As cases of murine typhus in Texas are on the rise and occurring in more counties in the state, researchers are investigating the spread of the flea-borne disease.
Most of the cases of murine typhus, or endemic typhus, in the United States occur in California, Hawaii, and Texas, according to the Centers for Disease Control and Prevention (CDC). Caused by the Rickettsia typhi bacteria, the disease is spread by infected fleas whose hosts are typically rats, though domestic cats and opossums can also carry the fleas. Murine typhus causes illness in humans when feces from the fleas gets into cuts or wounds in the skin. Within 2 weeks, symptoms of the infection set in and can include fever and chills, body aches, muscle pain, loss of appetite, nausea, vomiting, rash, and cough. While most cases resolve on their own, the antibiotic doxycycline is the recommended treatment, and untreated cases can lead to severe illness and damage to the liver, kidneys, heart, lungs, and brain.
In recent research published in the CDC’s journal Emerging Infectious Diseases, a study team led by Baylor College of Medicine researchers examined the number of cases and geographic spread of typhus group rickettsiosis (TGR) in Texas from 2003 to 2013. Texas reports the most number of cases of TGR of any state in the country, and while the disease is most prevalent in southern parts of the state where murine typhus is considered endemic, the recent study found evidence of TGR in expanded geographic locations in the state as well as an increase in the number of cases. From 2003 to 2013, there were 1,762 reported cases of TGR in Texas, of which 770 were confirmed and 992 were probable. While 9 counties reported cases of typhus in 2003, by 2013 there were 41 counties reporting cases.
“We are not exactly sure as to why we are seeing this trend,” the study’s lead author, Kristy Murray, DVM, PhD, said in an interview with Contagion®. “One theory is climate change. Another theory is that the infection is becoming re-established in reservoir populations. Murine typhus was widespread and prevalent in the 1940s, with over 4,500 cases reported per year. DDT campaigns effectively eliminated the flea vectors, which then eliminated the pathogen all the way down to the very southern part of the state. Since then, the pathogen has remained endemic in the Rio Grande Valley, albeit at very low levels. It’s possible that the pathogen is spreading more and more throughout the reservoirs and making its way back to the rest of the state.”
The researchers found that typhus illness onset during the study period peaked in June and July, though south Texas experiences a second peak in December and January. The median age of case-patients in the study was 33 years, and the highest attack rate occurred in those between 5 and 19 years of age. In addition to these findings, the Texas Department of State Health Services notes that from 2008 to 2016, the number of counties reporting cases of flea-borne typhus each year rose from 18 to 36, and the number of annual cases more than doubled, going from 157 to 364.
While there is no vaccine for murine typhus, individuals can take steps to minimize their risk of catching the disease. “The best way to prevent murine typhus is to eliminate exposure to fleas,” says Dr. Murray. “This is best achieved by removing and preventing entry of rodents or other small mammals from homes and using flea prevention products on pets to prevent infestations.”