. microti, an emerging bacterial pathogen transmitted by rodents.
Footnotes
Acknowledgment
We thank Dr. Ladislav Nekvasil, a general practitioner, for technical help with collection of the patient's sera.
Authors' Contributions
Z.H. contributed to conceptualization (equal), writing original draft (equal), and review and editing (equal). A.K. carried out clinical diagnosis and treatment of the patient (lead), data collection (equal), and review and editing (equal). J.N. was involved in writing original draft (equal), formal analysis (equal), and review and editing (equal). I.R. was in charge of conceptualization (equal), writing original draft (equal), formal analysis (equal), and review and editing (equal). All authors read and approved the final version of this article.
Ethical Approval Statement
The patient provided informed consent to the use of her data and clinical samples for the purposes of this study.
Consent for Publication
Written informed consent for publication was obtained from all authors of the study.
Author Disclosure Statement
No conflicting financial interests exist.
Funding Information
The study was financially supported by the Ministry of Health of the Czech Republic (Reg. No. NU21-05-00143).