Showing papers by "University of Peradeniya published in 1999"

Phylogenetic Analysis of Rhinosporidium seeberi’s 18S Small-Subunit Ribosomal DNA Groups This Pathogen among Members of the Protoctistan Mesomycetozoa Clade

Abstract: For the past 100 years the phylogenetic affinities of Rhinosporidium seeberi have been controversial. Based on its morphological features, it has been classified as a protozoan or as a member of the kingdom Fungi. We have amplified and sequenced nearly a full-length 18S small-subunit (SSU) ribosomal DNA (rDNA) sequence from R. seeberi. Using phylogenetic analysis, by parsimony and distance methods, of R. seeberi's 18S SSU rDNA and that of other eukaryotes, we found that this enigmatic pathogen of humans and animals clusters with a novel group of fish parasites referred to as the DRIP clade (Dermocystidium, rossete agent, Ichthyophonus, and Psorospermium), near the animal-fungal divergence. Our phylogenetic analyses also indicate that R. seeberi is the sister taxon of the two Dermocystidium species used in this study. This molecular affinity is remarkable since members of the genus Dermocystidium form spherical structures in infected hosts, produce endospores, have not been cultured, and possess mitochondria with flat cristae. With the addition of R. seeberi to this clade, the acronym DRIP is no longer appropriate. We propose to name this monophyletic clade Mesomycetozoa to reflect the group's phylogenetic association within the Eucarya.

Malaria vectors in a traditional dry zone village in Sri Lanka.

Abstract: Malaria transmission by anopheline mosquitoes was studied in a traditional tank-irrigation-based rice-producing village in the malaria-endemic low country dry zone of northcentral Sri Lanka during the period August 1994-February 1997. Adult mosquitoes were collected from human and bovid bait catches, bovid-baited trap huts, indoor catches, and pit traps. Mosquito head-thoraces were tested for the presence of Plasmodium falciparum and P. vivax, and blood-engorged abdomens for the presence of human blood by ELISAs. House surveys were done at two-day intervals to record cases of blood film-confirmed malaria among the villagers. A total of 7,823 female anophelines representing 14 species were collected. Trends in anopheline abundance were significantly correlated with rainfall of the preceding month in An. annularis, An. barbirostris, An. subpictus, An. vagus, and An. varuna, but were not significant in An. culicifacies and An. peditaeniatus. Malaria parasite infections were seen in seven mosquito species, with 75% of the positive mosquitoes containing P. falciparum and 25% P. vivax. Polymorph PV247 was recorded from a vector (i.e., An. varuna) for the first time in Sri Lanka. Computations of mean number of infective vector (MIV) rates using abundance, circumsporozoite (CS) protein rate, and human blood index (HBI) showed the highest rate in An. culicifacies. A malaria outbreak occurred from October 1994 to January 1995 in which 45.5% of village residents experienced at least a single disease episode. Thereafter, malaria incidence remained low. Anopheles culicifacies abundance lagged by one month correlated positively with monthly malaria incidence during the outbreak period, and although this species ranked fifth in terms of abundance, infection was associated with a high MIV rate due to a high CS protein rate and HBI. Abundance trends in other species did not correlate significantly with malaria. It was concluded that An. culicifacies was epidemiologically the most important vector in the study area.

Multiple host feeding in field populations of Anopheles culicifacies and An. subpictus in Sri Lanka

Abstract: Summary A histological technique was used to detect the multiple blood-feeding of female mosquitoes, within the same gonotrophic cycle, in field populations of the malaria vectors Anopheles culicifacies and An.subpictus (Diptera: Culicidae) at a village in the low country of Sri Lanka, during 1994–96. Among 3306 An.culicifacies and 871 An.subpictus engorged females examined, respectively, 34.4% and 30.4% were multiple-fed. In these two species, double meals accounted for 92.7% and 89.5%, and triple meals for 7.3% and 10.5% of multiple meals, respectively. More females of An.culicifacies (53.7%) than An.subpictus (44.5%) multiple-fed on different nights. Multiple feeding rates in the two species were independent of sample size and field abundance. In An.culicifacies, but not An.subpictus, these rates were proportional to ambient temperature but not to humidity. Bloodmeal ELISA showed that 8.3% of 242 An.culicifacies were human-fed and 80% of these (i.e. 6.6%) were concurrently bovid-fed. Combining the histological and ELISA data, it was estimated that multiple feeding involving a human host had occurred in 7.2% of the blood-feeding An.culicifacies population at this study site. Only 1.2% of 406 An.subpictus were human-fed and all of these were concurrently bovid-fed. Multiple bloodfeeding within the same gonotrophic cycle was attributed to a local ‘frequent feeding strategy’ in these primarily zoophagic and endophilic malaria vectors. Unfortunately this strategy enhances their human-biting rate and hence their vectorial capacity.

Serologic evidence for an epizootic dengue virus infecting toque macaques (Macaca sinica) at Polonnaruwa, Sri Lanka.

Abstract: Dengue is one of the most rapidly emerging diseases in the tropics. Humans are the principal reservoir of dengue viruses. It is unclear if nonhuman primates also serve as a reservoir of human dengue viruses under certain conditions. In this study, a cross-sectional serologic survey was carried out to characterize the pattern of transmission of a recently identified dengue virus among toque macaques in Sri Lanka. The results indicated that an epizootic dengue virus was active among the macaques. A single epizootic had taken place between October 1986 and February 1987 during which 94% of the macaques within the 3 km2 study site were exposed to the virus. The epizootic was highly focal in nature because macaques living 5 km from the study population were not exposed to the virus. The transmission of dengue viruses among macaques in the wild may have important public health implications.

Insecticide cross-resistance spectra and underlying resistance mechanisms of Sri Lankan anopheline vectors of malaria.

Abstract: Present status of insecticide resistance was investigated in two major vectors of malaria; An. culicifacies and An. subpictus, collected from a high malaria transmission area in Sri Lanka during 1996/1998. Adult and larval bioassays were carried out to obtain log-probit mortality lines for malathion, propoxur, permethrin and chlorpyrifos. Respective LD50 values were 4.45%, 0.002%, 0.16% and 0.001% for An. culicifacies and 0.66%, 0.004%, 0.004% and 0.04% for An. subpictus. Adults were also tested for WHO standard discriminating dosages of malathion, propoxur, permethrin, DDT, cypermethrin, deltamethlin and lambda cyhalothrin. Both populations were highly resistant to DDT. An. culicifacies was more resistant to malathion and An. subpictus was more resistant to chlorpyrifos. About 25% of both populations were resistant to permethrin. An. culicifacies was susceptible to propoxur, deltamethrin and lambda cyhalothrin and An. subpictus to cypermethrin and lambda cyhalothrin. Adult mosquitos were individually tested for their insecticide detoxifying enzyme activities and altered target-site, acetylcholinesterase. High general esterase activity indicated the presence of amplified esterase genes in both populations. Native gel electrophoresis resolved one elevated esterase isoenzyme, with high affinity to organophosphates, from each species. Malathion carboxylesterase mechanism was present in both populations. Higher glutathione-S-transferase activity was marked in An. subpictus. Synergistic studies showed the possible involvement of monooxygenases in resistance in both species. Acetylcholinesterase activity of approximately 80% of both populations was not inhibited by a standard dosage of propoxur. Low resistance to carbamates shows that the impact of agricultural pesticides is not significant in the development of resistance especially in An. culicifaies. Pyrethroids, other than permethrin, can be successfully used in vector control programs. Carbamates will be an alternative.

The relationship between the acid and alkaline phosphatase activity and the adherence of clinical isolates of Candida parapsilosis to human buccal epithelial cells

Abstract: Candida parapsilosis is an emerging fungal pathogen implicated in many diseases, especially in compromised hosts. Candidal colonization and infection depends on the initial ability to adhere to host surfaces, which in turn depends upon the cell wall components and the allied structures of both the host and the fungus. Examination of a miscellaneous collection of 24 C. parapsilosis isolates, from both superficial and deep infections, for their potential pathogenic traits displayed a relationship between the phosphatase activity measured with p-nitrophenol phosphate and adhesion of the yeasts to human buccal epithelial cells (BECs). Significant intraspecies differences were seen in both the alkaline and acid phosphatase activity as well as in their adhesion to BECs (p<0.0001). The acid phosphatase activity of the superficial isolates was significantly greater (152%) than that of the systemic isolates (p = 0.0352). A highly significant positive correlation was also established between the yeast adhesion to BECs and both the acid (r = 0.88, p<0.0001) and alkaline (r = 0.9, p<0.0001) phosphatase activity. These relationships, described here for the first time, imply that phosphatases of Candida species may play a crucial role in potentiating their virulence.

Histopathological diagnosis of subcutaneous Dirofilaria repens infection in humans.

Abstract: The host tissue response in humans, based on a study of biopsies of 14 subcutaneous nodules caused by Dirofilaria repens is described. The response was characterized by accumulation of eosinophilic material or eosinophilic pus adjacent to the parasite with surrounding granulomatous inflammation associated with extensive eosinophil infiltration of the surrounding tissue. Unlike with fungal lesions, fat necrosis was conspicuously absent. Nodules were all less than 3 cm in size. Fifteen percent of the smaller nodules (less than 1 cm) and 30% of the larger nodules required extensive examination of tissue to visualize the parasite. It is concluded that when typical tissue reactions are seen, extended histological processing is indicated for accurate diagnosis of dirofilariasis, by demonstrating the parasite.

Selection of passive elements for a three-level inverter based static synchronous compensator

Abstract: Mathematical models for a three phase three-level static synchronous compensator (STATCOM) working with both fundamental frequency modulation and selective harmonic elimination modulation are described. The mathematical models were obtained by assuming that the power system and the operation of the STATCOM are on a balanced three-phase basis. The mathematical models were simplified to obtain the STATCOM AC side current, the DC capacitor voltage and the ripple for both switching strategies. These simplified design tools were validated using the exact model. The resonance between the DC side capacitance and the coupling reactance was studied using the mathematical model and the resonance frequency for the three-level STATCOM was obtained. The resonance frequency was validated against results of electromagnetic computer simulations. Using the design tools developed and considering the resonance studies, the process for selection of the size of DC side capacitors for a small STATCOM was demonstrated.

In vitro studies on the mechanisms of endospore release by Rhinosporidium seeberi.

Abstract: Studies of Rhinosporidium seeberi have demonstrated that this organism has a complex life cycle in infected tissues. Its in vivo life cycle is initiated with the release of endospores into a host's tissues from its spherical sporangia. However, little is known about the mechanisms of sporangium formation and endospore release since this pathogen is intractable to culture. We have studied the in vitro mechanisms of endospore release from viable R. seeberi's sporangia. It was found that watery substances visibly stimulates the mature sporangia of R. seeberi to the point of endospore discharge. The internal rearrangement of the endospores within the mature sporangia, the opening of an apical pore in R. seeberi's cell wall, and the active release of the endospores were the main features of this process. Only one pore per sporangium was observed. The finding of early stages of pore development in juvenile and intermediate sporangia suggested that its formation is genetically programmed and that it is not a random process. The stimulation of R. seeberi's sporangia by water supports the epidemiological studies that had linked this pathogen with wet environments. It also explains, in part, its affinities for mucous membranes in infected hosts. The microscopic features of endospore discharge suggest a connection with organisms classified in the Kingdom Protoctista. This study strongly supports a recent finding that placed R. seeberi with organisms in the protoctistan Mesomycetozoa clade.

Immunolocalization of an endogenous antigenic material of Rhinosporidium seeberi expressed only during mature sporangial development.

Abstract: We investigated the immunolocalization of Rhinosporidium seeberi's antigens using sera from individuals infected with R. seeberi and tissue from Sri Lankan patients with rhinosporidiosis. The tissues were fixed in LR white resin, thin sectioned, fixed onto nickel grids and evaluated by transmission electron microscopy for the presence of R. seeberi's sporangia. The tissue samples were reacted with the patients's sera and then labeled with protein A colloidal gold (PACG) for immunolocalization. It was found that the PACG had fixed to antibodies that specifically recognized an internal electron lucent layer situated immediately under the mature sporangium's wall. Strikingly, the endospores, the juvenile and intermediate sporangia did not undergo PACG labeling. This study found that the expression of this antigen occurs only in the final developmental stages of R. seeberi's mature sporangia. Our data may explain why circulating antibodies to R. Seeberi were not detected before in studies that used endospores as antigen in immunoassays. This is the first report in which an antigenic material with a potential role in the immunology of rhinosporidiosis has been detected.

Androgen metabolism in response to oestradiol-17beta and progesterone in human gingival fibroblasts (HGF) in culture.

Abstract: The modulation of androgen metabolism by oestrogen and progesterone in HGF has been investigated, to elucidate hormone modulatory mechanisms, in periodontal disease presentation and healing responses. Duplicate incubations of HGF were performed in Eagle's MEM for 24 h with either 14C-testosterone/14C-4-androstenedione as substrate and serial concentrations of oestradiol-17beta, or progesterone (0.01-50 microg/ml). The effect of the anti- oestrogen tamoxifen on the action of oestradiol in HGF was also investigated. The medium was analysed and quantified for steroid metabolites. When 14C-testosterone was used as substrate, oestradiol stimulated the synthesis of 5alpha-dihydrotestosterone (DHT), 4- androstenedione (4-A) and the diols by 35%, 25% and 2-10-fold respectively (n=4; p<0.01), at optimal concentrations. Tamoxifen inhibited the stimulatory effects of oestradiol. Similarly, when 14C-4-androstenedione was used as substrate, there were 60% and 2-fold increases in the yields of DHT and testosterone respectively, with significant increases in the formation of the diols in response to oestradiol (n=4; p<0.001). Progesterone inhibited the formation of DHT and 4-A by 10-fold and 3-5-fold at effective inhibitory concentrations (n=4; p<0.001), when 14C- testosterone was used as substrate. Similarly, when 14C-4-androstenedione was used as substrate, progesterone decreased the yields of testosterone, DHT and the diols substantially. These results reinforce the potentially anabolic and catabolic roles of oestradiol and progesterone, respectively. This may partly explain the modulatory mechanisms involved, in periodontal disease presentation during altered hormonal states and healing responses in the inflamed periodontium.

Diagnosis of oral premalignant and malignant lesions using cytomorphometry.

Abstract: In this study cytomorphometry has been applied to smears collected from the buccal mucosa. Normal cells and the cells collected from lesions with no dysplasia, dysplasia and squamous. cell carcinoma were differentiated using discriminant analysis based on nuclear and cell diameter values. Cytomorphometrically the dysplastic and malignant cells were well discriminated from the normal cells. A sensitivity of 89%, specificity of 89.7%, positive predictive value of 80% and negative predictive value of 94.4% were obtained when comparing non-dysplastic lesions with dysplastic lesions.

Differential effects of soil properties on leaf nitrogen release

Abstract: Identifying the determinants of the N dynamics of plant prunings or litter is important for the efficient management of agroecosystems in order to improve their productivity. The plant materials in these ecosystems are managed as soil surface mulches or are incorporated into the soil. Numerous studies have been conducted to investigate which plant chemical parameter best governs N release. In these studies, different plant materials have been incorporated into a soil with a set of known characteristics. The objective of the present study was to examine the effects of different soil properties on N release from plant leaves, when they were incorporated into soils under non-leaching conditions. A laboratory incubation experiment (for 8 weeks) was carried out with dried and ground leaves of six leguminous plants and wild sunflower, which were mixed with three soils (alfisol; ultisol, udult; ultisol, humult). Leaf cellulose was the major chemical parameter that determined leaf N release in the alfisol and ultisol, udult. In the ultisol, humult, the C/N ratio and hemicellulose concentration were better related to N release. Cellulose was not a good indicator of N release in the ultisol, humult, possibly due to a low soil pH which did not favour the activity of the cellulose-degrading enzymes of microbes active in decomposition. Soil pH determined the specific C source that was used to generate energy for microbial action and N mineralization/immobilization. It also had an effect on the nitrification of the mineralized N. The levels of labile soil C fractions governed the mode or nature of N release (i.e. mineralization or immobilization). The levels of labile leaf C fractions incorporated into the soils governed the extent of N release. The soil N concentration in the decomposable organic matter pool, as compared to the leaf N concentration, determined whether leaf N limited its own release. It is recommended from this study that, in grouping different leaf materials as sources of N, the properties of soils into which they are incorporated should also be considered, in addition to leaf quality in terms of its chemical composition. In future studies, the relationships identified under laboratory conditions in this experiment should be verified under field conditions.

Trade in Asian elephant ivory in Sri Lanka

Abstract: Elephants Elephas maximus have declined in range and number in the wild in Sri Lanka, from c. 12,000 at the turn of the nineteenth century to c. 4000 today. While in the distant past the decline in elephant numbers was due largely to indiscriminate killing by sportsmen and trophy hunters, today elephants are being killed primarily because they interfere with agriculture. Human–elephant conflicts have increased substantially in the recent past and ivory poaching has become a byproduct of such conflicts. Elephant tusks have been used traditionally in the ivory-carving industry in Sri Lanka since the time of the ancient kings. Until the turn of the century, very little ivory was imported from Africa because there was a plentiful supply of tuskers locally available. Sri Lankan ivory carvers started to use African ivory in 1910. Today ivory and fake-ivory products are sold openly to tourists in some 86 shops in the island. Before the listing of the African elephant in Appendix I of the Convention on International Trade in Endangered Species (CITES), the value of raw ivory in Sri Lanka used to be $US228–285 per kg. After the listing, the price fell to $US72 per kg, reflecting a drastic drop in the demand for ivory from tourists. Many ivory carvers have switched to other jobs or are using substitutes (such as bone and horn) to produce fake-ivory carvings. Only about 7.5 per cent of bulls in Sri Lanka are tuskers and they are under poaching pressure outside protected areas. Given the rarity of tuskers in Sri Lanka, promotion of trade in ivory products, even locally, may pose a serious threat to their long-term survival in the wild.

Patterns of political violence and responses of the government in Sri Lanka, 1971–1996

Abstract: The main objective of this article is to examine the causes and pattern of insurrections and the responses of governments in Sri Lanka. It is the argument of the paper that social expansion and lack of economic and political development have created guerrilla organizations such as the Janatha Vimukthi Peramuna (JVP) and the Liberation Tigers of Tamil Eelam (LTTE). Consequently, the polity of Sri Lanka has been confined to the left‐wing insurgency and ethnic insurgency respectively. The paper has identified the lack of a national policy as a major constraint of the problem. It is recommended that there should be a viable conflict resolution mechanism along with political reforms as a solution to the problem of violence in the island.

Insecticidal natural products: new rocaglamide derivatives from Aglaia roxburghiana.

Abstract: An Erratum for this article has been published in Pest Management Science 56(5) 493 (2000). In the course of the screening for novel, naturally occurring pesticides from the plant family Meliaceae, an extract of the stem bark of Aglaia roxburghiana was found to exhibit significant insecticidal activity. In addition to rocaglamide, a known insecticide isolated from several species of the genus Aglaia, 15 new natural products were isolated from this plant. Isolation and structure elucidation of the natural products is described. The outstanding insecticidal activities of some of the compounds as well as a structure–activity relationship study are presented. © 1999 Society of Chemical Industry

Effects of Irrigation at Different Growth Stages and Source‐Sink Manipulations on Yield and Yield Components of Mung Bean, Vigna radiata (L.) Wilczek, in Dry and Intermediate Zones of Sri Lanka

Abstract: Irrigation is a management option available to farmers in the subhumid zones of Sri Lanka to increase mung bean yields during the dry Yala season. The objective of this study was to quantify the yield gain in response to irrigation at different stages of the crop and thereby determine the most suitable stage/s of irrigation. Four field experiments were conducted during Yala in 1995 and 1996 at two sites, Maha-Illuppallama (MI) and Kundasale (KS). Eight irrigation regimes consisting of all possible combinations of irrigation at three growth stages of the crop were defined. The respective growth stages were vegetative (from germination to appearance of first flower), flowering (from appearance of first flower to 75 % pod initiation) and pod-filling (from 75% pod initiation to maturity). The treatments which received irrigation during two or more stages had significantly higher yields (793-1396kg ha -1 ) than those which received irrigation during only one stage (401-756kg ha -1 ) with the lowest yield being shown by the rain-fed treatment (227-396 kg ha -1 ). When at least two stages can be irrigated, irrigation during the flowering and pod-filling stages was most effective. Irrigation during flowering produced the highest yield gain when only one stage could be irrigated. Seed yield showed a strong positive correlation with number of pods m -2 . Fifity per cent depodding caused yield reductions at both sites, indicating sink limitation. In contrast, 50 % defoliation reduced the yields only at MI where the number of pods m -2 was greater than at KS. Hence, source limitation was present only when the number of pods was higher.

Feeding of dairy cattle in the forest-garden farms of Kandy, Sri Lanka.

Abstract: A survey on feeding practices was conducted with 60 farmers belonging to four categories (15 farmers in each): male farmers without off-farm income (M–), male farmers with off-farm income (M+), female farmers without off-farm income (W–), and female farmers with off-farm income (W+). Data on herd size, feeds offered, milk production, chest girth, reproduction and management were collected monthly over a period of 1 year. In addition, samples of fodder and concentrates were collected monthly and analysed for dry matter (DM), organic matter (OM), crude protein (CP) and in vitro organic matter digestibility (OMD). Of the 550 rations analysed, grass was included in 99.8% of all rations, followed by gliricidia (65%), creepers (50%) and jak leaves (32%). Consequently, the rations were high in OMD (47–59%) and CP (7.8–23.5%). High-protein forage or coconut cake or both were also included as a supplement in 92% of the rations. Both M– and W– farmers had larger (p<0.001) herds (mean 1.8 animal units (AU) per household) than their counterparts with off-farm income (mean 1.44 AU/household), but only the male farmers without off-farm income achieved higher feeding levels (84.4 vs 65.6–72.1 g digestible organic matter (DOM)/kg0.75 per day) and milk production (6.4 vs 5.3–5.7 L/lactating cow). The lower production of animals kept by female and M+ farmers was related to lower feeding levels. M– farmers realized higher feeding levels than their M+ counterparts. W– farmers did not collect extra feed in response to higher levels of production. It was concluded that dairy farming in the mid-country of Sri Lanka is particularly important for poorer households without income from off-farm employment.

Purification of the endospores and sporangia of Rhinosporidium seeberi on Percoll columns.

Abstract: Human rhinosporidial tissue was used as the source of the various developmental stages of Rhinosporidium seeberi - endospores with electron dense bodies, juvenile, and immature sporangia. After homogenisation in phosphate buffered saline (PBS) and removal of tissue fragments by centrifugation, the rhinosporidial bodies were isolated on centrifuged Percoll columns with gradients of densities or on triple-layered columns of varying density. The separated bands, after repeated washing in PBS gave bodies free from human tissue as shown on Leishman and PAS staining and indirect immunofluorescence with rabbit and human patients' anti-rhinosporidial sera. Sonicates of these bodies were tested on agarose gel for precipitation with antisera, and on SDS-PAG electrophoresis and Coomassie Blue staining. Percoll columns were shown to be capable of isolating these stages of R. seeberi, free from human tissue and contaminating bacteria.

Anesthesia and surgery in pediatric patients with low hemoglobin values

Abstract: A low preoperative hemoglobin (Hb) concentration creates a dilemma for the anesthetist to proceed or not. The authors prospectively studied the perioperative morbidity of 200 healthy infants and children (age range 3 mon-5 years) with preoperative Hb values > or = 7 g/dl, undergoing cleft lip and palate surgery under general anesthesia. The patients were later categorized according to preoperative Hb level group A: Hb 7-10 g/dl and group B: Hb > 10 g/dl and the results were compared. One or more episodes of hypoxemia (SpO2 < 91%) were recorded in 8 patients in group A and 6 in group B during airway management. All patients had stable cardiovascular parameters except for transient bradycardia during desaturations. Recovery was similar and rapid. There were no differences in perioperative morbidity between the two groups. However, the safety of general anesthesia in infants and children with difficult airways is questionable when the oxygen reserve is reduced in anemia.

Sources of Ethnic Inequality in Vietnam

Abstract: Vietnam's ethnic minorities tend to be concentrated in remote areas and have lower living standards than the ethnic majority. How much is this due to poor economic characteristics versus low returns to characteristics? Is there a self-reinforcing culture of poverty in the minority group? We find that differences in returns to productive characteristics are an important explanation for ethnic inequality. There is evidence of compensating behavior on the part of the minorities. The results suggest that to redress ethnic inequality, policies need to reach minorities within poor areas and explicitly recognize behavioral patterns that have served them well in the short term, but intensify ethnic differentials in the longer term.