A 37-year-old man presents to an emergency department in Doha, Qatar. He reports that he has had a minor fever on and off for the past 4 days and notes that a day ago he developed a headache, had 3-4 episodes of nonbilious vomiting, loose stools, and stomach cramps. He also reports a red rash on both feet.
His past medical history is not significant. He tells clinicians he is not married, lives with a cousin, and has been employed in a plastics factory for the past 3 years.
The patient is admitted and in addition to the macular erythematous rash over both feet, clinical exam reveals tachycardia, mild tachypnea, blood pressure of 100/70 mm Hg, and a Glasgow coma scale score of 15 with no neck stiffness.
Laboratory tests show thrombocytopenia (103×103/μl, reference 150–400×103/μl), along with high serum concentrations of…
- Creatinine (155 μmol/L; reference 62–106 μmol/L)
- Urea (11 mmol/L; reference 2.76–8.07 mmol/L)
- Total bilirubin (100 μmol/L; reference 0–21 µmol/L)
- Aspartate aminotransferase (80 U/L; reference 0–40 U/L)
- Alanine aminotransferase (98 U/L; reference 0–41 U/L)
- C-reactive protein (355 mg/L; reference 0–5 mg/L)
Chest x-ray reveals mild bilateral haziness.
Based on a provisional diagnosis of acute gastroenteritis with acute kidney injury, clinicians start the patient on empirical treatment with ceftriaxone 2 gm in 2 liters of IV fluids over 6 hours; fluids and antibiotics are continued in the hospital.
On his second day in the hospital, the patient becomes increasingly tachypneic and tachycardic. His temperature spikes to 38.3°C, and he has an episode of hypoglycemia (2.9 mmol/L; reference 3.3–5.5 mmol/L).
On the third day, the patient’s tachycardia, tachypnea, and hypotension worsen and he is transferred to the intensive care unit. After a blood culture reveals gram-negative bacilli, clinicians initiate treatment with piperacillin/tazobactam. Later that day, he develops respiratory distress and he is intubated and ventilated.
On the fourth day, the patient’s blood pressure drops, and he requires vasopressors and a higher positive end-expiratory pressure to maintain acceptable blood pressure levels and partial pressure of oxygen.
Results of a blood culture the next day are positive for Streptobacillus moniliformis, and clinicians make a diagnose of rat bite fever (RBF). After the team consults with a microbiologist and infectious disease specialist, the patient is started on intravenous penicillin G, at a dose of two million units every 4 hours, and he improves rapidly.
On day 6, the patient’s condition is markedly improved, and he is weaned off the ventilator and his vasopressor is tapered.
He is discharged the next day, and over the following week, the patient’s renal function and acidosis improve, and he is extubated. An echocardiogram returns normal results, which combined with his clinical course, suggest that heart failure and infective endocarditis are unlikely. He is discharged from the hospital.
Although the patient denies being bitten by a rat, further history-taking suggests he may have had exposure to rats in his house and workplace; he also admits to often leaving food uncovered at both sites.
Discussion
Clinicians presenting this first documented case in Qatar of RBF note that in this region, education about animal contact is needed to prevent the disease. This particular zoonotic bacterial infection caused by infection with S. moniliformis, S. notomytis, or S. minus is rarely reported throughout the world.
The team notes that the patient’s presentation with sepsis and multi-organ failure requiring ventilatory support is unusual. High doses of penicillin G, however, produced rapid improvement.
RBF is spread by rats, gerbils, and mice, and may be transmitted from rodent to rodent as well as to humans. While humans can become infected directly through a rodent’s bite or scratch, approximately 30% of patients diagnosed are not aware of having been bitten or scratched by a rodent, reports indicate.
Historically, over 50% of cases have occurred in children, with a greater risk among those living in poverty. RBF is most often caused by two types of gram-negative, anaerobic bacteria: S. moniliformis and S. minus. The former is a highly pleomorphic, filamentous nonmotile gram-negative rod, and is estimated to cause RBF in about 10% of individuals bitten by rats. In contrast, RBF due to S. notomytis – which has a similar presentation – only rarely causes the disease in humans.
Consumption of water or food contaminated by rodent feces can cause other types of fever such as Haverhill fever, which the case authors note may explain their patient’s case, given his food-handling practices.
RBF symptoms generally develop about 2 weeks after initial transmission, typically with abrupt fever (92%), migrating polyarthralgia (66%), rash (61%), and nausea/vomiting (40%). The rash may be macular, papular, or petechial, and tends to affect the hands and feet most often.
Diagnosis is based on detection of the causative bacteria in the skin, blood, synovial fluid, or lymph nodes, although tests for the presence of anti-bacterial antibodies tests may be diagnostic. This particular patient was diagnosed through a positive blood culture.
In rare cases, infection can result in conditions such as disturbed consciousness. In these more serious manifestations, there is a risk that RBF might lead to such critical complications as spinal epidural abscess, mitral valve endocarditis and septic arthritis, acute tetraplegia, and vertebral osteomyelitis.
Complications of RBF can include endocarditis, myocarditis, pericarditis, systemic vasculitis, polyarteritis nodosa, meningitis, hepatitis, nephritis, amnionitis, pneumonia, and focal abscesses. Most fatalities occur in patients who develop endocarditis, usually the presence of pre-existing valvular heart disease.
Untreated RBF has a fatality rate of 7-10%. Two deaths have been reported in previously healthy adults in the U.S. in 2003; both patients died after developing fulminant sepsis — one due to a rat bite in a pet store, and the other most likely from a sick pet rat.
The antibiotic of choice for the treatment of RBF, especially in the absence of complications, is intravenous penicillin G, at a recommended dose of 400,000–600,000 IU/day for 1-2 weeks.
Because of the patient’s presentation with severe complications, he was treated with 2 MIU of IV penicillin G every 4 hours. Patients allergic to penicillin can be treated with 100 mg b.i.d. Other possible options include clindamycin, erythromycin, and ceftriaxone, although the authors note that the dosage and treatment duration for these have not been established.
Researchers have suggested that vector-borne diseases pose a significant public health problem, with a number of “old” diseases resurging in recent decades alongside newly emerging infectious diseases.
Conclusion
The case report authors conclude that zoonotic diseases in general and RBF in particular raise concern due to their ambiguous presentation and the difficulty of identifying the causative microorganism, which may result in a significant risk of delay or failure in diagnosis. In addition, the team notes, it is important to educate people about the possible dangers of animal contact.
Last Updated October 19, 2020
Disclosures
The case report authors noted no conflicts of interest.
The authors also note that the study was approved by the Institutional Review Board of Hamad Medical Corporation, which waived the requirement for informed consent.
Source: MedicalNewsToday.com
