By: Austin Weynand, MHS
You are managing a small primary care clinic just off the highway in Galveston County. A young child is brought in by their parents; they’ve been running a fever and headache for two days, but they are otherwise not too ill. With a keen eye you
notice a rash on their trunk, another clue towards your diagnosis, albeit a nonspecific one. There are many things that cause rashes. It would be wise to ask about the child’s animal and outdoor exposures, but would you be thinking of that?
If you did, you might get to the root cause – fleas.
In 2012, Dr. Lucas Blanton identified two cases of murine typhus, a flea-borne illness caused by the bacteria Rickettsia typhi, in Galveston.1 This was an important discovery; though cases often appear in parts of the southern United
States, it hadn’t been seen on the island since the 1950s (thought to be due to aggressive vector control strategies with DDT).2,3 UTMB’s Rickettsial Research Laboratory conducted a seroprevalence study to see just how many cases might have snuck under the nose of Galveston clinicians. Among sera of 500 Galveston residents, 1.2% had IgG antibodies against R. typhi.
“[Had] murine typhus reemerged because doctors were simply aware and looking for it? There is some truth to this,” Dr. Blanton explains. He has a theory on the northward expansion of the disease through cat fleas (Ctenocephalides felis)
feeding on opossums, since murine typhus has traditionally been found in Texas’ Rio Grande Valley. To find answers, they conducted a second, broader seroprevalence study,
this time expanding to the rest of the county. Among the sera of 528 residents, 7.8% had antibodies as identified through indirect immunofluorescence assay – a significant increase from nearly a decade ago.4 The geometric mean of
their antibody titers had also increased significantly since 2013, implying more recent infections among this cohort.
Armed with this new information, Dr. Blanton can now ponder: Why and how has the pathogen reemerged? He explains how researchers have classically attributed murine typhus to fleas of rats; but animal trapping data from Southern California in the late
1960s connected infected fleas predominantly to the Virginia opossum.5 Subsequent studies similarly implicated opossums in Texas.6,7 Suburban sprawl and the changing environment (including that due to climate change) may have
allowed their proliferation. Those fleas may interact with domestic cats as a “bridge host,” and therein lies a possible explanation for Dr. Blanton’s findings. “Some threshold has clearly been met to allow their spread,”
he says.
But back to the hypothetically infected child. The case fatality rate is less than 1%,2 but symptoms can still become serious – and the infection is often difficult to classify. Dr. Blanton quotes an old adage: “For every case of
murine typhus seen as a doctor, several go unrecognized”. So, while this child would be treated with antibiotics and almost certainly recover, public health vigilance is very important. In Dr. Walker’s Rickettsial Research Laboratory,
there are plans to further investigate vector control strategies for fleas, as well as ways to mitigate their zoonotic cycle spreading typhus between humans and animals. Dr. Blanton himself will be working on these projects. He is also researching
Rocky Mountain Spotted Fever (including a recently published One Health vaccine study).8 His research profile can be found here.
To see more information about typhus morbidity in Galveston, try here.