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S A Ewing

Publications and source records attributed to S A Ewing.

At least 73 records · Page 4Linked to original sources
PubMed1991

Ehrlichiosis in children.

Tick-borne rickettsiae of the genus Ehrlichia have recently been recognized as a cause of human illness in the United States. In the years 1986-1988, 10 cases of ehrlichiosis were diagnosed in children in Oklahoma. Fever and headache were universal: myalgias, nausea, vomiting, and anorexia were also common. Rash was observed in six patients but was a prominent finding in only one. Leukopenia, lymphopenia, and thrombocytopenia were common laboratory abnormalities. Six patients were treated with tetracycline, three with chloramphenicol, and one was not treated with antibiotics: all recovered. The onset of illness in spring and early summer for most cases paralleled the time when Amblyomma americanum and Dermacentor variabilis are most active, suggesting that one or both ticks may be vectors of human ehrlichiosis in Oklahoma.

Animals↗
PubMed1990

Failure to transmit Ehrlichia canis (Rickettsiales: Ehrlichieae) with Otobius megnini (Acari: Argasidae).

An ear tick, Otobius megnini (Dugès) recovered from a child who had serologic evidence of ehrlichiosis, was examined for Ehrlichia species microscopically and by inoculation into a susceptible dog; no evidence of infection was found in the tick. Experimental transmission of E. canis by laboratory-reared O. megnini was attempted; neither transstadial nor transovarial transmission occurred.

Animals↗
PubMed1990

Neurologic abnormalities in a patient with human ehrlichiosis.

Human ehrlichiosis is a tick-borne rickettsial disease characterized by fever, headache, myalgias, anorexia, and occasionally rash. In our patient, changes in mental status, upper motor neuron signs, cerebrospinal fluid pleocytosis, and increased serum protein levels were found in association with serologically confirmed ehrlichiosis and were most likely due to vasculitis involving the central nervous system. Intraleukocytic inclusions, although observed in our case, have been infrequently found in other reported cases of ehrlichiosis.

Adult↗
PubMed1990

Epidemiologic and clinical characteristics of persons with serologic evidence of E. canis infection.

The results of a serosurvey of Oklahomans for the presence of antibody to Ehrlichia canis is reported. Paired serum specimens, from patients lacking the serologic criteria for diagnosis of Rocky Mountain spotted fever (RMSF), were tested. A four-fold increase in E. canis-IFA antibody was found in 16/144 (11 percent) of these paired serum samples. Patients with serologic evidence of E. canis infection had a mean age of 34 years, 69 percent were male, and 63 percent lived in a town less than 10,000 population. Signs and symptoms included: fever 94 percent, headache 94 percent, fatigue 94 percent, anorexia 81 percent, nausea 60 percent, and rash 44 percent. When compared to control patients, whose sera were submitted for RMSF testing but did not meet serologic criteria for RMSF or E. canis, case-patients were more likely to have had leukopenia (OR = 4.9, 95 percent Cl = 1.2, 19.0) and tick exposure (OR = 9.5, 95 percent Cl = 1.4, 62.7). The results suggest E. canis, or a closely related agent, is a cause of human illness. Ticks are probable vector.

Adult↗
PubMed1990

Intermediate site of development of Anaplasma marginale in feeding adult Dermacentor andersoni ticks that were infected as nymphs.

The development of Anaplasma marginale in midgut epithelial cells was studied in feeding, transmitting adult Dermacentor andersoni ticks. Laboratory-reared ticks experimentally infected as nymphs were allowed to feed from 1 to 9 days on susceptible calves. Gut tissues from ticks were collected on each day they fed (total, 9 days) and were processed for light and transmission electron microscopy. Colonies of A marginale were abundant during the first 6 days of feeding, after which numbers decreased. Colonies were adherent to the basement membrane of gut cells early during feeding, with resultant flattening of the colonies. Colonies also were seen in muscle cells on the hemocoel side of the basement membrane. Morphologic features of A marginale within muscle cells varied and were similar to those observed in gut cells. In addition, however, a large reticulated form in the colonies was observed in muscle cells and appeared to give rise to small particles by budding. Development of A marginale in muscle cells appears to represent an intermediate site of development between those in gut and in salivary glands.

Anaplasma↗
PubMed1990

Experimental transmission of a granulocytic form of the tribe Ehrlichieae by Dermacentor variabilis and Amblyomma americanum to dogs.

Transstadial transmission of granulocytic Ehrlichieae in dogs was attempted using ticks, Amblyomma americanum and Dermacentor variabilis. Ticks were exposed by feeding as nymphs on acutely infected pups; adult ticks then fed to repletion on susceptible adult dogs that were monitored daily for signs of infection. Evidence of transmission was not observed in control dogs or in those exposed to D variabilis. In contrast, dogs exposed to A americanum developed serologic or clinical evidence of infection, but organisms were not seen in blood smears until corticosteroids were administered, causing recrudescence and accompanying parasitemia. At 12 days after subinoculation of blood obtained from donor adult dogs, before corticosteroids were administered, a febrile response, thrombocytopenia, and appearance of morulae in neutrophilic granulocytes were observed in 2 susceptible recipient dogs.

Animals↗
PubMed1990

Development and infectivity of Anaplasma marginale in Dermacentor andersoni nymphs.

The development of Anaplasma marginale was studied in Dermacentor andersoni nymphs after they had fed on a calf with ascending Anaplasma infection. Gut tissues were collected on day 4 of tick feeding, from newly replete (fed) nymphs and on postfeeding days (PFD) 5, 10, 15, 20, and were processed for light and electron microscopy to determine density of A marginale colonies. Homogenates of gut tissues were prepared from nymphs collected on the same days and inoculated into susceptible, splenectomized calves to test for infectivity. Anaplasma colonies were detected in gut cells on PFD 5, 10, 15, and 20. Although colony density appeared to be higher on PFD 10 and 15, differences were not significant. Nymphal type-1 colonies were detected in highest numbers on PFD 5 and 10, transitional colonies were seen in highest numbers at PFD 10 and 15, and nymphal type-2 colonies were observed only on PFD 20. Gut homogenates that were collected from ticks at 4 days of feeding, when newly replete, and on PFD 20 caused anaplasmosis when injected into susceptible calves, but homogenates made from ticks collected on PFD 5, 10, and 15 were not infective. The data indicate that of the colony types of A marginale that develop in replete nymphs, nymphal type-1 and transitional colonies may contain organisms that are not infective for cattle.

Anaplasma↗
PubMed1989

Transstadial and attempted transovarial transmission of Anaplasma marginale by Dermacentor variabilis.

Transstadial and transovarial transmission of Anaplasma marginale by Dermacentor variabilis were attempted with with ticks exposed to the organism once by feeding as larvae or nymphs, and twice by feeding as larvae and nymphs. Typical colonies of A marginale were in gut tissues of adults that were infected as larvae, larvae and nymphs, and as nymphs; repeated exposure of ticks did not appear to result in an increase in the number of colonies in the gut of subsequently molted adults nor did it affect severity of the clinical disease that developed in cattle they fed on. In contrast, colonies of A marginale were not found in the midgut epithelium of unfed nymphs exposed as larvae, even though companion nymphs transmitted the parasite, causing severe clinical anaplasmosis in susceptible calves. The organism was not transmitted transovarially by F1 larvae or nymphs from the groups exposed as parent larvae, nymphs, larvae and nymphs, and as adults. Some of the calves fed on by F1 progeny had a few erythrocytic marginale bodies that looked suspiciously like A marginale, as well as postchallenge exposure prepatent periods that were longer than other calves in the transovarial transmission study. Sera from these calves were tested for antibody to A marginale, using a highly sensitive immunoblot technique. Antibodies were not detected in any of the sera.

Anaplasma↗
PubMed1989

Detection of colonies of Anaplasma marginale in salivary glands of three Dermacentor spp infected as nymphs or adults.

Salivary glands from males of 3 Dermacentor species (D andersoni, D variabilis and D occidentalis) that were infected with either the Virginia or Idaho isolate of Anaplasma marginale as nymphs or adults were examined for colonies of A marginale by use of light and electron microscopy. Prior to dissection of salivary glands, exposed ticks were held at 25 C for 15 to 18 days, followed by a 3-day incubation at 37 C. Ticks of 2 species transmitted A marginale to calves; the third tick species was confirmed infected by demonstration of typical colonies in tick gut cells, but transmission was not attempted; Colonies of A marginale were seen with light microscopy in salivary glands of all 3 species of ticks; they were located in acinar cells that contained simple granules. Colonies varied morphologically from small, compact ones to larger structures that contained distinct organisms and often were adjacent to the host cell nucleus. Electron microscopy confirmed that the colonies were rickettsial organisms. Morphologic features of A marginale varied and included reticulated forms, forms with electron-dense centers, and small particles; these various forms were similar to those described previously in midgut epithelial cells of ticks. We believe that the organism seen within tick salivary glands may replicate in the glands before its transmission to the vertebrate host.

Anaplasma↗
PubMed1988

Ichthyophthirius (Ciliophora): population studies suggest reproduction in host epithelium.

Evidence that Ichthyophthirius multifiliis trophonts may reproduce within the epithelium of the host was obtained from experimental infections of channel catfish. Mean number of parasites spontaneously leaving the fish increased from 0 on day 3 postexposure (PE) to 66.5 per fish on day 7 PE. Mean population density in fin, however, increased five-fold from day 3 to day 5 PE in the absence of opportunity for reinfection. At day 3 PE, 100% of parasite loci in fin and gill arches contained solitary trophonts. At day 4 PE, 10% of loci in fin contained clusters of two trophonts; at day 7 PE, 69% contained clusters of two or more trophonts. The first clusters of four trophonts in fin were observed day 5 PE and of eight trophonts, day 8 PE. Trophonts in clusters were flattened against one another.

Animals↗
PubMed1988

Preliminary studies of the development of Anaplasma marginale in salivary glands of adult, feeding Dermacentor andersoni ticks.

On each day of feeding on susceptible calves, salivary glands obtained from groups of adult ticks that transmitted Anaplasma marginale were examined for A marginale colonies by use of light microscopy and transmission electron microscopy. On day 8 of feeding, salivary glands were examined, using fluorescein-labeled antibody and methyl green-pyronine stain. Use of fluorescein-labeled antibody consistently revealed small numbers of fluorescent foci in salivary gland acinar cells obtained from ticks that had fed for 8 days. Colonies of A marginale were seen by transmission electron microscopy only in salivary gland acini of male ticks; these colonies could not be identified, using light microscopy, in companion 1-micron plastic sections stained with Mallory stain. Methyl green-pyronine stain, used commonly to detect theilerial parasites in tick salivary glands, did not differentiate A marginale from cytoplasmic inclusions normally found in salivary gland acinar cells.

Anaplasma↗
PubMed1987

Persistence of colonies of Anaplasma marginale in overwintering Dermacentor variabilis.

Dermacentor variabilis were infected as nymphs with Anaplasma marginale by allowing the ticks to feed on a single infected donor calf. Two weeks after molting to the adult stage, the ticks were allotted into 1 of 3 groups and were allowed to overwinter at room temperature (25 C) in the laboratory (group 1), cold storage (4.5 C) in the laboratory (group 2), or outdoors in leaf litter (group 3). Persistence of A marginale was assessed by determining density of colonies (number of colonies/0.1 mm2 of gut tissue examined) in tick gut specimens at 3, 5, 7, 9, and 12 months after molting to the adult stage. Colonies of A marginale were found in all groups at every density evaluation period. Highest colony densities were observed uniformly in specimens collected at month 7 (May); densities decreased at month 9 and were lowest at month 12. Statistical analysis indicated that ticks subjected to cold storage and to outdoor conditions had similar colony densities of A marginale; the density curve in these 2 groups indicated significant quadratic effects over time, with peak densities in May. Mean colony density in ticks kept at room temperature fit a different quadratic equation. The morphologic data indicated that A marginale overwinters in Dermacentor variabilis, and that increasing numbers of organisms are found from January to May.

Anaplasma↗
PubMed1987

Infectivity of three Anaplasma marginale isolates for Dermacentor andersoni.

Three isolates of Anaplasma marginale--Virginia (VAM), Illinois (IAM), and Florida (FAM)--were compared for infectivity for Dermacentor andersoni. The isolates were selected, in part, because of a tail-like appendage that has been demonstrated in the VAM and IAM, but not in the FAM. Ticks were exposed to the isolates as nymphs either naturally by feeding on a calf with anaplasmosis or artificially by percutaneous inoculation with infected bovine erythrocytes. They were examined for infectivity after molting to the adult stage by determining their capability to transmit the disease to susceptible calves and by demonstrating colonies in tick gut sections. Only those ticks exposed to the VAM proved to be infected with A marginale; ticks naturally exposed and those artificially infected with this isolate transmitted the disease to susceptible calves. Colonies of A marginale were observed only in gut tissues of ticks naturally infected with VAM. The IAM (appendage present) and FAM (appendage absent) could not be found in ticks exposed by either method, indicating that factors other than the presence of inclusion appendages may be involved in infection of ticks by A marginale.

Anaplasma↗
PubMed1986

Trypanosoma cruzi infection in a dog from Oklahoma.

A dog with signs of weakness, labored breathing, and generalized edema was examined. It was heavily infested with fleas and had wounds resulting from a recent fight. Hematologic findings were not remarkable, except for parasites in the blood. The dog was treated for fleas and given antibiotics, but was euthanatized when it failed to respond. Blood and tissue specimens were found to contain Trypanosoma cruzi, and the serum contained antibodies to the organism. We believe this is the first confirmed case of T cruzi infection in dogs from Oklahoma. The public health implications of this finding are underscored by a report on the detection of T cruzi in raccoons in the same season and geographic area.

Animals↗