Vector control: methods for use by individuals and communities

by Jan A. Rozendaal, World Health Organization, 1997. pound85.00 (xii +412 pages) ISBN 92 4 154494 5.

Schistosomiasis in newly reclaimed areas in Egypt. 2--Patterns of transmission

The distribution, abundance and seasonality of infected Biomphalaria alexandrina and Bulinus truncatus were studied for 2 years (1992-1994) in two newly reclaimed areas, namely El Manayef and El-Morra areas located on both sides of Suez Canal near Ismailia City. The results confirm the occurrence of transmission of both Schistosoma mansoni and S. haematobium since infected snails of both species were recovered in these areas. This consequently proves that reclamation of parts of the desert utilizing Nile water had led to spread of schistosomiasis to these areas. Analysis of the data shows that the infected snails, especially B. alexandrina, were found clustered in a relatively few numbers of transmission sites and furthermore the greater majority of these sites were found located within a less number of transmission foci. This pattern of focality is clearly demonstrated by Geographical Information System (GIS) produced maps. Infected B. alexandrina snails fluctuated seasonally showing 2 peaks, a minor peak in August and a higher one in November. Only one peak of infected B. truncatus was recognized in July.

Schistosomiasis in newly reclaimed areas in Egypt. 1-distribution and population seasonal fluctuation of intermediate host snails

Two newly reclaimed areas located west & east of Suez Canal, namely El Manayef area and El Morra area, were studied for patterns of distribution and population seasonal fluctuation of Biomphalaria alexandrina and Bulinus truncatus, the intermediate host snails of Schistosoma mansoni and S. haematobium, respectively. In this study Geographic Information System (GIS) techniques were utilized for producing maps and analyzing the results. Habitats of the two vector snail species were categorized into suitability levels depending on the frequency with which snails were collected over a 12 months period. Data obtained from the most suitable habitats were only used for studying the seasonal fluctuation of snail population. The results showed that both study areas were almost similar in major physico-chemical parameters. However, oxygen content in canals was higher than in drains and conductivity was higher in drains than in canals. As regards snail distribution and density, most snails of both considered species were clustering in much fewer numbers of sites, more pronouncedly in the case of Biomphalaria than Bulinus. Population density of snails was significantly higher in El-Manayef area than in El-Morra area and in canals than in drains. Both species exhibited 2 population peaks/year, the peaks of Biomphalaria were in March-April & August in both study areas, while for Bulinus these peaks occurred in March-May and August in El-Manayef area and in May and March, respectively, in El-Morra area.

Community based studies on childhood mortality in a malaria holoendemic area on the Tanzanian coast

Demographic surveillance of children under 5 years of age was undertaken over a 2 year period in a rural area of coastal Tanzania where holoendemic malaria conditions exist. The mean annual entomological innoculation rate (EIR) during the period under study was 234 infective bites per person. There were 192 deaths in children and 1130 live births during the 2 years. Of these, 148 were infant deaths giving an infant mortality rate of 131/1000 live births (95% CI 101, 154). There were 44 deaths in children 1-4 years of age and the overall child mortality rate was 10/1000 (95% CI 6.1, 14.3). Using verbal autopsy questionnaires, 56% of the deaths under 4 years were tentatively attributed to malaria.

Cercariometry in the study of Schistosoma mansoni transmission in Egypt

The recovery of Schistosoma mansoni cercariae was studied in experimental ditches and natural irrigation canals using a continuous operating centrifuge and a water suction sampling technique. Recovery of cercariae from static water in the ditches where caged infected Biomphalaria alexandrina snails were placed showed that cercariae recovered were more with increase of infected snails and decrease of water volume and were most abundant in the proximity of the snails which produced them. Shade or heavy vegetation cover reduced the recovery of cercariae. Results suggest also strong seasonal differences in diurnal patterns of cercarial recovery. An early morning peak with large number of cercariae occurred during hot weather while in cooler seasons cercariae appear in fewer numbers but persist for most of the day. Obtained information, beside contributing to knowledge of cercarial behaviour, should help to optimize taking water sample and consequently to increase efficiency of cercariometry techniques. In the natural irrigation system, cercariometry was significantly more sensitive in detecting transmission foci than snail sampling by a dip net.

Changes in weight gain and anaemia attributable to malaria in Tanzanian children living under holoendemic conditions

We investigated the effect of Plasmodium falciparum malaria on weight gain and haematocrit in Tanzanian children aged 6-40 months following a malaria control scheme which combined insecticide-impregnated bed nets with chloroquine chemotherapy on demand. Data from 7 villages (3 intervention and 4 control) were collected before, and one year after, the implementation of the programme. Initially, 82% of the children were parasitaemic, 78% were anaemic (i.e., packed cell volume < 33%) and 38% were underweight (i.e., 2 standard deviations below their weight-for-age Z score). One year after implementation of the programme, children not protected by the bed nets grew 286 g less (95% confidence interval [CI] 171-402 g) in a 5 months period and were twice as likely to be anaemic (95% CI 1.4-2.7) than were children not using impregnated bed nets. Our results indicated that, under holoendemic conditions, P. falciparum infection has a marked effect on both weight gain and anaemia.

Prevention of snail miracidia interactions using Phytolacca dodecandra (L'Herit) (endod) as a miracidiacide: an alternative approach to the focal control of schistosomiasis

The effect of endod berry extract against schistosome miracidia has been tested to determine the sensitivity of these organisms to the molluscicide and to see whether miracidia subjected to sublethal doses of the toxicant will be able to infect their specific host snails. Short contact (30 min) LC50 of endod extract with miracidia of Schistosoma mansoni was 8.2 parts per million (p.p.m.) (95% CL 5-13). However, exposure of S. haematobium to sublethal doses of 3 p.p.m. for 30 min or overnight in open air ponds reduced their infectivity 3.5-5.6-fold when compared with controls. It is suggested that the toxicant could be used in low doses at transmission foci to reduce schistosome infection in snails. This could be done by using a controlled release system to apply the toxicant material at such foci where transmission is likely to occur.

Filtration, centrifugation and mouse exposure for the detection of schistosome cercariae in water

Three methods for detection of schistosome cercariae in water were studied under laboratory and simulated field conditions in Egypt. Water samples tested by filtration and centrifugation quantitatively reflected the density of cercariae in moderately turbid canal water (30 Nephelometry Turbidity Unites, NTU). When tested in waters of increasing turbidity, the centrifuge gave more consistent results than the filtration system. The centrifugation technique was more efficient in processing the water samples and took almost half the time of filtration. Mouse exposure was useful in detecting cercariae, but was not quantitative. However, there was a significant improvement in worm recovery when mice were more close together in the floatation device. Mouse exposure was also expensive and cumbersome to use. It appears from the present results that the technique of choice for further cercariometric work under Egyptian conditions may be centrifugation.

Changes in malaria associated morbidity in children using insecticide treated mosquito nets in the Bagamoyo district of coastal Tanzania

A community based malaria control intervention using insecticide treated mosquito nets (IMN) has been implemented and tested in 13 villages of the Yombo Division, Bagamoyo District in the Coastal Region, Tanzania, an area holoendemic for P. falciparum malaria. Following extensive sociological research into local perceptions of malaria, the programme was implemented. It wa decided by consensus that village mosquito net committees would be the appropriate local level implementors. These were formed and provided with IMN's which were sold to villagers at subsidised cost. The income was invested for use by the committees for sustaining the activity. Use patterns were determined and high coverages were obtained among the community, particularly after promotions e.g. plays, school meetings etc. Malaria morbidity was measured among children 6-40 months of age in 7 index villages prior to the intervention in 1992 and in a comparison study between 3 villages using nets and 4 villages not using nets in 1993. Examination of the 7 cohorts of children was done from June to October each year covering the period of most severe transmission. The children using nets showed marked improvement in several malariometric indices. Following an initial clearance of parasitaemia with sulphadoxine/pyrimethamine, when compared with unprotected children, those with nets were slower to become re-infected (Relative Risk 0.45), had lower parasitaemias and showed marked improvement in anaemia (RR 0.47). Use of IMN's produced a 54% reduction in the prevalence of anaemia among young children. Attempts are being made to ensure that the programme is locally sustained.

Anaemia and Plasmodium falciparum infections among young children in an holoendemic area, Bagamoyo, Tanzania

Although the aetiology of anaemia in tropical areas is multifactorial, Plasmodium falciparum malaria is commonly associated with anaemia in children living in holoendemic malaria areas. Such an association was examined in a population based study of 338 children 6 to 40 months of age living in the Bagamoyo area of Tanzania. Stepwise regression analysis showed that fever and parasitaemia were effective in predicting anaemia and that the anaemic condition was age dependent. The majority of the children were iron deficient, followed by normochromic macrocytic anaemias. There was strong evidence in this age group that the anaemia was associated with malaria and not geohelminth infection. The importance of malaria and anaemia as a cause of childhood morbidity in Africa is discussed. This condition has taken on new significance with the realization that blood transfusions commonly used to treat severe anaemia are a major vehicle for Human Immunodeficiency Virus (HIV) transmission.

Gastrointestinal dysfunction and disaccharide intolerance in children infected with human immunodeficiency virus

Because gastrointestinal dysfunction is a major problem in children with human immunodeficiency virus (HIV) infection, we utilized breath hydrogen measurements to determine the relationship between disaccharide malabsorption and gastrointestinal dysfunction in HIV-infected children. We found a strong association between lactose intolerance and persistent diarrheal disease in this population (p less than 0.007, Mann-Whitney U test). We also found evidence of sucrose malabsorption and persistent diarrheal disease in three of the children. Extensive microbiologic evaluations failed to reveal an etiologic agent related to the occurrence of gastrointestinal symptoms. Our findings indicate that disaccharide intolerance is a common occurrence in HIV-infected children with persistent diarrheal disease. Careful attention to dietary intake may be required to ameliorate clinical symptoms and to maintain adequate nutrition.

Effects of improved water supply and sanitation on ascariasis, diarrhoea, dracunculiasis, hookworm infection, schistosomiasis, and trachoma

A total of 144 studies were analysed to examine the impact of improved water supply and sanitation facilities on ascariasis, diarrhoea, dracunculiasis, hookworm infection, schistosomiasis, and trachoma. These diseases were selected because they are widespread and illustrate the variety of mechanisms through which improved water and sanitation can protect people. Disease-specific median reduction levels were calculated for all studies, and separately for the more methodologically rigorous ones. For the latter studies, the median reduction in morbidity for diarrhoea, trachoma, and ascariasis induced by water supplies and/or sanitation was 26%, 27%, and 29%, respectively; the median reduction for schistosomiasis and dracunculiasis was higher, at 77% and 78%, respectively. All studies of hookworm infection were flawed apart from one, which reported a 4% reduction in incidence. For hookworm infection, ascariasis, and schistosomiasis, the reduction in disease severity, as measured in egg counts, was greater than that in incidence or prevalence. Child mortality fell by 55%, which suggests that water and sanitation have a substantial impact on child survival. Water for personal and domestic hygiene was important in reducing the rates of ascariasis, diarrhoea, schistosomiasis, and trachoma. Sanitation facilities decreased diarrhoea morbidity and mortality and the severity of hookworm infection. Better water quality reduced the incidence of dracunculiasis, but its role in diarrhoeal disease control was less important than that of sanitation and hygiene.