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Biomedical subjects

Jonathan E Myers

Publications and source records attributed to Jonathan E Myers.

11 recordsLinked to original sources
PubMed2006

The relationship between reproductive outcome measures in DDT exposed malaria vector control workers: a cross-sectional study.

BACKGROUND: The utility of blood reproductive endocrine biomarkers for assessing or estimating semen quality was explored. METHODS: A cross-sectional study of 47 DDT exposed malaria vector control workers was performed. Tests included blood basal and post gonadotrophin releasing hormone (GnRH), luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone, sex hormone binding globulin (SHBG), estradiol (E2) and inhibin; a questionnaire (demographics and general medical history); a physical examination and semen analysis. Semen parameters were determined using either/or or both WHO or the strict Tygerberg criteria. Relationships between semen parameters and endocrine measures were adjusted for age, duration of abstinence before sampling, presence of physical abnormalities and fever in the last two months. All relationships between specific endocrine hormones were adjusted for age and basal SHBG. RESULTS: Multiple logistic regression showed a consistent positive relationship (prevalence odds ratio (POR) = 8.2, CI:1.4-49.2) between low basal inhibin (< 100 pg/ml) and low semen count (< 40 million) and density (< 20 million/ml); consistent positive, but weaker relationships (1 > POR < 2) between abnormally low semen count as well as density and baseline and post GnRH FSH; and positive relationships (POR = 37, CI:2-655) between the prevalence of high basal estradiol (> 50 pg/ml) and abnormal morphology (proportion < 5%) and low motility (proportion < 50%). Most of the expected physiological relationships between specific endocrines were significant. CONCLUSION: The study has demonstrated that low basal inhibin, elevated basal FSH and high basal E2 can serve as markers of impaired semen quality.

Journal Article↗
PubMed2005

Evaluation of an HIV/AIDS peer education programme in a South African workplace.

OBJECTIVES: To evaluate a South African workplace HIV/AIDS peer-education programme running since 1997. METHODS: In 2001 a cross-sectional study was done of 900 retail-section employees in three geographical areas. The study measured HIV/AIDS knowledge, attitudes towards people living with HIV/AIDS, belief about self-risk of infection, and condom use as a practice indicator. The impact of an HIV/AIDS peer-education programme on these outcomes was examined. RESULTS: Training by peer educators had no significant impact on any outcome. Fifty-nine per cent of subjects had a good knowledge score, 62% had a positive attitude towards people with HIV/AIDS, 34% used condoms frequently, and the majority of participants (73%) believed they were at low risk of infection. Logistical regression showed that a very small proportion of the variance in the four outcomes was explained by potential determinants of interest (8% for knowledge, 6% for attitude, 7% for risk and 17% for condom use). CONCLUSIONS: The HIV peer-education programme was found to be ineffective and may have involved an opportunity cost. The programme contrasts with more costly comprehensive care that includes antiretrovirals. The private sector appears to have been as tardy as the public sector in addressing the epidemic effectively.

Acquired Immunodeficiency Syndrome↗
PubMed2004

The long-term effects of DDT exposure on semen, fertility, and sexual function of malaria vector-control workers in Limpopo Province, South Africa.

Hormonally active chemicals in the environment such as DDT have been associated with declining male reproductive health, especially semen quality. A cross-sectional study of 60 workers was performed near the Malaria Control Center (MCC) in Tzaneen, Limpopo Province, South Africa. Tests included a questionnaire (sexual function, fertility, and job history), a physical examination of the reproductive system, and semen analysis (produced via coitus interruptus or masturbation). Sperm count, density, and motility using the World Health Organization criteria and morphology using the strict Tygerberg criteria were determined. Serum o'p' and p'p' isomers of DDE, DDT, and DDD were measured. Forty-eight (81.0%) participants produced a semen sample, while all completed the questionnaires and physical examination. The mean sperm count was 93.8+/-130.3 million, and sperm density was 74.6+/-85.1 million/mL. The mean normal morphology score was 2.5+/-1.8% of subjects. Eighty-four percent of morphology scores were below either the WHO or the Tygerberg criteria, with the highest individual score being 6%. Self-perceived current problems with sexual function ranged between 10% and 20%. The most prevalent genital abnormality was abnormal testis disposition at 71%. There were few significant associations between DDT exposure measures (measured as years worked at MCC and serum DDT) and reproductive outcomes. p'p'-DDT was negatively associated with semen count (beta=-3.7+/-1.7; P=0.04; R2=0.05 adjusted for age, abstinence, physical abnormality, and fever in last 2 months). While the semen quality in the study was less than normal, no strong evidence for a DDT effect was found.

Animals↗
PubMed2004

The hormonal effects of long-term DDT exposure on malaria vector-control workers in Limpopo Province, South Africa.

DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] compounds, used in many developing countries, including South Africa, for the control of malaria vectors, have been shown to be endocrine disruptors in vitro and in vivo. The study hypothesis was that male malaria vector-control workers highly exposed to DDT in the past should demonstrate clinically significant exposure-related anti-androgenic and/or estrogenic effects that should be reflected in abnormalities in reproductive hormone levels. A cross-sectional study of 50 workers from three camps situated near the Malaria Control Center (MCC) in Tzaneen was performed. Tests included blood sampling before and after a gonadotropin-releasing hormone (GnRH) challenge (100 microg). Serum o'p' and p'p' isomers of DDE, DDT, and DDD and basal and post-GnRH challenge hormone levels, including luteinizing hormone, follicle-stimulating hormone, testosterone, sex hormone-binding globulin, estradiol (E2), and inhibin, were measured. The mean number of years worked at the MCC was 15.8+/-7.8 years and the mean serum DDT was 94.3+/-57.1 microg/g of lipid. Mean baseline E2 levels (62.4+/-29.9 pg/mL) exceeded the laboratory reference range. Associations between DDT exposure measures (years worked at the MCC and DDT compounds) and hormonal outcomes were weak and inconsistent. The most important finding was a positive relationship of baseline E2 and baseline testosterone with DDT compounds, especially with p'p'-DDT and -DDD. The strongest association found, adjusted for age and SHBG, was between baseline estradiol and p'p'-DDT (beta=1.14+/-0.33 pg/mL/microg/ g lipid, P=0.001, R2=0.31, n=46). An overall anti-androgenic mechanism best explains the results, but with a number of inconsistencies. Associations might be due to chance, as multiple comparisons were made. The results therefore do not suggest an overt anti-androgenic or estrogenic effect of long-term DDT exposure on hormone levels, but correlations do exist in a manner that is not understood.

Adult↗
PubMed2004

Exploration of different methods for measuring DDT exposure among malaria vector-control workers in Limpopo Province, South Africa.

DDT compounds are used in many developing countries, including South Africa, for the control of malaria vectors. This study investigated biological exposures among workers in relation to job history. A cross-sectional study of 59 workers at the Malaria Control Centre (MCC) in Tzaneen, South Africa, was performed. Tests included a job history questionnaire and the measurement of serum o'p' and p'p' isomers of DDE, DDT, and DDD, corrected for serum total lipids. Forty-seven (80%) workers donated a blood sample for the determination of serum DDT. The mean number of years worked at the MCC (malaria years) was 15.8+/-7.8 years and the mean serum DDT was 94.3+/-57.1 microg/g of lipid. There were no significant associations between short-to-medium-term serum DDT exposure measures (o'p'-DDE and o'p' and p'p' isomers of DDD and DDT) and malaria years. The long-term exposure measure, p'p'-DDE, was significantly associated with malaria years (beta=3.0+/-1.2 microg/g lipid/year; P=0.001; n=47; adjusted for age), but only 27% variance of p'p'-DDE was explained. Blood total DDT uncorrected for lipid content was strongly related to corrected levels (B=0.74+/-0.48, P=0.00, R2=0.77), but uncorrected p'p'-DDE had a weaker association (B=0.0024+/-0.0013, P=0.074; R2=0.53) with malaria years than did corrected levels (beta=0.042+/-0.017; P=0.016; R2=0.56). The results show that serum DDT levels for malaria vector-control workers in South Africa with a long-term spraying history are high. Job history information on DDT exposures must be very detailed in order to provide valid estimates of exposure.

Animals↗
PubMed2003

Nervous system effects of occupational manganese exposure on South African manganese mineworkers.

Occupational exposure to airborne manganese dust has been shown to produce adverse effects on the central nervous system. Four hundred and eighty-nine blue and white collar manganese mineworkers from South Africa were studied cross-sectionally to investigate the nervous system effects of medium to low occupational manganese exposures. The different facilities included underground mines, surface processing plants, and office locations. A job exposure matrix was constructed using routine occupational hygiene data. Exposure variables included years of service, a cumulative exposure index (CEI) and average intensity of exposure (AINT) across all jobs, and blood manganese. Endpoints included items from the Q16, WHO-NCTB, SPES, and Luria-Nebraska test batteries, and a brief clinical examination. Potential confounders and effect modifiers included age, level of education, past medical history including previous head injury, previous neurotoxic job exposures, tobacco use, alcohol use and home language. Associations were evaluated by multiple linear and logistic regression modeling. Average exposure intensity across all jobs was 0.21mg/m(3) manganese dust. Multivariate analyses showed that none of the symptom nor test results were associated with any measure of exposure including blood manganese, after adjustment for confounders. This relatively large null study indicates that manganese miners exposed on average across all jobs to MnO(2) at levels near the American Conference of Governmental Industrial Hygienists Threshold Limit Value (ACGIH TLV) are unlikely to have a subclinical neurotoxicity problem.

Adult↗
PubMed2003

The nervous system effects of occupational exposure on workers in a South African manganese smelter.

Five hundred and nine production workers at a manganese (Mn) smelting works comprising eight production facilities and 67 external controls were studied cross-sectionally for Mn related neuroehavioural effects. Exposure measures from personal sampling included Mn in inhalable dust as cumulative exposure indices (CEI) and average intensity (INT). Biological exposure and biological effect measures included blood (MnB), urine (MnU) manganese and serum prolactin. Endpoints included items from the Swedish nervous system questionnaire (Q16), World Health Organisation neurobehavioural core test battery (WHO NCTB), Swedish performance evaluation system (SPES), Luria-Nebraska (LN), and Danish product development (DPD) test batteries, and a brief clinical examination. Potential confounders and effect modifiers included age, educational level, alcohol and tobacco consumption, neurotoxic exposures in previous work, past medical history, previous head injury and home language. Associations were evaluated by multiple linear and logistic regression modelling. Modelling assumptions were tested. Average exposure intensity across all jobs ranged from near 0 (0.06 microg/m3) for external controls to 5.08 mg/m3 for inhalable Mn, and was greater than the ACGIH TLV for 69% of subjects. Results from the large number of tests performed resolved into three groups. Group 1 shows differences between external unexposed referents and all the exposed and/or differences between internal low exposed referents and the rest of the exposed but no further exposure-response relationships. It includes the Santa Ana, Benton and digit-span tests from the WHO NCTB; the hand tapping and endurance tapping tests from the SPES; Luria-Nebraska item 2L; questionnaire items tired, depressed, irritated, having to take notes in order to remember things, and subjects' perception that they had sex less often than normal; a test of clinical abnormality; and increased sway under two conditions (eyes open without foot insulation, eyes open with foot insulation). Group 2 shows the presence of a more substantive exposure-response relationship. It consists of only two tests: and includes the WHO digit-symbol test (although the major impact is at low exposure and therefore counterintuitive, arguably placing this test in group 3) and the LN item 1R which has a step to a poorer score at high exposure. Group 3 contains the overwhelming majority of test results (almost all the questionnaire items, almost all the DPD tests including tremor, sway and diadochokinesia, and serum prolactin) which were either null or counterintuitive (did not make sense). The CEI was the strongest predictor of test abnormalities, except for the clinical test which was more strongly associated with blood manganese. Despite a comprehensive range of endpoints, and levels of exposure ranging from environmental to industrial, this large study of Mn workers found little convincing evidence for a continuum of effects, contributing further questions to current debates about the adequacy of the current ACGIH TLV.

Adult↗
PubMed2003

The utility of biological monitoring for manganese in ferroalloy smelter workers in South Africa.

Five hundred and nine workers at a manganese (Mn) smelting works comprising eight production facilities and 67 external controls were studied cross-sectionally. Exposure measures from personal sampling included inhalable dust, cumulative exposure indices (CEI) and average intensity (INT = CEI/years exposed) calculated for the current job at the smelter and also across all jobs held by subjects. Biological exposure was measured by Mn in the blood (MnB) and urine (MnU) and biological effect was measured by serum prolactin. Average lifetime exposure intensity across all jobs ranged from near 0 (0.06 microg/m3) for unexposed external referents to 5 mg/m3. Atmospheric exposures and MnB and MnU distributions were consistent with published data for both unexposed and smelter workers. Associations between biological exposures and groups defined by atmospheric exposures in the current job were substantial for MnB, less so for MnU and absent for serum prolactin. Random sampling of MnB measurements representative of a group of workers with more than 1-2 years of service in the same job and notionally homogenous exposure conditions could serve as a cross-sectional predictor of atmospheric Mn exposure in the current job, as well as for surveillance of Mn exposure trends over time. Correlations at the individual level were only modest for MnB (33% of the variance in log atmospheric Mn intensity in the current job was explained by log MnB), much worse for MnU (only 7%). However, a receiver operating characteristic (ROC) analysis was performed which showed that it is possible to use a MnB cut-off of 10 microg/l (the 95th percentile in the unexposed) to good effect as a screening tool to discriminate between individual exposures exceeding and falling below a relatively strict atmospheric Mn exposure threshold at the ACGIH threshold limit value (TLV) of 0.2 mg/m3. MnU has no utility as a measure of biological exposure nor does serum prolactin as a measure of biological effect.

Alloys↗
PubMedDate not supplied

Addressing the challenges of underdevelopment in environmental and occupational health in southern Africa.

Since 1996, the University of Michigan's Fogarty International Center training and research program in Environmental and Occupational Health (EOH) in Southern Africa has contributed to capacity development in the 14 countries of the Southern African Development Community. Methods include training citizens from the region in master's, doctoral, and short-term focused programs; assisting the development of graduate programs in EOH at institutions, developing resources for distance-based degree programs; direct support ofjunior and mid-level researchers, and organizing regional short courses and regional conferences. Substantial EOH resources now present in South Africa are leveraged to assist capacity development in the rest of the region. The program's successes appear to be due to strong regional leadership and oversight structures, a strategy of developing EOH resource centers in several countries, and close collaboration with other regional and international EOH programs.

Africa, Southern↗