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Biomedical subjects

A Fenwick

Publications and source records attributed to A Fenwick.

At least 37 records · Page 2Linked to original sources
PubMed1985

Snails and aquatic vegetation in Gezira irrigation canals.

All 38 minor canals in a limited area of the Gezira Irrigated Area were surveyed four times over a 2-year period to determine the aquatic and semi-aquatic vegetation types found and their distribution. A more detailed 2-year study of the correlation between snail density and aquatic vegetation was carried out in 18 of these canals. A total of 22 different species of weed were recorded, with floating and submerged weeds being more widespread and dense in the clear, slow-moving water at the end of the irrigation season in March/April, than in the turbid flood waters in October. The schistosome vector snails Biomphalaria pfeifferi and Bulinus truncatus were found in conjunction with aquatic weeds and B. pfeifferi in particular increased in numbers as weed growth continued. In the second season of the study when mechanical weed clearing and regular focal mollusciciding was being carried out there was a noticeable reduction in weed density but repopulation was rapid. Snail numbers were reduced by mollusciciding and/or weed clearance in four canals, but outside the focal target canal stretches the weed clearance alone did not substantially reduce the snail populations.

Agriculture↗
PubMed1983

A field trial using praziquantel (BiltricideR) to treat Schistosoma mansoni and Schistosoma haematobium infection in Gezira, Sudan.

A field trial was conducted in the Gezira, Sudan, to evaluate the acceptability and efficacy of praziquantel, a new schistosomicide. In one Arab village 350 patients with Schistosoma mansoni were randomly assigned to two treatment groups and given 1 X 40 mg kg-1 (Group A) or 2 X 20 mg kg-1 given four to six hours apart (Group B). In two small settlements (camps) 2 km distant from the Arab village 38 patients with S. mansoni and 43 with concurrent S. mansoni and S. haematobium infections were given 1 X 40 mg kg-1. Side effects were mild and limited to the first 24 hours after treatment. The main complaints were abdominal pain, diarrhoea, urticaria and/or vomiting and were most common in the camp residents (79%) with 60% of Group A and 45% of Group B having one or more side effects. One month after treatment 'cure' rates were: Camps 63%, Group A 84% and Group B 96%, and the reduction in egg output was over 95%. After 12 months re-infection was greater in the camps. As there was no significant difference in the egg output reduction between the two treatment regimes, praziquantel is recommended for mass chemotherapy in Gezira at the logistically simpler regimen of 1 X 40 mg kg-1.

Adolescent↗
PubMed1983

Marking snails with nail varnish as a field experimental technique.

The use of nail varnish to mark snails for release and recapture in aquatic habitats in the Gezira Irrigation Canals has been evaluated. The nail varnish withstood immersion in canal water and adhered to the snail shell. The recovery of marked snails from a backwater site in a slow moving canal was satisfactory and indicated the usefulness of the technique in predicting changing patterns of immigration and emigration of snails. The method may also indicate ecological changes which affect the stability and mobility of snail populations and yield data on growth rates and longevity.

Animal Identification Systems↗
PubMed1981

The role of field irrigation canals in the transmission of Schistosoma mansoni in the Gezira Scheme, Sudan.

This study was carried out to determine the importance of small field irrigation canals (abu eshreens)-of which there are over 22 000 in the Gezira Scheme- in the transmission of schistosomiasis. The observations were made during a 12-month period, November 1976-November 1977. The results indicated that during the 4-year crop rotation the abu eshreens supported snail populations in only two seasons, when they were irrigating crops of either, cotton or groundnuts. Thus, when agricultural labourers built temporary dwellings on the abu eshreen banks during these periods, the probability of finding infected snails was high. The maximum risk periods occurred during vegetable harvesting (including groundnuts) (October-December) and in the cotton picking season (January-April). Certain special situations lead to some abu eshreens playing an even greater and more predictable role in transmission. These occur when abu eshreens: (a) irrigate eucalyptus or fruit trees; (b) irrigate a block inspector's garden; or (c) are situated very close to permanent villages. Possible control measures to reduce the transmission potential of abu eshreens are discussed. These include improved maintenance and the use of either focally sprayed or slow-release molluscicides.

Agriculture↗
PubMed1981

Human excretion behaviour in a schistosomiasis endemic area of the Geizira, Sudan.

A 12-month study of the excretory behaviour of resident and migrant labourers in Gezira, Sudan, was undertaken to contribute base-line information towards the development of a new control strategy. Of 398 observed acts of excretion 70% of urinations and 93% of defaecations occurred in sites far removed from any water body. After excretion only 31% people washed themselves (and only 7.1% actually washed their genital region directly into a water body). People excreting far from water were as likely to wash afterwards as those excreting near a water body. This finding contradicted previous expectations based on the hygienic precepts of Islam. The results show that privacy is a more important consideration than proximity of water in the selection of a site for excretion, and suggest that there is only limited regular contamination by S. mansoni eggs under the observed conditions.

Adolescent↗
PubMed1976

A large-scale snail control trial with trifenmorph in the Gezira irrigation scheme, Sudan.

A large-scale field trial was carried out during December 1973 to assess the effect of trifenmorph on Bulinus truncatus and Biomphalaria pfeifferi in 379 000 feddans ( approximately 159 000 ha) of the Gezira irrigation system in the Sudan. The commercial formulation used (Frescon) is an emulsifiable concentrate containing 16.5% trifenmorph. Five dispensers were used to add the commercial product to the water continuously for 7.5 days; 18 121 litres were used to treat 28.4 million m(3) of water. In addition, each minor canal was hand-sprayed from the tail to 300 m upstream of the last open field outlet pipe; 360 litres of the commercial formulation were used for this operation.A minimum concentration of 0.035 mg trifenmorph per litre of water was produced at the head of each minor canal. The use of caged snails showed that a concentration as low as 0.015 mg/litre was sufficient to produce 100% mortality in B. truncatus in 7.5 days; this is equivalent to a concentration x time product of 0.12 mg/litre days.

Animals↗
PubMed1975

Aerial application of N-trityl morpholine to irrigation canals in Sudan.

Using a crop-spraying aircraft modified to give a coarse spray, the feasibility of aerial application of the molluscicide N-trityl morpholine to minor canals on the Gezira has been proved. In January 1973, seven canals were sprayed at dosages of 0-1 p.p.m., 0-2 p.p.m., 0-5 p.p.m. and 1-0 p.p.m. Chemical analysis indicated that about 70% of the chemical was present in the water 5-15 hours after the spray, and snail exposure to the sprayed canals indicated that all dosages applied were lethal to Biomphalaria snails. Bulinus snails, which are less susceptible to the molluscicide, were killed only by the 0-5 p.p.m. and 1-0 p.p.m. dosages. Sampling of the natural snail populations of the canals confirmed these results. In March 1973, an area of 464 sq km was treated by drip-feed of 0-1 p.p.m. N-trityl morpholine to kill snails in the main and major canals, and then by aerial spraying 56 of the 58 minor canals in the area. Despite the high winds which disrupted the spray timetable, the canals were successfully treated in 9-5 hours flying-time within seven days. A very high initial snail kill was indicated by both caged snail exposure and natural snail population sampling. However, in excellent snail breeding conditions the area was reinfested with snails within two months. The cost of the application was only 5% of the chemical cost, and aerial spraying in March and May will almost certainly be incorporated in an annual snail control programme.

Aircraft↗
PubMed1972

Effect of a control programme on transmission of Schistosoma mansoni on an irrigated estate in Tanzania.

Three methods were used to measure the level of transmission of infections of Schistosoma mansoni on an irrigated sugar estate in northern Tanzania. The studies were carried out over a period of 3 years, during a programme for the control of the host snail Biomphalaria pfeifferi. During the second and third years a mass diagnosis and treatment campaign against the infection was also carried out. Examinations for infection were made in newly employed subjects on arrival and after 6 and 12 months. Two studies were made in young children at an interval of 18 months, to determine age prevalence curves. In the third method, subjects were examined for infection 18 months after being found free from infection in a previous survey. Results are compared with data recorded in a previous study, made before snail control was commenced. The results suggest that the control programme has led to a great reduction in the incidence of S. mansoni on the estate.

Agricultural Workers' Diseases↗
PubMed1972

The effect of Schistosoma mansoni infection of the productivity of cane cutters on a sugar estate in Tanzania.

In an attempt to justify future snail control on an irrigated sugar estate in Tanzania, the effects of Schistosoma mansoni infection on the productivity of apparently healthy cane cutters were investigated. The bonus earnings of cane cutters who were found to be infected with S. mansoni were compared, retrospectively, with earnings of uninfected cane cutters during the years 1968-69. For one 6-month period a more detailed study was made to correlate bonus earnings with actual output in tons of cane cut. It was found that in the four 6-month periods the mean bonus earnings of the uninfected cane cutters exceeded the mean bonus earnings of the infected men by 11.0%, 11.4%, 6.0%, and 13.7%, respectively. In all except the third period these differences were statistically significant. After treatment for S. mansoni infection, the workers were able to improve their earnings relative to both infected and uninfected workers. In a more detailed study of some of the workers during the third 6-month period, it was discovered that a 4% difference in bonus earnings represented a 1% difference in output. Taking into account the variations of bonus earnings it was estimated that the overall difference in productivity between infected and uninfected workers was 3-5%.

Agricultural Workers' Diseases↗
PubMed1972

The costs and a cost-benefit analysis of an S. mansoni control programme on an irrigated sugar estate in northern Tanzania.

On a sugar estate in northern Tanzania, an integrated control programme against Schistosoma mansoni was carried out during the three years 1968-70 inclusive. The costs of that programme are defined, the costs of future snail control in the same area are estimated, and an attempt is made to evaluate the cost-benefit ratio of schistosomiasis control in the estate. The total expenditure on snail control was US $23 538, of which US $17 371 was spent on molluscicides and US $5 135 on labour. This represents an annual expenditure of approximately US $1.31 per estate resident. In the mass diagnosis and treatment campaign the main items in the total expenditure of US $37 043 were labour (US $13 724), drugs (US $4 218), hospital charges (US $8 262), and lost working days (US $8 760). It is estimated that the recurrent annual expenditure necessary to keep S. mansoni at a low level in the future would be US $7 714 on snail control and US $1 832 on detecting and treating new cases; however, the institution of a snail control programme would reduce the need for chemotherapy and would result in recurrent annual savings of US $7 448. In addition, it was estimated from a productivity study that savings of about US $14 000 per year could result if treatment of infected workers raised productivity by 5%. The goodwill that resulted from the protection of wives and children against schistosomiasis would be a further benefit. When all factors are taken into account, snail control appears to be a feasible economic proposition.

Agricultural Workers' Diseases↗
PubMed1972

The effect of a control programme against Schistosoma mansoni on the prevalence and intensity of infection on an irrigated sugar estate in northern Tanzania.

On an irrigated sugar estate in northern Tanzania a control programme against Schistosoma mansoni was carried out during 1968-70. Through the routine use of molluscicides, the population of Biomphalaria pfeifferi snails was kept at a greatly reduced level. Concurrently a mass campaign was carried out to detect residents who were infected with S. mansoni so that they might be treated. The effect of these measures on the overall prevalence of the disease was measured by random studies before and after the mass diagnosis and treatment. The techniques used for mass diagnosis, for treatment, and for the prevalence studies are described, and the results of the control programme are presented and discussed. In the mass diagnosis campaign over 90% of the population were examined and 2 286 courses of treatment were administered to 1 922 persons. The combination of chemotherapy and snail control led to a significant reduction in the number of S. mansoni. infections. In field workers the prevalence was reduced from 59% in early 1969 to 31% in late 1970. In nonfield workers the reduction was from 36% to 15% and in the wives of employees from 28% to 14%. The main reasons why the prevalence was not reduced further were considered to be the failure of the drugs used to effect a complete parasitological cure and the inability of the mass diagnosis campaign to detect light infections. It was estimated that the overall reduction in the number of eggs released into the community as a result of the control programme was about 85%.

Adult↗
PubMed1970

Attempts to eradicate snails from impounded water by the use of N-tritylmorpholine.

This paper records attempts to overcome the problems of using a powerful but non-ovicidal molluscicide (N-tritylmorpholine) in eradicating snails from a dam by treating the water twice in 14 days. The first treatment was aimed at the existing snail population and the second at snails hatched from eggs that survived the first application. At each treatment an over-all concentration of 0.25 ppm was applied by spraying a 16% emulsifiable concentrate of N-tritylmorpholine from shore and boat to the water surface. The snails, Biomphalaria pfeifferi and Lymnaea natalensis, were first seen again 8 weeks from the start of the application in the region of 2 inlet furrows. When pretreatment levels of snails were again reached, a second double treatment was applied, again at an over-all concentration of 0.25 ppm but using a 50% paste formulation applied over 3 days for 3 hours per day to the inlet furrows. The snail kill was again 100% as measured by the sampling technique used but again young snails appeared 9 weeks later. The author concludes that single treatments at 5-week intervals probably represent the best means of control with N-tritylmorpholine.

Animals↗