LETTERS Tularemia in a by PCR and culture, and 1 was posi- submitted to BOL for F. tularensis test- tive by PCR alone; F. tularensis was ing by PCR and culture. None of these Park, Philadelphia, identifi ed only in animals found dead. readily available surveillance activities Pennsylvania The 2 woodchucks tested negative by resulted in identifying tularemia except PCR and culture. The 2004 isolate and in the rabbits found dead in the zoolog- To the Editor: Tularemia is a 2006 isolates were identifi ed by CDC ical park. Additionally, no cases of hu- bacterial zoonosis caused by the gram- as type A F. tularensis and were found man tularemia were reported to PDPH negative, nonmotile coccobacillus genetically identical by pulsed-fi eld during this period, despite distribution Francisella tularensis, which is en- gel electrophoresis. of a health alert to medical providers to demic in lagomorphs in North America These additional 2006 positive heighten clinical suspicion for the dis- (1,2). Tularemia is considered a pos- fi ndings triggered efforts to use avail- ease. Furthermore, the organism was sible biological weapon of terrorism able resources to identify other tula- not detected by routine environmental (Centers for Disease Control and Pre- remia sources: the Philadelphia De- monitoring of air samples by the city’s vention [CDC] category A) because of partment of Public Health (PDPH) BioWatch sensors. its high infectivity, ease of dissemina- heightened surveillance for tularemia Even though this limited investi- tion, and considerable ability to cause by requesting that other city agen- gation failed to identify additional F. illness and death in humans (3). The cies and wildlife rehabilitation cen- tularensis infections in humans and in BioWatch Program monitors the en- ters report and submit for testing any any of the animals and ticks tested, the vironment in urban areas throughout mammals found dead from unknown cluster of infections in rabbits in Phil- the United States for F. tularensis and causes. (City agencies reported a few adelphia indicates that F. tularensis other potential bioterrorism agents. larger mammals, e.g., groundhogs and is present in the environment in suf- The epidemiology of many of these raccoons, dead from trauma; these ani- fi cient numbers to cause a noteworthy pathogens in urban ecosystems is not mals were not tested.) The zoological die-off of animals (i.e., 6 rabbits in a well understood; reservoirs may not be park continued routine illness monitor- 0.5-square-mile area over a 5-month known or suspected, which leads to an ing of collection animals, animals on period). Environmental biomonitors inability to differentiate natural infec- grounds, and staff. In addition, during in other metropolitan areas have been tion from a bioterrorism event. We de- October 2006 and March 2007, the triggered by reported detection of tu- scribe a cluster of tularemia infections PDPH collected ticks on the outskirts laremia on at least 2 occasions in the (in the absence of identifi ed human of a heavily wooded area with fre- past 5 years—Houston in 2003 and illness or environmental detection) in quent foot traffi c ≈1.5 miles from the the Washington, DC, National Mall in 2 feral rabbits found in a 0.5-km area of site where the rabbits were found dead. 2005 (5). a large city park in Philadelphia, Penn- (The specifi c tick collection method This investigation underscores sylvania, USA. involved dragging a white cotton bath that F. tularensis identifi cation in the During the spring and summer of towel along the edge of a wooded area; environment requires a systematic ap- 2006, a total of 14 eastern cottontail this activity took place during the hours proach beyond environmental biomon- rabbits (Sylvilagus fl oridanus) and 2 of 10:00 AM–2:00 PM Other tick-drag- itoring, random convenience sampling, woodchucks (Marmota monax) were ging attempts during August 2007, on and increased passive surveillance for found dead or trapped and euthanized the outskirts of a heavily wooded area human cases. Standard methods such (2 rabbits only) at a zoological park. ≈0.5 miles away that was accessible to as serologic studies of wildlife may not The animals were necropsied, and foot traffi c but across the river from the be available to resource-limited urban specimens of liver and spleen were zoological park, yielded no results.) A institutions. Possible strategies such as sent to the Pennsylvania Bureau of total of ≈30 deer ticks (Ixodes scapu- the collection of ticks, specifi cally the Laboratories (BOL) for F. tularensis laris, which are not a known vector for American dog tick, Dermacentor vari- culture and PCR. Two years earlier, tularemia) were collected each month; abilis (a known vector for tularemia), in the spring of 2004, a single rabbit no other species were identifi ed. These from animals upon entry into urban found dead at this same location had tick specimens were submitted to BOL animal shelters and mapping of areas tested positive for F. tularensis; PCR for F. tularensis testing by PCR and cul- where the animals were found need to and culture identifi ed the organism ture. During November and December be considered if resources are limited. in liver and spleen. Of the 14 rabbits 2006, 5 crayfi sh (Procambarus acutus Additional research is necessary to submitted in 2006 for F. tularensis acutus, cited as a possible reservoir for understand the occurrence of disease testing, 6 were positive (collection type B tularemia by Anda et al.) (4), caused by F. tularensis in humans and dates ranged from March through were trapped from a pond near the site animals, especially in urban environ- August). Five of these were positive where the rabbits were found dead and ments (6). 1482 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 14, No. 9, September 2008 LETTERS Acknowledgments viron Microbiol. 2004;70:3733–5. DOI: scrub typhus (3). Two amplifi cation We thank the following persons and 10.1128/AEM.70.6.3733-3735.2004 reactions were performed, a real-time institutions for their assistance in obtain- quantitative PCR with a probe target- Address for correspondence: Julie R. Sinclair, ing and identifying specimens: Amy Han- ing the O. tsutsugamushi 47-kDa outer CDC Quarantine Station–Philadelphia, P.O. cock-Ronemus, Paul Mead, Ted Nuttall, membrane protein gene with appropri- Box 144, Essington, PA 19029, USA; email: Brigette Husband, and Kerry Pollard; the ate primers and probes (4) and a stan- [email protected] Department of Parasitology, College of dard PCR targeting a 372-nt fragment Veterinary Medicine, University of Penn- of the 56-kDa protein gene (3). sylvania; the Schuylkill Wildlife Rehabili- Buffy coat samples from 11 tation Center; and the Philadelphia Depart- (17.5%) patients were positive for O. ment of Public Health. tsutsugamushi in the real-time quanti- tative PCR and 56-kDa antigen gene Julie R. Sinclair, Alisa Newton, PCR (Table). All 11 patients were Keith Hinshaw, George Fraser, Genotyping from Vientiane or Vientiane Prov- Patrina Ross, Esther Chernak, of Orientia ince. PCR products for the 56-kDa Caroline Johnson, tsutsugamushi from gene fragments were purifi ed and se- quenced as described (3). Comparison and Nancy Warren Humans with Scrub Author affi liations: Centers for Disease (3,5) of amplicons for the 11 patients Control and Prevention, Atlanta, Geor- Typhus, Laos with each other and with GenBank gia, USA (J.R. Sinclair); Philadelphia Zoo, sequences identifi ed 6 genotypes. Per- To the Editor: Rickettsial dis- Philadelphia, Pennsylvania, USA (A. New- centages of nucleotide sequence simi- eases have been only recently identi- ton, K. Hinshaw); Pennsylvania Bureau of larity with other sequences available in fi ed as underrecognized but important Laboratories, Lionville, Pennsylvania, USA GenBank ranged from 95.9% to 100% causes of fever of unknown origin (G. Fraser, N. Warren); and Philadelphia (Table). Interpretation of our results in Laos. In 2006, 63 (14.8%) of 427 Department of Public Health, Philadelphia was also supported by recent phyloge- adults with negative blood cultures (P. Ross, E. Chernak, C. Johnson) netic studies that compared sequences admitted to Mahosot Hospital in Vien- of the entire 56-kDa type-specifi c anti- DOI: 10.3201/eid1409.071690 tiane had scrub typhus, an infection gen gene of isolates from Thailand (6). caused by Orientia tsutsugamushi and LaoUF238 and LaoUF220 genotypes References transmitted by the bite of larval trom- clustered with those of strains related biculid mites (1). O. tsutsugamushi to the Karp serotype, and LaoUF136 1. Farlow J, Wagner DM, Dukerich M, Stan- is characterized by a wide antigenic ley M, Chu M, Kubota K, et al. Francisella and LaoUF187 clustered with geno- tularensis in the United States. Emerg In- diversity, and isolates are convention- types of strains related to the Gilliam fect Dis. 2005;11:1835–41. ally classifi ed on the basis of reactiv- serotype (2). Other genotypes found in 2. Feldman KA. Tularemia. J Am Vet Med ity with hyperimmune serum against this study were grouped in 2 clusters Assoc. 2003;222:725–30. DOI: 10.2460/ prototype strains (e.g., Karp, Kato, javma.2003.222.725 that contained genotypes identifi ed in 3. Dennis DT, Inglesby TV, Henderson HA, Gilliam, Kawasaki, Kuroki, or Shimo- Thailand (5) and Taiwan (7) that have Bartlett JG, Ascher MS, Eitzen E, et al. goshi). The 4 hypervariable regions not been linked to a reference serotype Tularemia as a biological weapon. JAMA. within the 56-kDa type-specifi c anti- (Table). 2001;285:2763–73. DOI: 10.1001/jama. gen of O. tsutsugamushi, which is lo- 285.21.2763 Detection of O. tsutsugamushi in 4. Anda P, Segura del Pozo J, Diaz Garcia cated on the outer membrane surface, humans in Laos provides useful infor- JM, Escudero R, Garcia Pena FJ, Lopez are considered to play an essential role mation on genotypes prevalent in this Velasco MC, et al.