A sometimes fatal bacterial disease carried by fleas and lice appears to be spreading more often, and over a larger swath of territory in Texas than it did a decade ago, a new study suggests.
The authors aren’t sure how to explain the increase in murine typhus cases, though one suggested the “rampant” population of opossums in Texas may not be helping. The flea that can transmit the bacteria, called Ctenocephalides felis or the cat flea, infests opossums as well as rodents.
The condition has been traditionally found in southern Texas, in places where there is more poverty, said Melissa Nolan Garcia, a pediatric tropical medicine instructor at Baylor College of Medicine in Houston.
“However, when we are starting to see more cases in San Antonio, Houston, and Dallas … I think we’re starting to see a little bit of a shift,” she told STAT.
“We really don’t know why there’s an increase and we weren’t able to hypothesis too about that in this paper. Really the main point was just to bring home the fact that we’re starting to see a geographic expansion and that we’re starting to see more cases.”
The study was published online Wednesday in Emerging Infectious Diseases, a journal of the Centers for Disease Control and Prevention.
The authors — from Baylor College of Medicine and Texas Children’s Hospital, as well as the Texas Department of State Health — looked through Texas health records for recorded cases of typhus group rickettsiosis, a cluster of closely related diseases caused by a type of bacteria called rickettsia. Under state law, doctors are required to report all cases they diagnose.
The disease is also seen in Southern California, but this group only studied data from Texas.
While the researchers looked for cases of three diseases in this cluster, one was not found and another was seen only rarely. Most cases were caused by Rickettsia typhi, which is more commonly called murine typhus.
The researchers charted the number and geographic distribution of cases from 2003 to 2013. In the first year of the period, only 27 people were diagnosed with the disease; the cases were spread out over nine counties. And in the first few years of the study period, the annual count was around 100 cases.
But from 2008 the number of cases each year more than doubled and the number of counties reporting the disease climbed to 41. Of the 1,762 cases reported over the decade, nearly 60 percent — 1,047 — were sick enough to require hospitalization, and four people died.
Bites from infected fleas trigger the infection. In some people, the disease is mild and resolves on its own. In fact, the researchers believe their findings underestimate the problem, because only those sick enough to need care would have been tested.
Symptoms include fever, headache, rash, chills, loss of appetite, nausea, vomiting, and achy muscles. Young children and teenagers made up the largest group among the diagnosed cases. Nolan Garcia suggested children may be more likely to play with pets that have picked up infected fleas.
The disease can be effectively treated with antibiotics, if it is diagnosed early enough. But the disease shares symptoms with a number of diseases and this diagnosis is not top of mind for many doctors.
Patients who become severely ill — some end up in intensive care — can face a long recovery. But why some people get better without treatment while others become critically ill is not known.
“This is sadly a very neglected disease we don’t know a lot about,” Nolan Garcia said.
Dr. Lucas Blanton, of the University of Texas Medical Branch, in Galveston, was pleased to see this paper published, for that reason. An infectious diseases physician, Blanton has been studying rickettsial diseases.
He agreed there appear to be more cases, and cases found in more parts of Texas. But he wondered if the geographic spread the authors reported was a true expansion of the disease-causing fleas — or growing awareness of murine typhus among doctors, who are then more likely to spot it.
Blanton noted that in the first half of the last century, the disease was more widespread. “At one time it was all over the Southeast United States,” he said. But spraying of the pesticide DDT in the 1940s drove down flea populations, which slashed the number of human cases.
Still, it didn’t drive out the disease entirely, and doctors in Texas and Southern California should include it on their list of possibilities when faced with patients with fever, headache, and rash.
“Even if numbers are small compared to other infectious diseases … the remedy is so simple. Being able to treat a patient with a relatively inexpensive antibiotic and have them get better quickly means a lot,” Blanton said. “And all it really requires is awareness.”