Tolerance and accumulation of lead in Vetiveria zizanioides and its effect on oil production.

Experiments were conducted to evaluate lead tolerance and accumulation in vetiver grass Vetiveria zizanioides (L.), grown in hydroponics and a pot study and to examine the effect of lead on vetiver oil production. Elevated concentrations of lead decreased the length of shoots and roots of plants. However, vetiver grown in highly contaminated soils showed no apparent phytotoxicity symptoms. Lead concentrations in the shoots and roots of vetiver plants grown in hydroponics were up to 144 and 19530 mg kg-1 and those grown in soil were 38 and 629 mg kg-1, respectively. Lead had an effect on vetiver oil production and composition by stimulating oil yield and the number of its constituents. Oil yield ranged from 0.4-1.3%; the highest yields were found in plants grown in nutrient solution with 100 mg Pb l-1 for 5 weeks (1.29%) and 7 weeks (1.22%). The number of total constituents of vetiver oil also varied between 47-143 compounds when lead was present in the growth medium. The highest number (143) was found in plants grown in soil spiked with 1000 mg Pb kg-1. The predominant compound was khusimol (10.7-18.1%) followed by (E)-isovalencenol (10.3-15.6%). Our results indicated that lead could increase the oil production of vetiver.

Monoclonal antibodies against Schistosoma mekongi surface tegumental antigens.

Monoclonal antibodies were produced from naturally infected BALB/c mice. Thirteen hybridomas which were found to produce monoclonal antibodies against surface tegumental antigens of Schistosoma mekongi by ELISA assay were used in this study. The antigen specificities of hybridomas reactive with surface tegumental antigens were characterized and localized by immunoblotting analysis and Avidin-Biotin method. Of the 13 hybridomas, only three produced monoclonal antibodies to the single epitopes in the surface tegumental antigens. These epitopes (125 kDa, 97 kDa and 38 kDa) have been found to be the major antigenic components of the surface tegument of S. mekongi. The 38 kDa antigen was found to associate with the surface tegumental layers, the muscular layers lying just beneath the tegument, as well as in the gut surface. The 97 and 125 kDa antigens were detectable only in the surface tegumental area. The biochemical identity of these proteins or glycoproteins is unknown. However, these antigens have also been described in S. japonicum and S. mansoni.

The host-parasite relationship between the Saudi Arabian Schistosoma mansoni and its intermediate and definitive hosts. 3. Effects of duration of exposure and cercarial concentration on the infection of mice by S. mansoni cercariae.

The percentage infection rate, worm burden and worm recovery rate in mice increased with an increase in the duration of exposure to cercariae. However, mice exposed to cercariae for 4 min had the same worm burden and worm recovery rates as those exposed for 16 min. Mice exposed to 80 and 160 cercariae each exhibited the highest percentage infection rates. The worm burden was highest in mice exposed to 160 cercariae each, while the worm recovery rate was highest in those exposed to 80 cercariae per mouse.

Scanning electron microscopic study of the tegumental surface of the hybrid schistosome between Schistosoma mekongi and S. japonicum-like (Malaysian).

Hybridization experiments between the two non-sibling species of schistosomes, Schistosoma mekongi in man and S. japonicum-like (Malaysian) in rodents, were carried out. Two laboratory-bred snail species, Tricula aperta (beta race), the snail host of S. mekongi and Robertsiella kaporensis, the snail host of S. japonicum-like (Malaysian), were used for the production of cercariae. Cross mating between S. mekongi and S. japonicum-like (Malaysian) were achieved in the laboratory by the usual procedure of exposing snails to single miracidia of each species, then exposing mice to cercariae emanating from two snails only, each infected with a different species. Hybrid eggs and miracidia were used to infect snails of both species. The resultant F1 cercariae were used to infect mice. It was shown in this study that the attempt to cross these two species of schistosomes could be achieved in the laboratory, but the results provided very low yield of hybrid worms and eggs. F1 hybrid adult worms from S. mekongi male and S. japonicum-like (Malaysian) female were obtained and examined for the microtopography of the tegument by scanning electron microscopy. The tegumental surface of the hybrid male schistosome resembled the male parent, S. mekongi, with a few characters which resembled the male, S. japonicum-like (Malaysian). The surface tegument of the hybrid male worm was characterized by the presence of highly-branched and perforated ridges interspersed with a large number of papillae all over the body surface with the heaviest concentration on the middle portion of the body. There were four types of papillae present; the pleomorphic papillae; the cratered papillae, with or without cilia; the hemispherical sensory papillae with cilia; and the fungiform papillae. Spines were absent on the body surface except in the oral and ventral suckers and in the gynecophoral canal. The tegument lining the gynecophoral canal was characterized by the presence of low ridges with scattered papillae with small number of short spines in the posterior portion of the canal. In contrast to the male, the female hybrid worm had numerous spines all over the body surface with the most concentration in the posterior region. Among the spines were low perforated ridges. Two types of papillae were present in the female hybrid; the cratered papillae, with or without cilia, and the hemispherical papillae.

The host-parasite relationship between the Saudi Arabian Schistosoma mansoni and its intermediate and definitive hosts. 1. S. mansoni and its local snail host Biomphalaria arabica.

The infectivity of miracidia of the Saudi Arabian isolate of S. mansoni in Bi. arabica was found to be influenced by such factors as miracidial dose, water temperature and salinity. The pre-patent period of S. mansoni in Bi. arabica was 30 to 33 days. Miracidial dose had no effect on the mortality of snails during the pre-patent period. The infection rate increased as the miracidial dose was increased. However, cercarial production was highest in snails exposed to 1 miracidium each and decreased as the miracidial dose was increased. Water temperature during exposure had an influence on the mortality, infection rate and cercarial production in Bi. arabica exposed to S. mansoni miracidia. The infection rate was highest in snails exposed at 28 degrees and 34 degrees C. No infection of Bi. arabica occurred at the temperature of 10 degrees C. The number of cercariae per snail per day was highest in snails exposed to miracidia at 34 degrees C. It was demonstrated that salinity had an influence on the infection of Bi. arabica with miracidia of S. mansoni. The infection rate in snails decreased as the salinity increased up to 4,500 mg/l, above which no infection occurred. The daily pattern of cercarial emergence was rhythmic, whereby 94.7% of the total daily production was released within 6 h from infected Bi. arabica, with a peak between 11 a.m. and 1 p.m.

The host-parasite relationship between the Saudi Arabian Schistosoma mansoni and its intermediate and definitive hosts. 2. Effects of temperature, salinity and pH on the infection of mice by S. mansoni cercariae.

The infectivity of cercariae of the Saudi Arabian isolate of S. mansoni was found to be influenced by factors such as water temperature, salinity and pH. The optimum exposure temperature which resulted into the highest worm burdens and worm recovery rates in mice was 28 degrees C. However, the percentage infection rate was highest at a temperature range of 10 degrees to 34 degrees C. Mice were successfully infected with cercariae of S. mansoni at salinities of 0.5 to 6,400 mg/l. The highest worm burden and worm recovery rate occurred in mice infected by cercariae at a salinity of 100 mg/l, while the percentage infection rate was highest at a salinity range of 0.5 to 1,600 mg/l. Mice exposed to cercariae at the pH of 4.4 and 9.4 did not develop any infection. The percentage infection rate was highest in mice exposed to cercariae at a pH range of 6.4 to 8.4. However, both the worm burden and worm recovery rates were highest in mice at pH 5.4.

Biology of Robertsiella kaporensis snails and Malaysian Schistosoma.

Studies on the bionomics and host-parasite relationship of Robertsiella kaporensis and Malaysian Schistosoma were investigated. The study was divided into 4 parts: cultivation of snails, R. kaporensis, and maintenance of Malaysian Schistosoma life cycle, daily cercarial shedding cycle in R. kaporensis, miracidial load and cercarial shedding pattern and the infectivity of Malaysian Schistosoma cercariae. R. kaporensis were cultured in the laboratory with the use of plastic container provided with fine sand. The snails were fed with diatoms and Saraca leaves. The development period for the snail eggs was about 20-30 days, the young grew to maturity in 14-15 weeks, and the average growth rate of snails was 0.23 mm per week. The daily cercarial shedding cycle of snails had shown that the peak emergence of cercariae of Malaysian Schistosoma occurred at night, between 6-10 pm. The miracidial load which yielded the best results in terms of percentage infection rates of snails and cercarial output was the miracidial concentration of 8 miracidia per snail. The study on infectivity of Malaysian Schistosoma cercariae has shown that there was a decrease in infectivity of the cercariae to mammalian hosts as the cercariae increased in age. The percentage infection rate of mice and numbers of worms recovered were highest in mice infected with cercariae of 0-1/2 hr. old. Infection of cercariae fell rapidly after the cercariae were 16 hr. old.

Effects of cercarial concentration and length of exposure on the infection of mice by Schistosoma japonicum and S. mekongi cercariae.

The effects of cercarial concentration and length of exposure on the infection of mice by Schistosoma japonicum and S. mekongi were studied under laboratory conditions. For all cercarial concentrations of 10, 20 and 30, mice exposed for 1 min acquired little or no infection. Total worm recovery tended to rise with an increase either in cercarial concentration or exposure time. The highest infection rate and worm burden were obtained in mice exposed for 64 min to 30 cercariae per mouse. The present investigation suggested that exposures of 1 min or less carried little risk of infection at low cercarial concentration. There was a greater risk of infection in prolonged exposure to low cercarial concentration. Prolonged exposures to high cercarial concentration carried the greatest risk of high infection rate and worm burden.

Study on Schistosoma sinensium in Fang district, Chiangmai province, Thailand.

A survey on human infection and possible natural definitive host of Schistosoma sinensium was carried out in Fang District, Chiangmai Province, North Thailand, where Tricula bollingi snails which harbour cercariae of S. sinensium inhabits. Stool examination of the people in the two villages along the stream, where T. bollingi were found, was by formalin-ether concentration technique and by Stoll's method. The stools were found to be negative for S. sinensium eggs. Field rats were also trapped and examined for the presence of S. sinensium. Adult worms and eggs of S. sinensium were found in the mesenteric veins and livers, respectively, of the field rats, Rattus rattus, captured in the rice fields along the stream.

Effects of physico-chemical factors on the infection of mice with Schistosoma japonicum and S. mekongi cercariae.

The three physico-chemical characteristics of water tested-pH, temperature and salinity were found to affect the infection of mice by cercariae of S. japonicum and S. mekongi. For both species of schistosomes, the range of optimal pH that showed highest infection and worm recovery rates was between 5.4-7.4 and decreased as the pH increased. Cercariae exposed to temperatures between 15 degrees-30 degrees C showed the highest infection and worm recovery rates. As temperature decreased or increased, the infection and worm recovery rates decreased. Sodium chloride concentration at low level (0.5-200 ppm) did not have great effect on the infection and worm recovery rates. The infection and worm recovery rates decreased as salinity increased. High sodium chloride concentration at 3200 ppm for S. mekongi cercariae and at 6400 ppm for S. japonicum cereariae inhibited cercarial penetration and no infection occurred.

Susceptibility of snail vectors to Oriental anthropophilic Schistosoma.

Laboratory experiments were carried out to study the susceptibility of snail vectors to Oriental anthropophilic Schistosoma. Oncomelania hupensis hupensis was readily infected with the local strain of Schistosoma japonicum (Chinese strain), and also infected with S. japonicum (Philippines strain). O.h. quadrasi was only susceptible to its S. japonicum (Philippines strain). The Oncomelania races were refractory to S. mekongi, S. japonicum-like species (Malaysian strain). Tricula aperta (beta race) was readily infected with S. mekongi, S. sinensium and S. japonicum-like species from Malaysia, but not S. japonicum. T. bollingi was susceptible to S. sinensium and S. mekongi. Robertsiella kaporensis was only susceptible to the local strain, S. japonicum-like species from Malaysia. Geographical isolation may be the cause of these differences in compatibility between the snail vectors and the schistosome parasites.

Scanning electron microscopic study of the tegumental surface of adult Schistosoma sinensium.

The SEM study of tegumental surface of adult Schistosoma sinensium reveals that the male tegument lacks tubercles or bosses; instead it is corrugated with small pits or perforated ridges. On the dorsal surface, spines are present whose number and size progressively increase towards the posterior end of the body. In addition, there are three types of papillae interspersed among the ridges and spines. The first type of papillae has crater-like holes surrounded by a circular doughnut-shaped elevation; some are ciliated and others are non-ciliated. They are generally found on the dorsal and ventral surfaces. The second is sensory papillae which are hemispherical in shape bearing apical cilia. They are found to be concentrated around the oral sucker and on the posterior end of the worm. The third is fungiform papillae without cilia which are found on the posterior end. There are short spines present on the tegument lining the gynecophoral canal of the male worm. The tegument of the female S. sinensium is corrugated with ridges on the ventral surface. Small spines are present on the anterior portion of the dorsal surface. They become larger and increased in number towards the posterior end of the worm. The three types of papillae are present but they are much fewer and less developed than those in the male worm.

Scanning electron microscopy of the tegumental surface of adult Schistosoma spindale.

The tegumental surfaces of adult male and female of Schistosoma spindale were studied by scanning electron microscopy. In general, the body surface of the male appears to be fairly uniform from anterior end to posterior end. It is characterized by the presence of transverse ridges and papillae of various types. These papillae are distributed fairly regularly over the whole body surface of the worm. The tegument lining the gynecophoral canal of the male worm is covered with numerous spines interspersed with papillae, some without cilia and some with crater-like holes in the centres and apical cilia. The tegument of the female worm is covered with smooth and perforated ridges and sensory bulbs with apical nodules.

Scanning electron microscopy of adult Schistosoma incognitum.

The integumental surfaces of adult Schistosoma incognitum were studied by scanning electron microscopy. The anterior part of the male which bears oral and ventral suckers is spongy in appearance due to the presence of ridges, while the middle and posterior parts are covered with numerous bosses with variable numbers of spines. Surfaces between bosses possess tegumental papillae. Bosses disappear at the edge of the gynecophoral canal which is composed of ridges. They are replaced by variable forms of papillae. The lining of the gynecophoral canal is composed of ridges and papillae, free of spines, with small number of sensory bulbs. The female tegument is relatively smooth and appears to be pitted with minute spines around the oral and ventral suckers. The posterior end of the body, in the vicinity of the excretory pore, is composed of prominent anteriorly directed spines with trabeculae and sensory bulbs.

Comparative methods of infecting mice with Schistosoma mekongi.

Experiments were carried out to investigate the most suitable cercarial concentration and method of exposure for the experimental mice infected with cercariae of Schistosoma mekongi. Swiss albino mice of 2 months old were exposed individually by three methods exposure : abdominal skin exposure, tail immersion and subcutaneous injection. Cercarial concentrations of 10 to 20 cercariae per mouse were used for each method of exposure. In general, it was observed that both the infection rate and total worm recovery rose with an increase in cercarial concentration. The highest percentage infection rate and total worm recovery was found in mice infected with 20 cercariae per mouse by the abdominal skin exposure method.

Scanning and transmission electronmicroscopy of Mekong Schistosoma eggs and adults.

Eggs and adult males and females of Mekong Schistosoma were studied by scanning and transmission electronmicroscopy. The observation of the eggs by the scanning and light microscopy revealed fine shell fenestration and a prominent knoblike spine. There are marked differences between the surface structures of male and female as studied by scanning and transmission electronmicroscopy. The surface of the male schistosome is moderately rough while that of the female is relatively smooth. SEM reveals certain basic features such as spines in the oral sucker, minute spines and folds in the gynecophoral canal of the male, and general features of male and female tegumental surfaces. The observations of the cross sections of adult schistosomes by transmission technique revealed certain features such as spines or ridges, and mucin droplets on the surface, the smooth muscles lining the integument, the mucin-producing cells and numerous lipid droplets in the body of the Schistosoma.