Infection of lung cavitations in a young dog owner with Hodgkin’s lymphoma caused by Pasteurella multocida, without a dog bite: confirmed zoonotic transmission by tagmentation microbiome analysis

Abstract

Pasteurella multocida is a known pathogen in humans, mostly reported after animal bite incidents. Atraumatic infections have been described, especially in immunocompromised patients. A 20-year-old patient with a history of stage IV Hodgkin’s lymphoma with cavitating pulmonary lesions presented with a bilateral pneumonia. Shortly after finishing antibiotic treatment, she quickly developed the same symptoms of pneumonia. Bronchoscopy showed a large cavity in the right upper lobe and P. multocida was isolated from all bronchial cultures. The transmission route of P. multocida via the patient’s dog was confirmed by sampling the full genome of the dog’s mouth, which matched the unique P. multocida sequences found in the patient. This case demonstrates the importance of accurately determining the aetiology of the patient’s symptoms, and Pasteurella infection should be considered in all immunocompromised patients with domestic animal contact, even without a bite incident.

Background

Pasteurella is a genus of small Gram-negative coccobacilli, commensal in a variety of animals including dogs and cats but not in humans. Pasteurella multocida is the most common pathogenic species and has a carriage rate of approximately 80% in cats and 40% in dogs.

Animal-to-human transmission has been documented in several cases, and most infections were caused by bites. However, licks from the animal have also been reported as a source for severe P. multocida infections.¹

Immunocompromised individuals are at particular risk of severe P. multocida infection. Especially patients with cirrhosis, haematological malignancies, or solid organ transplantation are at marked risk.^2–4

The prognosis for patients infected with P. multocida depends on the site of infection and underlying medical conditions. Mortality rates of approximately 30% in cases of bacteraemia have been reported.⁵

We describe an immunocompromised patient presenting with P. multocida infection, without a dog bite. This case report shows the complex presentation of this disease and difficulties in making the correct diagnosis. We aim to raise awareness of this type of invasive infections in order to reduce delays in future similar cases.

Case presentation

A 20-year-old female patient with a history of stage IV Hodgkin’s lymphoma with cavitating pulmonary lesions presented to the emergency department. She had been treated with escalated bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine and prednisone, but after one cycle her treating physician decided to switch to doxorubicin, bleomycin, vinblastine and dacarbazine for toxicity reasons.

During treatment, neutropenic fever occurred due to a bilateral pneumonia and broad-spectrum antibiotics and antimycotics were given (meropenem 1000 mg intravenous three times daily and voriconazole 200 mg oral twice daily, respectively). Because bleomycin-induced lung injury could not be excluded, prednisolone 40 mg oral once daily was also administered. Blood and sputum cultures, and molecular investigations for the presence of atypical respiratory pathogens remained negative. Because of substantial improvement the patient was discharged from the hospital with oral antibiotics (amoxicillin/clavulanate 500/125 mg three times daily) and antimycotic treatment was continued.

Two days after finishing antibiotic and antimycotic treatment, the patient was readmitted to the hospital with recurring fever, chills and coughing. She had not been in contact with birds, nor had she visited a sauna. No one else in her environment was ill. Further history-taking revealed she had close contact (ie, kissing and licking) with her dog, but did not have any bite incidents. On physical examination she was moderately ill, with hypotension (blood pressure 92/54 mm Hg), tachycardia (pulse rate 117 bpm), mild tachypnoea (respiratory rate 16/min) and fever (temperature 38.5°C). Furthermore, there were no abnormalities in physical examination, in particular no pulmonary abnormalities.

Investigations

Laboratory results showed haemoglobin 7.9 mmol/L (7.5–10), thrombocytes 361*10⁹/L (150–400), leucocytes 10.7*10⁹/L (4–10) without neutropenia, potassium 3.2 mmol/L (3.3–4.8), creatinine 43 μmol/L (49–90), C-reactive protein 3 mg/L (<5) and lactate dehydrogenase 325 U/L (135–225).

Blood cultures, sputum cultures and molecular investigations for atypical respiratory pathogens remained negative. Chest X-ray was repeated and showed the well-known cavitations, but the infiltrative abnormalities were clearly decreased (figure 1). Atelectasis of the middle lobe was still noticeable.

Figure 1.

Chest X-ray at presentation: In the right upper lobe a large cavity is present, which has been the location of the patient’s Hodgkin’s lymphoma at diagnosis. Although differences between the X-rays are minor, a small pile of debris seems to be located at the bottom of the cavity.

Differential diagnosis

The differential diagnosis at this point was wide-ranging: a community-acquired pneumonia and a superinfection on top of a viral upper respiratory tract infection were considered. Atypical (bacterial) infections caused by Mycoplasma, Legionella, or Pneumocystis jiroveci and mycotic infections such as aspergillosis and invasive candidiasis were also kept in mind. Bleomycin-induced lung injury could not be excluded at that moment.

Treatment

Because of negative blood and sputum cultures during previous hospitalisations with pulmonary symptoms, cefuroxime 1500 mg intravenous three times daily was administered empirically according to Dutch national antibiotic guidelines.⁶

Outcome and follow-up

Because of the known cavitations and persisting pulmonary symptoms shortly after discontinuation of antibiotic treatment, we decided to perform a bronchoscopy with bronchoalveolar lavage (BAL). This bronchoscopy showed an impressive cavity in the right upper lobe containing a considerable amount of white debris. BAL fluid was obtained and cultured. Based on the findings of the bronchoscopy, a mycotic infection was highly suspected and, awaiting the results of the cultures, voriconazole 4 mg/kg intravenous twice daily was added to the antibiotic treatment.

P. multocida was isolated in all cultures of the BAL fluid. A fungal infection was not identified. These isolates were susceptible to beta-lactam antibiotics including penicillin, determined by VITEK antibiotic susceptibility testing (AST-344). Therefore, we switched our antibiotic therapy to penicillin 12 million units/day by continuous infusion for the first two weeks followed by 4 weeks of ceftriaxone 2000 mg intravenous once daily. Voriconazole was stopped.

When presenting with this infection the patient had one nine-year-old male dog. To prove route of transmission from her dog, the patient’s permission was obtained for sampling the dog’s mouth and oropharyngeal mucosa, usually the natural habitat of pasteurellaceae. Unfortunately, the dog had died the day before and was preserved at the veterinary clinic at −20°C. In consultation with the veterinarian surgeon, three swabs from the throat and both cheeks were taken after thawing overnight.

The full genome of the patient’s P. multocida was sequenced and compared with the dog’s microbiome obtained by Illumina tagmentation sequencing (Illumina Nextera XT, Eindhoven, The Netherlands). This resulted in matches of unique P. multocida sequences which proved that the P. multocida strain found in the patient originates from the dog’s oral microbiome (figure 2).⁷

Figure 2.

Data analysis pipeline elucidating the origin of the patient’s P. multocida. The genome of the patient’s isolate was sequenced by Illumina Nextera XT whole-genome sequencing at an Illumina Miniseq benchtop NGS sequencer (Illumina, Eindhoven, the Netherlands). A total of approximately 4.9 million 150 bp reads (1) were used to determine a whole-genome contig using GenBank sequence CP008918.1 (P. multocida ATCC43137) as alignment reference sequence (2,3). The dog’s microbiome was determined by Illumina Nextera XT tagmentation sequencing (4). A custom-made pipeline was built for the alignment of the patient’s P. multocida contig to the full dog’s microbiome (5). Subsequently, a total of 833 out of 14 million reads were found using Bowtie2 alignment allowing close (97%) but not unique similarities to the patient’s P. multocida genome to reveal strain-related sequence alignments (6). These 833 reads were analysed for >99% coverage, >98% similarity and annotation based on GenBank for other than 16SrRNA or 23SrRNA sequences to select for highly suspicious strain-specific sequences (7). This reveals a final number of 21 sequences from which one is 100% genetically similar to an existing P. multocida strain and therefore ambiguous to be strain-specific. Ten sequences are >99% specific for P. dagmatis, but <94% specific for P. multocida and have to be excluded as a strain-specific match (8). The final 10 sequences were unique for P. multocida with a similarity between 98.7% and 99.3% (9). Because those 10 single nucleotide polymorphism-containing sequences (SNPs) are located throughout the genome, comprising structural ribosomal proteins, cell-wall associated enzymes and enzymes involved in DNA repair, and thus suggestive for strain-specific SNPs, these sequences from the dog’s microbiome have to be considered as unique for the P. multocida strain found in the patient’s lung (10). The 10 sequences (22 SNPs in total) comprised error rates with quality-scores (Phred-scores) of 14 (2 SNPs), 21 (1 SNP), and 37 (19 SNPs), respectively. This indicates that the majority of the SNPs has a Phred-score of 37 implying an error rate below 0.0002 which is at least 10-fold lower than the expected estimated error rate of the Illumina MiSeq platform of 0.0021.⁷ The patient’s P. multocida genome has been deposited under GenBank accession number CP026744.1.

After finishing 6 weeks of intravenous antibiotic treatment, our patient remained free of symptoms. Despite her good clinical condition, we considered her high risk for recurrent pulmonary infections. She therefore underwent a thoracotomy to remove the large cavity in her right upper lobe. After lobectomy, the patient only had some symptoms of coughing up small amounts of thick mucus and after a period of frequent upper respiratory infections, she fully recovered.

Discussion

Infection with P. multocida can result in a variety of symptoms based on the severity and site of the infection, for example, a mild tissue infection or disastrous meningitis. However, P. multocida infections without a bite incident are very rare and associated with severe comorbidity and immunocompromising conditions. An underlying lung disease, for instance, a pre-existing lung cavity, is a known risk factor for P. multocida pneumonia.

Respiratory tract infections with P. multocida are rare and have no typical characteristics. Symptoms can vary from pharyngitis and otitis media to pneumonia, empyema, and lung abscess. Due to its rarity, P. multocida may not be suspected as the infecting pathogen. Symptoms, onset, and findings during physical examination and chest radiography vary widely.⁸

In this case, Pasteurella infection was not directly considered. Our patient presented with fever and coughing. Chest X-ray did not demonstrate new findings. At presentation we did not ask if the patient had pets, we only asked if she had been in contact with birds. Although initially the patient did benefit from the antibiotic treatment, the pulmonary symptoms recurred when antibiotics were discontinued. Initially no pathogen was identified, BAL was performed, which revealed P. multocida in the pre-existing lung cavity as the causative agent for the recurrent inflammatory symptoms. To our knowledge, only one case of P. multocida in a pulmonary cavitation has been previously described in the medical literature, although this case concerned a patient with fatal massive pulmonary haemorrhage. Our case demonstrated once more the value of a further investigation to determine the exact aetiology of a patient’s symptoms, especially in patients with known comorbidities. In soft tissue infections following cat scratches or cat or dog bites or licks, Pasteurella is the most suspicious organism causing infection. Immunocompromised patients with a history of domestic animal contact are in particular risk and therefore the possibility of Pasteurella infection should be considered in those patients presenting with serious infections, for example, pneumonia.

We have managed to confirm the transmission route of a non-human commensal pathogen by culturing the patient’s dog. Although this has been described before, new molecular technologies were used to gain evidence for the suspected transmission route.^{7 9} After confirmation of the source of this very severe P. multocida infection, questions may arise on formulating more strict guidelines regarding the interaction with domestic animals during intensive chemotherapy or other immunocompromising treatment and interventions. In our opinion, strengthened by this case, immunocompromised pet owners should be educated by physicians to minimise the risk for invasive zoonotic infections.

Patient’s perspective.

After a long period of persistent fever, I was admitted to the hospital. I was treated with several antibiotics but I did not really recover. Because my diagnosis remained unclear, I underwent a bronchoscopy. I was very nervous and the sedation did not work well for me, meaning that the bronchoscopy could not be performed adequately. Because the doctors did not know which microorganism I had at that moment, they could not treat me accurately.

My illness worsened and I became shorter of breath, which eventually even led to admission to the intensive care unit. I received a lot of medication, including prednisolone, to reduce my shortness of breath. Fortunately, the prednisolone did seem to work and I felt increasingly better. After two weeks of rehabilitation, I was discharged from the hospital.

I was allowed to slowly reduce the dose of prednisolone. When I was almost off the prednisolone, the fever recurred and I had to be readmitted to the hospital. Considering that the bronchoscopy failed the first time and sedation did not work out well, this time bronchoscopy was fortunately carried out under general anaesthesia. Therefore, the doctors could perform the bronchoscopy as well as possible this time. The results showed that I had a Pasteurella infection. The doctors were very surprised, and I was treated with penicillin intravenously for 6 weeks.

Since this bacterium is mainly present in animals, my just deceased dog’s saliva was investigated. Finally, it turned out that, due to my reduced immune system, I was infected with the bacterium of my own dog. Fortunately, the treatment has been successful and I am disease-free for over 22 months.

Learning points.

• Pasteurella multocida infections in patients are rarely identified due to the pathogen’s wide range of clinical symptoms and lack of experience with this organism.

• Further investigation should be performed to determine the exact aetiology of a patient’s symptoms, especially in patients with known comorbidities.

• Contact with domestic animals (including non-traumatic) could suggest P. multocida as potential pathogen, especially in immunocompromised patients or patients with pre-existing lung disease.

• Immunocompromised pet owners should be educated by physicians to minimise the risk of severe invasive zoonotic infections.