Combined pneumonia and glandular tularemia following a tick bite in an immunocompromised patient

Abstract

Francisella tularensis can cause a broad spectrum of clinical manifestations depending on the route of inoculation. In northeastern France, tick bites are a frequent route of transmission. Typically, vector-borne inoculation results in glandular or ulceroglandular forms, whereas aerosol exposure causes pulmonary forms. We report the case of a 72-year-old immunocompromised woman (rheumatoid arthritis treated with methotrexate) who developed pneumonia six days after a tick bite, diagnosed four weeks later with a glandular tularemia. Although Francisella tularensis was not isolated from the lungs, a diagnosis of pulmonary tularemia was suspected at the adenitis stage based on serology and Polymerase chain reaction testing performed on the affected lymph node. The patient was successfully treated by ciprofloxacin. This case underscores the possibility of pulmonary tularemia following tick bites and the fact that multiple clinical forms may coexist in the same patient. Physicians should consider tularemia in case of pneumonia, especially when suggestive factors such as tick exposure or adenitis are present.

Highlights

• •A 72-year-old immunocompromised woman developed a pneumonia combined with glandular tularemia after a tick bite.
• •Tularemia should be considered in pneumonia cases associated with relevant suggestive factors such as tick exposure or adenitis.
• •Immunocompromised patients may develop unusual presentation, through bacteriemia leading to secondary localization including pneumonia.
• •In pneumonia resistant to β-lactam or occurring after a risk exposure, including tick bite, tularemia should be considered.

Background

Tularemia is a zoonosis caused by Francisella tularensis, a facultative intracellular Gram-negative coccobacillus, divided into two subspecies: F. tularensis subsp. tularensis (Group A) and F. tularensis subsp. holarctica (Group B) [[1], [2], [3]]. Francisella tularensis transmission occurs via direct contact with rabbits, hares, and rodents, or indirectly through inhalation of aerosols, contact with contaminated hydro-telluric environment or ingestion of contaminated food or water. While lagomorphs (e.g., Sylvilagus spp., Lepus spp.) and rodents (e.g., Microtus spp., Arvicola terrestris) are primary hosts, numerous other species can act as reservoirs [4,5]. Vector-borne transmission include: mosquito-borne transmission in Northern Europe, particularly in Sweden and Finland, horse flies and deer flies, though less frequently, in the United States and tick-borne transmission, particularly in regions such as northeastern France, where Ixodes ricinus is prevalent [2]. Due to its severity and high infectivity, only 10–15 organisms are sufficient to cause infection through skin or respiratory exposure, including severe, life threatening, pulmonary forms, F. tularensis is classified as a potential Category A bioterrorism agent by the Centers for Disease Control and Prevention [1,2,6,7].

Recent studies show an increase of tularemia in Europe, North America, and parts of Asia [2,5,[8], [9], [10]]. Clinical manifestations vary with transmission routes. Pulmonary forms typically results from inhalation while glandular forms are due to direct contact and oropharyngeal to ingestion of contaminated food or water [2,8,11]. We report a case of a 72-year-old immunocompromised woman who developed a pneumonia following a tick bite, as well as an inguinal lymphadenopathy detected later.

Case report

A 72-year-old woman with rheumatoid arthritis treated with methotrexate (15 mg/week) removed a tick from her left popliteal fossa on April 28, 2025 (Alsace, Northeastern France). On May 3, she developed fever, fatigue, rhinitis, and a persistent cough. On May 20, her general practitioner diagnosed community-acquired pneumonia and prescribed amoxicillin. Laboratory tests revealed an inflammatory syndrome (C-reactive protein [CRP] 157 mg/L) and leukocytosis (11.07 × 10 ³/mm³, neutrophils 8.97 × 10 ³/mm³). Polymerase chain reaction (PCR) tests for Severe Acute Respiratory Syndrome Coronavirus 2, Influenza A/B, Respiratory Syncytial Virus, Bordetella pertussis, B. parapertussis, and Mycoplasma pneumoniae were negative. After 48 h without improvement and rising CRP (199 mg/L), therapy was switched to amoxicillin-clavulanic acid. A chest X-ray revealed left lower lobe bronchopneumonia with a small pleural effusion (Fig. 1).

Fig. 1.

Chest X-ray with left pulmonary condensation (arrow).

She was referred to the emergency department on May 25 for worsening symptoms, and treatment was switched to azithromycin. Symptoms improved gradually, though fatigue and low-grade fever persisted. On June 7, she developed a painful left inguinal adenitis that fistulized by June 20. A computed tomography scan confirmed a 14 × 1.2 cm subcutaneous collected adenitis and thrombosis of the internal saphenous vein (Fig. 2), CRP was 159 mg/L, and the patient was hospitalized. Infectious disease consultation prompted tularemia serology and PCR of the collection/adenitis, both of which were positive, confirming the diagnosis of tularemia. She was treated with ciprofloxacin 500 mg twice daily for 14 days, leading to symptom resolution and normalization of inflammatory markers.

Fig. 2.

Abdominal computed tomography scan showing a left collected adenitis of the inguinal fossa (arrow).

Discussion

Tularemia incubation ranges usually from 2 to 6 days but may extend from 1 to 15 days.

Classical ulceroglandular tularemia symptoms begin with a flu-like syndrome followed by the appearance of an eschar and satellite adenitis localized in the axillar (30%), inguinal, submandibular, cervical, and mediastinal regions. However, tularemia has many clinical presentations, including ulceroglandular and glandular, oculoglandular (conjunctivitis), oropharyngeal, typhoid, and respiratory forms [2,8,11].

Various complications such as bacteriemia, meningitis, endocarditis, pleural involvement and hepatic or renal failure have been described in rare cases and are more likely in type A disease and in patients with underlying conditions like in our case [3,8].

Tick bites, a frequent route of inoculation in northeastern France as highlighted in a recent small case series report, [2] are responsible for the glandular or ulceroglandular forms. Pulmonary forms are usually related to inhalation and are either exclusive or associated with intrathoracic adenopathy; they are frequently described without peripheral adenitis [12]. The typhoidal form may occur after inoculation via different routes.

In our case, the tick bite occurred, and the first symptoms appeared about 5 days later. This was followed by the diagnosis of pneumonia, 22 days later and, ultimately, by the diagnosis of the glandular form in the same territory of the tick bite. The attending physician did not consider the diagnosis of tularemia and therefore did not perform specific tests for tularemia at the pneumonia stage. Therefore the possibility of pneumonia caused by another infectious agent, which resolved with azithromycin, cannot be entirely ruled out. However, the interval between the tick bite and the onset of pneumonia, the negative results of microbiological tests performed at that stage, and the lack of response to beta-lactams therapy, strongly suggest, in our view, a diagnosis of pulmonary tularemia. The possibility of a concomitant pulmonary infection and an unnoticed/infraclinic glandular form is probable; however, this case highlights that vector-based tularemia can lead to pulmonary forms. Respiratory forms are an becoming an increasing clinical presentation of tularemia in France, accounting for 50% of cases in 2024 [13] and present with a variety of symptoms such as high fever, dry or productive cough, nausea/vomiting, dyspnea, and chest pain. Pneumonia affecting one or more lobes may be observed and may sometimes be fatal without treatment in type A cases, rarely in type B [14]. Tularemia may also mimic lung cancer [12]. Diagnosis of tularemia is often delayed, as primary care physicians are generally unaware of tularemia in general and pulmonary forms in particular, which are more challenging and nonspecific. Diagnosis is most often based on blood cultures, or serology which becomes positive after 1–2 weeks, with a detection rate of more than 90% at 10 days of evolution with a specificity of more than 90%, or PCR of lymph nodes, pleural effusion, or pulmonary lavage. The patient had a poor clinical course under penicillin, and resistance to β-lactam treatment in the presence of tularemia risk factors can be an important diagnostic clue. The patient experienced resolution of her respiratory symptoms after azithromycin, an antibiotic not routinely recommended for tularemia but with activity against the pathogen [15,16]. However this treatment probably partially efficient favored a late consultation. However, treatment was unable to prevent progression of the adenitis, which was complicated by fistulization of an adenitis (limb), a complication frequently observed when appropriate treatment is delayed beyond 2 weeks [17].

The immunocompromised status of the patient may have also contributed to the unfavorable course and dual localization of the diseases. Few data are available on the impact of immunosuppression in tularemia, but patients with lymphomas or HIV infection or those receiving corticosteroids or chemotherapy appear to be at higher risk of severe forms [14]. Pulmonary forms are increasing and are associated with poorer outcomes, especially in immunocompromised patients [2]. This case describes a pneumonia following a tick bite with a bacteremia suspected to be the cause of the lung contamination. Hematogenous dissemination of the bacteria seems possible and is responsible for pneumonia in 10%–15% of cases [9,14,18]. Therefore, this case underscores this possibility after inoculation of F. tularensis by vectors. Although two different routes of exposure on the same day—aerosolization and a tick bite to the back of the knee—cannot be ruled out, this seems improbable.

In many cases, limited medical awareness of tularemia can lead to delayed appropriate treatment [14,19,20] and poor outcomes, particularly in immunocompromised patients. Physicians should therefore consider tularemia in cases of pneumonia, especially when resistant to β-lactam. A history of contact with wild animals, environmental exposure, tick bites, or the presence of concomitant adenitis is important elements that should be carefully investigated.

Conclusion

This case underscores the possibility of pulmonary tularemia following tick bites and the association of multiple clinical forms (pulmonary and glandular). Physicians should consider tularemia in case of β-lactam resistant acute or subacute pneumonia, especially in immunosuppressed patients, when adenitis or risk factors such as tick bites are present.

Ethics declaration

Written informed consent to take part in the study and to publish the article has been obtained from all participants or their legal representatives. The privacy rights of participants have been observed.

This study was performed in compliance with relevant laws, regulatory frameworks and guidelines where the research took place. Ethics committee approval was not required under relevant laws and institutional guidelines. Not required for a case report Written Consent Obtained

Ethics

Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

Declaration of Generative AI and AI-assisted technologies in the writing process

None.

Funding

None.

CRediT authorship contribution statement

Theo Van Gucht: Writing – review & editing, Writing – original draft, Conceptualization, Investigation, Methodology. Presenna Suntharasarma: Writing – review & editing, Data curation. Alia Barthel: Writing – review & editing, Data curation. Mahsa Mohseni-Zadeh: Writing – review & editing, Data curation. Guillaume Gregorowicz: Writing – review & editing, Resources, Data curation. Olivier Augereau: Writing – review & editing, Resources, Data curation. Victor Gerber: Writing – review & editing, Data curation, Validation, Visualization. Martin Martinot: Writing – review & editing, Writing – original draft, Supervision, Conceptualization, Data curation, Investigation, Validation.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

The data supporting the findings of this report are available from the corresponding author upon reasonable request.