Human schistosomiasis

Schistosomiasis or bilharzia is a tropical disease caused by worms of the genus Schistosoma. The transmission cycle requires contamination of surface water by excreta, specific freshwater snails as intermediate hosts, and human water contact. The main disease-causing species are S haematobium, S mansoni, and S japonicum. According to WHO, 200 million people are infected worldwide, leading to the loss of 1.53 million disability-adjusted life years, although these figures need revision. Schistosomiasis is characterised by focal epidemiology and overdispersed population distribution, with higher infection rates in children than in adults. Complex immune mechanisms lead to the slow acquisition of immune resistance, though innate factors also play a part. Acute schistosomiasis, a feverish syndrome, is mostly seen in travellers after primary infection. Chronic schistosomal disease affects mainly individuals with long-standing infections in poor rural areas. Immunopathological reactions against schistosome eggs trapped in the tissues lead to inflammatory and obstructive disease in the urinary system (S haematobium) or intestinal disease, hepatosplenic inflammation, and liver fibrosis (S mansoni, S japonicum). The diagnostic standard is microscopic demonstration of eggs in the excreta. Praziquantel is the drug treatment of choice. Vaccines are not yet available. Great advances have been made in the control of the disease through population-based chemotherapy but these required political commitment and strong health systems.     

Human schistosomiasis in Cameroon. I. Distribution of schistosomiasis

The status of schistosomiasis in Cameroon was examined in a nationwide survey of 5th grade schoolchildren. Five hundred twelve schools were surveyed; 19,524 urine and 22,166 stool samples were examined. The 3 northern provinces, which comprised 29% of the population, had 87% of all urinary and 82% of all intestinal cases. These provinces have a low seasonal rainfall. The presence of temporary bodies of water and of molluscan intermediate hosts adapted to this environment permits intense transmission of schistosomiasis haematobium and mansoni. In the rest of the country, the distribution of Schistosoma haematobium and S. mansoni was highly focal. S. intercalatum endemic areas were restricted to the equatorial forest and were small with low prevalences and intensities.     

昭觉县人群血吸虫病感染情况分析

昭觉县地处四川省西部大凉山腹地，平均海拔2000多m，血吸虫病疫区位于县境西部与西昌交界的山区，疫区人口2000多人，为彝族聚集区。其主要农作物有水稻、玉米、烤烟、大蒜。疫区一般都是人力耕种，少量使用畜力，没有农机耕作。农民在田间插秧、洗衣等活动，接触疫水时极易感染血吸虫病。就近几年的检查结果作如下分析。     

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

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

Human schistosomiasis mansoni: immune responses during acute and chronic phases of the infection

Schistosoma mansoni infection may occur either as an acute infection in individuals who have recently visited an endemic area, with no previous contact with the parasite, or as a lasting chronic disease, if not interrupted by specific chemotherapy. The acute phase is characterized by symptoms such as fever, cough, diarrhea, anorexia, and arthralgias in combination with leukocytosis and eosinophilia, and a high cellular immune response to schistosome antigens especially those from the parasite's eggs. In the chronic phase, most patients living in endemic areas are asymptomatic, and their immune responses to egg antigens are modulated. A few develop periportal fibrosis of the liver, which may result in the hepatosplenic form of the disease. The humoral response (IgG, IgM and IgE) in acute patients to egg and worm antigens does not differ from the chronic phase. However, a high level of IgG and IgM antibodies to KLH were detected in acute patients. Acute patients express a considerably higher in vitro cellular responsiveness than do chronic patients, especially to egg antigens. They present a mixed profile of Th1 and Th2 cytokines. Ultrasound examinations of endemic population reveal a high heterogeneity between the patients as regards the presence and intensity of periportal fibrosis. Most patients are asymptomatic and their immune responses to schistosoma egg antigens (SEA) are modulated. In contrast, a high percentage of patients with incipient fibrosis (early stage of hepatosplenic) responded strongly to SEA. Patients with advanced hepatosplenic disease were likely to be non-responders to SEA. Most of the chronic patients presented a Th2 profile with low production of interferon-gamma (IFN-gamma). The intensity of infection favors the production of interleukin (IL)-10. After adjusting for age, sex, and intensity of infection, a strong correlation was observed between the production of IL-13 and the degree of fibrosis. Chronic asymptomatic patients and those with incipient fibrosis expressed very high levels of heterogeneity of their antibody responses. IgG response to soluble worm antigen preparation (SWAP) was distinct and significantly higher in hepatosplenic patients than in those asymptomatic or with incipient fibrosis. Levels of IgG4 to SEA were significantly higher in sera from patients with incipient fibrosis as compared to uninfected and hepatosplenic groups. Polyclonal idiotypic antibodies and their fragments F(ab')2, directly stimulate in culture T cells of schistosomiasis patients in presence of IL-1. Polyclonal idiotypic antibodies are able to modulate in vitro granuloma formation around SEA-polyacrylamide. The importance of idiotypes for protection or pathology in schistosomiasis is still not clear.     

Pulmonary schistosomiasis

Schistosoma infection is one of the most common infectious diseases, limited in the past only to the endemic countries. With the enormous increase in migration and travel, we encounter more and more cases in developed, nonendemic countries. Although the disease has been known for many years from studies in the endemic countries, the new patient population of nonimmune travelers presents with a different clinical pattern that requires further investigation. One of the features of the disease in the nonendemic population is pulmonary involvement that seems to be much more common than previously suspected. The differences between the nonimmune population with the early pulmonary involvement and the population of endemic areas with late pulmonary involvement are summarized in Table 1. Clinicians in the Western countries have a higher chance of encountering the early (acute) form of the disease, although immigrants from endemic countries may present with late (chronic) schistosomiasis. In the differential diagnosis of pulmonary pathology, especially when accompanied by eosinophilia, schistosomal infection should be considered. The travel history of the patient is mandatory for an evaluation.     

Appendiceal schistosomiasis

Twenty surgical specimens of appendiceal schistosomiasis were reviewed retrospectively. They constituted 1 percent of 1984 appendices seen among approximately 15,000 surgical specimensexamined at free central laboratories serving the Igbos of Nigeria, West Africa. Oviposition bySchistosoma haematobium was classified according to its association with suppurative appendicitis and normal appendices. Seven of ten infested appendices obtained at curative operations showed suppurative appendicitis, whereas eight of nine infested appendices removed at incidental appendectomies were negative. One interval appendectomy was also negative. It is postulated that utilization of this novel classification on a worldwide basis will help to end the controversy concerning the etiologic role of schistosome ova in acute appendicitis.     

Genital schistosomiasis

Schistosomiasis is the most serious helminthic infection in the United Kingdom. Female genital schistosomiasis affects 9-13 million women worldwide, mainly in areas where Schistosoma haematobium is endemic. With increasing tourism to these areas, this diagnosis is being encountered more frequently in the West. We present 2 cases of vulval schistosomiasis that were presented to our department in 1999 and 2000.     

Hepatic schistosomiasis

Opinion statement Praziquantel is the treatment of choice for schistosomiasis because of its efficacy, ease of administration, limited side effects, and low cost. Praziquantel has been so effective that alternative therapies are increasingly difficult to obtain, and the development of novel medications has been limited. The possibility of praziquantel resistance is a grave concern. Low cure rates for praziquantel have been reported in several countries, but despite widespread use, no significant loss of efficacy has occurred to date. The primary goal of antischistosomal therapy is parasite eradication, which reduces the likelihood of chronic complications, including advanced hepatic fibrosis. Mild to moderate hepatic fibrosis results from the immune response to schistosome eggs deposited in the portal venules and reverses with successful treatment. Most individuals clear schistosomiasis with a single course of therapy. Repeat doses cure the majority of patients in whom eradication does not occur after the initial dose. A secondary goal of therapy for patients with persistent or recurrent infection is egg burden reduction, which also reduces the risk of hepatic fibrosis and lowers community spread. Community eradication programs in highly endemic regions use periodic retreatment to limit chronic schistosomiasis’ morbidity. Advanced liver fibrosis and portal hypertension due to chronic schistosomiasis are irreversible. Variceal bleeding is the primary cause of death in hepatic schistosomiasis. The bleeding risk is best reduced through use of β-blocker prophylaxis or endoscopic banding or sclerotherapy. Surgical management of varices, including splenectomy with esophagogastric devascularization or selective shunts such as the distal splenorenal, is effective in patients with recalcitrant bleeding. Because hepatic synthetic function is normal in patients with schistosomiasis, procedures that reduce portal pressures may lower hepatic perfusion and cause hepatic impairment. The risk of encephalopathy after shunt surgery is higher in patients with schistosomiasis than in those with cirrhosis. For these reasons, nonselective shunt surgery such as the proximal splenorenal or the transjugular intrahepatic portosystemic shunt should not be performed in patients with advanced hepatic schistosomiasis.     

Colorectal schistosomiasis

The role of colonoscopic polypectomy for schistosomal polyps was studied. The results showed that, in spite of the large number of polyps, a total of 404 polyps were removed from 20 patients. The procedure is feasible with minimal complications. A marked reduction of rectal bleeding occurred in half the patients, and the remaining half had minimal symptoms. Colonoscopic polypectomy gives equal results to colonic excision for schistosomal polyps.     

Hepatic schistosomiasis

Schistosomiasis is a major, worldwide cause of morbidity and mortality. Disease from the organism Schistosoma mansoni results from egg deposition in the liver, intestines, and other organs and is associated with an intense, granulomatous response from the human host. Clinical manifestations range from mild to severe intestinal forms, and hepatosplenic schistosomiasis, which is associated with hepatic fibrosis, portal hypertension, esophageal varices, and splenomegaly. This article presents information about the epidemiology, immunopathogenesis and clinical aspects of the disease, the relationship between hepatic schistosomiasis and viral infections, diagnosis, therapy, and control strategies for schistosomiasis.     

血吸虫病传播阻断地区新发晚期血吸虫病调查

2004-2011年黄山市共有新发晚期血吸虫病人240例,均为临床诊断病例。患者主要分布在原历史疫情较重的区县;其中以2007年和2008年发现最多;60岁以上者占79.16%;患者类型以腹水型和巨脾型为主,分别占66.25%和31.66%。调查结果表明,传播阻断地区仍有新发晚期血吸虫病发生。因此,要加强对历史病人的监测和诊治。