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Biomedical subjects

B K Johnson

Publications and source records attributed to B K Johnson.

At least 19 recordsLinked to original sources
PubMed2000

New studies on the heat resistance of hamster-adapted scrapie agent: threshold survival after ashing at 600 degrees C suggests an inorganic template of replication.

One-gram samples from a pool of crude brain tissue from hamsters infected with the 263K strain of hamster-adapted scrapie agent were placed in covered quartz-glass crucibles and exposed for either 5 or 15 min to dry heat at temperatures ranging from 150 degrees C to 1,000 degrees C. Residual infectivity in the treated samples was assayed by the intracerebral inoculation of dilution series into healthy weanling hamsters, which were observed for 10 months; disease transmissions were verified by Western blot testing for proteinase-resistant protein in brains from clinically positive hamsters. Unheated control tissue contained 9.9 log(10)LD(50)/g tissue; after exposure to 150 degrees C, titers equaled or exceeded 6 log(10)LD(50)/g, and after exposure to 300 degrees C, titers equaled or exceeded 4 log(10)LD(50)/g. Exposure to 600 degrees C completely ashed the brain samples, which, when reconstituted with saline to their original weights, transmitted disease to 5 of 35 inoculated hamsters. No transmissions occurred after exposure to 1, 000 degrees C. These results suggest that an inorganic molecular template with a decomposition point near 600 degrees C is capable of nucleating the biological replication of the scrapie agent.

Animals↗
PubMed2000

Immunophenotyping of peripheral blood, ranges of serum chemistries and clinical hematology values of healthy chimpanzees (Pan troglodytes).

This paper presents clinical chemistry, hematology and immunophenotyping data from 102 chimpanzees over a 2-year period. The groupings were: 3 years or less, 4-7 years, and 8 + years. These data are intended to augment formerly published information on these parameters and to serve as a concise reference guide for primate veterinarians and researchers for whom these data may be useful. This study has larger samplings than previously published data and more panel constituents by immunophenotyping.

Animals↗
PubMed1999

Thermodynamic basis for a variational model for crystal growth.

Variational models provide an alternative approach to standard sharp interface models for calculating the motion of phase boundaries during solidification. We present a correspondence between objective functions used in variational simulations and specific thermodynamic functions. We demonstrate that variational models with the proposed identification of variables are consistent with nonequilibrium thermodynamics. Variational models are derived for solidification of a pure material and then generalized to obtain a model for solidification of a binary alloy. Conservation laws for internal energy and chemical species and the law of local entropy production are expressed in integral form and used to develop variational principles in which a "free energy," which includes an interfacial contribution, is shown to be a decreasing function of time. This free energy takes on its minimum value over any short time interval, subject to the laws of conservation of internal energy and chemical species. A variational simulation based on this model is described, and shown for small time intervals to provide the Gibbs-Thomson boundary condition at the solid-liquid interface.

Journal Article↗
PubMed1997

Phylogenetic analysis of simian T-lymphotropic virus Type I (STLV-I) in common chimpanzees (Pan troglodytes): evidence for interspecies transmission of the virus between chimpanzees and humans in Central Africa.

Serum and peripheral blood leukocytes from the chimpanzees (Pan troglodytes) of the colony of the Laboratory of Central Nervous System Studies, National Institute of Neurological Disorders and Stroke, NIH, were tested for the presence of STLV-I-specific antibodies and proviral DNA. Antibodies were determined by gelatin particle agglutination and Western blot (WB) assays utilizing HTLV-I antigens. Proviral DNA was detected by four PCR assays targeting three different regions of STLV-I genome: the fragments of the env and pol genes and LTR. Twenty of twenty-two DNA samples from WB-positive animals were PCR positive. None of the DNA samples from WB-negative (n = 5) and WB-indeterminate (n = 4) animals was PCR positive. The results of the nested and double nested env PCR tests were fully concordant; the seminested LTR PCR test was much less sensitive. The DNA sequences from the env (483 bp) and the pol (200 bp) genes and LTR (705 bp) were determined for six, two, and two chimpanzee STLV-I isolates, respectively. Phylogenetic analysis revealed that chimpanzee STLV-I isolates can be attributed to three clades. The first of these clades (SS-PTR1/CSA) included STLV-I isolates from the chimpanzees and West African subspecies of African green monkeys (Cercopithecus a. sabaeus). The other clades (S-PTR2 and S-PTR3) included STLV-I isolates only from chimpanzees. However, both S-PTR2 and S-PTR3 clustered together with Central African HTLV-I comprising the human/simian clade (HS-HSA/PTR). This pattern of phylogenetic clustering suggests that interspecies transmission of STLV-I occurred between chimpanzees and African green monkey subspecies as well between chimpanzees and human populations in Central Africa.

Africa, Central↗
PubMed1996

Characterization of a new Marburg virus isolated from a 1987 fatal case in Kenya.

In 1987, an isolated case of fatal Marburg disease was recognized during routine clinical haemorrhagic fever virus surveillance conducted in Kenya. This report describes the isolation and partial characterization of the new Marburg virus (strain Ravn) isolated from this case. The Ravn isolate was indistinguishable from reference Marburg virus strains by cross-neutralization testing. Virus particles and aggregates of Marburg nucleocapsid matrix in Ravn-infected vero cells, were visualized by immunoelectron microscopic techniques, and also in tissues obtained from the patient and from inoculated monkeys. The cell culture isolate produced a haemorrhagic disease typical of Marburg virus infection when inoculated into rhesus monkeys. Disease was characterized by the sudden appearance of fever and anorexia within 4 to 7 days, and death by day 11. Comparison of nucleotide sequences for portions of the glycoprotein genes of Marburg-Ravn were compared with Marburg reference strains Musoki (MUS) and Popp (POP). Nucleotide identity in this alignment between RAV and MUS is 72.3%, RAV and POP is 71%, and MUS and POP is 91.7%. Amino acid identity between RAV and MUS is 72%, RAV and POP is 67%, and MUS and POP is 93%. These data suggest that Ravn is another subtype of Marburg virus, analogous to the emerging picture of a spectrum of Ebola geographic isolates and subtypes.

Adolescent↗
PubMed1996

Older adults and sexuality: a multidimensional perspective.

The purpose of this study was to describe the multidimensional nature of sexuality in men and women age 55 and older and compare these men and women on selected dimensions of sexuality. The community-based sample of 161 older adults (men = 69, women = 92) completed a 77-item, anonymous questionnaire. Gender differences were found for selected demographics, health and health-related variables, and selected aspects (sexual interest, participation, and satisfaction) of sexual activities. MANOVA yielded a significant multivariate F indicating men and women differed on the combination of seven dependent variables (self-esteem, intimacy, and sexual knowledge, attitudes, interest, participation, and satisfaction) while univariate Fs did not yield significant gender differences on each of the dependent variables. Study results described a multidimensional view of sexuality and aging which can be used to increase nurses' understanding of selected gender differences of older adults' sexuality.

Aged↗
PubMed1993

Long-term observations of human immunodeficiency virus-infected chimpanzees.

Twenty-seven chimpanzees inoculated with material presumed to contain human immunodeficiency virus (HIV) between June 1983 and February 1985 were studied. The animals were examined on four to six occasions between 1989 and 1992 for serologic, virologic, hematologic, immunophenotypic, as well as clinical signs of HIV infection and compared to five uninfected control animals. The 19 animals that had seroconverted within 244 days of inoculation remained antibody positive, whereas those that did not seroconvert within 244 days of inoculation remained antibody negative 6 to 8 years later. HIV antigen was demonstrated at least once in lymphocyte cultures from 12 of the 19 antibody positive chimpanzees during this period. Nested polymerase chain reaction amplified proviral DNA in lymphocytes from 14 of the 19 animals. No proviral DNA was detected in antibody-negative animals. Antibody titers were generally higher in animals from which virus was recovered in lymphocyte cultures [granulocyte-macrophage (GM) titer, 1:8427] compared to virus-negative animals (GM titer, 1:3608). Mean total white blood cell and lymphocyte subtype counts were similar in the HIV-infected animals and uninfected controls. The high antibody levels and Western blot profiles, over periods as long as 9 years in these chimpanzees, suggest continuous stimulation of the immune system by HIV antigen although virus was detected only sporadically in the peripheral blood. No illness suggestive of immunodeficiency was seen.

Animals↗
PubMed1991

Observations after human immunodeficiency virus immunization and challenge of human immunodeficiency virus seropositive and seronegative chimpanzees.

Two human immunodeficiency virus (HIV)-seropositive chimpanzees (A-3 and A-86c) infected 4 yr earlier with HIV, along with one uninfected animal (A-36), were inoculated intramuscularly three times in a year with a gamma-irradiated gp120-depleted HIV immunogen in incomplete Freund's adjuvant. Both previously infected animals promptly developed an anamnestic humoral antibody response after the first dose, and the uninfected animal developed a primary humoral response to the first dose and then an anamnestic response to the second dose. Although HIV had been recovered repeatedly from the seropositive animals, they became persistently virus-culture negative at the time of or just before the first inoculation of the immunogen. Intravenous challenge with 40 chimpanzee-infectious-doses of a heterologous HIV strain (HIVIIIB) was done 4 mo after the third inoculation in the three treated chimpanzees and in an untreated control animal (A-189a). The immunized naive animal (A-36) and the unimmunized control (A-189a) became infected, and virus has been isolated from their peripheral blood mononuclear cells for greater than 2 yr after challenge. However, the two previously infected chimpanzees (A-3 and A-86c) resisted challenge and have remained virus negative by peripheral blood mononuclear cell cocultivation for greater than 2 yr of observation after challenge; moreover, no evidence of reinfection was detectable by PCR. Despite the in vivo resistance, however, peripheral blood mononuclear cells from the resistant animals (A-3, A-86c) remained susceptible to infection by HIV in vitro. These findings reveal that a state of immunity can develop and/or be induced to control and/or prevent HIV infection in the chimpanzees. In the absence of any detectable level of neutralizing antibody in A-3 and a low level in A-86c, the patterns of the responses to challenge seen in the four animals suggest that the cell-mediated immune mechanism must have played a significant role in the resistant chimpanzees both in control of their HIV infection and in their resistance to challenge.

Animals↗
PubMed1991

Detection of hantavirus RNA in tissues of experimentally infected mice using reverse transcriptase-directed polymerase chain reaction.

Detection of hantaviruses, the etiological agents of hemorrhagic fever with renal syndrome (HFRS), by virus isolation using experimental animals or cell culture is time-consuming. A more rapid but equally specific method is needed. We used a reverse transcriptase-directed polymerase chain reaction (RT-PCR) to detect hantavirus genomic sequences and compared its sensitivity with conventional virus isolation. RNA, extracted by the guanidinium isothiocyanate-cesium chloride method from hantavirus-infected Vero E6 cells and from tissues of infant mice inoculated intracerebrally with 100 LD50 of hantavirus, was initially reverse transcribed using avian myeloblastosis virus reverse transcriptase. The resulting complementary DNA (cDNA) was used as template to amplify the glycoprotein 2-encoding region of the hantavirus M segment. With this method, Vero E6 cell cultures infected with Hantaan virus strains 76-118 (prototype) and HV114 (an isolate from the urine of an HFRS patient in China) were positive, while control cultures were negative. Brain, lung, and heart tissues from hantavirus-infected mice were positive by RT-PCR at 5, 8, and 11 days after intracerebral inoculation. The specificity of the positive results was confirmed by restriction endonuclease digestion of the amplified fragments with AluI and HpaI. The sensitivity of the RT-PCR was equal to cell culture amplification but required less time. This method is being adapted for detection of hantavirus genomic sequences in clinical specimens and postmortem tissues from patients with HFRS.

Animals↗
PubMed1991

Stress, coping, and adjustment in female adolescent incest victims.

Although previous literature on incest has dealt extensively with the nature, parameters, and effects of such abuse, it has not focused on the role of coping in the psychological adjustment of victims. Forty-five female adolescent incest victims in treatment completed questionnaires regarding their current adjustment, characteristics of their molest, their perceptions of the stressful aspects of the molestations, how they appraised the molestations, and how they coped with the fact that it occurred. The majority of the girls in this study had been sexually abused by a father figure (82%). The coping strategies of wishful thinking and tension reduction, the lack of maternal support at the time of reporting, and appraisals of threat and "holding self back" accounted for 70% of the variance in self-reported distress. The coping strategies of detachment, seeking social support and appraisal of hold self back accounted for 38% of the variance in adolescent's global psychopathology as rated by their therapists. In light of these findings, the implications of the need to address appraisals and coping efforts in research and therapy with incest victims was emphasized.

Adaptation, Psychological↗
PubMed1991

Serological evidence of arboviral infections among humans of coastal Kenya.

A serosurvey was conducted during September 1987 for evidence of human arboviral infections in the Coast Province of Kenya. Sera were collected from 1624 outpatients at three hospitals and tested for antibody to eight arboviruses by the indirect immunofluorescent antibody technique. Antibody prevalence rates were: Rift Valley fever, 2.8%; Sindbis, 2.6%; dugbe, 2.1%; dengue-2, 1.0%; West Nile, 0.9%; chikungunya, 0.7% and Nairobi sheep disease, 0.3%. Evidence of Crimean-Congo haemorrhagic fever viral antibody was not detected. The data suggested low arbovirus activity since 1982, when an epidemic of dengue occurred in this region, and revealed the first evidence of dugbe viral infection among humans in Kenya.

Adolescent↗
PubMed1990

Comparison of human immune responses to purified Vero cell and human diploid cell rabies vaccines by using two different antibody titration methods.

Antibody responses to a conventional rabies preexposure regimen of a new purified Vero cell rabies vaccine (PVRV) and a human diploid cell vaccine (HDCV) were compared in 80 healthy Kenyan veterinary students. Forty-three of the students received the PVRV and 37 received the HDCV on days 0, 7, and 28. Antibody responses were monitored by using the rapid fluorescent-focus inhibition test (RFFIT) and an inhibition enzyme immunoassay (INH EIA) on days 0, 7, 28, and 49. Both vaccines elicited a rapid antibody response. A good correlation between the RFFIT titers and the INH EIA titers was obtained (r = 0.90). Our results also showed that the INH EIA was more reproducible and might therefore be a suitable substitute for the more expensive and less reproducible RFFIT. The geometric mean titers determined by both tests in the two groups of students were statistically similar during the test period. The RFFIT and the INH EIA gave comparable geometric mean titers, which differed significantly only on day 28 in the PVRV group. The effect of the new PVRV is comparable to that of the more expensive HDCV, as determined by the present test systems. The PVRV could therefore be the vaccine of choice, especially in tropical rabies-endemic areas, where the high cost of the HDCV has confined its use to a privileged few.

Animals↗
PubMed1985

Regional variation in prevalence of antibody against human T-lymphotropic virus types I and III in Kenya, East Africa.

The prevalence of antibodies against HTLV-III and -I was studied among populations of 6 distinctly different regions of Kenya, an equatorial African country in which AIDS has rarely been observed. Overall, 21% of subjects had ELISA reactions suggesting the presence of antibody against HTLV-III. The frequency of HTLV-III antibodies was highest among the Turkana people (50%) and lowest among the Masai (8%). Prevalence increased with age but was not related to sex. The pattern of ELISA-detected antibody against HTLV-I was similar. The specificity of these antibodies was supported by Western blot analysis of a subset of sera with high and low ELISA ratios, in which 66% and 73% of those with ELISA ratios considered positive (= greater than 5.0 in this study) also had a profile of bands consistent with HTLV-III and HTLV-I respectively. The antibodies detected were not cross-reactive between HTLV-III and HTLV-I on Western blot analysis. In a series of subjects with various parasitic and infectious diseases, patients with idiopathic splenomegaly and with schistosomiasis had a high proportion of antibodies against both HTLV-III and HTLV-I. This survey shows that reactivity in the ELISA HTLV-III and HTLV-I assays are common among Kenyans but vary considerably by region.

Adolescent↗