Simultaneous Electrochemical Detection of Dopamine and Uric Acid via Au@Cu-Metal Organic Framework.

The incorporation of noble metals with metal-organic frameworks (MOFs) are conducive to the simultaneous electrochemical detection of analytes owing to multiple accessible reaction sites. Herein, Au@Cu-metal organic framework (Au@Cu-MOF) is successfully synthesized and modified as a screen-printed carbon electrode (SPCE), which serves as an excellent electrocatalyst for the oxidation of dopamine (DA) and uric acid (UA). The sensor shows a linear range from 10 µM to 1000 µM, with sensitivity and detection limit of 0.231 µA µM-1 cm-2 and 3.40 µM for DA, and 0.275 µA µM-1 cm-2 and 10.36 µM for UA. Au@Cu-MOF could realize the individual and simultaneous electrochemical sensing of DA and UA, with distinguishable oxidation peak potentials. Moreover, it exhibits reproducibility, repeatability, and stability. Ultimately, the sensor provides an avenue for an ultrasensitive label-free electrochemical detection of DA and UA.

Human schistosomiasis in Puerto Rico: reduced prevalence rate and absence of Biomphalaria glabrata.

A combined epidemiologic and malacologic survey of schistosomiasis in Puerto Rico was carried out in areas where previous surveys had reported the prevalence of the disease. This limited survey, with 495 persons examined, found a low prevalence (0.6%) of Schistosoma mansoni infections. The infections were restricted to three people more than 36 years of age. No infections were detected in children 16 years of age or less, and this cohort comprised 57.8% of the study group. Malacologic surveys of the four streams, 10 rivers, and eight lakes throughout the island revealed the absence of intermediate host Biomphalaria glabrata and the presence of Thiara granifera, a competitive species of B. glabrata and the predatory snail Marisa cornuarietis. We believe that the absence of B. glabrata is the primary reason for the sustained reduction in the prevalence of schistosomiasis in Puerto Rico.

First record of Angiostrongylus cantonensis (Chen, 1935) (Nematoda: Metastrongylidae) in the Dominican Republic.

Rats, Rattus norvegicus, trapped in some sections (barrios) of the city of Santo Domingo, the capital of the Dominican Republic showed that 5 of them from two barrios harbored the nematode Angiostrongylus cantonensis in the pulmonary artery. Macerated and digested terrestrial snails, Subulina octona, collected from the backyards of houses where the rats were trapped contained L2 and L3 larvae of the nematode. The morphology of the adult worms and the larvae was consistent with that described for A. cantonensis in the literature. This is the first report of this Oriental and Western Pacific nematode in the Dominican Republic and the fourth in the Americas. Gastrointestinal hemorrhage, a rare symptom due to another species, the American A. costaricensis, which occurs in mesenteric arterioles of rodents and humans, is in the recent literature; the patient was a 41-year old Dominican. Thus the Dominican Republic is the first country in the Western Hemisphere to have the two species of Angiostrongylus.

The influence of selected environmental parameters on the toxicity of Bayluscide to Schistosoma mansoni miracidia.

Laboratory studies were conducted to investigate the influence of selected environmental parameters on the toxicity of Bayluscide to Schistosoma mansoni miracidia. Test results indicated that temperature, pH, hardness and salinity of the water exerted profound effects on miracidial survival and that the miracidicidal action of bayluscide was highly influenced by these factors. In summary, this chemical was found to be more effective in killing the miracidia of S. mansoni in waters of higher temperatures, lower values of pH (acidic waters), lower degrees of hardness (soft waters) and lower levels of salt (freshwaters). The implications of such studies in the control of schistosomiasis transmission are addressed.

Toxicity evaluation of Bayluscide and malathion to three developmental stages of freshwater snails.

Laboratory studies were conducted to assess the conditions under which the use of malathion in ricelands of Cameroon may impact the transmission of schistosomiasis. Helisoma trivolvis and Biomphalaria havanensis were selected as test organisms due to the lack of intermediate snail hosts in the U.S. Using Bayluscide as a reference molluscicidal compound, malathion was tested against snail eggs, juveniles, and adults. Snail eggs were more susceptible to Bayluscide and malathion than juvenile snails which in turn were more susceptible than adult snails. A Bayluscide concentration of 0.200 mg/L caused 100% mortality to adults of both snail species after 24 h exposure. This relatively high toxicity of Bayluscide to freshwater snails is one of the reasons why it has been recommended by the World Health Organization as the molluscicide of choice for control of schistosome-bearing snails. The concentrations of malathion resulting in 100% kill of adult snails after 24 h exposure were 1,200 mg/L for H. trivolvis and 500 mg/L for B. havanensis. After 48 h exposure, these concentrations were reduced to 500 mg/L and 300 mg/L, respectively. Therefore it is expected that the use of malathion for insect control in ricelands of Cameroon may affect the survival of freshwater snails including the intermediate hosts of bilharziasis.

Toxicity evaluation of ammonium sulphate and urea to three developmental stages of freshwater snails.

Studies were performed to evaluate the toxic effects of ammonium sulphate and urea (chemical fertilizers currently applied in ricelands of Cameroon) against eggs, juveniles, and adults of two species of freshwater snails (Helisoma trivolvis and Biomphalaria havanensis). Results obtained from ammonium sulphate tests indicated 24-h LC50 values of 558 mg/L and 669 mg/L for eggs; 393 mg/L and 526 mg/L for juveniles, and 701 mg/L and 657 mg/L for adults of H. trivolvis and B. havanensis, respectively. Similar analysis with urea revealed LC50 values of 14,241 mg/L and 13,532 mg/L for eggs; 18,255 mg/L and 24,504 mg/L for juveniles and 30,060 mg/L and 26,024 mg/L for adults of H. trivolvis and B. havanensis, respectively. Following 48 h exposure, the concentrations of ammonium sulphate killing 100% of snails were 1,250 mg/L and 1,000 mg/L for the adults of H. trivolvis and of B. havanensis, respectively. Those of urea were computed to be 25,000 mg/L for H. trivolvis and 35,000 mg/L for B. havanensis. In rice culture in Cameroon, these fertilizers are applied at doses of 100 kg/ha (ammonium sulphate) and of 150 kg/ha (urea); hence, the above found concentrations lethal to snails appeared to be 10 to 13 times (ammonium sulphate) and to be 165 to 235 times (urea) higher assuming an average water depth of 10 cm in these ricefields. Therefore, the use of ammonium sulphate and urea as chemical fertilizers in ricelands of the Republic of Cameroon might adversely affect the survival of freshwater snails only in the case of spills or of stressful environmental conditions. Under normal laboratory conditions, both chemicals show a low molluscicidal activity with urea being about 25 to 35 times less potent than ammonium sulphate.

Displacement of Biomphalaria glabrata by Thiara granifera under natural conditions in the Dominican Republic.

After a study of the population dynamics of Biomphalaria glabrata snails in several breeding places in the Dominican Republic, the snail Thiara granifera was introduced in some B. glabrata habitats. T. granifera became established in one point in one habitat in the town of Quisqueya, in the east of the country. Around this point of establishment 6 points were selected in order to observe the population dynamics of both species of snails and the chemical and biological characteristics at each point. Four of these points already harbored B. glabrata. One control point was selected also harboring B. glabrata. After 14 months of observations, the results showed that T. granifera was competing with and displacing B. glabrata. This competition does not seem to be competition for food or vital space. Rather, B. glabrata avoids the presence of T. granifera and moves away to new areas, and this is possibly due to a chemical substance(s) secreted by T. granifera or by physical contact with the large number of individuals of T. granifera.

The effects of ammonium sulphate and urea upon egg hatching and miracidial survival of Schistosoma mansoni.

The effects of various concentrations of ammonium sulphate and urea on egg hatching and miracidial survival of S. mansoni were tested in order to determine if the use of these fertilizers in the ricelands of the Republic of Cameroon could affect the transmission of schistosomiasis. Results indicate that hatching of eggs and survival of miracidia varied with concentrations of tested chemicals and times of exposure. Exposure of S. mansoni eggs to 0.20%-1.00% ammonium sulphate or to 0.50%-4.00% urea reduced their ability to hatch and produce miracidia. A chemical concentration of 1.00% ammonium sulphate or 4.00% urea was found to be sufficient to produce complete inhibition of hatching. High concentrations of both chemicals not only inhibited miracidial emergence but also may be ovocidal. Results obtained from miracidial survival tests indicated that LC5, LC50 and LC95 values for ammonium sulphate were 0.07%, 0.80% and 10.61% after 2 hours of exposure; 0.03%, 0.16% and 0.90% after 4 hours of exposure; and 0.30%, 0.20% and 0.40% after 6 hours of exposure respectively. Similar statistical analyses revealed that the LC5, LC50 and LC95 values for urea were 0.22%, 1.90% and 16.25% after 2 hours of exposure; 0.28%, 0.57% and 1.14% after 4 hours of exposure; and 0.13%, 0.27% and 0.57% after 6 hours of exposure respectively. Although the two fertilizers exerted some adverse effects on S. mansoni eggs and miracidia at relatively high concentrations, neither of them was found to be of practical value. Ammonium sulphate and urea concentrations effective in killing S. mansoni eggs and miracidia were about one to two orders of magnitude greater than the actual field application rates.

The effects of bayluscide and malathion on the survival of Schistosoma mansoni miracidia.

Laboratory experiments were conducted to assess the toxic effects of bayluscide and malathion against Schistosoma mansoni miracidia. The results indicate that survival of miracidia varied with times of exposure and concentrations of tested chemicals. Statistical analyses reveal that LC5, LC50 and LC95 for bayluscide were 0.04 ppm, 0.06 ppm and 0.12 ppm after 2 hours of exposure; 0.02 ppm, 0.03 ppm and 0.06 ppm after 4 hours of exposure; and 0.01 ppm, 0.02 ppm and 0.04 ppm after 6 hours of exposure respectively. These data indicate that bayluscide is much more toxic to the first stage larvae of schistosomes than to snail intermediate hosts cited in the literature. Application of lower concentrations of molluscicide in the transmission sites is thus expected to curtail the survival of miracidia; therefore controlling schistosomiasis at relatively low costs. Such applications also reduce the risk of toxicity to non target organisms present in the aquatic environment. Statistical analysis of the results of tests using malathion gave LC5, LC50 and LC95 values of 83.38 ppm, 153.11 ppm and 245.85 ppm after 2 hours of exposure; and 76.86 ppm, 116.48 ppm and 172.04 ppm after 4 hours of exposure respectively. These data indicate that the use of malathion as an insecticide in tropical ecosystems may also affect the survival and viability of schistosome miracidia. Such uses could help reducing the risk of schistosomiasis transmission in these particular locations.

Schistosomiasis mansoni in the Dominican Republic; prevalence and intensity in various urban and rural communities, 1982-1987.

Surveys to detect foci of schistosomiasis mansoni endemicity in the Dominican Republic were carried out from 1982 to 1987 and showed that the disease is far more widely distributed in the country than previously thought. New foci (San Rafael del Yuma, Batey Palo Bonito, Maicillo, Nisibon and additional barrios in the city of Higuey) were found in the eastern provinces, and other completely new foci (Bayaguana, Sabana Rey (Cotui) and Jarabacoa) in the center of the country and in the National District (Guerra) were also detected. Prevalence rates in the various barrios (sections) of the city of Higuey varied between 7.4% and 24.6%, whereas they were 10.2% in Maicillo, 7.8% in El Valle and 9.9% in El Seibo. The intensity of infection was very low as judged by eggs per gram of feces. Serodiagnosis using the circumoval precipitin test raised the infection rate from that indicated by stool examination, as in Maicillo, or both results were equal, as in Las Palmillas.

Human schistosomiasis in Cameroon. II. Distribution of the snail hosts.

A nationwide survey for snail hosts of human schistosomes was carried out in Cameroon between 1985 and 1988. In total, 668 sites at 432 locations were sampled. In the arid, northern half of the country (tropical climatic zone), where both intestinal and urinary schistosomiasis are hyperendemic, Biomphalaria pfeifferi was the only Schistosoma mansoni host and Bulinus globusus and B. senegalensis the most common S. haematobium hosts. In that region, these snails occurred almost exclusively in temporary bodies of water. Taking into account results from a companion study on the distribution of schistosomiasis in humans, our results clearly show that temporary water bodies in the tropical zone are the principal foci of transmission. These findings disagree with commonly held views about schistosome transmission in Cameroon. B. truncatus, a S. haematobium host, was also present in the tropical zone but was found principally in perennial habitats. Although some perennial habitats were important transmission sites, they represent only a small portion of the overall problem. B. truncatus is the principal S. haematobium host in the wetter southern half of the country where schistosomiasis haematobium is highly focal. Biom. camerunensis was far more common than Biom. pfeifferi in the South but did not occur where S. mansoni prevalence rates were high; thus it appears to be a poor host. B. forskalii, the sole host of S. intercalatum in Cameroon, occurs widely throughout the country; however, the schistosome is restricted to a small region in the South.

Biological control of Biomphalaria glabrata by Thiara granifera under laboratory conditions.

The effect of the snail Thiara granifera on the snail Biomphalaria glabrata, intermediate host of Schistosoma mansoni in the Dominican Republic, was evaluated. Plastic aquaria, 3 and 1.5 gallons in capacity, were used. The aquaria were either unpartitioned or partitioned by a fine screen into two equal compartments, and the two snail species were introduced in different proportions. The results over a 1-year period showed that T. granifera effectively reduced the fecundity of B. glabrata, especially when the initial densitites of the two species were equal or where T. granifera was more abundant. There was still competition, although starting at a later date, when the density of T. granifera was half that of B. glabrata. The competitive interaction does not seem to be due to competition for food but to a chemical factor(s), possibly water-soluble pheromones.

[Preliminary study of the molluscacide properties of guayacil: a raw extract of Guayacum officinale]. / Estudio preliminar de las propiedades molusquicidas del guayacil: extracto crudo de Guayacum officinale.

This paper reports the results of a preliminary study of the mollusk-killing properties of guayacil, a raw extract of the plant Guayacum officinalis, on Biomphalaria glabrata. Mollusks are exposed to several concentrations of the substance for periods ranging from 1, 6, and 24 hours and then were allowed to recover, according to the recommendations of the World Health Organization. The results indicate that guayacil has molusk-killing properties with an LC50 of 0.45 ppm and an LC90 of 0.95 ppm at 24 degrees C. Larger concentrations of 1 ppm resulted in 100% death rate, while 0.1 ppm did not prove lethal. All parts of the plant contain the active ingredient. Concentrations lower than 1 ppm are not lethal for flora or fauna.

Schistosomiasis mansoni in the Dominican Republic; prevalence and intensity in the city of Higuey by coprological and serological methods.

The prevalence and intensity of infection with Schistosoma mansoni were determined in a sample of the population of the city of Higuey, Dominican Republic. The quantitative formol-ether stool sedimentation technique of Ritchie, as modified by Knight et al., was performed on stools from 1,025 (65.5%) of 1,563 individuals greater than 1 year old. The highest prevalence rates (21.4%) were observed in women 25-29 years old and in men 15-19 years old (20%). The maximum fecal egg count was in the 15- to 19-year age group, with a geometric mean of 30 eggs/g feces among men and 15.8 eggs/g feces in men and women. The overall prevalence of S. mansoni-infection was 11.8% with a geometric mean excretion of 8.8 eggs/g feces. In addition, the circumoval precipitin test was carried out on 639 sera and 110 (17.2%) were positive, increasing the prevalence in all age groups. Examination of Biomphalaria glabrata snails collected in early 1986 showed 7.8% to be positive for S. mansoni cercariae. Despite the moderate prevalence rates and the low intensity of infection among the human population, we consider Higuey to be an important focus of schistosomiasis in the Dominican Republic. The sensitive coprological and serodiagnostic techniques we employed have helped to identify the age- and sex-specific groups most deserving of treatment in order to reduce transmission of infection and disease prevalence.

Suitability of six lymnaeid snails for infection with Fasciola hepatica.

The suitability of Fossaria (Bakerilymnaea) cubensis and Pseudosuccinea columella from Louisiana as intermediate hosts for Fasciola hepatica was compared to P. columella and Stagnicola elodes from Ann Arbor, MI, S. attenuata from Hidalgo, Mexico, Lymnaea gedrosiana from Iran and L. natalensis from Senegal. P. columella from LA was shown to be a more suitable host (51.3% became infected) than F. (B.) cubensis (15.2% and 26.4% of two populations became infected). The infection rate for P. columella from MI, was 50% and for L. gedrosiana was 32.5%, whereas L. natalensis, S. elodes and S. attenuata were refractory. F. (B.) cubensis and P. columella have some degree of suitability as intermediate hosts for F. hepatica under laboratory conditions, but field observations of their habitat in southern LA and characteristic management of cattle indicate that the former snail is more important as an intermediate host in this enzootic area. Tissue sections of suitable snails had few histopathological effects but physical damage caused by rediae was pronounced, mainly in the digestive gland and in the mantle.

Experimental infection with Schistosoma mansoni of Biomphalaria straminea from different parts of the northeast of Brazil

Na regiäo oeste do Estado da Bahia habitam caramujos das espécies Biomphalaria glabrata e B. straminea os quais, em geral, näo coexistem no mesmo habitat. No Estado do Ceará os únicos hospedeiros intermediários de Schistosoma mansoni säo da espécie B. straminea. Neste levantamento näo foram detectados B. straminea naturalmente infectados, nem no Ceará e Bahia. Espécimes de B. straminea, tendo B. glabrata como controle, foram utilizados experimentalmente a fim de se determinar sua suscetibilidade frente a amostras portorriquenhas de S. mansoni. Os referidos B. straminea mostraram baixa suscetibilidade apresentando as seguintes taxas de infecçäo: 1,1% dentre os caramujos de Redençäo-Ceará; 2,3% naqueles provenientes de Pentecoste-Ceará e 2,9% dentre os espécimes colectados em S. Desidério na Bahia. O lote controle, B. glabrata amostra NIH, apresentou elevadas taxas de infecçäo frente àquela amostra de S. mansoni. Além desta cepa portorriquenha utilizou-se também uma cepa bahiana de S. mansoni cujo teste experimental com B. straminea de Säo Desidério também demonstrou baixas taxas de infecçäo, numa média de 3,6%. Aparentemente, a baixa suscetibilidade de B. straminea ao S. mansoni, a despeito da elevada densidade destes caramujos, está em correlaçäo com a prevalência de esquistosomose muito elevada no Ceará como mostram os resultados de levantamentos coproscópicos realizados pela SUCAM

Assessment of schistosomiasis in the Dominican Republic.

Active transmission of intestinal schistosomiasis is currently limited to the southeastern part of the Dominican Republic. A population-based stool survey in 1980 detected 4 asymptomatic individuals among 114 selected at random in 2 towns and a rural community in El Seibo Province. The distribution of the transmitting snail, Biomphalaria glabrata, considerably exceeds that of Schistosoma mansoni, extending to the National District and capital city of Santo Domingo and well into certain central valley provinces. There is evidence that transmission sites have shifted during the past three decades because of urban development, molluscicidal activities and, perhaps, introduction of competing mollusks. In spite of intermittent control activities, the combination of domestic and recreational use of streams with consequent fecal contamination, and the extended distribution of B. glabrata indicates that the potential for new transmission foci is as great today as it was 10 years ago. This potential transmission of S. mansoni is a continuing threat to public health in the Dominican Republic.

Description of redia and cercaria of Paragonimus peruvianus from experimentally infected Aroapyrgus colombiensis of Condebamba Valley, Peru.

Although no natural infections with lung flukes were encountered in the hydrobioid snail Aroapyrgus colombiensis from streams in the Condebamba Valley, Peru, laboratory-bred snails were readily susceptible to infection with miracidia of Paragonimus peruvianus. The redia and cercaria are described for the first time for those of neotropical lung flukes. Cercariae inside rediae did not have a stylet and development was apparently completed outside the rediae in snail tissues. The microcercous xiphidiocercaria had 2 groups of gland cells on each side; the outer consisted of 5 cells and the inner of 3 cells, all with ducts opening at the stylet. The excretory bladder was large, often triangular, was thick-walled, and of 1 layer of cuboidal cells. The redia lacked procrusculi and had a short intestine which was slightly longer than the pharynx.