Curtis L. Fritz

Cases of Cat-Associated Human Plague in the Western US, 1977–1998

Exposure to cats infected with Yersinia pestis is a recently recognized risk for human plague in the US. Twenty-three cases of cat-associated human plague (5 of which were fatal) occurred in 8 western states from 1977 through 1998, which represent 7.7% of the total 297 cases reported in that period. Bites, scratches, or other contact with infectious materials while handling infected cats resulted in 17 cases of bubonic plague, 1 case of primary septicemic plague, and 5 cases of primary pneumonic plague. The 5 fatal cases were associated with misdiagnosis or delays in seeking treatment, which resulted in overwhelming infection and various manifestations of the systemic inflammatory response syndrome. Unlike infections acquired by flea bites, the occurrence of cat-associated human plague did not increase significantly during summer months. Plague epizootics in rodents also were observed less frequently at exposure sites for cases of cat-associated human plague than at exposure sites for other cases. The risk of cat-associated human plague is likely to increase as residential development continues in areas where plague foci exist in the western US. Enhanced awareness is needed for prompt diagnosis and treatment.

Spatial analysis of plague in California: niche modeling predictions of the current distribution and potential response to climate change

BackgroundPlague, caused by the bacterium Yersinia pestis, is a public and wildlife health concern in California and the western United States. This study explores the spatial characteristics of positive plague samples in California and tests Maxent, a machine-learning method that can be used to develop niche-based models from presence-only data, for mapping the potential distribution of plague foci. Maxent models were constructed using geocoded seroprevalence data from surveillance of California ground squirrels (Spermophilus beecheyi) as case points and Worldclim bioclimatic data as predictor variables, and compared and validated using area under the receiver operating curve (AUC) statistics. Additionally, model results were compared to locations of positive and negative coyote (Canis latrans) samples, in order to determine the correlation between Maxent model predictions and areas of plague risk as determined via wild carnivore surveillance.ResultsModels of plague activity in California ground squirrels, based on recent climate conditions, accurately identified case locations (AUC of 0.913 to 0.948) and were significantly correlated with coyote samples. The final models were used to identify potential plague risk areas based on an ensemble of six future climate scenarios. These models suggest that by 2050, climate conditions may reduce plague risk in the southern parts of California and increase risk along the northern coast and Sierras.ConclusionBecause different modeling approaches can yield substantially different results, care should be taken when interpreting future model predictions. Nonetheless, niche modeling can be a useful tool for exploring and mapping the potential response of plague activity to climate change. The final models in this study were used to identify potential plague risk areas based on an ensemble of six future climate scenarios, which can help public managers decide where to allocate surveillance resources. In addition, Maxent model results were significantly correlated with coyote samples, indicating that carnivore surveillance programs will continue to be important for tracking the response of plague to future climate conditions.

Seroepidemiology of Emerging Tickborne Infectious Diseases in a Northern California Community

A seroprevalence and risk factor study of emerging tickborne infectious diseases (Lyme disease, ehrlichiosis, and babesiosis) was conducted among 230 residents of a semirural community in Sonoma County, California. Over 50% of residents reported finding a tick on themselves in the preceding 12 months. Samples from 51(23%) residents were seroreactive to antigens from one or more tickborne disease agents: 1.4% to Borrelia burgdorferi, 0.4% to Ehrlichia equi, 4.6% to Ehrlichia chaffeensis, and 17.8% to the Babesia-like piroplasm WA1. Only 14 (27%) of these seroreactive residents reported one or more symptoms compatible with these diseases. Seroreactivity was significantly associated with younger age (<16 years), longer residence in the community (11-20 years), and having had a physicians diagnosis of Lyme disease. In northern California, the risk of infection with these emerging tickborne diseases, particularly in children, may be greater than previously recognized.

Isolation and Characterization of Borrelia hermsii Associated with Two Foci of Tick-Borne Relapsing Fever in California

ABSTRACT Relapsing fever, caused by the spirochete Borrelia hermsii and transmitted by the soft tick Ornithodoros hermsi, is endemic in many rural mountainous areas of California. Between 1996 and 1998, 12 cases of relapsing fever associated with two exposure sites in northern California were investigated. Follow-up at exposure sites included collection of soft ticks and serum specimens from sylvatic rodents. Attempts to cultivate spirochetes were made through inoculation of patient blood into mice and by feeding Ornithodoros ticks on mice. Three isolates of B. hermsii were recovered from two blood specimens and one pool of ticks. The protein and plasmid profiles of the three isolates were comparable to those of previous B. hermsii isolates from the western United States. Western immunoblotting of patient sera demonstrated an expanding immunologic response to antigens within four distinct molecular weight regions by 3 to 4 weeks postonset. Antibody to B. hermsii was detected in sera from 4 of 11 yellow-pine chipmunks (Tamias amoenus); no other rodent species collected were seropositive.

Meningitis Due to a “Bartonella washoensis”-Like Human Pathogen

ABSTRACT We report the second human case of infection caused by an organism identified as the proposed Bartonella species, “B. washoensis.” The organism was isolated from a blood sample from a patient presenting with meningitis and early sepsis. Oropsylla montana fleas were implicated as the vector for disease transmission in this case.

Exposure to rodents and rodent-borne viruses among persons with elevated occupational risk

Persons who have frequent contact with rodents as part of their occupation may be at increased risk of exposure to rodent-borne viruses such as Sin Nombre virus (SNV), the agent of hantavirus pulmonary syndrome, and Whitewater Arroyo virus (WWA), a New World arenavirus. Eighty-one persons with possible occupational exposure to rodents completed questionnaires and provided specimens for serologic testing. Seventy-two participants reported handling rodents as part of their job. The mean total number of rodents handled during participants’ careers was approximately 2200. IgG antibody to lymphocytic choriomeningitis virus was detected in serum from one (1.2%) participant. IgG antibody to SNV, WWA, and Amapari viruses was not detected in any of the serum specimens. Despite considerable exposure to rodents, participants did not have significant serological evidence of exposure to rodent-borne viruses.

Predominant Kidney Involvement in a Fatal Case of Hantavirus Pulmonary Syndrome Caused by Sin Nombre Virus

A 27-year-old woman presented to a hospital with symptoms resembling pyelonephritis; respiratory distress did not develop until nearly a day after admission and she subsequently died. The Unexplained Deaths and Critical Illnesses Project of the Centers for Disease Control and Prevention confirmed Sin Nombre virus infection by the results of serological testing and sequencing of the viral genome; staining of Sin Nombre virus antigen in the pulmonary capillaries was relatively weak.

Serologic Evidence for Borrelia hermsii Infection in Rodents on Federally Owned Recreational Areas in California

Tick-borne relapsing fever (TBRF) is endemic in mountainous regions of the western United States. In California, the principal agent is the spirochete Borrelia hermsii, which is transmitted by the argasid tick Ornithodoros hermsi. Humans are at risk of TBRF when infected ticks leave an abandoned rodent nest in quest of a blood meal. Rodents are the primary vertebrate hosts for B. hermsii. Sciurid rodents were collected from 23 sites in California between August, 2006, and September, 2008, and tested for serum antibodies to B. hermsii by immunoblot using a whole-cell sonicate and a specific antigen, glycerophosphodiester phosphodiesterase (GlpQ). Antibodies were detected in 20% of rodents; seroprevalence was highest (36%) in chipmunks (Tamias spp). Seroprevalence in chipmunks was highest in the Sierra Nevada (41%) and Mono (43%) ecoregions and between 1900 and 2300 meters elevation (43%). The serological studies described here are effective in implicating the primary vertebrate hosts involved in the maintenance of the ticks and spirochetes in regions endemic for TBRF.

Use of a chitin synthesis inhibitor to control fleas on wild rodents important in the maintenance of plague, Yersinia pestis, in California.

Abstract A study was designed to test the insect development inhibitors fluazuron and lufenuron for the control of fleas on sylvatic rodents as an adjunct to the control of plague. Historical data of flea burden from 15 prior years of study at Chuchupate Campground, Ventura County, CA, were compared to six years of treatment period data to determine if fluazuron and lufenuron were effective in controlling flea densities. The insect development inhibitors, delivered systemically via a feed cube, reduced flea loads effectively on California ground squirrels (Spermophilus beecheyi), long-eared woodrats (Neotoma macrotis), and mice (Peromyscus spp.) but not on Merriams chipmunks (Tamias merriami).