Experimental infection of tick cells with Nipah virus.

Nipah virus (NiV), a highly pathogenic henipavirus of the family Paramyxoviridae, which causes fatal encephalitis in 40-70% of affected patients, was first reported in Malaysia over 20 years ago. Pteropid bats are the natural hosts of henipaviruses, and ticks have been proposed as a possible link between bats and mammalian hosts. To investigate this hypothesis, infection of the tick cell line IDE8 with NiV was examined. Presence of viral RNA and antigen in the NiV-infected tick cells was confirmed. Infectious virions were recovered from NiV-infected tick cells and ultrastructural features of NiV were observed by electron microscopy. These results suggest that ticks could support NiV infection, potentially playing a role in transmission.

Experimental infection of tick cells with Nipah virus

@#Nipah virus (NiV), a highly pathogenic henipavirus of the family Paramyxoviridae, which causes fatal encephalitis in 40-70% of affected patients, was first reported in Malaysia over 20 years ago. Pteropid bats are the natural hosts of henipaviruses, and ticks have been proposed as a possible link between bats and mammalian hosts. To investigate this hypothesis, infection of the tick cell line IDE8 with NiV was examined. Presence of viral RNA and antigen in the NiV-infected tick cells was confirmed. Infectious virions were recovered from NiV-infected tick cells and ultrastructural features of NiV were observed by electron microscopy. These results suggest that ticks could support NiV infection, potentially playing a role in transmission.

Detection in Malaysia of a Borrelia sp. From Haemaphysalis hystricis (Ixodida: Ixodidae).

Spirochetes from the Borrelia genus are known to cause diseases in humans, namely Lyme disease and relapsing fever. These organisms are commonly transmitted to humans by arthropod vectors including ticks, mite, and lice. Here, we report the molecular detection of a Borrelia sp. from a Haemaphysalis hystricis Supino tick collected from wildlife in an Orang Asli settlement in Selangor, Malaysia. Phylogenetic analyses of partial 16s rRNA and flaB gene sequences revealed that the Borrelia sp. is closely related to the relapsing fever group borreliae, Borrelia lonestari, Borrelia miyamotoi, and Borrelia theileri, as well as a number of uncharacterized Borrelia sp. from ticks in Portugal and Japan. To our knowledge, this is the first report of a Borrelia sp. detected in H. hystricis, and in Malaysia. The zoonotic potential of this Borrelia sp. merits further investigation.

Radiological progression and its predictive risk factors in silicosis.

OBJECTIVES: To investigate the risk factors predicting radiological progression in silicosis in a prospective cohort study of patients with silicosis who were previously exposed to silica from granite dust. METHODS: From among a total of 260 patients with silicosis contracted from granite work, 141 with available serial chest x ray films of acceptable quality taken over a period of 2 to 17 (mean 7.5) years, were selected for study. Ninety four (66.7%) had ended exposure 5 or more years previously (mean 10.1 years, maximum 28 years). Radiological progression was assessed by paired comparison of the initial and most recent radiographs, with two or more steps of increase in profusion of small opacities according to the 12 point scale of the International Labour Organisation (ILO) classification of radiographs of pneumoconiosis, taken from the majority reading by a panel of three independent readers. RESULTS: Overall, 37% of patients with silicosis had radiological evidence of progression. From the initial radiographs, 24 (31.6%) of those with radiological profusion category 1, 15 (37.5%) of those with radiological profusion category 2, and 13 (52%) of those with complicated silicosis (including all seven with category 3 profusion of small opacities) showed radiological progression. As expected, progression was more likely to be found after longer periods of follow up (the interval between the two chest x ray films) with a 20% increased odds of progression for every additional year of follow up. After adjustment for varying intervals of follow up, the probability of radiological progression was found to be significant if large opacities were present in the initial chest x ray film. Progression was also less likely to be found among those who had ended exposure to silica longer ago, although the result was of borderline significance (p=0.07). Tuberculosis was also associated with increased likelihood of progression (borderline significance). CONCLUSIONS: There is a high probability of radiological progression in silicosis after high levels of exposure to granite dust among workers who were followed up for up to 17 years. A significant risk factor is the extent of radiological opacities in the initial chest x ray film. The probability of progression is also likely to be reduced with longer periods after the end of exposure.

The significance of aches/pains among workers in an electronics factory.

Three hundred and fifteen female workers with at least three months' employment history in a factory manufacturing disk drives were studied. Each worker completed a self-administered questionnaire on their personal particulars, hours of work, opinion on the work and the workplace and the presence and severity of aches/pains experienced over the past one month. One hundred and forty one (44.8%) of the workers had complaints of aches/pains. Of these, 81 (57.5%) reported an improvement in their symptoms during their off-days. 59 (41.8%) had symptoms affecting two or more sites. The most commonly affected sites were the hands and shoulders, followed by the head and back. There was no significant difference in the prevalence of symptoms between workers from the different work stations. Ninety four (66.7%) of these workers reported that the pains that were severe enough to affect their activities. 76 (53.9%) had to seek some form of medical treatment while 33 (23.4%) had to be on medical leave. However, the physical examinations of this group of workers were normal. The symptoms appeared to be influenced by their attitude towards work. A significantly higher number of workers with symptoms expressed dissatisfaction with work and had complaints of a noisy and cold environment. The study showed that workers' morale and the quality of the work environment may play an important role in improving their general well-being.

Biomarkers of exposure to low concentrations of benzene: a field assessment.

OBJECTIVE: To carry out a comprehensive field investigation to evaluate various conventional and recently developed biomarkers for exposure to low concentrations of benzene. METHODS: Analyses were carried out on environmental air, unmetabolised benzene in blood and urine, urinary trans, transmuconic acid, and three major phenolic metabolites of benzene: phenol, catechol, and hydroquinone. Validations of these biomarkers were performed on 131 never smokers occupationally exposed to the time weighed average benzene concentration of 0.25 ppm (range, 0.01 to 3.5 ppm). RESULTS: Among the six biomarkers studied, unmetabolised benzene in urine correlated best with environmental benzene concentration (correlation coefficient, r = 0.76), followed by benzene in blood (r = 0.64). When urinary metabolites were compared with environmental benzene, trans, trans-muconic acid showed a close correlation (r = 0.53) followed by hydroquinone (r = 0.44), and to a lesser extent with urinary phenol (r = 0.38). No correlation was found between catechol and environmental benzene concentrations. Although unmetabolised benzene in urine correlates best with benzene exposure, owing to serious technical drawbacks, its use is limited. Among the metabolites, trans, trans-muconic acid seems to be more reliable than other phenolic compounds. Nevertheless, detailed analyses failed to show that it is specific for monitoring benzene exposures below 0.25 ppm. CONCLUSION: The overall results suggest that most of the currently available biomarkers are unable to provide sufficient specificity for monitoring of low concentrations of benzene exposure. If a lower occupational exposure limit for benzene is to be considered, the reliability of the biomarker and the technical limitations of measurements have to be carefully validated.

Occupational respiratory diseases in Singapore.

Occupational respiratory disease statistics in Singapore from 1970 to 1993 were reviewed. Silicosis was the most common occupational respiratory disease in the 1970s and 1980s. About 78% of the cases were from granite quarries. With progressive reduction in dust levels and the closure of some quarries, there has been a decline in cases. From 1990 to 1993, occupational asthma was the most common occupational respiratory disease and more cases are expected with increasing awareness of the condition. The most common causative agent was isocyanates accounting for about 34% of cases. Of the asbestosis and malignant mesothelioma cases, about 70%-80% were from the one and only asbestos cement factory. With the closure of this factory and the increasing restrictions on the use of asbestos, cases of asbestosis are expected to decline in the long term. However, malignant mesothelioma cases may continue to surface because of the long latent period and the potential risk with low and brief exposures to asbestos. It is important to probe for possible occupational exposures (both present and past) in a patient with respiratory symptoms or disease.

Symptoms, lung function, and diurnal variation in peak expiratory flow rate among female solderers in the electronics industry.

The purpose was to determine if solderers had increased diurnal variation (DV) in peak expiratory flow rate (PEFR) and chronic impairment of lung function. A cross-sectional study of 150 female operators doing manual soldering using flux-cored (rosin-based) solder wire and 52 administrative staff from two electronics factories was carried out. They answered a questionnaire, had their forced expiratory volume in 1 sec (FEV1) and forced vital capacity (FVC) measured and their 3-hourly PEFR monitored for 5 working days. The DV in PEFR was the difference in the daily maximum and minimum PEFR expressed as a percentage of the maximum. Six solderers with smoking history were excluded from the analysis. Solderers had a significantly higher prevalence of work-related eye (14.6%) and nose (10.4%) irritation. The prevalence of cough, breathlessness, and wheezing was low. There was no overt case of occupational asthma. The DV in PEFR of 6.0% was not increased. The analysis of FEV1 and FVC was restricted to Chinese only (101 solderers and 51 controls): these were not significantly different. Solderers with 5 or more years of exposure had a significantly lower FEV1/FVC (%) of 88.4% after adjustment for age. In conclusion, solderers with 5 or more years of exposure may have a mild obstructive effect apart from smoking, asthma, or age.

Impact of statutory medical examinations on control of noise-induced hearing loss.

Noise at work is ubiquitous and presents a major occupational health problem in many countries. Prolonged exposure to loud noise can cause deafness of varying degrees. This is insidious in the early stages, but can be detected by audiometric examination. In the prevention of noise-induced hearing loss, control of noise at its source would be ideal. But for practical purposes, a multipronged approach is often necessary. Every noisy workplace should set up an in-plant Hearing Conservation Programme (HCP) which includes periodic audiometric examination of workers. In Singapore, since 1985, workers in many noisy workplaces are required to undergo statutory pre-employment and annual audiometric examinations arranged by their employers. The examinations are carried out by Designated Factory Doctors who have undergone a course of training in occupational health and are registered with the Labour Ministry. The doctors' role includes advising workers and employers on the prevention of noise-induced deafness (NID). Doctors notify cases of NID to the Ministry of Labour which conducts investigations where indicated. Since NID is insidious, workers with the condition would not be detected in the early stages without an audiometric examination. With the introduction of the statutory examinations, more noise-exposed workers were examined and cases of early hearing impairment picked up. The statutory medical examinations have helped to highlight the problem of the noise hazard. Individual companies are able to monitor the noise problem in their workplaces, using the audiometric results to supplement the noise assessments. Susceptible workers can be identified and followed up more closely, and health education intensified.(ABSTRACT TRUNCATED AT 250 WORDS)

Skin disorders among hand solderers in the electronics industry.

Full-time solderers (n = 150) and non-soldering administrative staff (n = 52) were interviewed and examined to determine the prevalence of work-related rashes, to assess their acne status and to measure their forehead skin sebum levels with a Sebumeter. The period prevalence rates (of ever having a work-related skin rash since working as a solderer) for the 82 solderers using multicored solder wire and for the 68 workers using liquid flux were 19.5 per cent and 10.3 per cent respectively. Among the liquid flux solderers, 29 used cotton gloves. The prevalence rate of work-related skin rashes was 3.4 per cent in this group, compared to 15.4 per cent among the 39 ungloved workers. A similar finding was noted among the multicored solder wire users (9 per cent of the 11 gloved workers and 21 per cent of the 71 ungloved workers). On examination, six solderers (all ungloved multicored flux users) had work-related dermatitis of the hands or fore-arms. The point prevalence rate of work-related dermatitis among all solderers was 4 per cent. For non-occupational dermatitis, the point prevalence rate was 2.7 per cent among the solderers and 4 per cent among the administrative staff. The point prevalence and severity of acne among the 150 solderers were the same as those of the 52 administrative workers who were of a similar age and sex distribution. Forehead skin sebum levels, after adjusting for possible confounding factors such as age, atopic status and time elapsed since the last face wash, were also similar in the two groups of employees.(ABSTRACT TRUNCATED AT 250 WORDS)

Further evidence of human silica nephrotoxicity in occupationally exposed workers.

It has previously been shown that granite workers with heavy exposure to silica had glomerular and proximal tubular dysfunction evidenced by increased urinary excretions of albumin, alpha-1-microglobulin (AMG), and beta-N-acetyl-glucosaminidase (NAG). The investigation was replicated in another group of granite workers to further elucidate the exposure effect relation. The urinary excretion of albumin, alpha-1-microglobulin (AMG), beta-2-microglobulin (BMG), and beta-N-acetyl-glucosaminidase (NAG) was determined in two groups of granite workers with low and high exposure to silica. Low molecular weight proteinuria and enzymuria were significantly correlated with duration of exposure in the high but not the low exposure group. These increases were most pronounced in those with 10 or more years of heavy exposure, and in those with radiological evidence of pulmonary fibrosis, particularly those with rounded small opacities denoting classical silicosis. These results provide further evidence that prolonged and heavy exposure to silica is associated with nephrotoxic effects in granite workers.

Exposure to neurotoxic metals among workers in Singapore: an overview.

The extent of occupational exposure to inorganic lead, manganese, arsenic and inorganic mercury in Singapore was determined from the results of Statutory Medical Examinations and environmental monitoring carried out by the Department of Industrial Health in 1989. There were 786 workers exposed to lead. Of these, 7.8 per cent had blood levels greater than 40 micrograms/dl. There were 67 workers exposed to mercury, 11.9 per cent of whom had urinary mercury levels greater than 50 micrograms/l. There were 101 and 144 workers exposed to arsenic and manganese respectively. None of the biological samples exceeded the health-based limits. A review of local studies showed that some of the exposed workers had neurophysiological and neurobehavioural changes.

Tinnitus in noise-exposed workers.

Tinnitus is said to be a common complaint of workers who are exposed to noise. We studied the prevalence and characteristics of tinnitus in 647 noise-exposed workers who had been notified as cases of noise-induced deafness. One hundred and fifty-one had tinnitus, giving a prevalence of 23.3 per cent. The tinnitus was bilateral in 42.4 per cent of cases, and of high frequency in 44.4 per cent. In 23.8 per cent it was associated with other symptoms. About 30 per cent of those with tinnitus complained that it interfered with daily activities like telephone conversation and sleep. The workers with tinnitus had consistently higher hearing thresholds at both high and low frequencies than those with no tinnitus. This finding remained even after adjusting for differences in sex, age and ethnic group composition and in the noise exposure duration. Workers are often told that noise exposure causes deafness, but little is mentioned about tinnitus. Awareness of the possible occurrence of tinnitus may encourage workers to cooperate more actively in a company hearing conservation programme.

Neurobehavioural effects on workers in a video tape manufacturing factory in Singapore.

This study was carried out in a video tape manufacturing factory in Singapore where workers were exposed to mixed solvents consisting of methyl ethyl ketone (MEK), cyclohexanone (CHE), tetrahydrofuran (THF), and toluene (TOL). The objectives were to quantify workers' exposure to the various solvents and to evaluate if there were any neurobehavioural changes among the workers compared to controls. Nineteen exposed workers out of the workforce of forty-five were studied. Twenty-six workers (with no exposure) matched for ethnic group, age, and years of education served as controls. Eight-hour personal environmental samples were analyzed for the 19 workers along with symptom questionnaires, clinical examinations, and neurobehavioural tests including the Santa Ana Dexterity, Finger Tapping, Digit Span, and Visual Reproduction tests. The mean TWA concentrations for MEK, THF, CHE, and TOL were all below the current American Conference of Governmental Industrial Hygienists Threshold Limit Values (TLV). However, the total solvents concentration index exceed unity in one of the work areas. Significant differences were observed for prevalence of headache, and eyes and nose irritation among the exposed workers. There were also significant differences for the Santa Ana test for both-hands, Digit Span test and Visual Reproduction test. However, no dose-effect relation between behavioral scores and airborne solvent exposure was noted. The study suggests that solvent-exposed workers in video tape manufacturing plants may have poorer visual motor control and recent memory impairment (visual and verbal) than unexposed workers. Dermal absorption of solvents may have played a role in these results by increasing workers exposure.

Diurnal variation in peak expiratory flow rate among workers exposed to toluene diisocyanate in the polyurethane foam manufacturing industry.

The diurnal variation in peak expiratory flow rate (PEFR) was studied in 26 mixers from eight factories making polyurethane foam, who were exposed to toluene diisocyanate (TDI), and 26 unexposed controls matched for age, race, and smoking. They were all men. The mean diurnal variation in PEFR of the mixers was 6.2%, which was significantly higher than the 4.3% for controls. Six mixers had a diurnal variation of greater than 15% on at least one day compared with none among the controls. There was, however, no overt cause of occupational asthma. All but one of the 24 environmental samples taken exceeded the short term exposure limit of 0.02 ppm for TDI. This accounted for the high prevalence (50%) of irritative symptoms such as cough and eye irritation. Forced expiratory volume in one second (FEV1) and FEV1/forced vital capacity (FVC) (%) was negatively correlated with duration of exposure to TDI. Foam workers may still have high exposure to TDI, high prevalence of irritative symptoms, increased diurnal variation in PEFR and evidence of chronic airway obstruction, particularly in those with greater than or equal to 10 years of exposure.

An epidemiological survey of respiratory morbidity among granite quarry workers in Singapore: radiological abnormalities.

This report presents baseline findings from the first of a series of epidemiological studies to evaluate inter alia the effects of control measures introduced in 1972-79 to reduce dust exposure in all quarries in Singapore. The prevalence of radiological abnormalities among 219 currently employed quarry workers were estimated according to a number of parameters of dust exposure. Large-sized chest x-ray films were read, independently and in random order, by a panel of three experienced readers, who were "blinded" to the personal particulars and exposure of the subjects, using standard chest x-ray films to record opacities according to the International Standard Classification of Radiographs of Pneumoconioses. Silicosis as defined by radiological small opacities (both rounded and irregular) of profusion 1/1 or greater as read by at least two readers were noted in 11 subjects. The prevalence of silicosis was 12.5% in highly exposed drilling and crushing workers, and 0.8% in maintenance and transportation workers with low level exposure to granite dust. Among those who were first exposed to granite dust after 1979, no cases of silicosis were noted in any quarry worker. It is concluded that reduction in dust exposure since 1979 has so far been successful in producing nil or negligible risks of silicosis among active quarry workers over ten years, but further follow-up studies are needed.

An epidemiological survey of respiratory morbidity among granite quarry workers in Singapore: chronic bronchitis and lung function impairment.

Respiratory symptoms of chronic bronchitis and measurements of lung function were studied in an epidemiological survey of the total population of workers currently employed in granite quarries in Singapore. There were 85 rock drilling and crushing workers with current exposure in high levels of silica dust. Their respiratory parameters were studied with reference to an internal comparison group of 154 quarry maintenance and transport workers with low dust exposure, and an external comparison group of 148 Telecoms postal delivery workers with no granite dust exposure. The highly exposed workers showed greater prevalences of chronic cough and phlegm, a mean reduction of 5% in forced expiratory volume in one second (FEV1) and forced vital capacity (FVC). The increased respiratory morbidity were independent of other factors such as age and smoking. Similar results were also noted after excluding those with silicosis (defined radiologically as profusion greater than 1/1 as read by at least two of three readers). This study strongly indicates a demonstrable risk of "occupational" bronchitis (mucus hypersecretion) and obstructive and restrictive lung function impairment, apart from the "classical" risk of silicosis. Measures taken to protect the health of workers exposed to silica dust should also be based on considerations taken to protect against the risk of these respiratory disorders as well.

Monitoring of exposure to cyclohexanone through the analysis of breath and urine.

Occupational exposure to cyclohexanone was studied for 59 workers through the analysis of environmental air, alveolar air, and urinary cyclohexanol. Environmental cyclohexanone exposure was measured by personal sampling with a carbon-felt passive dosimeter. Cyclohexanone in alveolar air and cyclohexanol in urine were determined with gas chromatography with a flame ionization detector. The end-of-shift urinary cyclohexanol levels correlated well with the time-weighted average environmental cyclohexanone values (r = 0.66). Urinary cyclohexanol corrected for creatinine correlated best with cyclohexanone in air (r = 0.77); when corrected for specific gravity, it gave a similar correlation coefficient (r = 0.73). When the time-weighted average of the exposure was 25 ppm, the corresponding calculated concentration for urinary cyclohexanol was 54.5 mg/1, 23.3 mg/g of creatinine, or 43.5 mg/l at a specific gravity of 1.018. The relationship between cyclohexanone exposure and its concentration in exhaled breath was found to be poorer than that for cyclohexanone exposure and the urinary metabolite (r = 0.51).