Effects of repeated praziquantel treatment on schistosomiasis mekongi morbidity as detected by ultrasonography

Application of Dendrimers for Treating Parasitic Diseases

Despite advances in medical knowledge, parasitic diseases remain a significant global health burden and their pharmacological treatment is often hampered by drug toxicity. Therefore, drug delivery systems may provide useful advantages when used in combination with conventional therapeutic compounds. Dendrimers are three-dimensional polymeric structures, characterized by a central core, branches and terminal functional groups. These nanostructures are known for their defined structure, great water solubility, biocompatibility and high encapsulation ability against a wide range of molecules. Furthermore, the high ratio between terminal groups and molecular volume render them a hopeful vector for drug delivery. These nanostructures offer several advantages compared to conventional drugs for the treatment of parasitic infection. Dendrimers deliver drugs to target sites with reduced dosage, solving side effects that occur with accepted marketed drugs. In recent years, extensive progress has been made towards the use of dendrimers for therapeutic, prophylactic and diagnostic purposes for the management of parasitic infections. The present review highlights the potential of several dendrimers in the management of parasitic diseases.

Morbidity associated with Schistosoma mekongi and concurrent helminth infection in Lao People's Democratic Republic

In 2006, some 7 years after the halt of a multi-year schistosomiasis control programme, a study was conducted in the southern part of Lao People's Democratic Republic to determine the morbidity associated with Schistosoma mekongi and concurrent helminth infection. In two S. mekongi-endemic districts, Khong and Mounlapamok, 640 individuals aged 9-40 years were randomly selected. Two stool samples were obtained from each participant and subjected to the Kato-Katz technique for helminth diagnosis. Morbidity was assessed by clinical examination and abdominal ultrasonography. Multiple logistic regression analysis was employed to relate S. mekongi infection with morbidity indicators. In Khong district, S. mekongi prevalence was 13-fold higher than in Mounlapamok district (57.7% vs. 4.4%, p < 0.001). Likewise, we observed significantly more often palpated hepatomegaly (15.5% vs. 5.4%) and splenomegaly (9.6% vs. 0.4%). Abdominal ultrasonography revealed that, in Khong district, liver and spleen morbidity occurred more frequently (e.g., enlarged left liver lobe: 89.2% vs. 68.7%, p < 0.001). Single species infection with S. mekongi was associated with enlarged peri-portal vein (adjusted odds ratio (aOR) 47.7, 95% confidence interval (CI) 4.2-85.7, p = 0.002), as was S. mekongi-Opisthorchis viverrini co-infection (aOR 2.2, 95% CI 1.1-4.5, p = 0.020). In conclusion, our study shows that in 2006, several years after the halt of the Lao schistosomiasis control programme that emphasised preventive chemotherapy, S. mekongi infection again had reached high prevalence rates. Infection with S. mekongi was associated with substantial hepatosplenic morbidity. Schistosomiasis control measures were re-instigated in 2010. In view of the ultimate goal to eliminate schistosomiasis, rigorous surveillance and public health responses tailored to the social-ecological settings and long-term programme commitment are warranted.

Collaborative RNAS+ research: Priorities and outcomes

Over the past 20 years, RNAS⁺ has been generating research results from highly collaborative projects meant to promote and advance understanding in various aspects of schistosomiasis. Epidemiological studies in endemic countries like the Philippines, the People's Republic of China (PR China), the Lao People's Democratic Republic (Lao PDR) and Cambodia clarified the role of reservoir hosts in transmission and the use of spatio-temporal methods such as remote sensing and geographical information systems (GIS) in surveillance of schistosomiasis. Morbidity studies proposed factors that might influence development of fibrosis, anaemia and malnutrition in schistosomiasis. Immune responses in schistosomiasis continue to be an interesting focus in research to explain possible development of resistance with age. Results of evaluation of candidate vaccine molecules are also presented. New diagnostics are continually being developed in response to the call for more sensitive and field applicable techniques that will be used for surveillance in areas nearing elimination of the disease. Several studies presented here show the insufficiency of mass drug administration (MDA) with praziquantel in eliminating the disease. Emphasis is given to an integrated control approach that can be accomplished through intensive and extensive intersectoral collaboration.

Is Opisthorchis viverrini Emerging in Cambodia?

Opisthorchis viverrini infection is widely prevalent in Southeast Asia. In Cambodia information on this helminth infection is scare. Recent reports suggest that O. viverrini is an emerging public health problem. We aimed to synthesize all information in relation to the infection, epidemiology, and morbidity of O. viverrini in Cambodia; from published as well as thus far unpublished sources. First reports on O. viverrini date back to 1995. In 2006 an O. viverrini initiative was launched by the national helminth control program. Since then O. viverrini has been reported in all - except two - provinces. Villages with high prevalences (>20%) were found in provinces from Preah Vihear to Takeo. The infection has a highly focal distribution. In many villages no infections were detected. O. viverrini infection was also reported in cats, dogs and intermediate hosts. No report on morbidity associated with O. viverrini was found. The current evidence suggests that O. viverrini infection remains underreported in Cambodia. It is likely that the transmission will further increase in the future with potentially serious consequences for human health.

Schistosomiasis

Schistosomiasis (bilharzia) is a neglected tropical disease caused by parasitic flatworms (blood flukes) of the genus Schistosoma, with considerable morbidity in parts of the Middle East, South America, Southeast Asia and, particularly, in sub-Saharan Africa. Infective larvae grow in an intermediate host (fresh-water snails) before penetrating the skin of the definitive human host. Mature adult worms reside in the mesenteric (Schistosoma mansoni and Schistosoma japonicum) or pelvic (Schistosoma haematobium) veins, where female worms lay eggs, which are secreted in stool or urine. Eggs trapped in the surrounding tissues and organs, such as the liver and bladder, cause inflammatory immune responses (including granulomas) that result in intestinal, hepato-splenic or urogenital disease. Diagnosis requires the detection of eggs in excreta or worm antigens in the serum, and sensitive, rapid, point-of-care tests for populations living in endemic areas are needed. The anti-schistosomal drug praziquantel is safe and efficacious against adult worms of all the six Schistosoma spp. infecting humans; however, it does not prevent reinfection and the emergence of drug resistance is a concern. Schistosomiasis elimination will require a multifaceted approach, including: treatment; snail control; information, education and communication; improved water, sanitation and hygiene; accurate diagnostics; and surveillance-response systems that are readily tailored to social-ecological settings.

Mass drug administration and the global control of schistosomiasis: successes, limitations and clinical outcomes

PURPOSE OF REVIEW

Preventive chemotherapy is advocated for the global control and elimination of schistosomiasis. Despite the well known short-term benefits of treating patients for schistosomiasis, the impact of mass drug administration (MDA) campaigns to control the disease in the long term remains unresolved.

RECENT FINDINGS

Many studies have advocated the success of MDA programs in order to attract donor funds for elimination efforts but such successes are often short-lived given the drug does not alter the life cycle of the organism or prevent reinfection. Within a matter of months to years after halting treatment, the prevalence, intensity of infection and morbidity of disease return to baseline levels. Other mitigating factors contribute to the failings of MDA campaigns namely: poverty, poor drug coverage, poor drug compliance, and, in the case of Asiatic schistosomiasis, zoonotic transmission. Genetic and innate and acquired immunologic mechanisms complicate the epidemiologic picture of schistosomiasis globally, and may contribute indirectly to MDA shortcomings. The possibility of drug resistance is an ever present concern because of the sole reliance on one drug, praziquantel.

SUMMARY

Preventive chemotherapy is advocated for the global control and elimination of schistosomiasis. The short-term benefits of MDA campaigns are well documented but the long-term benefits are questionable.

China-Africa and China-Asia Collaboration on Schistosomiasis Control: A SWOT Analysis

Schistosomiasis, a disease caused by a trematode, parasitic worm, is a worldwide public health problem. In spite of great progress with regard to morbidity control, even elimination of this infection in recent decades, there are still challenges to overcome in sub-Saharan Africa and endemic areas in Southeast Asia. Regarded as one of the most successful countries with respect to schistosomiasis control, The People's Republic of China has accumulated considerable experience and learnt important lessons in various local settings that could benefit schistosomiasis control in other endemic countries. Based on an analysis of conceived strengths, weaknesses, opportunities and threats (SWOT) of potential collaborative activities with regard to schistosomiasis in Africa and Asia, this article addresses the importance of collaborative efforts and explores the priorities that would be expected to facilitate the transfer of Chinese experience to low- and middle-income countries in Africa and Asia.

Global health: neglected diseases and access to medicines

The World Health Organization has developed a comprehensive plan to deal with neglected tropical diseases (NTDs). Compared with a decade ago, more resources are being spent to address the problem of neglected diseases, and considerable progress has been made. However, NTDs remain neglected, deepening the global inequities in health. The current efforts do not implement a multiprong strategy and are effective in the short term, but do not generate long-term, sustainable solutions. This article discusses the current successes in providing access to medicine for treatment of a multitude of neglected diseases, and the opportunities to achieve global equality in health.

Schistosoma mekongi in Cambodia and Lao People's Democratic Republic

Schistosomiasis found in communities along the Mekong River in Cambodia and Lao People's Democratic Republic (Lao PDR) is caused by the blood fluke Schistosoma mekongi. Early observations on patients in 1957 revealed severe intestinal and hepatosplenic disease. High mortality rates and widespread disease were reported from the provinces of northern Cambodia (Stung Treng and Kratié) and southern Lao PDR (Champasack) in the early 1970s and 1990s. Control programmes built around mass drug administration, with praziquantel, and combined with information and education campaigns, were carried out. In Cambodia, such programmes were started in 1995 in the endemic provinces and sustained until today; these efforts resolved the public health problem of schistosomiasis mekongi and led to a significant reduction in transmission. In Lao PDR, the interventions started in the late 1980s, but suffered several interruptions which permitted transmission to resume. Today, a number of small foci continue to show substantial prevalence rates. The snail intermediate host, Neotricula aperta, is present in the Mekong River and some of its tributaries. There is evidence that the snail might not yet have reached its full geographical distribution emphasising the need to sustain vigilance. New infections with S. mekongi occur in the endemic population and travellers alike. Comprehensive guidelines for the elimination of S. mekongi and bilateral efforts between Cambodia and Lao PDR are required.

Schistosoma mekongi and Schistosoma japonicum: Differences in the distribution of eggs in the viscera of mice

The difference in the distribution of Schistosoma eggs in the viscera has not been clearly elucidated in the two closely related species Schistosoma japonicum and Schistosoma mekongi. In this study, we quantitatively compared the distribution of eggs in mice infected with the two species. In S. mekongi-infected mice, 56.6% to 69.4% of total eggs were found in the distal small intestine 9 to 15 weeks after infection, while in S. japonicum-infected mice, 48.8% to 71.8% of eggs were found in the proximal small intestine during the same period. There were significantly more eggs in the liver in mice infected with S. japonicum than in those infected with S. mekongi. The number of adult worms recovered did not differ between the two species during the study period. The total number of eggs laid in the tissues also did not differ between the two species at 12 to 15 weeks postinfection, but in the earlier period the total number of eggs was significantly fewer in S. mekongi-infected than in S. japonicum-infected mice, suggesting the delayed maturation of the former compared with the latter. These results clearly show that S. japonicum and S. mekongi exhibit different oviposition behavior in their hosts.

Liver morbidity due to Schistosoma mekongi in Cambodia after seven rounds of mass drug administration

Severe liver disease due to Schistosoma mekongi was frequent in northern Cambodia. Between 1995 and 2002, seven rounds of mass chemotherapy (praziquantel) reduced infection from 50% to below 3%. In 2002, we assessed hepatosplenic morbidity by historical, clinical and ultrasonographic investigations in adults (older than 14 years) from endemic (n=342) and non-endemic (n=103) areas (Kratie province). Clinical hepatomegaly (25 vs. 0%), splenomegaly (55 vs. 0%), reported blood in stool (41 vs. 20%) and abdominal pain (78 vs. 57%) were significantly higher in the endemic area. In this area, significantly more subjects reported a family history of death due to schistosomiasis (12 vs. 0%); 63% (vs. 0%) reported having at least three treatments of praziquantel in previous years; and only 11% (vs. 99%) had normal liver ultrasonographic examination. Periportal fibrosis with portal hypertension was diagnosed in 46% (vs. 0%) of people in this area; 18% (vs. 0%) and 5% (vs. 0%) of portal hypertension was classified as moderate and severe, respectively. People aged between 24 and 35 years were mostly affected. There was no gender difference. The pathology in the endemic district is most probably residual morbidity of S. mekongi infections. Contributions of co-infections (hepatitis) cannot be excluded. Careful monitoring of the affected communities is required.

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.