Schistosomiasis mekongi: from discovery to control

In the Mekong River basin, the first case of schistosomiasis was reported in 1957. In the 1960s, endemic areas of the infection, of which profiles were similar to those of schistosomiasis japonica, were discovered in Khong Island, Laos, to Kratie province, Cambodia. A new intermediate snail host; Neotricula aperta was identified and the Mekong strain of schistosome was elevated to a new species: Schistosoma mekongi in 1978. Baseline epidemiological surveillance was performed and schistosomiasis mekongi was described as a public health implication in the middle Mekong River basin. Because of political and economical confusion, endemic situation had become worse, and no control program had been implemented until mass treatment program with praziquantel on Khong Island in 1983. Since then, the prevalence of S. mekongi infection has rapidly decreased in each endemic area. Serological diagnosis has been useful to detect new but low endemic foci. Clinical manifestations of S. mekongi infection are similar to those of S. mansoni and S. japonicum infections. As the reduction of prevalence and intensity of S. mekongi infection, morbidity due to the disease has changed, and ultrasonographic examination is now useful to evaluate morbidity due to schistosomiasis mekongi. Transmission of the disease occurs in a couple of months during low water season. Control of N. aperta is difficult and long-lasting effective control measurements have, so far, not been available. In the next step for controling S. mekongi infection, mass treatment should be continued, and it is needed to combine other appropriate control activities.     

The evaluation of control measures against Schistosoma mekongi in Cambodia by a mathematical model

We constructed a mathematical model for the transmission of Schistosoma mekongi in Cambodia. The simulation of the model will be instrumental in planning schistosomiasis control measures. The model includes two definitive hosts, humans and dogs, as animal reservoirs. Dogs are recognized to play an important role in schistosomiasis transmission in Cambodia. For the purpose of dealing with age-specific prevalence and intensity of infection, the human population was classified into eight age categories in the model. To describe the seasonal fluctuation of the intermediate host population of S. mekongi, the "Post-Spate Survival" hypothesis was adopted for the population dynamics of Neotricula aperta present in the Mekong River. We carried out simulations to evaluate the effect of universal treatment (UT) and targeted mass treatment (TT) with praziquantel on the reduction in prevalence of S. mekongi. The simulations indicated that biyearly UT for 8 years or yearly TT for 5 years after three courses of yearly UT could reduce the prevalence to below 5% when a UT or TT coverage of 85% of inhabitants was achieved. The simulation suggested that the suppression of S. mekongi in Cambodia would be possible by UT or TT with a high coverage rate.     

Schistosoma mekongi: a prominent neutrophil chemotactic activity of egg antigen with reference to that of Schistosoma japonicum

Schistosoma mekongi causes granulomatous lesions around eggs deposited in the liver with neutrophil-rich inflammatory reactions in the early stage of the egg laying. To define the aspects of the typical pathogenesis of S. mekongi infection, we determined the difference between soluble egg antigen (SEA) from S. mekongi and S. japonicum with a focus on chemotactic factors for neutrophils or eosinophils. Mean volume and protein amount of S. mekongi eggs was 71 and 58% of those of Schistosoma japonicum eggs, respectively. Neutrophil chemotactic activity of S. mekongi SEA was about two times higher than that of S. japonicum. In contrast, eosinophil chemotactic activity of S. mekongi SEA was about half of that of S. japonicum SEA. Molecular analysis revealed that S. mekongi SEA contains higher molecular-weight components with a lower level of glycosylation, and this is likely to be related to the intense neutrophil chemotactic activity in comparison with S. japonicum SEA. The prominent chemotactic reactivity for neutrophils is likely to be involved in the typical pathogenesis of mekongi schistosomiasis.     

Schistosomiasis in Cross River State, Nigeria: 1. Prevalence and intensity of infection in Adim, Akamkpa Local Government Area

Mid-stream urine was randomly collected from 248 subjects in Adim. Blood and protein concentrations were determined semi-quantitatively using Combi-7 reagent strips. The urine samples were then processed and any ova of Schistosoma haematobium present were counted per 10 ml urine. Fresh stool samples were also randomly collected, processed and examined for S. masoni and other helminthic ova. The prevalence of S. haematobium in the area was 43.5% and this was found to be age-related but not sex-related. Mean egg count was 137.2 per 10 ml urine. Intense haematuria of 250 ery/microliters and proteinuria of 500 mg/dl accompanied the high egg counts. The stool examination showed no cases of Manson's schistosomiasis but polyparasitism with other intestinal helminths was common particularly among children under 10 years old. This is the first report of urinary schistosomiasis in this area and the high prevalence rate is consistent with the rice farming occupation of the natives of the area. The sensitive nature and the case of application of the reagent strips in determining heavy infections by measuring haematuria and proteinuria is once again confirmed.     

High susceptibility of Neotricula aperta gamma-strain from Krakor and Sdau in Cambodia to Schistosoma mekongi from Khong Island in Laos

Neotricula aperta gamma-strain snails collected from Krakor and Sdau in Cambodia were found to have the same or higher susceptibility to Schistosoma mekongi as N. aperta originally isolated from Khong in Laos. Infection rates of N. aperta gamma-strain snails exposed to 3 miracidia at week 8 were: Khong gamma-strain, 22.6%; Krakor gamma-strain, 33.3%; and Sdau gamma-strain, 67.4%. At week 10, the Sdau gamma-strain showed the highest infection rate of 83.3%. We thus found significantly high susceptibility of the Sdau gamma-strain to S. mekongi originally isolated from Khong. However, in another experiment, susceptibility of the Sdau gamma-strain was rather comparable to that of Khong and Krakor gamma-strain. We also found no significant differences in infection and survival rates between the Khong and Krakor gamma-strain when the snails were exposed to 3 or 6 miracidia. This is the first report to confirm the high susceptibility in the laboratory of N. aperta gamma-strain snails from endemic areas in Cambodia to S. mekongi originally isolated from Laos. The high susceptibility of N. aperta gamma-strain snails to S. mekongi in distant areas may be an important factor in the endemic transmission of human schistosomiasis.     

Increased vascularity in cervicovaginal mucosa with Schistosoma haematobium infection

Background

Close to 800 million people in the world are at risk of schistosomiasis, 85 per cent of whom live in Africa. Recent studies have indicated that female genital schistosomiasis might increase the risk of human immunodeficiency virus (HIV) infection. The aim of this study is to quantify and analyse the characteristics of the vasculature surrounding Schistosoma haematobium ova in the female genital mucosa.

Methodology/Principal Findings

Cervicovaginal biopsies with S. haematobium ova (n = 20) and control biopsies (n = 69) were stained with immunohistochemical blood vessel markers CD31 and von Willebrand Factor (vWF), which stain endothelial cells in capillary buds and established blood vessels respectively. Haematoxylin and eosin (HE) were applied for histopathological assessment. The tissue surrounding S. haematobium ova had a higher density of established blood vessels stained by vWF compared to healthy controls (p = 0.017). Immunostain to CD31 identified significantly more granulation tissue surrounding viable compared to calcified ova (p = 0.032), and a tendency to neovascularisation in the tissue surrounding viable ova compared to healthy cervical mucosa (p = 0.052).

Conclusions/Significance

In this study female genital mucosa with S. haematobium ova was significantly more vascularised compared to healthy cervical tissue. Viable parasite ova were associated with granulation tissue rich in sprouting blood vessels. Although the findings of blood vessel proliferation in this study may be a step to better understand the implications of S. haematobium infection, further studies are needed to explore the biological, clinical and epidemiological features of female genital schistosomiasis and its possible influence on HIV susceptibility.     

Cutaneous ectopic schistosomiasis.

Two cases of cutaneous schistosomiasis due to ectopic ova have recently been seen. Both patients presented with abdominal papular lesions, which were found on biopsy to contain schistosoma ova. To reach these abdominal sites mature worms probably migrate from the portal circulation to the paraumbilical veins, where they anastomose with veins of the caval system.     

Analysis of the effectiveness of control measures against Schistosoma mekongi using an intra- and inter-village model in Champasak Province, Lao PDR

Schistosomiasis mekongi is prevalent in the Khong district of Lao PDR, made up of one big island, Khong, and numerous small islands in the Mekong River. Schistosoma mekongi is spread by Neotricula aperta as the intermediate host along the Mekong River. Therefore, even if an epidemic of S. mekongi were stamped out in a certain village, infection may recur if the source of infection is a village located in the upper reaches of the Mekong River. The purpose of this study was to construct a mathematical model for the transmission of S. mekongi among villages from the upper to lower Mekong River to estimate the effect of control measures against it. The chief characteristic of the present model is competence in dealing with the spread of infection among villages through the Mekong River in consideration of the reduction in longevity of cercariae and miracidia and their diffusion in the river. The model also takes into account seasonal fluctuation in the water level of the Mekong River, which affects human behavior in terms of water contact. The results of simulations indicated that the prevalence of schistosomiasis mekongi would be suppressed to a low level for a long time in a village further downstream when universal mass treatment is performed in villages further upstream simultaneously.     

Differential diagnosis of schistosomiasis mekongi and trichinellosis in human.

An indirect (plate) ELISA and, a more convenient version, a dot-blot (membrane) ELISA have been developed using haemocyanin of a mollusk, Megathura crenulata, i.e. keyhole limpet haemocyanin (KLH) and purified, specific antigen of Trichinella spiralis (APTsAg) obtained from a monoclonal antibody-affinity column chromatography, for differential diagnosis of schistosomiasis mekongi and trichinellosis. Serum samples of patients with parasitologically confirmed trichinellosis were reactive to both antigens in both versions of ELISA while sera of patients with schistosomiasis mekongi were positive only to the KLH. Both ELISA were negative when used to test sera of normal controls and patients with gnathostomiasis, paragonimiasis and opisthorchiasis.     

Comparison of different techniques for detection of Gal-GalNAc, an early marker of colonic neoplasia

The tumor marker, D-galactose-beta [1-3]-N-acetyl-D-galactosamine (Gal-GalNAc, also known as T-antigen) can be identified by a very simple galactose oxidase-Schiff's (GOS) reaction either on tissues or on rectal mucus samples from patients with colorectal neoplasms. Gal-GalNAc is expressed in the neoplastic mucosa as well as the remote non-neoplastic mucosa. It is, however, not expressed in colonic mucosa of normal subjects. We studied the expression of Gal-GalNAc by GOS reaction, lectin reactivity and immunocytochemistry in 10 normal, .45 precancerous [5 Crohn's disease, 15 ulcerative colitis (5 without dysplasia and 10 with dysplasia), 25 tubular adenomas], and 25 adenocarcinoma cases. Normal mucosa remote from tubular adenoma and adenocarcinoma was also studied. The GOS method was compared with reactivity of the lectin jacalin and immunostaining with antibody to T antigen (Anti-Tag Ab). GOS reaction was negative in all of the 10 normal specimens. Of the 5 Crohn's disease specimens, 2 were positive and 3 negative. In the 5 ulcerative colitis cases without dysplasia, positive reaction was seen in 2 cases and negative in 3. Of the 10 cases of ulcerative colitis with dysplasia, 5 showed positivity in dysplastic areas, and 3 of these were also positive in remote non dysplastic mucosa. Twenty of 25 tubular adenomas yielded a positive reaction in the adenoma, 14 of them showing positivity also in remote mucosa; 3 cases showed a positive reaction only in remote mucosa. Of the 25 adenocarcinomas, 21 showed a positive reaction in the adenocarcinoma as well as the remote mucosa. GOS reaction was intense in well differentiated adenocarcinoma and weak in poorly differentiated adenocarcinoma. Intense reaction was also seen in the intracellular mucus of some aberrant crypts and morphologically normal crypts remote from adenocarcinoma and tubular adenoma. GOS reaction showed an overall sensitivity of 75.7% and specificity of 100% for cancer and precancerous lesions. Jacalin reactivity was slightly more sensitive (84.3%) but less specific (80%) and Tag Ab reactivity even less sensitive (50%) but as specific (100%) for neoplastic and dysplastic mucosa. We conclude that the detection of the carbohydrate moiety Gal-GalNAc varies with the technique used. Compared to other techniques, GOS reaction is extremely simple and has a high degree of sensitivity and specificity. It can be used for detection of this tumor marker in remote non-neoplastic mucosa of patients with neoplasia or at risk of developing neoplasia. It, therefore, could be used as a cost effective screening test in rectal biopsy specimens of such patients.     

Laxative-induced Diarrhoea: A Continuing Clinical Problem

Seven women spent an average of 127 days in hospital and were extensively investigated, including a laparotomy, before their complaints of abdominal pain, diarrhoea, and weight loss were shown to be due to excessive taking of laxatives. All denied taking laxatives and in none were the characteristic features of the effects of cathartics on the colon seen on sigmoidoscopy or radiological examination.Hypokalaemia and other electrolyte abnormalities were common and were thought to be due to a combination of severe diarrhoea and vomiting. The rectal mucosa was seen to be abnormal on biopsy only in the three patients who had taken senna preparations. The diagnosis was not easy and was finally established either by analysis of the urine and stools or by searching the patient''s ward locker.     

Multiple displacement amplification of DNA from human colon and rectum biopsies: bacterial profiling and identification of Helicobacter pylori-DNA by means of 16S rDNA-based TTGE and pyrosequencing analysis

Amplifying bacterial DNA by PCR from human biopsy specimens has sometimes proved to be difficult, mainly due to the low amount of bacterial DNA present. Therefore, nested or semi-nested 16S rDNA PCR amplification has been the method of choice. In this study, we evaluate the potential use of whole genome amplification of total DNA isolated from human colon and rectum biopsy specimens, followed by 16S rDNA PCR amplification of multiple displacement amplified (MDA)-DNA. Subsequently, a H. pylori-specific 16S rDNA variable V3 region PCR assay was applied directly on MDA-DNA and, combined with pyrosequencing analysis; the presence of H. pylori in some biopsies from colon in patients with microscopic colitis was confirmed. Furthermore, temporal temperature gradient gel electrophoresis (TTGE) of 16S rDNA amplicons using primers flanking variable regions V3, V4, and V9, was used to establish bacterial profiles from individual biopsies. A variation of the bacterial profiles in the colonic mucosa in microscopic colitis and in normal rectal mucosa was observed. In conclusion we find the MDA technique to be a useful method to overcome the problem of insufficient bacterial DNA in human biopsy specimens.     

Schistosoma malayensis n. sp.: a Schistosoma japonicum-complex schistosome from Peninsular Malaysia

Schistosoma malayensis n. sp., a member of the Schistosoma japonicum complex is described from Rattus muelleri in Peninsular Malaysia and 2 strains are characterized. The only morphological differences noted among adults from natural hosts were that S. malayensis are in general smaller than S. mekongi and S. japonicum. But these differences may be the result of host-induced variations and therefore are of little taxonomic value. To minimize the effects of host-induced variations, adult worms recovered from laboratory mice with similar worm burdens at 50-56 days postinfection were compared. These comparisons revealed only minor morphometric differences among these 3 species. Schistosoma malayensis eggs from naturally and experimentally infected hosts are most similar to those of S. mekongi, with eggs of both species being, in general, smaller than those of S. japonicum. The egg index for S. malayensis is usually higher than for S. japonicum and lower than for S. mekongi. Differences were noted in the developmental rates in mice for 2 isolates of S. malayensis, S. mekongi, and S. japonicum (Philippine strain), but relatively large differences observed between isolates of S. malayensis indicate that, in this case, the developmental rate is not a useful taxonomic character. Schistosoma malayensis is erected principally on the basis of differences, reported elsewhere, in the life histories and in the electrophoretic migration patterns of isoenzymes of adult worms as compared to S. mekongi and S. japonicum. These comparisons indicate that S. malayensis is more closely related to S. mekongi than to S. japonicum.     

Alteration of the angiotensin cascade by schistosome ova

In schistosomiasis mansoni, the parasite ova lodge in the microvasculature of organs and induce granulomas. It is assumed that factors derived from the ova activate circulating mediators that help initiate the inflammation. Components of the angiotensin system are in plasma and may have a role in inflammation. Therefore, whether ova could alter plasma angiotensin metabolism was determined. Incubation of 1 ml of plasma with up to 1,000 ova increased plasma AII (angiotensin II) concentration as measured by radioimmunoassay. HPLC analysis of [125I]AI (angiotensin I) metabolism in plasma suggested that ova can increase the conversion of AI to AII. Ova did not alter plasma angiotensin-converting enzyme activity. The ova themselves did not contain or release components of the angiotensin system during culture. It is concluded that interaction of ova with plasma can affect the angiotensin cascade.     

Imaging diagnosis of schistosomiasis japonica--the use in Japan and application for field study in the present endemic area

For detecting lesions-related schistosomiasis japonica, X-rays, scintillation scanning, ultrasonography (US), computed tomography (CT), magnetic resonance (MR) and endoscopic examinations with biopsies have been used in Japan. Liver fibrosis and calcified changes are detected by US and CT. Most of the lesions that are detected by endoscopic examinations are due to deposited ova of Schistosoma japonicum. Portal hypertension is detected by US, CT and gastroscopic examination. Because schistosome infection decreased rapidly in Japan, most of the studies on imaging diagnosis were performed on chronic lesions or sequelae of schistosomiasis. Most of the techniques were used on admitted patients in well-equipped hospitals. US was introduced in the 1970s as a safe, rapid, non-invasive and inexpensive technique and has been used for diagnosis in hospitals and screening in the fields. As a typical US image of the liver, septal formation by high echogenic bands like mosaic was described, and this network pattern was reported in the other endemic countries; China and Philippines. As an appropriate technique, US has been broadly used in developing countries. Not only for diagnosis in a hospital, but also for monitoring changes of morbidity, US is used in the community level. Network pattern related to the severity of S. japonicum infection, has not been described in S. mansoni or S. haematobium infection. Appearance of network pattern depends on pathological changes such as periportal fibrosis, postnecrotic fibrosis and calcified ova. For advanced studies on morbidity of schistosomiasis japonica, further research on pathological basis of network pattern and standardization of US diagnosis are necessary.     

Effects of praziquantel and artesunate on the tegument of adult Schistosoma mekongi harboured in mice

The effects of praziquantel and artesunate on the tegument of adult Schistosoma mekongi harboured in mice were compared using scanning electron microscopy (SEM). Forty-two mice infected with S. mekongi for 49 days were treated intragastrically with either 300 mg/kg praziquantel or 300 mg/kg artesunate. Mice were sacrificed 1 or 3 days post-treatment. Worms were collected by perfusion and examined by SEM. One to 3 days after administration of artesunate, the tegument of S. mekongi showed severe swelling, vacuolization, fusion of the tegumental ridges and loss or shortening of the spines on the trabeculae, collapse and peeling. Praziquantel induced similar tegumental alterations as those observed after administration of artesunate, but they were less severe. Three days post-treatment, there was evidence of recovery only in the case of praziquantel. The results of our study suggest that artesunate is more effective than praziquantel in causing tegumental damage in adult S. mekongi, and provides a basis for subsequent clinical trials.     

The pig as a host for Schistosoma mekongi in Laos.

A survey of helminths in domestic pigs was conducted in Khong District, Laos, to elucidate if these domestic animals could act as definitive hosts for Schistosoma mekongi and to obtain a general overview of their helminthological infection status. Fecal samples were collected from 98 pigs. Twelve pigs (12.2%) were found to excrete S. mekongi eggs. Infection was confirmed by detection of S. mekongi eggs in tissues of liver, rectum, and cecum of 2 pigs. A total of 75.8% of the pigs was infected with 1 or more helminth species. This study showed that pigs may act as a definitive host for S. mekongi.     

Schistosoma curassoni Brumpt, 1931 and S. bovis (Sonsino, 1876) in cattle in northern Nigeria

Schistosoma curassoni has been recovered from cattle in northern Nigeria. Rectal scrapings of 90 cows slaughtered at the Kano abattoir, Kano, Nigeria during March and April 1986 revealed a prevalence of 7.8% S. bovis and 2.2% S. curassoni. Further examination of the mesenteric and rectal veins of 502 cows showed that the overall prevalence of schistosomiasis was 31.1%. Local Bulinus globosus were infected successfully in the laboratory with s. bovis miracidia.     

Marked increase in gastric histidine decarboxylase activity in patients with hypergastrinemia.

Histidine decarboxylase (HDC) activity and histamine content were measured in endoscopic gastric biopsy specimens of 19 control subjects with normogastrinemia and 6 patients with hypergastrinemia. In controls, the HDC activity was 3 fold higher in fundic mucosa (120 +/- 13 fmol/min/mg protein, mean +/- S.E.) than in antral mucosa (39 +/- 5 fmol/min/mg protein). In patients with hypergastrinemia, an extremely high HDC activity (713 +/- 181 fmol/min/mg protein) was observed in fundic mucosa, although the HDC activity in antral mucosa was not significantly different from that of controls. The histamine content in fundic mucosa was also significantly higher in patients with hypergastrinemia than in controls but no significant difference was seen in histamine content in antral mucosa between the two groups. These results are compatible with the hypothesis that in man, as well as in rat, histamine synthesis in fundic mucosa is enhanced by gastrin.     

A retrospective histopathological survey of capillariasis in raccoons (Procyon lotor) from Oregon

A 2-yr retrospective survey (1995-1998) of 63 adult raccoons (Procyon lotor) from Oregon, northwestern United States, was conducted by histopathological examination of various tissues. An overall prevalence of capillariasis was recorded in 52% of the raccoons. Highest prevalence of nematodes (29/30, 97.7%) was present in the anal sacs, where variable numbers of nematodes, their ova, and extensive diffuse inflammatory cellular infiltrate were evident. Lesser numbers of nematodes were also seen in the mucosa of the anterior alimentary tract (mouth 2/63, tongue 10/62, esophagus 2/63) and in the urinary bladder (7/63). However, at these sites, there was a paucity of inflammatory infiltrate. The findings of this study indicate that capillariasis of the anal sacs is commonly seen in free-ranging raccoons in Oregon, and the infection is essentially subclinical because only 1 case of anal sac impaction has been reported. Measurements of the nematode and their ova from the anal sacs indicate that it is most likely a new capillariid species, which to date has not been fully described in raccoons. It is speculated that the high prevalence of anal sac infection by a Capillaria sp. in Oregon raccoons may also be true for raccoons in other parts of North America and in parts of Europe and Asia where this species has been introduced.