Ehrlichia DNA was identified by nested PCR in operculate snails (Pleuroceridae:Jugaspp.) collected from stream water in a northern California pasture in which Potomac horse fever (PHF) is enzootic. Sequencing of PCR-amplified DNA from a suite of genes (the 16S rRNA,groESLheat shock operon, 51-kDa major antigen genes) indicated that the source organism closely resembledEhrlichia risticii, the causative agent of PHF. The minimum percentage ofJugaspp. harboring the organism in the population studied was 3.5% (2 of 57 snails). No ehrlichia DNA was found in tissues of 123 lymnaeid, physid, and planorbid snails collected at the same site. These data suggest that pleurocerid stream snails may play a role in the life cycle ofE. risticiiin northern California.

We examined 11 naturally occurring isolates ofEhrlichia equiin horses and two human granulocytic ehrlichiosis agent isolates in California for sequence diversity in three genes.Ehrlichia equiisolates were from Sierra (n= 6), Mendocino (n= 3), Sonoma (n= 1), and Marin (n= 1) counties, and human granulocytic ehrlichiosis (HGE) agent isolates were obtained from Humboldt county. PCR with specific primers for 16S rRNA, 444Ep-ankandgroESLheat shock operon genes successfully produced amplicons for all 13 clinical samples. The 444Ep-ankgene of the HGE agent andE. equiisolates from northern California is different from the eastern U.S. isolates BDS and USG3. The translated amino acid sequence of thegroESLheat shock operon gene fragment is identical amongE. equi, the HGE agent, andE. phagocytophila, with the exception of the northern Californian equine CASOLJ isolate. Microheterogeneity was observed in the 16S rRNA gene sequences of HGE agent andE. equiisolates from northern California. These results suggest thatE. equiand the HGE agent found in California are similar or identical but may differ from the isolates of equine and human origin found in the eastern United States.

The first recognized cases of equine granulocytic ehrlichiosis in New England are described. The DNA sequence of the 16S rRNA gene of the causative ehrlichia was found to be identical to that of the human granulocytotropic ehrlichia, the agent of human granulocytic ehrlichiosis.

We report on the production and characterization ofEhrlichia risticii, the agent of Potomac horse fever (PHF), from snails (Pleuroceridae:Jugaspp.) maintained in aquarium culture and compare it genetically to equine strains. Snails were collected from stream waters on a pasture in Siskiyou County, Calif., where PHF is enzootic and were maintained for several weeks in freshwater aquaria in the laboratory. Upon exposure to temperatures above 22°C the snails released trematode cercariae tentatively identified as virgulate cercariae. Fragments of three different genes (genes for 16S rRNA, thegroESLheat shock operon, and the 51-kDa major antigen) were amplified from cercaria lysates by PCR and sequenced. Genetic information was also obtained fromE. risticiistrains from horses with PHF. The PCR positivity of snail secretions was associated with the presence of trematode cercariae. Sequence analysis of the three genes indicated that the source organism closely resembledE. risticii, and the sequences of all three genes were virtually identical to those of the genes of an equineE. risticiistrain from a property near the snail collection site. Phylogenetic analyses of the three genes indicated the presence of geographicalE. risticiistrain clusters.

Background: The synovial fluid test for alpha defensin has been reported to have an excellent performance in diagnosing periprosthetic joint infection (PJI). The purpose of this study was to evaluate the performance of the lateral flow test for synovial fluid alpha defensin by using the methods of a formal diagnostic accuracy study and to compare its performance with that of the laboratory-based alpha defensin test for PJI. Methods: We conducted a diagnostic accuracy study of the index lateral flow immunoassay for synovial fluid alpha defensin relative to the reference 2013 Musculoskeletal Infection Society (MSIS) multicriteria definition of PJI. The study included a prospective multicenter cohort of outpatients with a failed hip or knee arthroplasty and a supplemental control cohort of fresh synovial fluid specimens submitted by physicians for diagnostic PJI testing. Results: Among 57 patients with PJI and 248 patients without PJI in the overall prospective patient cohort, the sensitivity and specificity of the alpha defensin lateral flow test were 89.5% (95% confidence interval [CI]: 78.5% to 96.0%) and 94.8% (95% CI: 91.2% to 97.2%), respectively. The sensitivity increased to 94.3% (95% CI: 84.3% to 98.8%) after exclusion of 17 patients with grossly bloody aspirates (>1 million red blood cells/µL). Among the supplemental control cohort of fresh synovial fluid samples, including 65 samples from patients with PJI and 397 from patients without PJI, the sensitivity and specificity of the alpha defensin lateral flow test were 98.5% (95% CI: 91.7% to 100.0%) and 98.2% (95% CI: 96.4% to 99.3%), respectively. A comparison of the sensitivity and specificity of the alpha defensin lateral flow test with those of the alpha defensin enzyme-linked immunosorbent assay (ELISA) in the combined cohort did not demonstrate a significant difference in sensitivity (94.3% [95% CI: 88.5% to 97.7%] compared with 93.0% [95% CI: 87.1% to 96.7%]) or specificity (96.9% [95% CI: 95.3% to 98.1%] compared with 97.8% [95% CI: 96.4% to 98.8%]) (both p > 0.05). Conclusions: The results of this study demonstrate the solid diagnostic performance of the alpha defensin test and have resulted in the U.S. Food and Drug Administration (FDA) authorization of the lateral-flow test with an intended use as an aid in the clinical diagnosis of PJI. Level of Evidence: Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.