Aquaculture of Animal Species: Their Eukaryotic Parasites and the Control of Parasitic Infections

Parasites are very diverse and common in both natural populations and in stocks kept in aquacultural facilities. For most cultured species, there are important bacteria and viruses causing diseases, but eukaryotic parasites are also very important. We review the various combinations of aquacultured species and eukaryotic parasitic groups and discuss other problems associated with aquaculture such as eutrophication, zoonotic species, and invasive species, and we conclude that further development of aquaculture in a sustainable manner must include a holistic approach (One Health) where many factors (e.g., human health, food safety, animal health and welfare, environmental and biodiversity protection and marketability mechanisms, etc.) are considered.

An overview of human helminthioses in Vietnam: Their prevention, control and lessons learnt

In Vietnam, helminthioses remain a major threat to public health and contribute to the maintenance of poverty in highly endemic regions. Through increased awareness of the damaging effects caused by helminthioses, the Vietnamese government has implemented many national programs over the past 30 years for the prevention and control of the most important helminthioses, such as, lymphatic filariasis, soil transmitted helminths, food borne zoonotic helminths, and others. Various control strategies have been applied to reduce or eliminate these worms, e.g. mass drug administration, economic development, control of vectors or intermediate hosts, public health interventions through education, proper composting procedures for excreta potentially containing helminth eggs, and the expansion of food supply chains and improved technologies for the production and inspection of food products. These control measures have resulted in a significant reduction in the distribution and transmission of helminth infections and have improved the overall living conditions and health outcomes of the Vietnamese citizens. However, the persistence of several helminth diseases continues in some endemic areas, especially where poverty is widespread and local traditions include the consumption of raw foods, especially fish and meats. This manuscript provides an overview of the helminth infection prevention and control programs conducted in Vietnam, their achieved results, learned lessons, and future works.

THE DIVERSITY OF CERCARIAE FROM FRESHWATER SNAILS IN LOWLAND AREAS OF BINH DINH AND PHU YEN PROVINCES, VIETNAM

A survey was conducted in the lowland areas of Binh Dinh and Phu Yen provinces in south central Vietnam to study the diversity of digenean cercariae within freshwater snails. These regions are known as highly endemic areas for the transmission of liver flukes, Fasciola spp. and Opisthorchis viverrini. In total, 13 snail species were found, and 3 of these were dominant, comprising 51.9% of all collected snails, i.e., Bithynia funiculata, Melanoides tuberculata, and Radix auriculata. Cercariae were found in 5 snail species, and among these, Indoplanorbis exustus had the highest overall prevalence of infection (38.5%). No cercarial infections were found in viviparid and ampullariid snails. Morphological identification resulted in 10 cercariae types that were illustrated and measured. Among them, xiphidiocercariae and echinostomata were the most common, causing 70.55% of all cercariae infections. Bithynia species had the most diverse digenean fauna. Molecular data revealed the presence of cercariae of 13 digenean species, including O. viverrini. The 18S rDNA sequences of echinostomata and xiphidiocercariae type 3, which were shed from different snail hosts, were similar to 2 and 3 digenean species, respectively. In conclusion, our findings highlight the diversity of digenean fauna in Binh Dinh and Phu Yen provinces.

Molecular and morphological characterization of Dollfustrema bagarii (Digenea: Bucephalidae) metacercariae from aquaculture channel catfish (Ictalurus punctatus) in northern Vietnam

White grub metacercariae were found in the livers and kidneys of diseased specimens of an introduced channel catfish, Ictalurus punctatus (Rafinesque), in Vietnam. Based on morphological features and 28S rDNA sequence analysis, the isolated metacercariae were identified as Dollfustrema bagarii (Digenea: Bucephalidae) Moravec & Sey. Histopathological examination shows that encysted metacercariae can change the tissue structure of the infected organs and is often accompanied by haemorrhaging and the presence of eosinophilic granular cell infiltration. Degenerative changes were also observed.

Prioritize effluent quality, operational costs or global warming? - Using predictive control of wastewater aeration for flexible management of objectives in WRRFs

This study presents a general model predictive control (MPC) algorithm for optimizing wastewater aeration in Water Resource Recovery Facilities (WRRF) under different management objectives. The flexibility of the MPC is demonstrated by controlling a WRRF under four management objectives, aiming at minimizing: (A) effluent concentrations, (B) electricity consumption, (C) total operations costs (sum electricity costs and discharge effluent tax) or (D) global warming potential (direct and indirect nitrous oxide emissions, and indirect from electricity production) . The MPC is tested with data from the alternating WRRF in Nørre Snede (Denmark) and from the Danish electricity grid. Results showed how the four control objectives resulted in important differences in aeration patterns and in the concentration dynamics over a day. Controls B and C showed similarities when looking at total costs, while similarities in global warming potential for controls A and D suggest that improving effluent quality also reduced greenhouse gasses emissions. The MPC flexibility in handling different objectives is shown by using a combined objective function, optimizing both cost and greenhouse emissions. This shows the trade-off between the two objectives, enabling the calculation of marginal costs and thus allowing WRRF operators to carefully evaluate prioritization of management objectives. The long-term MPC performance is evaluated over 51 days covering seasonal and inter-weekly variations. On a daily basis, control A was 9-30% cheaper on average compared to controls A, D and to the current rule-based control. Similarly, control D resulted on average in 35-43% lower greenhouse gasses daily emission compared to the other controls. Difference between control performance increased for days with greater inter-diurnal variations in electricity price or greenhouse emissions from electricity production, i.e. when MPC has greater possibilities for exploiting input variations. The flexibility of the proposed MPC can easily accommodate for additional control objectives, allowing WRRF operators to quickly adapt the plant operation to new management objectives and to face new performance requirements.

Are Melanoides tuberculata and Tarebia granifera (Gastropoda, Thiaridae), suitable first intermediate hosts of Clonorchis sinensis in Vietnam?

Background

Two thiarid snail species, Melanoides tuberculata and Tarebia granifera have been reported as first intermediate hosts of the liver fluke Clonorchis sinensis; however, their role as true first intermediate hosts has not been verified. Thus, the present study aimed to clarify the suitability of these two snail species as first intermediate hosts of C. sinensis. This was accomplished by collecting snails from a highly endemic area for C. sinensis in Vietnam, the Thac Ba reservoir, and identifying shed cercariae using molecular techniques. We also conducted experimental infections of five snail species including M. tuberculata and T. granifera with eggs of C. sinensis.

Methodology/Principal findings

A total of 11,985 snails, representing 10 species were sampled. Five snail species, M. tuberculata, T. granifera, Lymnaea swinhoei, Parafossarulus manchouricus, and Bithynia fuchsiana were found shedding cercariae with an overall prevalence of infection ranging from 0.7% to 11.5%. Seven cercarial types were recorded. Cercariae of C. sinensis were only found in Parafossarulus manchouricus. Using a multiplex PCR approach for detecting C. sinensis infection, the prevalence in P. manchouricus was 4.2%. Additionally, all five snail species were experimentally exposed to C. sinensis eggs, however only P. manchouricus was successfully infected with an infection rate of 7.87%.

Conclusions/Significance

We confirmed that in the Thac Ba reservoir, Vietnam, the two thiarids, M. tuberculata and T. granifera are not suitable first intermediate hosts of C. sinensis. Only P. manchouricus was found infected by C. sinensis in nature, and was the only species that became infected experimentally.

Currently 13 snail species are reported as first intermediate hosts of Clonorchis sinensis, including two species of the Thiaridae, Melanoides tuberculata and Tarebia granifera. Both snail species have wide distributions in tropical and subtropical waters across the World, while the distribution of C. sinensis is much narrower and only occurs in endemic areas of East Asia. The role that these two thiarid snail species plays as successful hosts of C. sinensis, however, has been refuted in other studies. The present study was conducted to clarify this issue. Based on the results from field surveys in a newly discovered and highly endemic area for C. sinensis, as well as, data obtained under experimental conditions, we confirm that in Northern Vietnam, the two thiarid snail species are not successful first intermediate host of C. sinensis. C. sinensis was only detected in a single snail species, Parafossarulus manchouricus, through observation, molecular analyses and experimental infections.

Integrated model predictive control of water resource recovery facilities and sewer systems in a smart grid: example of full-scale implementation in Kolding

An integrated model predictive control (MPC) strategy to control the power consumption and the effluent quality of a water resource recovery facility (WRRF) by utilizing the storage capacity from the sewer system was implemented and put into operation for a 7-day trial period. This price-based MPC reacted to electricity prices and forecasted pollutant loads 24 hours ahead. The large storage capacity available in the sewer system directly upstream from the plant was used to control the incoming loads and, indirectly, the power consumption of the WRRF during dry weather operations. The MPC balances electricity costs and treatment quality based on linear dynamical models and predictions of storage capacity and effluent concentrations. This article first shows the modelling results involved in the design of this MPC. Secondly, results from full-scale MPC operation of the WRRF are shown. The monetary savings of the MPC strategy for the specific plant were quantified around approximately 200 DKK per day when fully exploiting the allowed storage capacity. The developed MPC strategy provides a new option for linking WRRFs to smart grid electricity systems.

Tilapia (Oreochromis niloticus) as a Putative Reservoir Host for Survival and Transmission of Vibrio cholerae O1 Biotype El Tor in the Aquatic Environment

Studies have reported the occurrence of Vibrio cholerae in fish but little is known about the interaction between fish and toxigenic V. cholerae as opposed to phytoplankton, which are well-established aquatic reservoirs for V. cholerae. The present study determined the role of tilapia (Oreochromis niloticus) as a reservoir host for survival and transmission of V. cholerae in aquatic environments. Three experiments were performed with one repetition each, where O. niloticus (∼2 g) kept in beakers were inoculated with four V. cholerae strains (5 × 10⁷ cfu/mL). Firstly, infected tilapia were kept in stagnant water and fed live brine shrimp (Artemia salina) larvae daily. Secondly, infected tilapia were kept without feeding and water was changed every 24 h. Thirdly, infected tilapia were fed and water was renewed daily. Infected tilapia and non-infected controls were sacrificed on days 1, 2, 3, 7, and 14 post-inoculation and V. cholerae were enumerated in intestinal content and water. Another experiment assessed the transmission of V. cholerae from infected to non-infected tilapia. The study revealed that El Tor biotype V. cholerae O1 and V. cholerae non-O1 colonized tilapia intestines and persisted at stable concentrations during the second week of the experiment whereas the Classical biotype was undetectable after 1 week. In stagnant water with feeding, V. cholerae counts dropped to 10⁵ cfu/ml in water and from 10⁷ to 10⁴ cfu/intestine in fish after 14 days. When water was renewed, counts in water decreased from 10⁷ to 10³ cfu/ml and intestinal counts went from 10⁶ to 10² cfu/intestine regardless of feeding. All strains were transmitted from infected to naïve fish after 24 h of cohabitation. Tilapia like other fish may play an essential role in the survival and dissemination of V. cholerae O1 in aquatic environments, e.g., the seventh pandemic strains mostly. In this study, tilapia were exposed to high concentrations of V. cholerae to ensure initial uptake and follow-up studies with lower doses resembling natural concentrations of V. cholerae in the aquatic environment are needed to confirm our findings.

Inflammation dynamics after praziquantel treatment of Schistosoma haematobium reflected by urinary eosinophil cationic protein

Background

This cohort study assessed urinary eosinophil cationic protein (ECP) as an indicator for urinary tract morbidity and inflammation indication related to single-dose or dual-dose praziquantel (PZQ) treatment.

Methods

Urinary ECP was measured at baseline, 24 h and 9 weeks after treatment (baseline 305, follow-up 204 participants, ages 2-40 years).

Results

ECP was significantly associated with the intensity of infection at baseline (p<0.05). Levels at baseline were 8.31 times higher (p<0.01) in participants with bladder morbidity than in those without. There was no correlation with kidney morbidity and no significant effect of a repeated dose of PZQ 40 mg/kg. Baseline ECP and ECP after 9 weeks were associated with microhaematuria (geometric mean ratio at baseline 7.56 [95% confidence limit {CL} 2.34-24.45]; p<0.01) and macrohaematuria (geometric mean ratio at baseline 6.22 [95% CL 2.71-14.24]; p<0.001). Mean levels of ECP dropped significantly during the first follow-up period and far less so in the second follow-up period (mean ECP at baseline: 70.8 ng/mL; ECP at 24 h: 24.5 ng/mL; ECP at 9 weeks: 14.6 ng/mL).

Conclusion

The urine ECP decrease happened immediately after treatment, reflecting the rapid action of PZQ on eggs in the bladder tissue. ECP in urine can be used as an indirect marker of the degree of local inflammatory reaction in the bladder and is not significantly affected by a repeated dose of PZQ.

Anemia and growth retardation associated with Schistosoma haematobium infection in Mali: a possible subtle impact of a neglected tropical disease

Background

The aim of this cross-sectional study was to investigate a possible association of Schistosoma haematobium with child growth development and describe a plausible schistosomiasis-related anemia in children and adults in a highly schistosomiasis endemic area of Mali.

Methods

Urine, feces and blood samples from 399 participants of both sexes (2-40 years of age) were analyzed and supplemented by anthropometric measurements.

Results

S. haematobium prevalence was 79.8%, S. mansoni 13.2% and Plasmodium falciparum 80.2%. S. haematobium infection intensity as five categories was significantly associated with anemia; i.e., odds of having anemia in the highest and the next highest category was 3.25 (95% CL 1.61-6.55; p<0.01) and 2.45 (95% CL 1.28-4.70; p<0.01), respectively, of that in the three lower categories combined after adjusting for age group and gender and the interaction between the two factors. Anemia was most pronounced in the 2-5 year olds males (55.5%, n=98). P. falciparum infection was not significantly associated with anemia. Stunting (body mass index [BMI] for age z-score<-2.00) was observed in 2.6% (2/78) of the 2-5 years olds and in 7.7% (14/182) in the 6-19 years age group. Lower BMI-z-scores (as continuous variable) were associated with anemia (p<0.05) while high intensity of S. haematobium infection was not significant when adjusting for age group and anemia. Participants with malaria infection had lower z-scores (as continuous variables) of weight and height for age. Lower height for age z-scores were also associated with anemia.

Conclusions

S. haematobium infection is likely to impact on child growth and possibly also anemia in all age groups and advocates for inclusion of whole populations into future control programes.

Infections by Hepatic Trematodes in Cats from Slaughterhouses in Vietnam

Domestic cats are a final host for some hepatic trematodes, and cat meat is used for human consumption in several parts of northern Vietnam. Since there is no tradition for commercial cat rearing in the area, cats are purchased alive from other areas as well, i.e., southern Vietnam and neighboring countries, and brought to slaughterhouses. This uncontrolled trade in live cats could pose a risk for spread of various parasites, including hepatic trematodes. Hence, in this study, we investigated the infections by hepatic trematodes in cats from the slaughterhouses. Cat livers were sampled from 12 slaughterhouses. Clonorchis sinensis and Platynosomum fastosum were found in 14 of 78 necropsied cats of local origin, while more than half of the non-local cats (170 of 318) were infected by C. sinensis, P. fastosum, or Opisthorchis viverrini. The non-local cats had higher prevalence (odds ratio = 6.61, P < 0.01, 95% CI: 2.34-19.41) and intensity of infection (count ratio = 6.47, P < 0.01, 95% CI: 1.77-23.59) by C. sinensis than local cats. Prevalence of P. fastosum infection did not differ significantly between the 2 groups of cats. Opisthorchis viverrini was found at low prevalence (2.5%) in non-local cats. The presence of O. viverrini in cats sampled in northern Vietnam and the high prevalence and intensity of infection in cats of non-local origin suggest that cats are transported over great distances, and this poses a risk of spreading these trematodes.

Organomegaly in Mali before and after praziquantel treatment. A possible association with Schistosoma haematobium

Continuous exposure to schistosome-infested water results in acute and chronic morbidity in all ages. We analysed occurence of organomegaly via ultrasonography and investigated a possible additive effect of dual-dose drug administration in 401 Schistosoma haematobium infected individuals from a highly endemic area in Mali. Mean intensity of infection at baseline (22.0 eggs per 10 ml) was reduced to 0.22 eggs per 10 ml 9 weeks after treatment (both treatments combined). Odds of persistent infection among those given dual-dose treatment was 41% of that in people given single dose (b = 0.41; p = 0.05; 95% CI 0.17-1.00), but after two years, 70.7% of the 157 participants, who completed the survey, were re-infected with no significant difference in prevalence and intensity of infection between treatment groups. Resolution of organomegaly occurred in all age groups after treatment. A novel association between Schistosoma haematobium infection and moderate portal vein enlargement was found in 35% (n: 55). Severe portal vein diameter enlargement was found in 3.2%. After two years, moderate hepatomegaly was present in 50.6%, moderate splenomegaly in 45.6% and moderate portal vein diameter enlargement in 19%. A subsequent dose of PZQ did not provide any additional long-term advantages.

Regional frequency analysis of short duration rainfall extremes using gridded daily rainfall data as co-variate

A regional partial duration series (PDS) model is applied for estimation of intensity duration frequency relationships of extreme rainfalls in Denmark. The model uses generalised least squares regression to relate the PDS parameters to gridded rainfall statistics from a dense network of rain gauges with daily measurements. The Poisson rate is positively correlated to the mean annual precipitation for all durations considered (1 min to 48 hours). The mean intensity can be assumed constant over Denmark for durations up to 1 hour. For durations larger than 1 hour, the mean intensity is significantly correlated to the mean extreme daily precipitation. A Generalised Pareto distribution with a regional constant shape parameter is adopted. Compared to previous regional studies in Denmark, a general increase in extreme rainfall intensity for durations up to 1 hour is found, whereas for larger durations both increases and decreases are seen. A subsample analysis is conducted to evaluate the impacts of non-stationarities in the rainfall data. The regional model includes the non-stationarities as an additional source of uncertainty, together with sampling uncertainty and uncertainty caused by spatial variability.

Biology and Control of Snail Intermediate Host of Schistosoma japonicum in The People's Republic of China

Schistosomiasis caused by Schistosoma japonicum is a severe parasitic disease in The People's Republic of China and imposed considerable burden on human and domestic animal health and socioeconomic development. The significant achievement in schistosomiasis control has been made in last 60years. Oncomelania hupensis as the only intermediate host of S. japonicum plays a key role in disease transmission. The habitat complexity of the snails challenges to effective control. In this review we share the experiences in control and research of O. hupensis.

Types of trematodes infecting freshwater snails found in irrigation canals in the East Nile locality, Khartoum, Sudan

Background

The planorbid freshwater snails of the two genera, Biomphalaria and Bulinus -have been vigorously studied due to the role they play as intermediate hosts of schistosomiasis. In Sudan specifically, most studies have focused on the chemical and ecological control of the two genera, but few studies have looked at their biological control. This study explored the coexistence of other species of freshwater snails and the two genera along with their trematode infections in relation to a number of environmental factors in the East Nile locality, Khartoum state, Sudan.

Methods

Freshwater snails from irrigation canals (abueshreens) were sampled monthly from January 2004 to December 2005. The snails were examined for trematode infections by cercarial emergence immediately after collection and then weekly for an additional four weeks to allow for the maturation of prepatent infections. Vegetation cover in the study sites as well as the physicochemical characteristics of the water, including temperature, were also recorded.

Results

A total of 10,493 snails, representing seven species, were collected. The most abundant species was Biomphalaria pfeifferi, representing 48.6 % of the sample. Overall, 14.1 % of the snails were found to be shedding some type of cercariae. Five species were found to have infections; among these the Bulinus truncatus species was found to be the most heavily infected, with an overall prevalence of 46.2 %. Double infections were recorded in only two B. truncatus snails and one Cleopatra bulimoides snail. Twenty different morphotypes of cercariae were recorded, seven of which appeared not to conform to previously described cercariae from Africa. Xiphidiocercariae type 1 was the most common type of cercariae recovered, accounting for 44.3 % of all infections. The density of snails tended to be lower during the summer months than the winter months, except for M. tuberculata snails, which were not affected by seasonal changes.

Conclusion

The findings of this study indicate that besides schistosomes, other larval trematodes are found, and some use the same intermediate hosts as the schistosomes. Further studies should be conducted to determine whether some of these trematodes could be manipulated for the biological control of schistosomiasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s40249-016-0108-y) contains supplementary material, which is available to authorized users.

Schistosoma haematobium and soil-transmitted Helminths in Tana Delta District of Kenya: infection and morbidity patterns in primary schoolchildren from two isolated villages

BACKGROUND

Schistosomes and soil-transmitted helminths (STH) (hookworm, Trichuris trichiura and Ascaris lumbricoides) are widely distributed in developing countries where they infect over 230 million and 1.5 billion people, respectively. The parasites are frequently co-endemic and many individuals are co-infected with two or more of the species, but information on how the parasites interact in co-infected individuals is scarce. The present study assessed Schistosoma haematobium and STH infection and morbidity patterns among school children in a hyper-endemic focus in the Tana River delta of coastal Kenya.

METHODS

Two hundred and sixty-two children aged 5-12 years from two primary schools were enrolled in the study. For each child, urine was examined for S. haematobium eggs and haematuria, stool was examined for STH eggs, peripheral blood was examined for eosinophilia and haemoglobin level, the urinary tract was ultrasound-examined for S. haematobium-related pathology, and the height and weight was measured and used to calculate the body mass index (BMI).

RESULTS

Prevalences of S. haematobium, hookworm, T. trichiura and A. lumbricoides infection were 94, 81, 88 and 46 %, respectively. There was no significant association between S. haematobium and STH infection but intensity of hookworm infection significantly increased with that of T. trichiura. Lower BMI scores were associated with high intensity of S. haematobium (difference =-0.48, p > 0.05) and A. lumbricoides (difference =-0.67, p < 0.05). Haematuria (both macro and micro) was common and associated with S. haematobium infection, while anaemia was associated with high intensity of S. haematobium (OR = 2.08, p < 0.05) and high hookworm infections OR = 4.75; p < 0.001). The majority of children had eosinophilia, which was significantly associated with high intensity of hookworm infection (OR = 5.34, p < 0.05). Overall 38 % of the children had ultrasound-detectable urinary tract morbidity, which was associated with high intensity of S. haematobium infection (OR = 3.13, p < 0.05).

CONCLUSION

Prevalences of S. haematobium and STH infections among the primary school children were high and the parasites were responsible for significant morbidity. A clear synergistic interaction was observed between hookworm and T. trichiura infections. Increased coverage in administration of praziquantel and albendazole in the area is recommended to control morbidity due to these infections.

The role of rice fields, fish ponds and water canals for transmission of fish-borne zoonotic trematodes in aquaculture ponds in Nam Dinh Province, Vietnam

Background

Fish-borne zoonotic trematodes (FZT), such as Clonorchis sinensis, Opistorchis viverini (Opisthorchiidae) and intestinal trematodes of the family Heterophyidae, constitute a public health hazard in Vietnam and infections with these trematodes has been linked to consumption of raw or undercooked fish from aquaculture. The FZT transmission pathways, however, are more complicated than just the presence of intermediate snail hosts in aquaculture ponds as ponds may exchange water with surrounding habitats such as rice fields and irrigation canals and thereby these surrounding habitats may be a source of snails and cercariae and contribute to FZT infection in cultured fish.

Methods

This is a longitudinal descriptive study on selected farms (n = 30) in Nam Dinh Province which is endemic for FZT. At each farm, we sampled one pond, a small irrigation canal used to supply the pond with water, and a nearby rice field. At each of these three sites, we estimated the density of the FZT intermediate snail hosts and determined their trematode infection status. Comparative analysis was performed for the prevalence and density of FZT infections in fish and snails.

Results

Species of the Thiaridae, and most notably Melanoides tuberculata, the most important host species for FZT belonging to the Heterophyidae, were particularly abundant in ponds and small canals, i.e. M. tuberculata was found in 27 ponds and 13 small canals. Bithynia fuchsiana, a potential host for both Heterophyidae and Opisthorchiidae, was rarely found in fish ponds but common in rice fields. A total of 12 types of cercariae were found in the snails and pleurolophocercous cercariae, primarily FZT, constituted about 40 % of all cercarial infections. The fish species cultured were mainly carp species and Haplorchis pumilio was the dominating trematode species infecting fish. Clonorchis spp. were not recorded in any of the ponds. FZT transmission to fish was intense during the summer period (May-June to November) but less intense during the winter months (December-January) partly because cercarial emergence ceases due to the low temperature.

Conclusion

Our findings highlight the complexity of FZT transmission within aquaculture farm settings and suggest that efforts to control these infections must take a holistic approach using interventions against all stages of the transmission cycle.

Identifying climate analogues for precipitation extremes for Denmark based on RCM simulations from the ENSEMBLES database

Climate analogues, also denoted Space-For-Time, may be used to identify regions where the present climatic conditions resemble conditions of a past or future state of another location or region based on robust climate variable statistics in combination with projections of how these statistics change over time. The study focuses on assessing climate analogues for Denmark based on current climate data set (E-OBS) observations as well as the ENSEMBLES database of future climates with the aim of projecting future precipitation extremes. The local present precipitation extremes are assessed by means of intensity-duration-frequency curves for urban drainage design for the relevant locations being France, the Netherlands, Belgium, Germany, the United Kingdom, and Denmark. Based on this approach projected increases of extreme precipitation by 2100 of 9 and 21% are expected for 2 and 10 year return periods, respectively. The results should be interpreted with caution as the best region to represent future conditions for Denmark is the coastal areas of Northern France, for which only little information is available with respect to present precipitation extremes.

An overview of freshwater snails in Asia with main focus on Vietnam

Freshwater snails have received much attention for their role as intermediate hosts for trematodes causing disease in people and animals such as schistosomiasis and various food-borne trematodes. While effective medical treatment exists for some of these diseases there is need for preventive measures to reduce transmission, e.g. control of intermediate hosts because transmission patterns are often complicated due to presence of reservoir final hosts. In order to implement control measures against the intermediate host snails with minimal impact on the freshwater ecosystems and their biodiversity, a profound knowledge on transmission patterns of the trematodes is required and this is partly related to distribution, habitat preferences, and seasonal variation in density of the intermediate host species. Identification of snail species can be problematic on the basis of morphological and anatomical characters alone as some species show morphological plasticity and similarly morphological differentiation of cercariae found in snails may be difficult and this could lead to biased perceptions of intermediate host spectra and transmission patterns. In this paper, we give an overview of the snail families and their medical and veterinary importance in Asia but with main focus on Vietnam.

Introgression in Lake Malaŵi: increasing the threat of human urogenital schistosomiasis?

For the last 15 years, we have studied the relationships among cichlid snail-eating fishes, intermediate snail-host density, and the prevalence of human infection of Schistosoma haematobium in Lake Malaŵi and concluded that the increase of human infection is correlated with the decrease in snail-eating fishes in the shallow waters of the lake. We postulated that a strain of S. haematobium from other parts of Africa, which was introduced into the Cape Maclear region of Lake Malaŵi by tourists, was compatible with Bulinus nyassanus-which is a close relative of B. truncatus, and interbred with the indigenous strain of S. haematobium, which ultimately produced via introgression a strain that can use both B. globosus and B. nyassanus as intermediate hosts. This actively evolving situation involving intermediate snail-host switching and decline of Trematocranus placodon, a natural cichlid snail predator, will impact on transmission of urogenital schistosomiasis within the local communities and on tourists who visit Lake Malaŵi.

Hygienic aspects of livestock manure management and biogas systems operated by small-scale pig farmers in Vietnam

Biogas digesters are widely promoted and increasingly used to treat and generate gas from pig slurry worldwide. The objective of this study was to describe manure management practices with focus on biogas digestion among small scale pig farmers in Hue (50 farmers) and Hanoi (96 farmers) and to assess fecal contamination levels in biogas effluent. Results showed that 84% of the farmers in Hanoi and 42% in Hue used both pig slurry and human excreta for biogas production. Biogas digestion only reduced E. coli concentrations by 1 to 2 log units to 3.70 ± 0.84 Escherichia coli (log10) cfu/ml on average in effluent as compared with raw slurry. Biogas effluent was commonly used to fertilize vegetables or discharged directly into the garden or aquatic recipients. Reduced problems with bad smells and flies were reported as main reasons for establishing a biogas digester. Further studies are needed to assess human and animal health hazards associated with the discharge and use of biogas effluent from small-scale biogas systems.

The ITS2 of the genus Bulinus: novel secondary structure among freshwater snails and potential new taxonomic markers

The freshwater snail genus Bulinus has been intensively investigated due to its role as intermediate host for trematode blood flukes that cause the debilitating disease schistosomiasis in man and livestock. Owing to taxonomic ambiguities within Bulinus, attention has often focused upon species delineation and several molecular methods have recently been used for identification and characterization purposes. Inspection of compensatory base changes (CBCs) in the secondary structure of the nuclear ribosomal internal transcribed spacer (ITS) has been used to differentiate species in other genera, and here we present a study investigating the presence of CBCs between species in the species groups within Bulinus. CBCs were present within B. forskalii and B. globosus indicating that these widely distributed taxa might constitute cryptic species complexes. However, other currently recognized species could not be distinguished by CBC analysis. The putative secondary structure of the very long ITS2 sequence of the B. reticulatus species group had an additional helix (DIIa) between DII and DIII not seen in other species groups of Bulinus. The accumulation and inspection of further ITS2 sequences will no doubt reveal additional variation between Bulinus populations, and CBCs should be incorporated in future taxonomic work in this group.

A very high infection intensity of Schistosoma mansoni in a Ugandan Lake Victoria Fishing Community is required for association with highly prevalent organ related morbidity

Background

In schistosomiasis control programmes using mass chemotherapy, epidemiological and morbidity aspects of the disease need to be studied so as to monitor the impact of treatment, and make recommendations accordingly. These aspects were examined in the community of Musoli village along Lake Victoria in Mayuge district, highly endemic for Schistosoma mansoni infection.

Methodology and Principal Findings

A cross sectional descriptive study was undertaken in a randomly selected sample of 217 females and 229 males, with a mean age of 26 years (SD ±16, range 7–76 years). The prevalence of S. mansoni was 88.6% (95% CI: 85.6–91.5). The geometric mean intensity (GMI) of S. mansoni was 236.2 (95% CI: 198.5–460.9) eggs per gram (epg) faeces. Males had significantly higher GMI (370.2 epg) than females (132.6 epg) and age was also significantly associated with intensity of infection. Levels of water contact activities significantly influenced intensity of infection and the highest intensity of infection was found among people involved in fishing. However, organomegaly was not significantly associated with S. mansoni except for very heavy infection (>2000 epg). Liver image patterns C and D indicative of fibrosis were found in only 2.2% and 0.2%, respectively. S. mansoni intensity of infection was associated with portal vein dilation and abnormal spleen length. Anaemia was observed in 36.4% of the participants but it was not associated with S. mansoni infection intensity. Considering growth in children as one of the morbidity indicators of schistosomiasis, intensity of S. mansoni was significantly associated with stunting.

Conclusion

Although organ-related morbidity, with the exception of periportal fibrosis, and S. mansoni infections were highly prevalent, the two were only associated for individuals with very high infection intensities. These results contrast starkly with reports from Ugandan Lake Albert fishing communities in which periportal fibrosis is more prevalent.

Schistosoma mansoni infection is one of the Neglected Tropical Diseases (NTDs) that perpetuate poverty, especially in Sub Saharan Africa. It is associated with hepatomegaly, splenomegaly or hepatosplenomegaly, liver fibrosis and anaemia. Control of schistosomiasis is now a priority in most endemic countries in Africa as a component of integrated control of NTDs using mass drug administration (MDA). Other than the new WHO strategic plan to eliminate schistosomiasis as a public health problem in WHO Africa region by 2020, the major target in the control of schistosomiasis has for a long time been reduction of its related morbidity. Epidemiological and morbidity studies are key in monitoring the impact of an intervention. However, epidemiology of schistosomiasis and its related morbidity have been shown to vary in different endemic areas and communities. We report on the epidemiology of S. mansoni infection and related morbidity in a community in Mayuge District along Lake Victoria in Uganda.

Use of black carp (Mylopharyngodon piceus) in biological control of intermediate host snails of fish-borne zoonotic trematodes in nursery ponds in the Red River Delta, Vietnam

Background

The risks of fish-borne zoonotic trematodes (FZT) to human health constitute an important problem in Vietnam. The infection of humans with these trematodes, such as small liver trematodes (Clonorchis sinensis and Opisthorchis viverrini), intestinal trematodes (Heterophyidae) and others is often thought to be linked to fish culture in areas where the habit of eating raw fish is common. Juvenile fish produced in nurseries are often heavily infected with FZT and since fishes are sold to aquaculture facilities for growth, control of FZT in these fishes should be given priority. Controlling the first intermediate host (i.e., freshwater gastropods), would be an attractive approach, if feasible. The black carp, Mylopharyngodon piceus, is a well-known predator of freshwater snails and is already used successfully for biological control of snails in various parts of the world including Vietnam. Here we report the first trials using it for biological control of intermediate host snails in nursery ponds stocked with 1-week old fry (10–12 mm in length) of Indian carp, Labeo rohita.

Methods

Semi-field and field experiments were set up to test the effect of black carp on snail populations. In the semi-field experiment a known quantity of snails was initially introduced into a pond which was subsequently stocked with black carp. In the field trial in nursery ponds, density of snails was estimated prior to a nursing cycle and at the end of the cycle (after 9 weeks).

Results

The results showed that black carp affect the density of snail populations in both semi-field and field conditions. The standing crop of snails in nursery ponds, however, was too high for 2 specimens to greatly reduce snail density within the relatively short nursing cycle.

Conclusions

We conclude that the black carp can be used in nursery ponds in Northern Vietnam for snail control. Juvenile black carp weighing 100 - 200g should be used because this size primarily prey on intermediate hosts of FZT and other studies have shown that it does not prey on fish fry of other species. It may be necessary to use a high stocking density of black carp or to reduce snail density in the nursery ponds using other measures (e.g. mud removal) prior to stocking fry in order for the black carp to keep the density of intermediate host snails at a very low level.

Long term study on the effect of mollusciciding with niclosamide in stream habitats on the transmission of schistosomiasis mansoni after community-based chemotherapy in Makueni District, Kenya

BACKGROUND

Schistosoma mansoni infection is a persistent public health problem in many Kenyan communities. Although praziquantel is available, re-infection after chemotherapy treatment is inevitable, especially among children. Chemotherapy followed by intermittent mollusciciding of habitats of Biomphalaria pfeifferi, the intermediate host snail, may have longer term benefits, especially if timed to coincide with natural fluctuations in snail populations.

METHODS

In this cohort study, the Kambu River (Intervention area) was molluscicided intermittently for 4 years, after mass chemotherapy with praziquantel in the adjacent community of Darajani in January 1997. The nearby Thange River was selected as a control (Non-intervention area), and its adjacent community of Ulilinzi was treated with praziquantel in December 1996. Snail numbers were recorded monthly at 9-10 sites along each river, while rainfall data were collected monthly, and annual parasitological surveys were undertaken in each village. The mollusciciding protocol was adapted to local conditions, and simplified to improve prospects for widespread application.

RESULTS

After the initial reduction in prevalence attributable to chemotherapy, there was a gradual increase in the prevalence and intensity of infection in the non-intervention area, and significantly lower levels of re-infection amongst inhabitants of the intervention area. Incidence ratio between areas adjusted for age and gender at the first follow-up survey, 5 weeks after treatment in the non-intervention area and 4 months after treatment in the intervention area was not significant (few people turned positive), while during the following 4 annual surveys these ratios were 0.58 (0.39-0.85), 0.33 (0.18-0.60), 0.14 (0.09-0.21) and 0.45 (0.26-0.75), respectively. Snail numbers were consistently low in the intervention area as a result of the mollusciciding. Following termination of the mollusciciding at the end of 2000, snail populations and infections in snails increased again in the intervention area.

CONCLUSION

The results of this study demonstrate that in the Kenyan setting a combination of chemotherapy followed by intermittent mollusciciding can have longer term benefits than chemotherapy alone.

Prevention and control of fish-borne zoonotic trematodes in fish nurseries, Vietnam

Reducing snails and trematode eggs in nursery ponds lowered trematode transmission among fish.

Worldwide, >18 million persons were infected with fish-borne zoonotic trematodes in 2002. To evaluate the effectiveness of interventions for reducing prevalence and intensity of fish-borne zoonotic trematode infections in juvenile fish, we compared transmission rates at nurseries in the Red River Delta, northern Vietnam. Rates were significantly lower for nurseries that reduced snail populations and trematode egg contamination in ponds than for nurseries that did not. These interventions can be used in the development of programs for sustained control of zoonotic trematodes in farmed fish.

Impacts of climate change on rainfall extremes and urban drainage systems: a review

A review is made of current methods for assessing future changes in urban rainfall extremes and their effects on urban drainage systems, due to anthropogenic-induced climate change. The review concludes that in spite of significant advances there are still many limitations in our understanding of how to describe precipitation patterns in a changing climate in order to design and operate urban drainage infrastructure. Climate change may well be the driver that ensures that changes in urban drainage paradigms are identified and suitable solutions implemented. Design and optimization of urban drainage infrastructure considering climate change impacts and co-optimizing these with other objectives will become ever more important to keep our cities habitable into the future.

Relationship between snail population density and infection status of snails and fish with zoonotic trematodes in Vietnamese carp nurseries

BACKGROUND

Fish-borne zoonotic trematodes (FZT) are a food safety and health concern in Vietnam. Humans and other final hosts acquire these parasites from eating raw or under-cooked fish with FZT metacercariae. Fish raised in ponds are exposed to cercariae shed by snail hosts that are common in fish farm ponds. Previous risk assessment on FZT transmission in the Red River Delta of Vietnam identified carp nursery ponds as major sites of transmission. In this study, we analyzed the association between snail population density and heterophyid trematode infection in snails with the rate of FZT transmission to juvenile fish raised in carp nurseries.

METHODOLOGY/PRINCIPAL FINDINGS

Snail population density and prevalence of trematode (Heterophyidae) infections were determined in 48 carp nurseries producing Rohu juveniles, (Labeo rohita) in the Red River Delta area. Fish samples were examined at 3, 6 and 9 weeks after the juvenile fish were introduced into the ponds. There was a significant positive correlation between prevalence of FZT metacercariae in juvenile fish and density of infected snails. Thus, the odds of infection in juvenile fish were 4.36 and 11.32 times higher for ponds with medium and high density of snails, respectively, compared to ponds where no infected snails were found. Further, the intensity of fish FZT infections increased with the density of infected snails. Interestingly, however, some ponds with no or few infected snails were collected also had high prevalence and intensity of FZT in juvenile fish. This may be due to immigration of cercariae into the pond from external water sources.

CONCLUSIONS/SIGNIFICANCE

The total number and density of potential host snails and density of host snails infected with heterophyid trematodes in the aquaculture pond is a useful predictor for infections in juvenile fish, although infection levels in juvenile fish can occur despite low density or absence infected snails. This suggests that intervention programs to control FZT infection of fish should include not only intra-pond snail control, but also include water sources of allochthonous cercariae, i.e. canals supplying water to ponds as well as snail habitats outside the pond such as rice fields and surrounding ponds.

Schistosomiasis in Lake Malaŵi villages

Historically, open shorelines of Lake Malaŵi were free from schistosome, Schistosoma haematobium, transmission, but this changed in the mid-1980s, possibly as a result of over-fishing reducing density of molluscivore fishes. Very little information is available on schistosome infections among people in lake-shore communities and therefore we decided to summarise data collected from 1998 to 2007. Detailed knowledge of the transmission patterns is essential to design a holistic approach to schistosomiasis control involving the public health, fisheries and tourism sectors. On Nankumba Peninsula, in the southern part of the lake, inhabitants of villages located along the shores of Lake Malaŵi have higher prevalence of S. haematobium infection than those living in inland villages. Overall prevalence (all age classes combined) of urinary schistosomiasis in 1998/1999 ranged from 10.2% to 26.4% in inland villages and from 21.0% to 72.7% in lakeshore villages; for school children prevalence of infection ranged from 15.3% to 57.1% in inland schools and from 56.2% to 94.0% in lakeshore schools. Inhabitants on the islands, Chizumulu and Likoma, also have lower prevalence of infection than those living in lakeshore villages on Nankumba Peninsula. This increased prevalence in lakeshore villages is not necessarily linked to transmission taking place in the lake itself, but could also be due to the presence of more numerous typical inland transmission sites (e.g., streams, ponds) being close to the lake. Temporal data witness of intense transmission in some lakeshore villages with 30-40% of children cleared from infection becoming reinfected 12 months later (also lakeshore village). The level of S. mansoni infection is low in the lakeshore communities. Findings are discussed in relation to fishing in the lake.

Density of Trematocranus placodon (Pisces: Cichlidae): a predictor of density of the schistosome intermediate host, Bulinus nyassanus (Gastropoda: Planorbidae), in Lake Malaŵi

From the mid-1980s, we recorded a significant increase in urinary schistosomiasis infection rate and transmission among inhabitants of lakeshore communities in the southern part of Lake Malaŵi, particularly on Nankumba peninsula in Mangochi District. We suggested that the increase was due to over-fishing, which reduced the density of snail-eating fishes, thereby allowing schistosome intermediate host snails to increase to higher densities. In this article, we collected data to test this hypothesis. The density of both Bulinus nyassanus, the intermediate host of Schistosoma haematobium, and Melanoides spp. was negatively related to density of Trematocranus placodon, the most common of the snail-eating fishes in the shallow water of Lake Malaŵi. Both these snails are consumed by T. placodon. Transmission of S. haematobium through B. nyassanus only occurs in the southern part of the lake and only at villages where high density of the intermediate host is found relatively close to the shore. Thus, we believe that implementation of an effective fish ban up to 100-m offshore along these specific shorelines in front of villages would allow populations of T. placodon to increase in density and this would lead to reduced density of B. nyassanus and possibly schistosome transmission. To reduce dependence on natural fish populations in the lake and still maintain a source of high quality food, culture of indigenous fishes may be a viable alternative.

Distribution of freshwater snails in family-based VAC ponds and associated waterbodies with special reference to intermediate hosts of fish-borne zoonotic trematodes in Nam Dinh Province, Vietnam

Fish-borne zoonotic trematodes, such as Clonorchis sinensis, heterophyids and others, constitute a public health concern in parts of northern Vietnam and infections with these trematodes are often thought to be linked to fish culture. One common fish culture system is the integrated fish-livestock (VAC) ponds where individual households have 1 or more ponds. Fish fry, mainly of various carp species, produced in hatcheries, not necessarily local, are introduced into nursery ponds and after approximately 6 weeks, juvenile fishes are transferred to household ponds, referred to as grow-out ponds. Grow-out ponds are usually fertilized with organic debris, including animal excreta, to stimulate algal growth and subsequently fish growth. This paper describes the distribution of freshwater snails and occurrence of trematode infections in these in VAC ponds and associated habitats as part of a major study on risk factors of FZT infections in cultured fish in two communes, Nghia Lac and Nghia Phu, Nghia Hung District, Nam Dinh Province. The area is under intense rice cultivation with an extensive canal network supplying fields and also household VAC ponds. A total of 16 snail species was found and four were widely distributed i.e. Angulyagra polyzonata, Melanoides tuberculata, Bithynia fuchsiana and Pomacea insularum. Snail diversity and counts were higher in nursery ponds than in grow-out ponds. Species of the families Thiaridae and Viviparidae were more abundant than other species in VAC ponds while species of the Bithyniidae, Stenothyridae and Planorbidae dominated in rice fields and small canals. Trematode infections were found in eight snail species and among these M. tuberculata had the highest overall prevalence of infection (13.28%). No trematode infections were found in species of the Viviparidae and Ampullaridae except for metacercariae. Parapleurolophocercous and pleurolophocercous cercariae constituted the most common type of cercariae recovered, contributing 40.6% of all infections followed by echinostome cercariae (35.0%) and xiphidiocercariae (17.3%). Bithynia fuschiana and M. tuberculata had the most diverse trematode fauna. C. sinensis was not recorded in this study. The VAC pond system in this area, is very important for transmission of minute intestinal trematodes while they play little role in transmission of C. sinensis as its intermediate hosts, bithynid snails, rarely occur in these ponds. From a public health perspective this is positive as the effects of infections with intestinal trematodes are considered mild. On the other hand it is possible that even such subtle effects could have importance in public health as transmission is very intense in the area. And this in combination with the aquaculture importance, reduced marketability of fishes with high metacercariae loads, warrants that control efforts against these trematodes are initiated to reduce transmission in this production system.