Multispecies coexistence of trees in tropical forests: spatial signals of topographic niche differentiation increase with environmental heterogeneity.

Neutral and niche theories give contrasting explanations for the maintenance of tropical tree species diversity. Both have some empirical support, but methods to disentangle their effects have not yet been developed. We applied a statistical measure of spatial structure to data from 14 large tropical forest plots to test a prediction of niche theory that is incompatible with neutral theory: that species in heterogeneous environments should separate out in space according to their niche preferences. We chose plots across a range of topographic heterogeneity, and tested whether pairwise spatial associations among species were more variable in more heterogeneous sites. We found strong support for this prediction, based on a strong positive relationship between variance in the spatial structure of species pairs and topographic heterogeneity across sites. We interpret this pattern as evidence of pervasive niche differentiation, which increases in importance with increasing environmental heterogeneity.

Predisposition to reinfection by intestinal helminths after chemotherapy in south Thailand.

Rates of reinfection by the intestinal helminths hookworm, Ascaris lumbricoides and Trichuris trichiura after chemotherapy were studied in two villages in Phang-Nga Province, southern Thailand. It was found that intensity of infection levels attained after reinfection correlated positively with pretreatment intensities of infection for all parasites. This implies that certain persons in the community are predisposed to receiving high numbers of worms, due either to environmental or personal risk factors. Therefore, it would be advantageous to identify such persons and treat them preferentially. Targeted chemotherapy, however, should be combined with efforts to identify the risk factors that vary within the community and direct educational efforts or environmental intervention towards the section of the community most affected by the parasites.

Prevalence, incidence, intensity and associated morbidity of intestinal helminths in south Thailand.

Intensive surveys for Ascaris lumbricoides, Trichuris trichiura and hookworm were carried out in two villages in Phang Nga Province, southern Thailand, in order to measure prevalence, estimate incidence and determine the relation between intensity of infection and morbidity before and after chemotherapy. The study populations were a small upland village community (Nai Tone) and a grade school in a small coastal village (Boh Saen). About half of the Nai Tone villagers were given a broad spectrum antihelminthic (albendazole), and the Boh Saen students were all treated successively with three drugs: piperazine citrate to treat for Ascaris, pyrantel pamoate to treat for hookworm, and mebendazole to treat for Trichuris. Stool examinations were made using the quick Kato smear technique, questionnaires were administered concerning a variety of possible symptoms, and anthropometric and blood biochemical parameters were measured both before and after treatment. The prevalence of Ascaris was 31.0 and 22.6%, hookworm was 89.1 and 88.0% and Trichuris was 59.7 and 77.8% in the Nai Tone and Boh Saen study populations, respectively. Average intensity of Ascaris was highest in the 0-9 year age class (greater than 32,000 epg) in Nai Tone Village. Hookworm intensity of infection was higher in males than in females in all age classes, and in Nai Tone Village at least 25% of males and 20% of females had 8000 or more epg of faeces. Trichuris intensity of infection was highest between 5 and 10 years of age in both populations. The only signs or symptoms showing a significant (P less than 0.05) difference between high and low classes of intensity of infection and a significant improvement (P less than 0.01) after drug treatment, were headache and flatulance in the case of hookworm infection in Boh Saen School. The presence of multiple infections made testing of hypotheses concerning particular parasite species difficult.

Incidence of endemic Opisthorchis viverrini infection in a village in northeast Thailand.

Incidence, measured as the proportion of persons whose stools become positive within one year, was studied in endemic Opisthorchis viverrini, the human liver fluke, in a northeastern Thai village over a two-year period. Incidence was higher in males than in females, especially in children under five years of age. It was at least 47% overall in the first year of the study, but declined to below 20% per year in the second. This is attributed to drying of a local water reservoir and decline in availability of infective stages in fish. The fluctuation of incidence is probably due to the large variations in rainfall from year to year. The rate of reversion from positive to negative varied from 2% to 6% per year.

Consistency of fecal egg output in patients with Opisthochiasis viverrini.

Counts of Opisthorchis eggs in two samples of feces arbitrarily taken 0-21 days apart from each of 209 patients from northeastern Thailand were carried out by Stoll's dilution technique. Based on the number of eggs/mg feces, each patient was classified as uninfected, lightly infected (less than 1 egg/mg), moderately infected (1-10/mg), heavily infected (greater than 10-50/mg), or very heavily infected (greater than 50/mg). The intensity of infection for each of the 209 individuals as shown by first and second counts was compared. Of the 209 individuals, 150 (71.8%) remained within the same egg excretion category, with all but five (2.4%) of the remainder being in an adjacent category. Statistical analysis showed no effect of variation in interval between stool counts on the accuracy or consistency of replicate counts.

Morbidity in relation to intensity of infection in Opisthorchiasis viverrini: study of a community in Khon Kaen, Thailand.

A study of the prevalence and intensity of opisthorchiasis viverrini in relation to morbidity as determined by standard medical examination was carried out in Nong Ranya, a small village containing 309 people in northeastern Thailand. Opisthorchis viverrini infection as determined by Stoll's quantitative egg count method had an overall prevalence of 94% and reached 100% prevalence in most age groups above the age of 10 years. With respect to intensity, 6% were uninfected, 26% had light (less than or equal to 1 eggs per mg [epmg] of feces), 37% moderate (greater than 1-10 epmg), 25% heavy (greater than 10-50 epmg), and 5% very heavy (greater than 50 epmg) infections. Peak intensity in both males and females occurred at age 40 and above. A history of eating "koipla" (a sauce consisting of ground up raw fish), of feeling weak, and of having right upper quadrant abdominal pains occurred most frequently in the infected groups and was correlated with intensity of infection. Regardless of intensity of infection, only a small proportion of the population were unable to carry out their routine activities. Anorexia, nausea or vomiting bore little relationship to the presence or intensity of infection. Hepatomegaly at the mid-clavicular line occurred in 14% of the population, mainly in the more heavily infected groups. Neither jaundice nor splenomegaly was observed in the population.

Measurement of incidence of the human liver fluke, Opisthorchis viverrini, in northeast Thailand.

A survey of a community in northeast Thailand where Opisthorchis viverrini is endemic permitted comparison of two methods of measuring incidence: direct determination of the rate at which an uninfected group became infected between two surveys a year apart, and estimation of incidence from age-specific prevalence data using a logarithmic regression method. Both methods revealed that incidence increased with age in young children, and estimation from age-prevalence data showed that the increase was roughly linear from near birth to about age 5 years, beyond which no clear trend in incidence was evident. A catalytic infection model incorporating an infection rate increasing from birth to age 5, and remaining constant thereafter, gave an excellent fit to age-prevalence profiles. Both methods of determining incidence are sensitive to errors in diagnosis, but the direct determination method is more sensitive to the presence of false negatives. A method for correcting this bias is given. The regression method, which was less sensitive to yearly variation in incidence and is easier to use, is recommended for preliminary surveys to identify villages with high transmission intensity.

Transmission of Angiostrongylus cantonensis through the giant African snail Achatina fulica: an experimental study.

Observations on transmission of the rat lung worm, Angiostrongylus cantonensis, from rats to the snail intermediate host. Achatina fulica, in a vacant lot in Bangkok are described. The prevalence of A. cantonensis increased with snail age until 200 days of age when it attained a plateau of 50-60%. The overall prevalence was 53%. The worm burden slowly rose with age until 200 days of age beyond which it remained relatively constant. The highest mean worm burden of 5,478 was observed in the oldest age group. The parasite distribution in the snail population was highly aggregated both within each age class and in the overall population. Experiments on susceptibility of snails to laboratory infection revealed that worm recovery was dependent on dose of first stage larval infection but was independent of snail size in the range of 4-8 cm. The percent worm recovery of third stage larvae was negatively correlated with dose of infection, and no density-dependent effects of worm burden on worm size were observed.

Isolation and characterization of dinucleotide microsatellite loci in the Asian elephant (Elephas maximus).

The endangered Asian elephant is found today primarily in protected areas. We characterized 18 dinucleotide microsatellite loci in this species. Allelic diversity ranged from three to eight per locus, and observed heterozygosity ranged from 0.200 to 0.842 in a wild population. All loci were in Hardy-Weinberg equilibrium, but linkage disequilibrium was detected between two loci in the wild, but not in the zoo elephants. These loci will be useful for the population-level studies of this species.

Inheritance of stereotyped gibbon calls.

Little is known about how vocal patterns develop in non-human primates, mainly because suitable controlled experiments are difficult to carry out on these animals. Results of isolation experiments and observations of interspecific hybrids suggest no greater role for vocal learning than exists in many other vertebrates, and less than has been found in birds. We have now studied vocal patterns of hybrids between white-handed gibbons (Hylobates lar) and pileated gibbons (Hylobates pileatus) in natural mixed-species groups, in a zone of interspecies contact in central Thailand, and in some captive mixed-species groups. We find that in female hybrids, the patterns of the loud and stereotyped 'great-calls' show no evidence of learning from parents, and appear to be under strong genetic control. Daughters maturing in groups with genetically unlike parents develop great-calls unlike those of their mothers, even though these calls develop only while the daughters sing simultaneously with their mothers.

A comparison of a modified quick-Kato technique and the Stoll dilution method for field examination for Opisthorchis viverrini eggs.

A modified quick-Kato technique and the Stoll dilution method for the diagnosis of Opisthorchis viverrini infection were compared from the standpoints of both replicability and sensitivity. One Stoll dilution preparation and two modified quick-Kato smears were prepared from single stool specimens collected from 221 persons in a village in north-eastern Thailand. Stool examinations were made in duplicate for each technique by two examiners, and the averages of the raw egg counts were used to estimate the intensity of infection. Statistical analyses revealed that the modified quick-Kato technique was slightly more sensitive, and thus would detect more positives, but was lacking in replicability and hence less suitable for measurement of individual intensity of infection. We therefore recommend the Stoll dilution technique for field surveys and measurement of individual intensity of O. viverrini infection.

Relationship between prevalence and intensity of Opisthorchis viverrini infection, and clinical symptoms and signs in a rural community in north-east Thailand.

In a large village in north-east Thailand, the overall prevalence of Opisthorchis viverrini infection (based on Stoll's quantitative egg count) was 89.5% in a total population of 1651 individuals. The prevalence was 32% in children under 5 years, 90% in those aged 5-9 years, and averaged 95.6% in age groups above 10 years. The mean faecal egg output (indicative of intensity of infection) was highest in the 40-49-year age group and remained relatively constant through older ages. In all age groups the prevalence and intensity of infection in both men and women were similar.A history of eating raw freshwater fish occurred more frequently in infected persons than in those uninfected. The following symptoms occurred significantly more frequently in groups with higher intensities of infection: weakness, flatulence or dyspepsia, and abdominal pain in the right upper quadrant. Nevertheless, infected persons did not report a reduced ability to work. Anorexia, nausea, vomiting, and diarrhoea were only weakly correlated with the intensity of infection. A palpable liver occurred more frequently in the infected groups and was correlated with intensity of infection. Icteric conjunctivae were observed in 2.2% of infected persons but not in the uninfected. Some 5-10% of the population had symptoms that were attributable to opisthorchiasis.

Opisthorchis viverrini infection and cholangiocarcinoma. A prospective, case-controlled study.

During a prospective, 24-mo case-controlled study, 551 patients from northeastern Thailand were independently evaluated for Opisthorchis viverrini infection, hepatobiliary tract disease, and hepatic carcinoma to determine whether there was any association between hepatic carcinoma and O. viverrini infection. Stool examination by the formalin-ether concentration method revealed O. viverrini ova in 389 (70.6%) patients. Of the 551 patients, 72 (13.1%) had both clinical and laboratory evidence of hepatobiliary tract disease, chronic liver disease, or hepatic carcinoma, alone or in combination. Of these 72 patients, 28 (38.9%) had a liver biopsy that revealed cholangiocarcinoma in 7 patients with O. viverrini ova in their stools, and in 4 patients without. In another patient with ova in the stool combined hepatocellular carcinoma and cholangiocarcinoma was found. In the 4 patients with cholangiocarcinoma who had no O. viverrini ova in their stools, ova were detected in the bile fluid aspirated from the intrahepatic biliary tree during exploratory laparotomy. An additional patient with clinically suspected cholangiocarcinoma and O. viverrini ova in stool had a left supraclavicular lymph node biopsy specimen taken that revealed metastatic adenocarcinoma; this adenocarcinoma was interpreted as compatible with cholangiocarcinoma. Cholangiocarcinoma, therefore, was found only in patients with O. viverrini ova in stool or in the intrahepatic biliary tree. Statistical analysis revealed that patients with known O. viverrini infection had a higher incidence of cholangiocarcinoma than did patients without such infection (X2 test, p less than 0.05).