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Biomedical subjects

R F Sturrock

Publications and source records attributed to R F Sturrock.

126 records · Page 7Linked to original sources
PubMed1966

The effect of sublethal doses of a molluscicide (Bayluscide) on the development of Schistosoma mansoni in Biomphalaria sudanica tanganyicensis.

The complete eradication of snails from waterbodies is rarely achieved with existing molluscicides. This communication describes laboratory experiments designed to show whether snails surviving such treatment are still capable of transmitting Schistosoma mansoni. The treatment, with Bayluscide, was given at various times during the development of the infection. Snails that survived treatment were as susceptible to infection as were untreated controls but, although the initial survival rate of infected snails was as good as that of uninfected snails, their ultimate survival rate was poorer. Treatment had no permanent effect on the development of the schistosome, although there is some evidence of a delay in some cases. Infected snails may survive a field application of Bayluscide and continue parasite transmission, and uninfected survivors are susceptible to infection. Thus, while it may curtail transmission dramatically, the use of molluscicides will not eliminate transmission in the absence of other measures to prevent infection of the surviving snails.

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Chemotherapy-based control of schistosomiasis haematobia. 3. Snail studies monitoring the effect of chemotherapy on transmission in the Msambweni area, Kenya.

Regular snail sampling was performed at 40 sites, representing the principal snail habitats, during a 4 year chemotherapy programme targetted at school-children in the Msambweni area of the coastal plain of Kenya. Populations of Bulinus africanus group snails, primarily from pools, showed seasonal variations, dropping when sites dried out and rising when they were refilled by the rains. Transmission, judged by the recovery of snails shedding typical fucocercous cercariae, continued throughout the treatment period at very low levels (less than 1% of the snails collected were infected) with peaks in October/November and in January/February after seasonal rains. Spatially, most infected snails were recovered from 2 large pools near the sea, close to the school that responded least well to the initial chemotherapy programme. Later, infected snails were found sporadically in inland pools, rice fields and temporary streams near another school where there was evidence of substantial reinfection as the study progressed. The snail findings are consistent with a reduction but not elimination of transmission associated with the chemotherapy programme.

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Schistosome migration in primates: a study in the olive baboon (Papio anubis).

The migration of isotopically labelled schistosomula of Schistosoma mansoni from the skin to the hepatic portal system of baboons was tracked by autoradiography of compressed organ preparations. Passage of schistosomula from skin to lungs was rapid between days 2 and 5, 72% of applied parasites being detected in the lungs at the latter time. There was an equally rapid migration from lungs to liver, 60% of the adult worm burden having arrived by day 9. Perfusion data indicated a final maturation of not less than 78%. No evidence was found to support or refute a systemic phase of migration. Thus, in comparison to rodents, schistosome migration in baboons appears to be faster and more successful, possibly because the lungs do not represent a significant obstacle to migration.

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Immunization of baboons with attenuated schistosomula of Schistosoma haematobium: levels of protection induced by immunization with larvae irradiated with 20 and 60 krad.

We have shown previously that baboons (Papio anubis) develop high levels (greater than 80%) of protection against challenge infection following immunization with Schistosoma haematobium cercariae irradiated with 20 krad. In the present study baboons were immunized with schistosomula irradiated with either 20 krad or 60 krad, with variations in the timing and number of larvae comprising each vaccination. Baboons immunized 2 or 3 times with schistosomula irradiated with 20 krad were significantly more protected (85-90%) against challenge infection than baboons similarly immunized with larvae receiving 60 krad (56-50% protection). Baboons immunized with schistosomula irradiated with 20 krad were better protected against challenge infection at 8 weeks after immunization than at 28 weeks after immunization. Protection was manifest by a reduction in worm numbers, tissue and excreta egg counts, gross pathology and, to a lesser extent, by stability of body weight and haematological indices following challenge. Enzyme-linked immunosorbent assay (ELISA) results of selected baboon sera showed few differences related to irradiation dose alone, but titres were higher in baboons receiving booster immunizations, and there was a significant correlation between titres immediately preceding challenge and the degree of resistance. Examination of responses to individual schistosomular surface antigens by immunoprecipitation and sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed no correlation between the pattern of antigens recognized and resistance status. As with the ELISA assay, an anamnestic response was detected after vaccination, while the amount of antibody present declined markedly with increasing time after individual immunizations.

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Differences in the rate of hepatosplenomegaly due to Schistosoma mansoni infection between two areas in Machakos District, Kenya.

The relationship between intensity of Schistosoma mansoni infection and the degree of related morbidity was suspected to differ locally within the Machakos district of Kenya. To test this possibility, prevalences of hepatomegaly and splenomegaly among 1483 school children were compared between 2 areas, Kangundo and Kambu, within this district. These areas, which were similar in many geographical and economic respects and populated by the same tribe (Akamba), had comparable levels of S. mansoni infection and no S. haematobium infection. A relationship was observed between the prevalence of hepatomegaly and intensity of S. mansoni infection, which showed no consistent difference between the 2 areas. In contrast, a relationship between the prevalence of splenomegaly and intensity of S. mansoni infection was observed only in the Kambu schools, and not in the Kangundo schools where the overall prevalence of splenomegaly was much lower. It was possible that part of the splenomegaly observed in Kambu was due to malaria. However, the observation that malaria and schistosomiasis in 2 Kambu schools were not positively correlated allowed approximations to be made of the relative contributions of each to the prevalence of splenomegaly. It was concluded that, in a school close to the river that formed the main transmission site of S. mansoni, schistosomiasis-related hepatosplenomegaly was present in at least 17% of children. The reason for the high prevalence in Kambu of hepatosplenic schistosomiasis remains uncertain, but it could include a synergistic interaction of schistosome infection with malaria.

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Nutritional status of children with schistosomiasis mansoni in two different areas of Machakos District, Kenya.

A possible association between nutritional status and Schistosoma mansoni infection or morbidity was investigated by comparing anthropometric indices among 362 children from 3 primary schools in Machakos District, Kenya. Matithini was a prosperous school in an area (Kangundo) of moderate intensity of schistosome infection but low associated morbidity. A second area (Kambu) showed more severe schistosome-associated morbidity: in this area, Kitengei school was prosperous and with high intensities of schistosome infection, while Misuuni school was less prosperous and with low intensities of infection. Nutritional status was assessed by measurement and appropriate standardization of height, weight and skinfold thickness and by questionnaires concerning diet. Children in Kangundo were better nourished than those in Kambu. Within Kambu, children from Misuuni showed low mean skinfold thickness and low mean weight-for-height ('wasting'): this was associated with a lack of dietary variety and of intake of animal products. In contrast, those from Kitengei showed low mean height-for-age ('stunting'). The relationship between intensity of schistosome infection and nutritional indices, although significant, was complex and not readily interpretable. However, intensity of infection was also correlated with hepatomegaly, which was more clearly related to nutritional status. Depending on the school, children with hepatomegaly were significantly more stunted and/or wasted than those without, and had less variety in their diet. Possible reasons for the observed associations are discussed and, of various possibilities, the hypothesis is suggested that schistosome-associated morbidity leads to a subsequent nutritional defect. This hypothesis can now be tested by appropriate intervention studies.

Adolescent↗
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Seroepidemiology and serodiagnosis of schistosomiasis in Kenya using crude and purified egg antigens of Schistosoma mansoni in ELISA.

The performance of antibody detection for the diagnosis of schistosomiasis has been evaluated in Kenya. Approximately 1500 blood samples from 3 areas with endemic schistosomiasis (Schistosoma mansoni only, S. haematobium only, and a mixed infection area), and from a non-endemic control area, were tested for their antibody reactivity in an enzyme-linked immunosorbent assay (ELISA). The results were compared with infection status determined by parasitological examination. Two test antigens were used: unfractionated S. mansoni egg homogenate (SEA), and CEF6, a previously described, partially purified fraction of SEA containing 2 cationic antigens. The antigens prepared from eggs of Kenya and Puerto Rico S. mansoni isolates gave very similar results. Bloods from patients with S. haematobium infection cross-reacted significantly with the two S. mansoni antigen preparations, but reactivity against CEF6 appeared more specifically indicative of S. mansoni infection. Of 254 blood samples from schoolchildren in the non-endemic area, 100% gave ELISA optical density readings at 492 nm (OD492) < 0.20 against SEA, and 98% were < 0.20 against CEF6. With 887 blood samples from subjects of all ages in the area endemic for S. mansoni alone, using an ELISA OD492 cut-off point of 0.20, SEA and CEF6 had sensitivities of 94% and 97% respectively, and specificities of 64% and 59% respectively. Increasing the OD492 cut-off value reduced the sensitivity and increased the specificity of both test antigens. Specificity of both antigens was poor with samples from 234 children in an area endemic for both S. mansoni and S. haematobium (< 20% for both antigens at an OD492 cut-off value of 0.20).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
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Preliminary study of urinary schistosomiasis in a village in the delta of the Senegal river basin, Senegal.

Three years after the first cases of urinary schistosomiasis infection were reported in the village of Mbodiene, Senegal, Schistosoma haematobium eggs were found in 87% of the inhabitants of this village; 30% were heavily infected (> 50 eggs per 10 mL urine). The prevalence of infection was very high in all age groups, but children showed more intense infections. No difference between sexes was found. In the special situation of a very high prevalence, test strips for proteinuria and haematuria are not very useful for the individual diagnosis of S. haematobium infection. Six and 12 weeks after treatment with a single dose of praziquantel (40 mg/kg), S. haematobium eggs were found in 25% and 30% of the treated subjects, respectively. Bulinus globosus was identified as intermediate host, but other snail vectors may also play a role. S. mansoni eggs were found in 1% of the population. Both S. haematobium and S. mansoni are spreading in the delta of the Senegal river.

Adolescent↗
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Efficacy and side effects of praziquantel treatment in a highly endemic Schistosoma mansoni focus at Lake Albert, Uganda.

The aim of the study was to assess the efficacy and side effects following single and repeated (6 weeks apart) praziquantel treatment (40 mg/kg) in a Schistosoma mansoni-endemic focus with long-standing transmission at Lake Albert in Uganda between December 1996 and January 1997. The results were based on 482 individuals, randomly representing all age and both gender groups. The cure rate following the first and second treatments was 41.9% and 69.1%, respectively. The cure rate was higher in adults than in children, irrespective of intensity of infection. In addition, the cure rate declined markedly with increasing intensity of infection. The reduction in intensity of infection was marked, being 97.7% and 99.6% after the first and second treatments, respectively. A pre- and post-treatment symptom questionnaire revealed a broad range of side effects, including abdominal pain and diarrhoea. However, no serious or long-lasting complications affecting compliance were observed. The marked reductions in faecal egg excretion and the acceptable level of side effects point to a single praziquantel treatment (40mg/kg) as the strategy of choice in such a highly endemic S. mansoni focus.

Adolescent↗
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Schistosomiasis mansoni in Kenya: relationship between infection and anaemia in schoolchildren at the community level.

Haematological surveys were carried out in 3 schools in 2 areas where Schistosoma mansoni is endemic in Machakos District, Kenya, before and after a treatment campaign using praziquantel. Earlier clinical impressions of differences in the levels of anaemia between the 2 areas were not confirmed. Although individual haemoglobin levels and haematocrits often fell below international norms, significant anaemia with abnormal red blood cell morphology was rare (< 5%), but varied between schools. Altitude could have accounted for some of these differences, but other factors, including diet and parasitism, were involved. Anaemia was associated with splenomegaly and, to a lesser extent, hepatosplenomegaly. Epidemic malaria (mainly Plasmodium falciparum) appeared to be the main cause of parasite-induced anaemia. There was no significant association with the scarce hookworm infections (mainly Necator americanus); nor did the much commoner S. mansoni cause severe anaemia at the community level, but haemoglobin levels dropped as its intensity increased. Treatment with praziquantel eliminated this trend except in a few subjects with splenomegaly alone (probably due to malaria) or with schistosomal hepatosplenic disease. Possible pathogenic mechanisms are reviewed, including the consumption of red blood cells by adult schistosomes as a possible cause of anaemia.

Adolescent↗
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Current concepts of snail control.

Schistosomiasis control was impossible without effective tools. Synthetic molluscicides developed in the 1950s spearheaded community level control. Snail eradication proved impossible but repeated mollusciciding to manage natural snail populations could eliminate transmission. Escalating costs, logistical complexity, its labour-intensive nature and possible environmental effects caused some concern. The arrival of safe, effective, single-dose drugs in the 1970s offered an apparently better alternative but experience revealed the need for repeated treatments to minimise reinfection in programmes relying on drugs alone. Combining treatment with mollusciciding was more successful, but broke down if mollusciciding was withdrawn to save money. The provision of sanitation and safe water to prevent transmission is too expensive in poor rural areas where schistosomiasis is endemic; rendering ineffective public health education linked to primary health care. In the tropics, moreover, children (the key group in maintaining transmission) will always play in water. Large scale destruction of natural snail habitats remains impossibly expensive (although proper design could render many new man-made habitats unsuitable for snails). Neither biological control agents nor plant molluscicides have proved satisfactory alternatives to synthetic molluscicides. Biologists can develop effective strategies for using synthetic molluscicides in different epidemiological situations if only, like drugs, their price can be reduced.

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Immuno-epidemiology of Schistosoma mansoni infections in a recently exposed community in Senegal.

Schistosoma mansoni was introduced in the Senegal basin around 1988, due to man-made ecological changes. Since 1991, we investigate a recent but very intense focus, Ndombo, a village near the city of Richard Toll where the outbreak was first described. Four cohorts, each a random sample (+/- 400 subjects each) from this community, were examined and followed up after treatment, starting at 8 month intervals over a 2-year period. Each cohort is examined parasitologically (Kato-Katz), clinically, serologically (circulating antigen and antibody profiles); treated with praziquantel 40 mg/kg; followed up 6-10 weeks, one and two years after treatment; and monitored for water contact patterns and local snail densities. In the first cohort, the prevalence was 91%, with a mean egg count of 663 epg. Prevalences are near 100% in all age groups, but egg counts decline strongly in adults. Antigen detection in serum and urine confirmed that the egg counts genuinely reflect variations of worm burdens, not e.g. of worm fecundity. This is surprising, as in this focus acquired immunity in adults should not have yet developed according to current hypothesis. The antigen detection assays (CAA/CCA) showed high sensitivity and quantitative power, and promising perspectives as a research tool and possibly as a method for non-invasive diagnosis and screening in urine. Epidemiological in subsequent cohorts were highly similar, although seasonal variations were observed possibly due to transmission fluctuations. Anti-AWA and anti-SEA IgE levels increased with age, while IgG4 peaked in the age-group 10 years and correlated well with egg counts.(ABSTRACT TRUNCATED AT 250 WORDS)

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