Showing papers by "Mahidol University published in 2002"

Alcohol, tobacco and breast cancer - Collaborative reanalysis of individual data from 53 epidemiological studies, including 58 515 women with breast cancer and 95 067 women without the disease

Abstract: Alcohol and tobacco consumption are closely correlated and published results on their association with breast cancer have not always allowed adequately for confounding between these exposures. Over 80% of the relevant information worldwide on alcohol and tobacco consumption and breast cancer were collated, checked and analysed centrally. Analyses included 58515 women with invasive breast cancer and 95067 controls from 53 studies. Relative risks of breast cancer were estimated, after stratifying by study, age, parity and, where appropriate, women's age when their first child was born and consumption of alcohol and tobacco. The average consumption of alcohol reported by controls from developed countries was 6.0 g per day, i.e. about half a unit/drink of alcohol per day, and was greater in ever-smokers than never-smokers, (8.4 g per day and 5.0 g per day, respectively). Compared with women who reported drinking no alcohol, the relative risk of breast cancer was 1.32 (1.19 - 1.45, P < 0.00001) for an intake of 35 - 44 g per day alcohol, and 1.46 (1.33 - 1.61, P < 0.00001) for greater than or equal to 45 g per day alcohol. The relative risk of breast cancer increased by 7.1% (95% CI 5.5-8.7%; P<0.00001) for each additional 10 g per day intake of alcohol, i.e. for each extra unit or drink of alcohol consumed on a daily basis. This increase was the same in ever-smokers and never-smokers (7.1 % per 10 g per day, P < 0.00001, in each group). By contrast, the relationship between smoking and breast cancer was substantially confounded by the effect of alcohol. When analyses were restricted to 22 255 women with breast cancer and 40 832 controls who reported drinking no alcohol, smoking was not associated with breast cancer (compared to never-smokers, relative risk for ever-smokers= 1.03, 95% CI 0.98 - 1.07, and for current smokers=0.99, 0.92 - 1.05). The results for alcohol and for tobacco did not vary substantially across studies, study designs, or according to 15 personal characteristics of the women; nor were the findings materially confounded by any of these factors. If the observed relationship for alcohol is causal, these results suggest that about 4% of the breast cancers in developed countries are attributable to alcohol. In developing countries, where alcohol consumption among controls averaged only 0.4 g per day, alcohol would have a negligible effect on the incidence of breast cancer. In conclusion, smoking has little or no independent effect on the risk of developing breast cancer; the effect of alcohol on breast cancer needs to be interpreted in the context of its beneficial effects, in moderation, on cardiovascular disease and its harmful effects on cirrhosis and cancers of the mouth, larynx, oesophagus and liver. (C) 2002 Cancer Research UK.

Malaria: current status of control, diagnosis, treatment, and a proposed agenda for research and development

Abstract: 564 Rolling back malaria is possible. Tools are available but they are not used. Several countries deploy, as their national malaria control treatment policy, drugs that are no longer effective. New and innovative methods of vector control, diagnosis, and treatment should be developed, and work towards development of new drugs and a vaccine should receive much greater support. But the pressing need, in the face of increasing global mortality and general lack of progress in malaria control, is research into the best methods of deploying and using existing approaches, particularly insecticidetreated mosquito nets, rapid methods of diagnosis, and artemisinin-based combination treatments. Evidence on these approaches should provide national governments and international donors with the costbenefit information that would justify much-needed increases in global support for appropriate and effective malaria control.

A Comparison of Imputation Techniques for Handling Missing Data

Abstract: Researchers are commonly faced with the problem of missing data. This article presents theoretical and empirical information for the selection and application of approaches for handling missing data on a single variable. An actual data set of 492 cases with no missing values was used to create a simulated yet realistic data set with missing at random (MAR) data. The authors compare and contrast five approaches (listwise deletion, mean substitution, simple regression, regression with an error term, and the expectation maximization [EM] algorithm) for dealing with missing data, and compare the effects of each method on descriptive statistics and correlation coefficients for the imputed data (n = 96) and the entire sample (n = 492) when imputed data are included. All methods had limitations, although our findings suggest that mean substitution was the least effective and that regression with an error term and the EM algorithm produced estimates closest to those of the original variables.

Liver fluke‐associated cholangiocarcinoma

Abstract: Background: Infection with liver flukes has been reported to be associated with bile duct malignancy. Methods: The review is based on a literature search (Medline) and, in some cases, direct contact with authors or principal investigators. Results: A large body of evidence indicates that Opisthorchis viverrini is a definite cause of human cholangiocarcinoma, whereas Clonorchis sinensis is a probable cause. The evidence regarding Opisthorchis felineus is insufficient to assess its role in carcinogenesis. Possible mechanisms of carcinogenesis include chronic irritation, nitric oxide formation, intrinsic nitrosation and activation of drug-metabolizing enzymes. Early detection of bile duct malignancy is difficult and not clinically available at present, although cholangiocarcinoma-associated soluble antigen has been reported in an experimental study to be a useful early marker of cancer development. Long-term survival after surgical treatment of liver fluke-associated cancer is similar to that reported in patients without liver fluke infestation. Conclusion: Liver fluke-associated cholangiocarcinoma is still a health problem in developing countries. Mechanisms of carcinogenesis should be explored further in order to reduce the impact of this disease. © 2002 British Journal of Surgery Society Ltd

An Outbreak of Eosinophilic Meningitis Caused by Angiostrongylus cantonensis in Travelers Returning from the Caribbean

Abstract: Background Outbreaks of eosinophilic meningitis caused by the roundworm Angiostrongylus cantonensis are rarely reported, even in regions of endemic infection such as Southeast Asia and the Pacific Basin. We report an outbreak of A. cantonensis meningitis among travelers returning from the Caribbean. Methods We conducted a retrospective cohort study among 23 young adults who had traveled to Jamaica. We used a clinical definition of eosinophilic meningitis that included headache that began within 35 days after the trip plus at least one of the following: neck pain, nuchal rigidity, altered cutaneous sensations, photophobia, or visual disturbances. Results Twelve travelers met the case definition for eosinophilic meningitis. The symptoms began a median of 11 days (range, 6 to 31) after their return to the United States. Eosinophilia was eventually documented in all nine patients who were hospitalized, although on initial evaluation, it was present in the peripheral blood of only four of the nine (44 percent)...

HLA-A and -B allele associations with secondary dengue virus infections correlate with disease severity and the infecting viral serotype in ethnic Thais

Abstract: Little is known of the role of classical HLA-A and -B class I alleles in determining resistance, susceptibility, or the severity of acute viral infections. Appropriate paradigms for immunogenetic studies of acute viral infections are dengue fever (DF) and dengue hemorrhagic fever (DHF). Both primary and secondary infections with dengue virus (DEN) serotypes 1, 2, 3 or 4, can result in either clinically less severe DF or the more severe DHF. In secondary exposures, a memory response is induced in immunologically primed individuals, which can both clear the infecting dengue virus and contribute to its pathology. In a case-control study of 263 ethnic Thai patients infected with either DEN-1, -2, -3 or -4, we detected HLA class I associations with secondary infections, but not in immunologically naive patients with primary infections. HLA-A*0203 was associated with the less severe DF, regardless of the secondary infecting virus serotype. By contrast, HLA-A*0207 was associated with susceptibility to the more severe DHF in patients with secondary DEN-1 and DEN-2 infections only. Conversely, HLA-B*51 was associated with the development of DHF in patients with secondary infections, and HLA-B*52 was associated with DF in patients with secondary DEN-1 and DEN-2 infections. Moreover, HLA-B44, B62, B76 and B77 also appeared to be protective against developing clinical disease after secondary dengue virus infection. These results confirm that classical HLA class I alleles are associated with the clinical outcome of exposure to dengue virus, in previously exposed and immunologically primed individuals.

Interactions between fleshy fruits and frugivores in a tropical seasonal forest in Thailand

Abstract: Large frugivores are considered to be important seed dispersers for many tropical plant species. Their roles as seed dispersers are not well known in Southeast Asia, where degraded landscapes typically lack these animals. Interactions between 259 (65 families) vertebrate-dispersed fruits and frugivorous animals (including 7 species of bulbul, 1 species of pigeon, 4 species of hornbill, 2 species of squirrel, 3 species of civet, 2 species of gibbon, 1 species of macaque, 2 species of bear, 2 species of deer, and 1 species of elephant) were studied for 3 years in a tropical seasonal forest in Khao Yai National Park, Thailand. The purpose was to examine the dietary overlaps among the large frugivores and the characteristics of fruits they consumed. Most fruit species are eaten by various kinds of frugivores; no close relationship between a particular fruit and a frugivore was found. The number of frugivore groups that served a given plant species was negatively correlated with seed size. Additionally, the fruit/seed diameters consumed by bulbuls were significantly smaller than consumed by the other nine groups. These trends of fruit characteristics were consistent with those observed elsewhere in Southeast Asia: small fruits and large, soft fruits with many small seeds are consumed by a wide spectrum of frugivores while larger fruits with a single large seed are consumed by relatively few potential dispersers. Importantly, these large, single-seed fruits are not consumed by the small frugivores that thrive in small forest fragments and degraded areas in Southeast Asia. To insure the natural seed dispersal process in the forest, an evaluation of all frugivore groups in the forest is urgently needed in Southeast Asia.

The nutrition and health transition in Thailand

Abstract: Objective: To explore and describe the nutrition and health transition in Thailand in relation to social and economic changes, shifts in food consumption patterns and nutritional problems, as well as morbidity and mortality trends. Design: This report reviews the nutrition and health situation and other related issues by compiling information from various reports and publications from several sources. Yearly statistics and reports from the National Statistical Office were used as well as data from the Food and Agriculture Organization (FAO) and national surveys on the nutrition and health situation of the Thai population. Results: Thailand has undergone social and economic transitions during the past three decades and is approaching the post-demographic transitional period. These are evidenced by an increase in life expectancy at birth of the population, and declines in the total fertility and infant mortality rates. The economic structure has also moved from agricultural to industrial. Industrial growth has surpassed that of the agricultural sector as indicated by a steady rise in the share of the industrial sector in the gross domestic product, which is greater than that of other sectors. At the same time, results from several nation-wide surveys indicate that the food consumption pattern of the population has changed considerably; Thai staples and side dishes are being replaced by diets containing a higher proportion of fats and animal meat. A shift in the proportion of expenditure on food prepared at home and that expended on purchased, ready-to-eat food, in both rural and urban settings, gives another reflection of the change in food consumption of the Thai population. The prevalence of overweight and obesity among children and adolescents has increased dramatically during the past 20 years and is more pronounced in children from private schools and urban communities than in those from public schools or rural areas. Among adults, results from two national surveys in 1991 and 1996 indicated that the problem of overweight and other risk factors for cardiovascular disease have increased significantly. In considering the overall causes of death among the Thai population, the leading causes are diet-related chronic degenerative diseases. Diseases of the circulatory system have become the number one cause of death in Thailand and cancer has ranked as the number three cause of death since the late 1980s. Conclusions: The rapid changes in food intake and lifestyle patterns in Thailand clearly demonstrate a significant impact on the shifting pattern of disease burden of the population. These changes should be monitored carefully and must be reversed through appropriate behaviour modification and the promotion of appropriate eating practices and physical activities.

Central Role of the Spleen in Malaria Parasite Clearance

Abstract: In acute malaria, red blood cells (RBCs) that have been parasitized, but no longer contain a malaria parasite, are found in the circulation (ring-infected erythrocyte surface antigen [RESA]-RBCs). These are thought to arise by splenic removal of dead or damaged intraerythrocytic parasites and return of the intact RBCs to the circulation. In a study of 5 patients with acute falciparum malaria who had previously undergone splenectomy, it was found that none of these 5 patients had any circulating RESA-RBCs, in contrast to the uniform finding of RESA-RBCs in all patients with acute malaria and intact spleens. Parasite clearance after artesunate treatment was markedly prolonged, although the parasites appeared to be dead and could not be cultured ex vivo. These observations confirm the central role of the spleen in the clearance of parasitized RBCs after antimalarial treatment with an artemisinin derivative. Current criteria for high-grade antimalarial drug resistance that are based on changes in parasitemia are not appropriate for asplenic patients.

The evolution of drug-resistant malaria: the role of drug elimination half-life.

Abstract: This paper seeks to define and quantify the influence of drug elimination half-life on the evolution of antimalarial drug resistance. There are assumed to be three general classes of susceptibility of the malaria parasite Plasmodium falciparum to a drug: Res0, the original, susceptible wildtype; Res1, a group of intermediate levels of susceptibility that are more tolerant of the drug but still cleared by treatment; and Res2, which is completely resistant to the drug. Res1 and Res2 resistance both evolve much faster if the antimalarial drug has a long half-life. We show that previous models have significantly underestimated the rate of evolution of Res2 resistance by omitting the effects of drug half-life. The methodology has been extended to investigate (i) the effects of using drugs in combination, particularly when the components have differing half-lives, and (ii) the specific example of the development of resistance to the antimalarial pyrimethamine-sulphadoxine. An important detail of the model is the development of drug resistance in two separate phases. In phase A, Res1 is spreading and replacing the original sensitive forms while Res2 remains at a low level. Phase B starts once parasites are selected that can escape drug action (Res1 genotypes with borderline chemosensitivity, and Res2): these parasites are rapidly selected, a process that leads to widespread clinical failure. Drug treatment is clinically successful during phase A, and health workers may be unaware of the substantial changes in parasite population genetic structure that predicate the onset of phase B. Surveillance programs are essential, following the introduction of a new drug, to monitor effectively changes in treatment efficacy and thus provide advance warning of drug failure. The model is also applicable to the evolution of antibiotic resistance in bacteria: in particular, the need for these models to incorporate drug pharmacokinetics to avoid potentially large errors in their predictions.

Relationships between dental calcification stages and skeletal maturity indicators in Thai individuals.

Abstract: The purpose of this study was to investigate the relationship between the stages of calcification of various teeth and skeletal maturity stages among Thai individuals. The study subjects consisted 139 male subjects and 222 female subjects ranging in age from 7 years to 19 years. A total of 361 hand-wrist and panoramic radiographs were obtained and analyzed. The tooth development of the mandibular canines, first and second premolars, and second and third molars were assessed according to the Demirjian's system. Skeletal age and skeletal maturity stages were determined from hand-wrist radiographs by using the method outlined in the atlas of Greulich and Pyle and the Fishman's system, respectively. The Spearman rank order correlation coefficient revealed significant relationships (r = 0.31-0.69, P < .01) between dental calcification stages and skeletal maturity stages. The second premolar was the tooth showing the highest correlation (r = 0.66 in male subjects, r = 0.69 female subjects). The third molar demonstrated the poorest correlation (r = 0.47 in male subjects, r = 0.31 in female subjects). The canine stage F for both sexes (63.2% for female subjects, 54.1% for male subjects) coincided with the MP3 stage. The second molar stage E for female subjects (51.4%) and stage G for male subjects (66.7%) were related to the S stage and the MP(3cap) stage, respectively. This suggests that tooth calcification stages from panoramic radiographs might be clinically useful as a maturity indicator of the pubertal growth period. However, further study is recommended in a larger sample size, and future studies should address development of the canines and second molars.

Safety and immunogenicity of tetravalent live-attenuated dengue vaccines in Thai adult volunteers: role of serotype concentration, ratio, and multiple doses.

Abstract: Dengue fever, caused by four serotypes of a mosquito-borne virus, is a growing problem in tropical countries. Currently, there is no treatment or vaccine. We evaluated safety and immunogenicity of two doses, given six months apart, of seven formulations of dengue tetravalent live-attenuated vaccine (containing different concentrations of the component viruses) versus placebo in 59 flavivirus-seronegative Thai adults. The first dose was the more reactogenic. Most volunteers experienced clinically moderate fever, headache, myalgia, eye pain or rash 7-11 days after injection, generally lasting three days or less. Modest decreases in platelets and neutrophils were observed. After one dose, 58% of dengue recipients seroconverted (neutralizing antibody level > or = 1:10) against > or = 3 serotypes; 35% seroconverted against all four. After the second dose, seroconversion was 76% and 71%, respectively. All subjects seroconverted to serotype 3 after one dose. Serotype 4 elicited the lowest primary response but the highest increase in seroconversion after the second dose.

Identification of immune-related genes in hemocytes of black tiger shrimp (Penaeus monodon).

Abstract: An expressed sequence tag (EST) library was constructed from hemocytes of the black tiger shrimp (Penaeus monodon) to identify genes associated with immunity in this economically important species. The number of complementary DNA clones in the constructed library was approximately 4 x 10(5). Of these, 615 clones having inserts larger than 500 bp were unidirectionally sequenced and analyzed by homology searches against data in GenBank. Significant homology to known genes was found in 314 (51%) of the 615 clones, but the remaining 301 sequences (49%) did not match any sequence in GenBank. Approximately 35% of the matched ESTs were significantly identified by the BLASTN and BLASTX programs, while 65% were recognized only by the BLASTX program. Of the 615 clones, 55 (8.9%) were identified as putative immune-related genes. The isolated genes were composed of those coding for enzymes and proteins in the clotting system and the prophenoloxidase-activating system, antioxidative enzymes, antimicrobial peptides, and serine proteinase inhibitors. Three full-length ESTs encoding antimicrobial peptides (antilipopolysaccharide and penaeidin homologues) and a heat shock protein (cpn10 homologue) are reported.

Histopathological Effects of Roundup, a Glyphosate Herbicide, on Nile tilapia (Oreochromis niloticus)

Abstract: The acute toxicity of Roundup, a glyphosate herbicide, to Nile tilapia, Oreochromis niloticus, was investigated with emphasis on histopathological effects. The values of 24-h, 48-h, 72-h and 96-h LC50 for young tilapia were 17.5, 17.1, 16.9 and 16.8 ppm, respectively, and those for adult tilapia were 46.9, 44.4, 40.0 and 36.8 ppm, respectively. They indicated that adult fish were more tolerant to Roundup than the much smaller young fish. Roundup concentration corresponding to the 96-h LC50 value for adult tilapia was used to study the effects of Roundup exposure in inducing histopathological changes of gills, liver and kidneys. In the gills, filament cell proliferation, lamellar cell hyperplasia, lamellar fusion, epithelial lifting and aneurysm were observed. In the liver, there was vacuolation of hepatocytes and nuclear pyknosis. Kidney lesions consisted of dilation of Bowman's space and accumulation of hyaline droplets in the tubular epithelial cells. These changes occurred predominantly in the 96-h exposure.

Use of rice husk ash as filler in natural rubber vulcanizates: In comparison with other commercial fillers

Abstract: Rice husk ash is mainly composed of silica and carbon black remaining from incomplete combustion. Both silica and carbon black have long been recognized as the main reinforcing fillers used in the rubber industry to enhance certain properties of rubber vulcanizates, such as modulus and tensile strength. In this study, two grades of rice husk ash (low- and high-carbon contents) were used as filler in natural rubber. Comparison was made of the reinforcing effect between rice husk ashes and other commercial fillers such as talcum, china clay, calcium carbonate, silica, and carbon black. Fourier transform infrared spectroscopy (FTIR) analysis was employed to study the presence of functional groups on the ash surface. The effect of silane coupling agent, bis(3-triethoxysilylpropyl)tetrasulfane (Si-69), on the properties of ash-filled vulcanizates was also investigated. It was found that both grades of rice husk ash provide inferior mechanical properties (tensile strength, modulus, hardness, abrasion resistance, and tear strength) in comparison with reinforcing fillers such as silica and carbon black. However, the mechanical properties of the vulcanizates filled with rice husk ash are comparable to those filled with inert fillers. The addition of silane-coupling agent has little effect on the properties of the ash-filled vulcanizates. This is simply due to the lack of silanol groups on the ash surface. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2485–2493, 2002