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Biological Health Hazard – Murine Typhus Outbreak: Texas (geographic expansion)


Published Date: 2017-03-17 18:26:45
Subject: PRO/AH/EDR> Murine typhus – USA: (TX) increase cases, geographic expansion, 2003-2013
Archive Number: 20170317.4908356

Date: Wed 15 Mar 2017
Source: Stat News [edited]

A sometime 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, called _Ctenocephalides felis_ or the cat flea that can transmit the bacteria 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 hypothesize 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 [Wed 15 Mar 2017] in Emerging Infectious Diseases, a journal of the Centers for Disease Control and Prevention [1]. 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 3 diseases in this cluster, 1 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 1st year of the period, only 27 people were diagnosed with the disease; the cases were spread out over 9 counties. And in the 1st few years of the study period, the annual count was around 100 cases. But from 2008 on, the number of cases each year more than doubled and the number of counties reporting the disease climbed to 41. Of the 1762 cases reported over the decade, nearly 60 percent (1047) were sick enough to require hospitalization, and 4 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 1st 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.”

[1. Murray KO, Evert N, Mayes B, et al. Typhus Group Rickettsiosis, Texas, USA, 2003-2013. Emerging Infectious Diseases. 2017;23(4):645-648. doi:10.3201/eid2304.160958. – Mod.ML]

[Byline: Helen Branswell]

Communicated by:

[The following has been extracted from reference 1 above:

“We characterized the epidemiology of typhus group rickettsiosis in Texas, USA. During 2003-2013, a total of 1762 cases were reported to the state health department. The number of diagnosed cases and geographic expansion increased over time. Physician awareness is critical to diagnose and effectively treat rickettsial infections.

“Typhus group rickettsiosis (TGR) is a fleaborne disease. In Texas, USA, most infections are attributed to _Rickettsia typhi_, the causative agent of murine typhus (1). Rare cases of another TGR, _R. prowazekii_, have been reported in south Texas (2).”

[_Rickettsia typhi_, the cause of murine typhus, is flea-borne, but _Rickettsia prowazekii_ , the cause of epidemic typhus, spreads between people by human body lice. Epidemic typhus occurs in developed countries sporadically, mainly in people who have acquired it while traveling or in immigrants from countries where the disease is endemic. Sporadic cases have also occurred in North America as a result of contact with southern flying squirrels that are infected with _R. prowazekii_ or infected flying squirrel nests ( – Mod.ML]

“The established reservoirs of murine typhus are _Rattus_ spp. rodents; however, opossums are thought to be an important reservoir in peridomestic settings, with the cat flea, _Ctenocephalides felis_, as the vector (3-5). Clinical disease in humans often is characterized by the classical triad of fever, headache, and rash, although 1 study found that rash was present in only 54 percent of cases and only 12.5 percent had the classical triad (6). Infections can be severe and potentially fatal if not treated appropriately (7).

“In the United States, Texas reports the most TGR cases annually, and TGR is considered endemic to the southernmost part of the state (8). Since the mid-2000s, public health authorities have observed an increase in the number of reported cases and geographic expansion into areas of the state to which TGR is not considered endemic. Our objective with this study was to characterize the epidemiology of TGR in Texas and identify high-risk geographic and demographic populations.

The Study
“The state of Texas mandates reporting of rickettsial diseases to the Texas Department of State Health Services (TxDSHS). TxDSHS maintains demographic, clinical, and environmental data on each case in a database for surveillance purposes. Confirmed cases of TGR were defined as clinically compatible illness with 1 of the following: 1) more or equal than 4-fold rise in antibody titer by immunofluorescent antibody, complement fixation, latex agglutination, microagglutination, or indirect hemagglutination antibody between acute and convalescent specimens; 2) a positive PCR result; 3) bacterial isolation from a clinical specimen; 4) positive immunofluorescence from tissue; or 5) a single IgM or IgG titer of more or equal than 1024 in the TGR-endemic area of south Texas or Travis County, beginning in 2007 and 2012, respectively. Probable cases were defined as clinically compatible illness and a single serologic titer of more or equal than 128 by immunofluorescent antibody, latex agglutination, microagglutination or indirect hemagglutination antibody or a single titer of more than 16 by complement fixation.

“During 2003-2013, a total of 1762 TGR cases (770 confirmed and 992 probable) were reported. We observed evidence of increased numbers of cases over time and expanded geographic locations. We know of no specific reason that would have prompted physicians to increase diagnosing or reporting cases. During the study period, case numbers reported ranged from 27 in 2003 to 222 in 2013 (Figure 1). An average of 102 cases were reported yearly during 2003-2007, which is less than half (209) of the average number reported during 2008-2013. As expected, illness onset peaked in June and July; however, in south Texas (more or equal than 28 degrees N), 2 peaks occurred: the 1st in summer (June and July) and the other in winter (December and January). The reason for this bimodal distribution of cases in south Texas is unknown and requires further investigation.

“TGR cases expanded geographically during the study period. In 2003, cases were reported from 9 counties in south Texas. By 2013, cases had been reported from 41 counties (Figure 2). Cumulative incidence was highest in south Texas; an average of 59.5 cases per 100 000 population were reported during the study period (Figure 2). Nueces County in south Texas had the highest cumulative incidence (139.9 cases/100 000 population). One county (Kenedy) in south Texas reported no cases; this is most likely due to this county’s low population count (416 persons) (10).

“Median age of case-patients was 33 years, and the highest attack rate was for 5-19-year-olds (10.4 cases/100 000 population). These findings contrast with a 1980s study of 345 murine typhus case-patients in south Texas for whom median age was 48 years, and only 5 (1.4 percent) case-patients were less than 11 years of age (6).

“Another potential limitation is the propensity of cross-reactions with other rickettsial pathogens. We would expect some degree of serologic cross-reaction between the 2 pathogens within the TGR group, _R. typhi_ and _R. prowazekii_; hence, we collectively call these diagnoses TGR, even though we presume most cases were attributed to _R. typhi_ infections. Serum reactive to typhus group antigen might cross-react, albeit infrequently and at a lower titer, to spotted fever group antigen (12). Finally, until 2015, TxDSHS included in the case definition for a confirmed case a single IgM titer more or equal 1024 in TGR-endemic areas. This decision was based on CDC’s criteria for diagnosing spotted fever rickettsiosis (13). As mentioned by CDC, a single IgM result is not ideal for diagnosing acute infections due to reduced specificity. Further research is needed to understand the true incidence of TGR in Texas.”

The full article, including the figures, tables and references, can be found at – Mod.ML

A HealthMap/ProMED-mail map can be accessed at:]

See Also

Murine typhus – USA: (TX) 20160723.4364997

Murine typhus – USA (02): (CA) opossum reservoir 20150307.3214752
Murine typhus – USA: (TX) 2013 20150221.3177260

Murine typhus – USA (02): (HI) 20140615.2539667
Murine typhus – USA: (CA) 20140322.2348945

Murine typhus – USA: (CA) 20131102.2035095

Murine typhus – USA (03): (CA) 20120816.1246475
Murine typhus – USA (02): (CA) 20120601.1153052
Murine typhus – USA: (TX) fatal 20120526.1145817

Murine typhus – USA (04): background 20110918.2841
Murine typhus – USA (03): (CA) 20110917.2831
Murine typhus – USA (02): (TX) 20110701.2000
Murine typhus – USA: (TX) 20110607.1734

Murine typhus – USA (04): (TX) 2008-2009 20091120.3995
Murine typhus – USA (02): (TX) 20090617.2240
Murine typhus – USA: (TX) 20090616.2228

Murine typhus – USA (CA) 20070816.2677

A ProMED-mail post
ProMED-mail is a program of the International Society for Infectious Diseases


Centers for Disease Control and Prevention – Emerging Infectious Diseases
Volume 16, Number 3—March 2010

Murine Typhus in Austin, Texas, USA, 2008


In August 2008, Texas authorities and the Centers for Disease Control and Prevention investigated reports of increased numbers of febrile rash illnesses in Austin to confirm the causative agent as Rickettsia typhi, to assess the outbreak magnitude and illness severity, and to identify potential animal reservoirs and peridomestic factors that may have contributed to disease emergence. Thirty-three human cases of confirmed murine typhus were identified. Illness onset was reported from March to October. No patients died, but 23 (70%) were hospitalized. The case-patients clustered geographically in central Austin; 12 (36%) resided in a single ZIP code area. Specimens from wildlife and domestic animals near case-patient homes were assessed; 18% of cats, 44% of dogs, and 71% of opossums had antibodies reactive to R. typhi. No evidence of R. typhi was detected in the whole blood, tissue, or arthropod specimens tested. These findings suggest that an R. typhi cycle involving opossums and domestic animals may be present in Austin.

Murine typhus, also known as endemic or flea-borne typhus, is caused by Rickettsia typhi, a gram-negative, obligate intracellular bacillus. This zoonotic disease is primarily maintained in rodent–flea cycles and is transmitted to humans when infected flea feces contaminate the flea feeding site or other skin abrasions (1). After an incubation period of 6–14 days, a nonspecific febrile illness may develop with symptoms of headache, arthralgia, abdominal pain, and confusion. Approximately 50% of patients also report the development of a diffuse macular or maculopapular rash, which starts on the trunk and spreads peripherally (sparing the palms and soles) nearly 1 week after the initial onset of fever and can last from 1 to 4 days. Although the disease is easily treated with doxycycline, it can be severe or even fatal if not diagnosed and treated properly (2,3).

Throughout its global distribution, R. typhi has been primarily concentrated in coastal urban areas where it is maintained among rats (Rattus spp.) and oriental rat fleas (Xenopsylla cheopis) (3). Within the United States, murine typhus is endemic in parts of California, Hawaii, and Texas, where <100 cases are reported annually (47) with a 1%–4% fatality rate when left untreated (3,4). Recent studies in southern Texas and California indicate that the classic rodent-flea cycle of R. typhi has been augmented in these suburban areas by a peridomestic cycle involving free-ranging cats, dogs, opossums, and their fleas (1,6,7). In addition, R. felis, which may produce a febrile illness in humans (8), may also circulate within these same zoonotic cycles (7,9). Although both agents have been documented in opossum-flea cycles in parts of southern Texas (7,9), these diseases are rare in the Austin/Travis County area. Though Austin is only 140 km from the Texas coast, where murine typhus is endemic, only 4 cases have been reported there in the past 25 years; 2 of those 4 cases were reported in September 2007 (Texas Department of State Health Services [TDSHS], unpub. data).

From March through July 2008, the Austin/Travis County Department of Health and Human Services (ATCDHHS) identified 13 cases of febrile illness, half of which had a rash or a severe headache, or both. Laboratory tests conducted at the TDSHS and the Centers for Disease Control and Prevention (CDC) indicated that these patients all had antibodies reactive to R. typhi. Active infection with R. typhi was also identified in 1 patient by PCR. In August 2008, TDSHS, CDC, and ATCDHHS initiated a detailed epidemiologic investigation to confirm the causative agent as R. typhi, to assess the outbreak magnitude and illness severity, and to identify potential animal reservoirs and peridomestic factors that may have contributed to disease emergence.


Adjemian J, Parks S, McElroy K, Campbell J, Eremeeva ME, Nicholson WL, et al. Murine Typhus in Austin, Texas, USA, 2008. Emerg Infect Dis. 2010;16(3):412-417.

National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)

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