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Christopher D Paddock

Publications and source records attributed to Christopher D Paddock.

44 records · Page 3Linked to original sources
PubMed2003

Predominance of Ehrlichia ewingii in Missouri dogs.

To investigate the species distribution of Ehrlichia present in Missouri dogs, we tested 78 dogs suspected of having acute ehrlichiosis and 10 healthy dogs. Blood from each dog was screened with a broad-range 16S rRNA gene PCR assay that detects known pathogenic species of Ehrlichia and ANAPLASMA: The species was determined by using species-specific PCR assays and nucleotide sequencing. Ehrlichia antibody testing was performed by using an indirect immunofluorescence assay with Ehrlichia chaffeensis as the antigenic substrate. The broad-range assay detected Ehrlichia or Anaplasma DNA in 20 (26%) of the symptomatic dogs and 2 (20%) of the asymptomatic dogs. E. ewingii accounted for 20 (91%), and E. chaffeensis accounted for 1 (5%) of the positives. Anaplasma phagocytophilum DNA was detected in one dog, and the sequences of regions of the 16S rRNA gene and the groESL operon amplified from the blood of this dog matched the published sequences of this organism. Antibodies reactive with E. chaffeensis were detected in 14 (67%) of the 21 PCR-positive dogs and in 12 (19%) of the 64 PCR-negative dogs. Combining the results of PCR and serology indicated that 33 (39%) of 85 evaluable dogs had evidence of past or current Ehrlichia infection. We conclude that E. ewingii is the predominant etiologic agent of canine ehrlichiosis in the areas of Missouri included in this survey. E. canis, a widely recognized agent of canine ehrlichiosis, was not detected in any animal. The finding of E. ewingii in asymptomatic dogs suggests that dogs could be a reservoir for this Ehrlichia species.

Animals↗
PubMed2003

Survey of ticks collected in Mississippi for Rickettsia, Ehrlichia, and Borrelia species.

From November 1999 through October 2000, we tested ticks collected from vegetation as well as from deer, dogs, and humans for spotted fever group (SFG) rickettsiae, Ehrlichia chaffeensis, and Borrelia spp. spirochetes. A total of 149 adult ticks representing four species was collected from 11 collection sites from southwestern to northern Mississippi. Amblyomma americanum was most commonly collected (n=68), followed by Ixodes scapularis (n=53). The bird tick, Ixodes brunneus (usually rare), was the third most commonly collected tick (n=17). Eleven Dermacentor variabilis were also collected. Ticks were cut longitudinally to make smears on three microscope slides. The remaining body parts were frozen at -65 degrees C for additional testing. Tick smears were stained by direct immunofluorescence assays (DFA) for Rickettsia spp. and Borrelia spp., while indirect immunofluorescence assays (IFA) were used for Ehrlichia spp. The corresponding tick for each positive smear was evaluated using PCR analysis. None of the 149 ticks tested was DFA positive for Borrelia spp. However, smears of 30 (20%) and 32 (22%) ticks reacted with anti-E. chaffeensis sera and anti-R. rickettsii conjugate (known to react with several members of the spotted fever group), respectively. None of the ticks staining with the IFA for Ehrlichia was positive for E. chaffeensis using PCR. However, 23 (72%) of 32 FA-positive ticks for SFG rickettsiae yielded amplicons of the appropriate size when tested using a PCR assay for SFG rickettsiae, corresponding to an overall infection rate with SFG rickettsiae among the collected ticks of 15%. Smears of 12 (71%) of 17 I. brunneus revealed abundant bacilliform bacteria. PCR amplification of DNA from a single I. brunneus containing these bacteria was performed using universal primers for the 16S rRNA gene as well as Borrelia-specific primers. The predominant sequence obtained using the universal primers did not match any sequence in GenBank, but it showed 91% identity with an endosymbiont of Acanthoamoeba. Other sequences represented in the top 50 Basic Local Alignment Search (BLAST) scores were primarily from soil bacteria, although some similarity to several Anaplasma species and Ehrlichia risticii was indicated. The significance of this finding remains undetermined.

Animals↗
PubMed2002

The ascendancy of Amblyomma americanum as a vector of pathogens affecting humans in the United States.

Until the 1990s, Amblyomma americanum was regarded primarily as a nuisance species, but a tick of minor importance as a vector of zoonotic pathogens affecting humans. With the recent discoveries of Ehrlichia chaffeensis, Ehrlichia ewingii, and "Borrelia lonestari," the public health relevance of lone star ticks is no longer in question. During the next 25 years, the number of cases of human disease caused by A. americanum-associated pathogens will probably increase. Based on current trajectories and historic precedents, the increase will be primarily driven by biological and environmental factors that alter the geographic distribution and intensity of transmission of zoonotic pathogens. Sociologic and demographic changes that influence the likelihood of highly susceptible humans coming into contact with infected lone star ticks, in addition to advances in diagnostic capabilities and national surveillance efforts, will also contribute to the anticipated increase in the number of recognized cases of disease.

Animals↗
PubMed2002

Reinfection with Ehrlichia chaffeensis in a liver transplant recipient.

Human monocytic ehrlichiosis is an emerging infection caused by Ehrlichia chaffeensis, but reinfection with this agent has not been described. We report a case of reinfection with E. chaffeensis after a 2-year interval in a 56-year-old liver transplant recipient with frequent tick attachments.

Antibodies, Bacterial↗
PubMed2002

Short report: concurrent Rocky Mountain spotted fever in a dog and its owner.

A sequential occurrence of Rocky Mountain spotted fever (RMSF) in a dog and its owner is described. Diagnosis of RMSF in the animal guided subsequent testing for and diagnosis of the same disease in the human patient. Previous reports of concurrent RMSF in dogs and their owners are reviewed, and the epidemiologic significance of this occurrence is discussed.

Aged↗
PubMed2002

Passive surveillance as an instrument to identify risk factors for fatal Rocky Mountain spotted fever: is there more to learn?

National surveillance for Rocky Mountain spotted fever (RMSF) dates from 1920; however, the collection of detailed epidemiologic, clinical, and laboratory data on RMSF by using case report forms began in 1970. Despite issues with compliance and changes in case definitions, surveillance data have permitted researchers to assess risk factors for fatal RMSF quantitatively. Factors consistently associated with increased risk of death include severity of disease, older age, lack of tick bite, absence of classic symptoms, delay in diagnosis and initiation of appropriate antibiotic treatment, and treatment with chloramphenicol only. In several studies, treatment with a tetracycline has been shown to be protective. The continuation of current passive surveillance activities may allow researchers to refine their estimates of risk but is unlikely to produce novel results. Modified surveillance activities could focus on evaluating the risk for fatal RMSF among special populations, monitoring appropriate antibiotic use, and assessing new diagnostic tests.

Diagnosis, Differential↗
PubMed2002

Assessing the magnitude of fatal Rocky Mountain spotted fever in the United States: comparison of two national data sources.

To assess the magnitude of fatal Rocky Mountain spotted fever (RMSF) and to evaluate the completeness of national surveillance for this occurrence from 1983 through 1998, two independent sources of RMSF mortality data were analyzed using a capture-recapture method. Two hundred twenty-four deaths reported through RMSF case report forms (CRFs) were compared with 304 RMSF-associated deaths recorded in the United States multiple cause-of-death (MCD) database. Demographic, geographic, seasonal, and temporal characteristics of decedents were remarkably similar between sources. Median annual deaths ascertained from CRF and MCD data sources were 11 (range = 5-35) and 18 (range = 5-39), respectively. Decedents were matched between sources by year, state, age, sex, race, and month-of-death; 111 deaths were matched to both sources, and percent concordance between CRFs and MCD data during the 16-year study period was 27% (range = 7-45%). An estimated 612 RMSF-associated deaths occurred during the study period (median = 37 per year, range = 16-64), suggesting that approximately 400 fatal cases of RMSF went unreported to national surveillance during the period 1983-1998, for an estimated completeness of CRF reporting of 36%.

Death Certificates↗