Sarah Strickland kept getting sicker - headaches, chills and a 103-degree fever, then a rash that covered much of her torso - but she didn't connect it to the critters that had just forced her out of her apartment near Rice University.

Strickland, then pursuing a master's degree in public health, had taken to crashing on a friend's futon, away from the baby opossums roaming her place after two adults nested in the converted home's crawl space.

Worried about meeting the deadline for her thesis, she cursed what she figured was just a virus that she had picked up,

"The doctors thought it was probably a virus too," Strickland said. "They said it'd clear up, that I'd be fine."

Turns out, Strickland had not a virus, but typhus, a bacterial scourge all but eradicated in most of the United States but making a comeback in Texas.

Strickland spent four days in a hospital receiving treatment and needed about a year to fully recover from the potentially fatal disease transmitted by fleas believed nowadays to be carried most abundantly by opossums and other backyard mammals that spread them to cats and dogs.

Between 2003 and 2013, typhus increased tenfold in Texas and spread from nine counties to 41, according to Baylor College of Medicine researchers

The numbers have increased since then.

Harris County, which reported no cases before 2007, had 32 cases in 2016, double the previous years' numbers.

Researchers do not know why the numbers are increasing.

Risk of hospitalization

In any case, the infection is severe enough that 60 percent of people who contracted the infection during the 10-year period had to be hospitalized. Four died, one in Houston.

"We can now add typhus to the growing list of tropical infections striking Texas," said Dr. Peter Hotez, founding dean of the National School of Tropical Medicine at Baylor and Texas Children's Hospital, "Chagas, dengue fever, Zika, chikungunya and now typhus - tropical diseases have become the new normal in south and southeast Texas."

Typhus was common in the United States through the 1940s - more than 5,400 people contracted the disease in 1944 - when rats that thrived among busy ports, such as Galveston, carried fleas infected with Rickettsia typhi.

An aggressive DDT campaign largely eliminated the problem in most U.S. areas - fewer than 100 cases were reported nationwide by the mid-1950s - though it never went away in the Rio Grande Valley.

It was Strickland's bout with the disease, in 2009, that first got the attention of Dr. Kristy Murray, a Baylor associate professor of infectious disease who had taught about typhus in the Valley but had not heard of it in modern-day urban centers, despite a focus on the tropical diseases that have emerged in Texas in recent times.

In the ensuing years, Murray heard enough anecdotal evidence of an increase in cases from local doctors that she decided to look at state data, combing through case histories to document the numbers and spot trends.

Murray was struck by the results, published recently in the journal Emerging Infectious Diseases, which showed 222 cases in Texas in 2013, many in Houston, Austin and San Antonio. That was up from just 30 reported cases in 2003, all in the southern part of the state, in counties such as Hidalgo and Nueces where the disease has remained an issue over the decades.

Affluent areas affected

Unlike many tropical diseases, which predominate in poor areas, the new cases of typhus were just as likely to be reported in more affluent areas, such as Bellaire and West University.

The highest rate of attack was in kids, 5 to 19 years old.

In 2016, according to the most recent state data, the number of Texas cases had risen to 364.

"We think this is a true increase, not just a growing recognition of the disease or increased surveillance," Murray said. "We're seeing a lot more cases in more areas and it's becoming a bigger burden. The positive is, it can be treated successfully if it's recognized."

The problem is, outside the Valley, typhus often is not recognized, and easily is confused with many viral ailments. In addition, today's doctors are not accustomed to looking for it, something Murray hopes the study remedies.

Delays in diagnosis make recovery more difficult. Strickland had become so dehydrated by the time she was hospitalized that she had to take the antibiotic intravenously, unable to simply swallow it. Her fever cleared quickly, but she had lost so much weight and muscle mass that she thinks she never has recovered athletically.

"It was truly life-changing," Strickland said. "I think in terms of 'before I had it' and 'after I had it.' "

Murray said she is surprised some of those infected survived given the severity of their symptoms. Many spent time in the intensive care unit.

Classic symptoms

Strickland had most of typhus' classic symptoms, but the infection also can cause achy muscles, nausea and vomiting.

A flea bite itself is not sufficient to transmit the infection, which occurs when people scratch bacteria-laden flea feces left by the flea into the bite or other wounds.

Dr. Lucas Blanton, an infectious disease specialist at the University of Texas Medical Branch at Galveston who documented that a majority of captured opossums carried the Rickettsia bacterium, said the new study is important because it will help raise awareness of a disease "often difficult for physicians to recognize and diagnose." He also said it should prompt further investigation, given the unknown cause of the spike in cases.

Enhance recognition

"One possibility includes better recognition of the infection by local physicians," said Blanton, noting a recent emphasis on the disease's symptoms at UTMB. "Another possibility is spillover of Rickettsia typhi from opossums and fleas (from the Valley) to communities that have been free of the disease for some time."

Murray suspects Blanton's latter theory, as well as climate change and globalization, are more likely explanations. She stressed the importance of flea protection for pets, noting the typhus bacterium is the one dogs and cats typically are scratching.

"People need to put typhus on their radar," Murray said. "This is a big comeback, not a minor one."