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Biomedical subjects

J E Dawson

Publications and source records attributed to J E Dawson.

At least 37 records · Page 2Linked to original sources
PubMed1996

The first isolation, in vitro propagation, and genetic characterization of Ehrlichia canis in Israel.

Ehrlichia canis, the etiologic agent of canine ehrlichiosis, was isolated in Israel from a naturally infected dog with acute signs of the disease. The organism designated E. canis 611, was passaged experimentally to a beagle, from which it was propagated in primary canine monocytes. The organism was then grown in vitro in a continuous canine cell line, DH82. Nine beagles subsequently injected with whole E. canis-infected blood all developed typical symptoms of ehrlichiosis. An indirect immunofluorescence antibody test to E. canis was developed and compared with a commercial kit, revealing a good correlation between the two assays. Transmission electron microscopy of DH82 cells infected with the Israeli strain of E. canis (611), revealed organisms similar to those described in the literature: two different forms of morulae appeared, one tightly, the other loosely, packed. The 16S rRNA gene sequence obtained from the Israeli Ehrlichia isolate was compared with other isolates, E. canis Oklahoma and E. canis Florida. The Israeli strain 16S rRNA had three nucleotide differences from the Oklahoma isolate, and four nucleotide differences from the Florida isolate, in addition to one nucleotide gap in each. The Israeli isolate was found to be 0.54% different from the Oklahoma strain, and 0.61% different from the Florida strain. There are the same magnitudes of differences displayed by the other most closely related group in the phylogenetic tree, namely Ehrlichia equi, Ehrlichia phagocytophilia and the human granulocytic ehrlichia.

Animals↗
PubMed1996

Persistent infection of C3H/HeJ mice by Ehrlichia chaffeensis.

Description of the pathobiology of the recently described zoonotic agent of human ehrlichiosis (Ehrlichia chaffeensis) would be greatly facilitated by the availability of a convenient experimental animal model of infection. We determined whether C3H/HeJ mice could sustain persistent infection by this predominantly monocyte-inhabiting rickettsia. Such mice rapidly produced an intense specific IgG response upon inoculation of ehrlichiae, and high titers were demonstrable for more than 6 months thereafter. Ehrlichiae were reisolated from the peripheral blood and spleen of 1 mouse at day 11 after inoculation. DNA of E. chaffeensis was more frequently detected within these tissues by polymerase chain reaction. Other candidate rodent models appeared to be poor hosts for this pathogen. About half of intact and virtually all splenectomized white-footed mice that were inoculated seroconverted. Sera from inoculated voles and hamsters did not react to antigens of E. chaffeensis. The C3H/Hej mouse becomes persistently infected by this rickettsia, and may serve as a useful model for studies of the immune response to the agent of human ehrlichiosis.

Animals↗
PubMed1996

Site-specific geographic association between Amblyomma americanum (Acari: Ixodidae) infestations and Ehrlichia chaffeensis-reactive (Rickettsiales: Ehrlichieae) antibodies in white-tailed deer.

Serum samples from white-tailed deer, Odocoileus virginianus Zimmermann, collected from 1982 through 1992 from the southeastern United States were tested for antibodies reactive to Ehrlichia chaffeensis Anderson, Dawson, Jones, & Wilson, the causative agent of human ehrlichiosis. Results were compared between areas based on known infestations of the lone star tick, Amblyomma americanum L., a suspected vector of E. chaffeensis. One hundred and twenty-five of 300 (41.7%) deer tested positive (> or = 1:128) for E. chaffeensis-reactive antibodies by fluorescent antibody analysis. Thirty of 30 (100%) collection areas known to be lone star tick infested contained deer that tested positive for E. chaffeensis-reactive antibodies, corresponding to 121/150 (80.7%) of deer examined. A few deer, 4/150 (2.7%) of those examined, from 2 of 30 (6.7%) areas where lone star ticks were not detected were positive for E. chaffeensis-reactive antibodies. This site-specific geographic association between A. americanum and the presence of E. chaffeensis-reactive antibodies in deer provides strong evidence that A. americanum is a natural vector of E. chaffeensis or a closely related species among white-tailed deer.

Animals↗
PubMed1996

A recombinant antigen from the heartwater agent (Cowdria ruminatium) reactive with antibodies in some southeastern United States white-tailed deer (Odocoileus virginianus), but not cattle, sera.

Recombinant baculovirus techniques were used to express the 260 amino acid carboxyterminal portion of the 32 kilodalton (kDa) major antigenic protein (MAP 1) of Cowdria ruminantium, the heartwater agent, as a fusion protein. The recombinant MAP 1 was fused to an aminoterminal independently antigenic octapeptide sequence (FLAG peptide). Recombinant MAP 1 was used as an immunoblotting antigen to evaluate numerous reference antisera against organisms of the tribe Ehrlichieae. Monoclonal and polyclonal C. ruminantium antibodies, monoclonal anti-FLAG ascites, and antisera to Ehrlichia canis and Ehrlichia chaffeensis reacted with this antigen. Twelve of 79 sera collected 1980 to 1992 from southeastern U.S. white-tailed deer (Odocoileus virginianus) were also unexpectedly immunoblot-positive to MAP 1. These 12 deer sera had, as a group, significantly (P < 0.01) greater anti-E. chaffeensis titers (previously determined) than the sera from MAP 1 immunoblot-negative deer living in the same areas. None of the 262 sera from cattle living in the same areas were immunoblot-positive to MAP 1. All of an additional 50 cervine sera from Michigan (USA), 72 bovine sera from northern U.S. cattle, and 72 sera from Puerto Rican cattle were also immunoblot-negative to MAP 1. Sera from African sheep which were falsely seropositive to authentic MAP 1 were also immunoblot-positive to the recombinant MAP 1. Unidentified Ehrlichia spp. capable of serologic crossreactivity with the heartwater agent appear to be present in some southeastern U.S. white-tailed deer but not cattle. These or related Ehrlichia spp. may also be found elsewhere in the world in non-cervine species.

Animals↗
PubMed1996

Ehrlichia-like 16S rDNA sequence from wild white-tailed deer (Odocoileus virginianus).

The reservoir hosts of Ehrlichia chaffeensis, etiologic agent of human ehrlichiosis are unknown. Initially, white-tailed deer (WTD) were serologically implicated as possible reservoirs of E. chaffeensis. Subsequent studies showed that WTD were susceptible to infection with E. chaffeensis and that deer-to-deer transmission by a tick vector, Amblyomma americanum, is possible under experimental conditions. To determine if wild WTD were infected with E. chaffeensis, whole blood was collected from 10 deer from Oklahoma and Georgia. All 10 deer had antibodies reactive to E. chaffeensis. Whereas E. chaffeensis was not isolated, restriction enzyme mapping and sequencing of the 16S rDNA gene revealed that a unique Ehrlichia-like agent was present. All 10 deer appeared to be infected with the same agent. We suspect that A. americanum is the vector of this new agent based upon the previously published temporal association between the appearance of E. chaffeensis seropositive WTD and A. americanum. However, the taxonomic and antigenic relationships, geographic distribution, epidemiology, and zoonotic potential of this agent are yet to be determined.

Animals↗
PubMed1996

Polymerase chain reaction evidence of Ehrlichia chaffeensis, an etiologic agent of human ehrlichiosis, in dogs from southeast Virginia.

OBJECTIVE: To ascertain whether dogs are naturally infected with Ehrlichia chaffeensis. ANIMALS: 74 dogs from 5 animal shelters and 1 kennel in 3 cities and 3 counties in southeastern Virginia were tested during June 1991. PROCEDURE: Blood was drawn from 74 dogs; 73 were tested serologically for antibodies reactive to E chaffeensis and E canis, and 38 were tested for the presence of E chaffeensis, E canis, and E ewingii by polymerase chain reaction (PCR). Serologic testing by indirect fluorescent antibody assay. Nested PCR used Ehrlichia wide outside primers to detect initial products, followed by use of species-specific primers for identification. RESULTS: 28 (38.4%) dogs had a positive test result (minimum titer, > or = 1:64) for antibodies reactive to E chaffeensis, and 28 (38.4%) had a positive reaction to E canis. PCR analysis indicated that 8 (42.1%) dogs were positive for E chaffeensis and 6 dogs (31.6%) were positive for E ewingii. All dogs had negative results of the PCR test for E canis. CONCLUSION: Dogs are potential reservoirs of E chaffeensis. CLINICAL RELEVANCE: Canine E chaffeensis infection may be more prevalent than E canis or E ewingii infection in this region of the United States.

Animals↗
PubMed1996

Attempted transmission of Ehrlichia canis by Rhipicephalus sanguineus after passage in cell culture.

OBJECTIVES: To compare the transmissibility by the brown dog tick, Rhipicephalus sanguineus, of a recent isolate of Ehrlichia canis (Ebony) with that of another isolate (Oklahoma) that had been passaged in cell culture, and to assess the genetic similarity of the 2 isolates as reflected in the nucleotide (NT) sequence of 16S rDNA. ANIMALS: 13 healthy dogs of various ages and breeds. PROCEDURE: Larval and nymphal ticks were acquisition fed on acutely infected dogs, and, after molting, they were transmission fed as nymphs and adults, respectively, on Ehrlichia-naive dogs. All dogs were monitored daily by blood smear evaluation for evidence of parasitized leukocytes and by physical examination for clinical signs of ehrlichiosis. Serologic and hematologic values were measured weekly. Using a nested polymerase chain reaction, the 16S rDNA was amplified, and the NT sequence of the template DNA was determined. RESULTS: The Ebony isolate of E canis was successfully transmitted to dogs by nymphal and adult ticks. In contrast, no ticks that fed on dogs harboring the cell-cultured isolate (Oklahoma) transmitted it to dogs. On the basis of 16S rDNA sequence, the 2 isolates were 99.9% similar, with only 1 NT difference. CONCLUSIONS: These results reconfirm the vector potential of R sanguineus for E canis. Passage of the Oklahoma isolate of E canis in cell culture apparently adversely affected its transmissibility by ticks, raising the possibility that cell-cultured isolates of this rickettsia may lose their affinity for ticks. Determination of 16S rDNA sequence suggests minor strain variation within the species E canis.

Animals↗
PubMed1995

Ehrlichiosis in a golf-oriented retirement community.

BACKGROUND: Ehrlichiosis due to Ehrlichia chaffeensis usually occurs sporadically or in small clusters, with an annual incidence estimated at 3 to 5 cases per 100,000 population in areas of endemic disease. The putative principal vector is the Lone Star tick (Amblyomma americanum). We investigated an outbreak of ehrlichiosis that occurred in June 1993 among members of a golf-oriented retirement community (community A) in Tennessee. The community is densely wooded and borders a wildlife-management area where deer are numerous. METHODS: We conducted a case-control study, using medical-history reviews, serologic testing, and testing with the polymerase chain reaction for E. chaffeensis infection. We also surveyed a sample of 10 percent of the households in community A and in another golf-oriented community (community B) more than 20 miles (32 km) from the wildlife-management area. Survey participants completed a questionnaire and provided specimens for serologic testing. In both communities, searches for ticks were undertaken. RESULTS: Eleven cases of symptomatic ehrlichiosis were identified in the case-control study, 10 of which were in community A (attack rate, 330 per 100,000). Of 311 surveyed residents of community A, 12.5 percent had serologic evidence of past E. chaffeensis infection, as compared with 3.3 percent of 92 in community B (relative risk in community A as compared with community B, 3.9; 95 percent confidence interval, 1.2 to 12.2). The risk of infection was associated with tick bites, exposure to wildlife, golfing, and among golfers, retrieving lost golf balls from the rough. Persons who never used insect repellent were more likely to have had infection than persons who did. In community A, thousands of Lone Star ticks were found; in community B, only three ticks were found. CONCLUSIONS: The high rate of E. chaffeensis infection in community A resulted from its proximity to a wildlife reserve. When outdoor recreational activities are common and concentrations of ticks are high, outbreaks of arthropod-borne zoonoses can be anticipated.

Adolescent↗
PubMed1995

Seroepidemiology of infections due to spotted fever group rickettsiae and Ehrlichia species in military personnel exposed in areas of the United States where such infections are endemic.

A prospective, seroepidemiologic study of spotted fever group rickettsiae (SFGR) and Ehrlichia infections was done among 1194 US military personnel exposed in a heavily tick-infested area of Arkansas in 1990. Seroconversion (4-fold) and seroprevalence rates were determined by indirect immunofluorescent antibody assays. Seroconversions to SFGR occurred in 30 persons (2.5%), whereas seroconversion to Ehrlichia species occurred in 15 (1.3%). The majority of seroconverters did not report symptoms (22/30 [73%] of SFGR seroconverters; 10/15 [67%] of Ehrlichia species seroconverters). History of tick attachment was associated with seroconversion to SFGR (relative risk [RR] = 4.3, P < .001) and Ehrlichia species (RR = 3.6, P < .05). Use of permethrin-impregnated uniforms significantly decreased risk of infection (P < .01); use of bed nets increased risk by 4-fold. Tickborne infections represent a significant threat to military personnel training in areas in which these infections are endemic.

Adolescent↗
PubMed1995

Experimental transmission of Ehrlichia chaffeensis (Rickettsiales: Ehrlichieae) among white-tailed deer by Amblyomma americanum (Acari: Ixodidae).

Ehrlichia chaffeensis Anderson, Dawson & Wilson, causative agent of human (predominantly monocytic) ehrlichiosis, was successfully transmitted experimentally by Amblyomma americanum (L.) to white-tailed deer, Odocoileus virginianus (Zimmerman). Deer were needle-exposed intravenously to E. chaffeensis in tissue-culture canine macrophage (DH82) cells, and 11 d later were exposed to laboratory-reared A. americanum larvae, nymphs, and adults for acquisition feeding. Three months after this feeding, naive deer and dogs were exposed to recently molted nymphs and adults. Attempted reisolation of the pathogen by way of tissue culture was successful from one needle-exposed deer but not from the tick-exposed deer or dogs. Based on serologic evidence and polymerase chain reaction data, both nymphal and adult ticks transmitted E. chaffeensis to naive deer but not to dogs.

Animals↗
PubMed1995

Temporal association of Amblyomma americanum with the presence of Ehrlichia chaffeensis reactive antibodies in white-tailed deer.

From 1981 through 1993, tick infestations and serum antibodies reactive to Ehrlichia chaffeensis, the causative agent of human ehrlichiosis, were monitored among white-tailed deer (Odocoileus virginianus) at Whitehall Experimental Forest, Clarke County, Georgia (USA). Neither ticks nor E. chaffeensis antibodies were detected during the first two years of the study. Infestations of the lone star tick (Amblyomma americanum), a suspected vector of E. chaffeensis, first were noted on deer in 1983. Prevalence and intensity of A. americanum sharply increased from 1985 to 1989, and prevalence was 100% from 1990 to 1993. Antibodies reactive to E. chaffeensis were first detected in 7% of deer sampled in 1986. Antibody prevalence increased to 21% in 1987 and was 100% from 1988 to 1993. This temporal association between the establishment of A. americanum and the appearance of E. chaffeensis antibodies provides evidence to support the concept that A. americanum could be a natural vector of E. chaffeensis. The high prevalence of antibodies among all age classes of deer also reaffirms that white-tailed deer may be sensitive natural sentinels for monitoring the distribution of E. chaffeensis.

Animals↗
PubMed1995

Antibodies against Rickettsiaceae in dogs of Setúbal, Portugal.

An indirect fluorescent antibody test was performed on sera collected from dogs housed in the municipal kennel of Setúbal to assess the prevalence of antibodies to Ehrlichia canis, the causative agent of canine ehrlichiosis and to Rickettsia conorii, agent of boutonneuse fever in humans. Two other members of the family Rickettsiaceae, Coxiella burnetii and Rickettsia typhi, were included in the serosurvey. Of the 104 dogs tested, 85.6% had antibodies to R. conorii, 50% to E. canis, 26.9% to R. typhi, and 4.8% to C. burnetii. These high seroprevalence rates of dogs with antibodies all year around against Rickettsiaceae suggest that physicians, public health officers and veterinarians should more frequently consider the diagnosis of these infections in Portugal.

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PubMed1994

Human ehrlichiosis in the United States, 1985 to 1990.

OBJECTIVE: To describe the epidemiology, clinical features, laboratory manifestations, response to therapy, and factors related to morbidity and mortality in a large group of patients with ehrlichiosis. DESIGN: Case-series. SETTING: Laboratory-based surveillance in the United States. PATIENTS: 237 patients whose serum had a fourfold increase or decrease in antibodies to Ehrlichia canis or E. chaffeensis. MEASUREMENTS: Epidemiologic, clinical, laboratory data, hospitalization, duration of illness, complications, and treatment response. RESULTS: From 1985 through 1990, 237 case-patients were identified in 21 states; rates exceeded 1 per 100,000 per year in only 5 counties. Incidence rates increased with age and were higher among men. Most case-patients had nonspecific illness and were not suspected of having a rickettsial infection. Many patients (60.8%) were hospitalized. Leukocyte and platelet counts typically decreased and liver function tests typically increased through day 7. Three (6.1%) of 49 outpatients treated only with tetracycline were hospitalized compared with 35 (92%) of 38 outpatients treated only with antibiotics other than tetracycline or chloramphenicol (P < 0.001). Among hospitalized patients, recovery was faster for those initially treated with tetracycline (median, 16 days) or chloramphenicol (median, 12 days) than for those initially treated with other antibiotics (median, 27 days; P = 0.03 for both comparisons). In a logistic regression analysis, severe illness or death was more probable among case-patients 60 years or older (odds ratio [OR], 4.60; 95% CI, 1.87 to 11.2) and among those who did not receive tetracycline or chloramphenicol until 8 or more days after symptom onset (OR, 4.38; CI, 1.36 to 14.0). CONCLUSIONS: The findings of this study are primarily representative of more seriously ill patients with human ehrlichiosis. Although rates are low, ehrlichiosis is found in many areas of the United States. Patients with a history of tick exposure, acute febrile illness, decreasing leukocyte counts, and decreasing platelet counts may have ehrlichiosis. Prompt treatment with tetracycline or chloramphenicol markedly decreases the morbidity.

Adolescent↗