D.M. Forsyth

Bio: D.M. Forsyth is an academic researcher. The author has contributed to research in topics: Schistosomiasis & Population. The author has an hindex of 2, co-authored 2 publications receiving 110 citations.

Urological complications of endemic schistosomiasis in school-children: Part 1. Usagara School☆

Abstract: An account is given of the effects produced by endemic urinary schistosomiasis upon the children attending different schools in the Mwanza Region of Tanzania. At Usagara, where the incidence of infection rises to become 100% in the children of standard 4, up to 37% of the standard 6 pupils have irreversible lesions of the urinary tract. Nearby, where infection is less prevalent, there is a coincident decrease in lesions of the urinary tract. It is firmly established that the lesions—calcified bladder, deformity of the ureter, and hydronephrosis—are due to schistosomiasis, and that their prevalence is related to the weight of infection. Lesions occur even in the youngest examined, aged 6, but the prevalence of deformity of the ureter probably increases with age. There is a very marked and significant difference between boys and girls, hydronephrosis being much rarer in girls, but other lesions are equally common. On the basis of urological disease only, endemic urinary schistosomiasis has a considerable adverse effect on the economy of a country such as Tanzania where foci of disease are widespread. Pulmonary and systemic hypertension were not seen as complications of urinary schistosomiasis in the children studied, but pathological blood urea levels occur.

Urological complications of endemic schistosomiasis in schoolchildren Part 2. Donge school, Zanzibar

Abstract: Stools and urine from all 517 pupils in Donge School, Zanzibar, were examined for schistosome eggs, those of S. haematobium being found in 50·8% of 315 boys and 36·6% of 202 girls. Intravenous pyelography was carried out on all boys, and on all those girls found to be voiding schistosome eggs. Data collected from 516 pupils included a precise location of normal residence, from which spot maps were prepared showing the origins of positive and negative cases. The primary object of the survey, to relate infection and its pathological effects to the epidemiological conditions at the source, was thereby attained. Infection was found to be highly focal, even in this apparently homogeneous population living within a short radius of one school. In one set of 9 neighbouring hamlets, 113 of 115 children were positive; in the remaining 27 hamlets, 29·9% were positive. These are termed the “bad” and “good” areas. In the bad areas infections were not only frequent, but also heavy, 68% of positives excreting more than 500 eggs per 10 ml. of midday urine. There was a marked decline in egg output with advancing age and it would seem that heavy infections were almost universal at the age of entry to school, being later partially overcome. Pathological lesions were found in the pyelograms of 46 of the 115, there being 21 calcified bladders, 45 deformed ureters and 20 hydronephroses. After standardization for age, the prevalence of calcified bladder and deformed ureter was almost identical in the two sexes, hydronephrosis being more common (though without statistical significance) in boys. All these conditions were established early and there was no difference in prevalence between young and old. In the good areas infections were mainly light, only 22% of positive urines having more than 500 eggs in 10 ml., and 32% having 32 or less. After age standardization there was no sex difference. Pathological lesions were found in the urograms of 17% of positive children. The sex distribution was the same as in the bad area, but age distribution differed. Calcified bladder was equally prevalent in positives under 14 (4·2%) and 14 or older (4·9%); the prevalence of deformed ureter increased markedly from 4·2% of the younger positives to 16·4% of the older, and hydronephrosis from 2·1% to 13·1%. This contrast with the bad areas is thought to be connected with the differing intensity of infection in the two areas. Hydronephrosis is a sequel, not a complication, presumably related to damage to the ureter or its outlet. However, although there is statistical correlation in different areas, no individual correlation between ureteric lesions and hydronephrosis was found. No evidence of any cardiovascular complication could be discovered. This, together with previous evidence, indicates that cor pulmonale does not exist in East African school-children. Preliminary follow-up studies of a few children show no evidence of reversion of pathological conditions to normal after apparent cure by treatment. The difference between bad and good areas is dependent on the limitation of available water in the former to a few virtually stagnant streams or pools, in which abundant Bulinus (Physopsis) nasulus and B. (Ph.) globosus maintain transmission, whereas elsewhere the availability of wells or running streams, or even a piped supply, makes use of pool water unnecessary.

Resistance to Schistosoma mansoni in Humans: Influence of the IgE/IgG4 Balance and IgG2 in Immunity to Reinfection after Chemotherapy

Abstract: The hypothesis of an association between human resistance to reinfection by the parasite Schistosoma mansoni and anti-larval immunoglobulin isotypes was tested by logistic regression in the presence of the explicative variables water contact, age, and sex. Of the seven isotypes tested (IgM, IgG1, IgG2, IgG3, IgG4, IgA, and IgE), only IgE, IgG4, and IgG2 showed an association (positive for IgE and negative for IgG2 and IgG4) with resistance to reinfection after chemotherapy. The opposite effects of IgE and IgG4 were undissociable in the analysis, indicating that these isotypes probably antagonize each other in protection. The negative association of IgG2 with resistance is consistent with the view that anti-carbohydrate antibodies may facilitate reinfection. Finally, epidemiologic and immunologic studies support the view that there is a progressive but slow development of acquired immunity in children and adolescents.

Epidemiology and control of human schistosomiasis in Tanzania

Abstract: In Tanzania, the first cases of schistosomiasis were reported in the early 19th century. Since then, various studies have reported prevalences of up to 100% in some areas. However, for many years, there have been no sustainable control programmes and systematic data from observational and control studies are very limited in the public domain. To cover that gap, the present article reviews the epidemiology, malacology, morbidity, and the milestones the country has made in efforts to control schistosomiasis and discusses future control approaches. The available evidence indicates that, both urinary and intestinal schistosomiasis are still highly endemic in Tanzania and cause significant morbidity.Mass drug administration using praziquantel, currently used as a key intervention measure, has not been successful in decreasing prevalence of infection. There is therefore an urgent need to revise the current approach for the successful control of the disease. Clearly, these need to be integrated control measures.

Regulation of parasite populations: A general theory of the epidemiology and control of parasitic infections

Abstract: The mechanisms by which parasite populations are regulated may be grouped into three types: regulation by the transmission process (type I), by the host population by such means as host mortality or sterile immunity (type II), and by the host individuals (type III), often by premunition and similar forms of incomplete acquired resistance The last two types are density-dependent feedback processes The concept of endemicity implies that these two types are operating The spatial arrangement of hosts and transmission patterns particularly affects type II regulation as does the distribution of parasites among hosts Highly endemic infections may sometimes have their focal variation in intensity of transmission obscured, and may show relatively separate yet contiguous transmission foci The most suitable control measures will depend on the type of parasite population regulation, and epidemiological study should include an experimental measure of the stability of the infection Types II and III of regulation here roughly correspond to the density-dependent regulation of animal ecologists, though type I may fall sometimes into this category