Francisella philomiragia is a distant cousin to Francisella tularensis, the cause of tularemia or “rabbit fever.” Unlike tularemia, however, F. philomiragia is an opportunistic pathogen that very rarely causes disease in people. In fact there have been only 17 reported cases over the past 40-year period. And the majority of these cases were in persons who were either immunocompromised or who had near-drowning experiences. It turns out that the bacteria lives in various natural water sources and in near-drowning cases, the individuals invariably get contaminated water into their lungs causing pneumonia and spread to their bloodstreams. In an article published this month in the journal Emerging Infectious Diseases, doctors report a case of F. philomiragia bloodstream infection in a man from France. However, this man was not the victim of a near-drowning experience, but had a rare skin disease called Sweet syndrome.
The man was 48-years old and lived near the coast of the North Sea. In addition to being diabetic, he was diagnosed with Sweet syndrome in 2012. Sweet syndrome – named after Dr. Robert Sweet who described the disease in 1964 – is characterized as a neutrophilic dermatosis, which means a skin disease associated with infiltration of white blood cells resulting in the appearance of red, tender vesicles and blisters, particularly on the head, neck, legs, and arms.
It is well-known that F. philomiragia likes to live in various natural water sources and is “salt loving” (what scientists call halophilic). In fact, the bacterium was first isolated in 1969 from a dying muskrat in Utah USA in the marshy waters that is part of the Great Salt Lake. Incidentally, I was part of a research team who isolated the bacterium from another aquatic environment – natural water springs – in Utah some 43 years later. It was also shown by researchers in Norway that the bacterium is ubiquitous in marine habitats in northern Europe. Given the patient’s residence in the coastal North Sea, and the fact that he had handled locally caught fish and shellfish before becoming sick, doctors suspect that the dermatosis lesions on the patient’s hands may have provided a portal of entry for F. philomiragia. The doctors also point out, however, that because the patient also had pneumonia, inhalation of aerosols from a contaminated environment could also have been a route of infection. Without a complete epidemiological investigation, it may never be known how this patient actually became infected with this rare bug. Dr. Louis Kreitmann, first author of the paper, stresses “further investigation is needed to better define the natural life cycle of this organism.”
Chris A. Whitehouse is a microbiologist and science writer who lives in Maryland. He writes extensively on emerging infectious diseases of humans and wildlife.