The epidemiology of schistosomiasis in Egypt: Gharbia Governorate.

Health questionnaires and parasitologic examinations of urine and stool were performed upon a stratified random sample of 14,344 individuals from 1,952 households in 34 rural communities in Gharbia Governorate of Egypt to investigate the prevalence of, risk factors for, and changing pattern of infection with Schistosoma sp. A subset, every fifth household, of 1,973 subjects had physical and ultrasound examinations to investigate prevalence of and risk factors for morbidity. Community prevalence of Schistosoma mansoni ranged from 17.9% to 79.5% and averaged 37.7%. The geometric mean egg count (GMEC) was 78.9 eggs/gram of feces. The prevalence and intensity of infection was 40-50% and 70-100 eggs/gram of feces in those > or =10 years of age. Schistosoma haematobium was detected in 5 of the 34 communities. The maximum infection rate was 2.8% and mean GMEC in the five communities was 2.1/10 ml of urine. The overall prevalence of S. haematobium in the governorate was 0.3%. Risk factors for infection with S. mansoni were male gender, an age >10 years, living in smaller communities, exposures to canal water, prior therapy for schistosomiasis, or blood in the stool (in children only). Morbidity detected by physical examination or ultrasonography did not correlate with S. mansoni infection in individuals with the exception of periportal fibrosis (PPF, odds ratio [OR] = 1.25). Periportal fibrosis was detected in more than half of the subjects by ultrasonography; 5.3% had grade II lesions and 1.0% had the most severe grade III changes. Risk factors for morbidity as manifested by ultrasonographically detected PPF were similar to those for infection. Periportal fibrosis had a negative relationship with abdominal pain (OR = 0.45) and hepatomegaly detected by physical examination and ultrasonography (ORs = 0.72 and 0.68), but it was associated with splenomegaly (ORs = 4.14 and 3.55). The prevalence of PPF, hepatomegaly, and splenomegaly increased with age. There was no relationship between community burden of schistosomiasis mansoni and any measurements of morbidity with the exception of splenomegaly detected by physical examination (r = 0.40). Schistosoma mansoni has almost completely replaced S. haematobium in Gharbia, which has a high prevalence and moderate intensity of S. mansoni infection. Periportal fibrosis was detected by ultrasonography in more than half of the subjects, and 1 in 16 had grade II and III lesions. The only relationship between PPF and other morbidity findings was its positive relationship with splenomegaly and negative association with hepatomegaly. Hepatic morbidity is common in communities in Gharbia but the role of schistosomiasis mansoni in this is uncertain.

Trend in the annual risk of tuberculous infection in Egypt, 1950-1996.

OBJECTIVE: To determine the trend in the risk of tuberculous infection in non-BCG vaccinated children in Egypt in the period 1950-1996. METHODS: In 1949-1952, a tuberculin survey was carried out in Egypt by the World Health Organization (WHO) covering 103 districts. In 1995-1997 a tuberculin survey was carried in 73 620 primary school children in grade one in the same districts, using international guidelines. The trend in tuberculous infection was determined by comparing the prevalence of Mantoux reactions of > or =6 mm in the two surveys in subjects without apparent BCG scar aged 6-7 years. For an estimate of current risk of infection the 17 mm cut-off point (number with 17 mm plus twice the number with greater than 17 mm) was used. RESULTS: In 1995-1997, 76% of children had a BCG scar. Infection prevalence estimates in 14 766 non-BCG-vaccinated children with a mean age of 6.7 years were 11.9%, 4.1%, and 2.1% for the cut-off points 6 mm, 10 mm, and 17 mm, respectively. Decline in the risk of infection was estimated to be in the order of 50% over 45 years, or 1.5% per year. The geometric mean annual risk of infection in the 6.7 years before the survey was estimated at 0.32% (95% confidence interval 0.27-0.40%). For Egypt, the incidence of smear-positive tuberculosis was estimated at 16 per 100000 population, giving a case detection rate of 85% (range 56-100%). CONCLUSION: This survey has shown that the size of the tuberculosis problem in Egypt is considerably smaller now than it was 45 years ago.

Ultrastructural localization of a protective 68,000 molecular weight antigen in Schistosoma mansoni.

Vaccination with SMW 68, an Mr 68,000 glycoprotein of Schistosoma mansoni, induces significant protection in mice against challenge schistosome infection. This resistance occurs without the use of adjuvants and without sensitizing animals to granuloma formation. Likewise, passive transfer of monoclonal antibody (MAb) 31-3B6 against SMW 68 confers partial protection against challenge infection. As a first step in understanding how the immune response to this molecule leads to resistance, SMW 68 was localized in three developmental stages of the parasite by immunoelectron microscopy using MAb 31-3B6 and polyclonal antisera raised against purified SMW 68. In cercariae and schistosomula, MAb 31-3B6 bound electron-dense granules within the head gland and similar granules in the preacetabular glands. In adult worms, SMW 68 or related antigens were found to be widely distributed in tissues. Binding of specific antisera was most pronounced in the gut and tegument of male worms, but less so in subtegumental muscles. We conclude that SMW 68 is presented to the immune system in various ways during parasite development. The protective protein or epitope is excreted, and presented on the surface and in the cytoplasm at various stages of the life cycle. The relationship of the location of this protein to its role in protective immunity is discussed.

Intensity of Schistosoma mansoni infection in a human population is inversely correlated with antibody response to SmW68, a protective parasite antigen.

Vaccination with SmW68, a Schistosoma mansoni surface antigen, significantly protects mice against challenge infection. To investigate the vaccine potential of SmW68 in clinical schistosomiasis, human antibody response to SmW68 was studied as a function of intensity of infection in a chronically infected Egyptian population. In 85 serum samples obtained randomly from families in El Gazairy (population 1,310), antibody to SmW68 (determined by ELISA) was found to increase significantly with age, reaching a plateau at 15-19 y, 1-5 y after peak prevalence and intensity of infection. Among infected individuals (n = 54), antibody response showed a significant inverse correlation (r = -.28, P less than .04) with intensity of infection. In isotype analysis, a higher IgM but not IgG response was significantly associated with low parasite burden. These studies demonstrate that significant antibody response to SmW68 could occur in chronically infected humans. Whether parasite burdens suppress circulating levels of antibody to SmW68 or whether enhanced antibody response to SmW68 represents acquired protective humoral immunity remains to be determined.

Isolation and characterization of a protective antigen for adjuvant-free immunization against Schistosoma mansoni.

A single, 68,000 m.w. glycoprotein antigen from adult Schistosoma mansoni was purified by immunoaffinity chromatography with the use of a newly developed, protective, anti-schistosome murine monoclonal antibody. Immunization with two doses of 0.5 microgram or 1 microgram of purified antigen, without adjuvants, afforded a mean 28% reduction in parasite recovery in CF1 mice, and 2-% reduction in parasite BALB/c mice. On immunoblotting, the 68,000 m.w. antigen was common to S. mansoni adults and schistosomula, whereas parasite eggs contained only cross-reacting low m.w. antigens of 19,100 and 16,000. Immunization resulted in the development of anti-antigen antibody and enhanced immediate cutaneous hypersensitivity to the 31-3B6 antigen. By contrast, delayed-type hypersensitivity and sensitization to circumoval granuloma formation were not observed in immunized mice. It was concluded that the 68,000 m.w. 31-3B6 antigen represents a candidate vaccine for adjuvant-free immunization against S. mansoni.