Efficacy of Metrifonate in a Highly Endemic Area of Urinary Schistosomiasis in Kenya

In a community in Kwale district, Kenya, selective mass chemotherapy with metrifonate caused a marked reduction in the intensity of Schistosoma haematobium infection from 46.5 to 9.4 eggs/hr and a sharp fall in prevalence of gross hematuria from 18.3% to 5.1%, although overall prevalence was reduced only slightly from 67.4% to 54%. The effect of metrifonate on cure rate and reduction of infection intensity was limited by both age and pretreatment infection intensity. Rate of improvement from gross hematuria was similar in all ages and in all classes of intensity of infection. Two doses of metrifonate reduced the prevalence of gross hematuria as much as 3 doses did, while the effect of a single dose on morbidity remains to be clarified

Epidemiological Studies on Schistosoma haematobium Infection in Coastal Area, Kenya : Cercarial Density at Water Contact Points and Identification of Species of Cercariae

ビルハルツ住血吸虫症の流行地であるケニア国クワレ地区ムワチンガ村において,住民によく利用されている水系から,特に利用頻度の高い2ケ所(Site 6,Site 19)を選び,水中のセルカリア密度を,Prentice(1984)の方法を用いて測定した。さらにセルカリアの種を同定するために,4匹ずつの未感染ハムスターを調査地の水に暴露し,約3カ月後剖検して住血吸虫の感染の有無について調べた.Site 6では,401の水からわずかに1隻のセルカリアが回収されただけで,4匹のハムスターには,いずれも住血吸虫の感染は見られなかった.これに対して,Site 19では81の水から231隻のセルカリアが検出され,また4匹のハムスターからも,合計31個体の住血吸虫成虫(雄20,雌11)が回収された.これらのハムスターの肝臓には多数の住血吸虫卵が見い出され,形態学的特徴からビルハルツ住血吸虫のものと同定された.住血吸虫症流行地のいろいろな水系の水の危険度を測定する際のセルカリオメトリーの有用性について考察した.The cercarial density in natural water was measured at two major water contact points in Mwachinga, Kwale, an endemic area of Schistosoma haematobium infection, by using the filtration technique of Prentice (1984). In addition, the sentinel animals, male golden hamsters, were immersed in water for the identification of species of schistosomes. Only one cercaria was recovered from 40 litters of water sample at one site. Neither adult worm nor egg was recovered from 4 sentinel animals which were immersed there. At the other site, 231 cercariae were detected in 8 liters of water sample. A total of 31 adult worms, 20 males and 11 females, were recovered from 4 sentinel hamsters. The eggs from the livers of hamsters were identified to be S. haematobium based on their morphological features. The practicability of cereariometry in detecting relative risk of infection in different water contact points was discussed

Epidemiological Studies on Schistosoma haematobium Infection in Coastal Area of Kenya : Diurnal fluctuation of cercarial density in natural water and measurement of the risk of infection after control by cercariometry

ビルハルツ住血吸虫症の流行地であるケニア国クワレ地区ムワチンガ村において,住民によく利用されている水系から,特に利用頻度の高い2ヶ所(Site 6, Site 19)を選び,水中セルカリア密度の日内変動をセルカリオメトリーにより測定した.測定は,メトリフォネートによる集団治療と水道水供給とを組み合わせたコントロール対策実施の前後2回にわたって行なった.(1983年11月及び1984年8月)Site 19では,コントロール対策実施前には,90リットルの水から合計567隻のセルカリアが検出され,水中のセルカリア密度は正午をピークとする日内変動を示した.コントロール対策実施後6ヶ月経た時点でも,90リットルの水から354隻のセルカリアが回収され,水中セルカリア密度は13時をピークとする日内変動を示した.このことから,Site 19では正午から午後1時にかけて感染の危険度が最も高く,早朝や夕方は低いことが考えられる.また,コントロール実施後でも、まだ感染の危険が相当残っていることが明らかとなった。一方, Site 6ではコントロール対策実施前に180リットルの水から2隻のセルカリアが検出されただけで,コントロール実施後には,セルカリアは回収されなかった。このようにもともとセルカリア密度の低い水系では,本実験で用いたセルカリオメトリーでコントロール対策が住血吸虫症の伝搬に及ぼす効果について評価することは困難と思われる.住血吸虫症コントロール対策が感染の危険度の減少に及ぼす効果を判定する際に,セルカリオメトリーを用いた場合の問題点について考察した.Cercariometry was carried out at 2 major water contact sites in an endemic area of urinary schistosomiasis, before and after the introduction of control measures against the disease. The natural water was examined for the presence of cercariae by filtration technique at one hour interval during the daytime. Before the control measures performed, at one of the sites, 567 cercariae were detected in 90 liters of water examined and the pattern of cercarial density was found to be diurnal with the highest density at noon. Six months after the implementation of control measures with a combination of treatment with metrifonate and provision of piped water, 354 cercariae were recovered from 90 liters of water examined and the pattern was also diurnal. At the another site, on the other hand, only 2 cercariae were found in 180 liters of water sample before the control and no cercariae were detected after the introduction of control measures. Evaluation of the impact of control measures on the risk of contracting the infection was discussed

Cercarial Density in the River of an Endemic Area of Schistosomiasis Haematobia in Kenya

The cercarial density in natural water and number of infected Bulinus globosus were monitored over a one-year period to identify the transmission foci in an endemic area of schistosomiasis haematobia in Kenya. Overall prevalence and intensity of infection of the study community were 59.2% and 10.9 eggs/10 ml of urine. Cercariometry was carried out on 456 occasions at 20 study sites while snail sampling was done on 465 occasions at the same sites over a one-year period. Cercariometry was exclusively done at flowing water habitats. The results showed the focality and seasonality of transmission. Cercariae were detected on 44 occasions at 11 sites. The detections were made on seven occasions at two study sites, six occasions at one site, four occasions at four sites, three occasions at one site, two occasions at two sites, and one occasion at one site. Densities of 1?4 cercariae/100 liters of water were found on 31 occasions. Five to nine cercariae/100 liters of water were found on seven occasions, 10?19 cercariae/100 liters of water were found on two occasions, and high cercarial densities greater than 20 cercariae/100 liters of water were found on four occasions. The highest count was 52 cercariae/100 liters of water. The presence of cercariae in natural water was shown to depend on the water temperature, but the intensity and duration of sunlight did not affect the presence of cercariae in water. The monthly variability of cercarial density was proportional to the number of infected snails. Cercarial density was highest in March and April, in the middle of the rainy season, whereas no cercariae were detected in cool dry season. The snail population peaked late in March, the beginning of the long rainy season, remained high for two months, and decreased rapidly late in May when heavy rain occurred. The overall infection rate of snails was 7.3% and the majority of infected snails were collected from March to May. There was no definite correlation between the presence or absence of cercariae and infected snails. Cercariae were frequently found where infected snails were absent and cercariae were sometimes absent where infected snails were present. Cercariometry and snail sampling remain quite complementary in identifying the transmission foci of schistosomiasis

Effect of mass chemotherapy and piped water on numbers of Schistosoma haematobium and prevalence in Bulinus globosus in Kwale, Kenya.

From June 1982 to May 1986 in a small village in Kwale, Kenya, we studied seasonal fluctuations in populations of Bulinus globosus, prevalence of Schistosoma haematobium infection in this snail, and effects of chemotherapy and piped water supply on infection rate of snails. In the perennially-flowing Pemba River, relatively small numbers of snails were collected; they were found only during the hot dry season (December to March). In a tributary stream, the Kadingo River, whose flow ceased at the end of both the cool and hot dry seasons, snail numbers peaked at the end of the cool dry season (October to November) and at the beginning of the hot dry season (January). Large numbers of infected snails were found in the Kadingo River from November to January (short rainy season and beginning of dry season). Selective mass chemotherapy with metrifonate and provision of piped water were begun in February and March 1984. These control measures achieved a significant reduction in the infection rate of snails (P < 0.001); the annual infection rate for the 2 years before treatment was 9.3% and 13.1%, and for the 2 years after treatment was 3.5% and 3.4%

Effect of Piped Water Supply on Human Water Contact Patterns in a Schistosoma haematobium-Endemic Area in Coast Province, Kenya

The effect of a piped water supply on human water contact in a Schistosoma haematobium-endemic area in Coast Province, Kenya was studied. After the construction of five community standpipes and one shower unit, there was a 35.1% reduction in the number of people observed using river water, a 44.1% reduction in the frequency of contact with river water, and a 25.4% reduction in the amount of contact. The frequency of river water contact per person also decreased significantly, but the amount of contact per person did not decrease. The total frequency of contact decreased significantly except for washing clothes by the river, washing utensils, and fishing. The frequency per person did not change for most of the activities and significantly increased for washing clothes. The frequency of river water contact in households with high piped water consumption showed a significant decrease compared with those with low piped water consumption. The volume of consumption of piped water was inversely proportional to the distance from the home to the community standpipe. These results indicate that in the study area, the effect of a piped water supply on river water contact behavior was heterologous while the total river water contact decreased significantly, and that the piped water had a beneficial effect on some villagers but very little effect on others

ケニア国クワレ地区のビルハルツ住血吸虫症の流行地におけるBulinus globosusとCleopatra ferrugineaの相互作用

Snail survey data collected in a small village in Kenya from April 1984 to March 1991 were used to analyze the interaction between Bulipuus globosus (intermediate host of Schistosoma haematobium) and Cleopatra ferruginea (unsusceptible snail). An inverse correlation was observed between the two snail populations. This finding leads to the suggestion that C. ferruginea has limiting effects on B. globosus population. The relative penetrative activity of S. haematobium miracidia into the two snail species was also examined. Miracidia penetrated C. ferruginea as well as B. globosus. Although selective mass-chemotherapy has been repeated every 2 years in our study area, the low infection rates in B. globosus were recorded in the year when large numbers of C. ferruginea and small numbers of B. globosus were collected. Therefore, C. ferruginea seems to diminish the transmission of S. haematobium; C. ferruginea reduce the number of S. haematobium miracidia which reach to B. globosus

Effect of communal piped water supply on pattern of water use and transmission of schistosomiasis haematobia in an endemic area of Kenya

An attempt was made to examine the long-term impact of the introduction of communal piped water supply on pattern of water use and transmission of schistosomiasis haematobia in an endemic area of Kenya. In the study area, Mtsangatamu, a control program based on repeated selective mass-chemotherapy had been carried out for 6 years from 1987 to 1993. The pre-treatment overall prevalence and intensity of infection in 1987 were 59.2% and 10.9 eggs/10 ml of urine (Muhoho et al., 1997). During the control program, the prevalence was kept at a low range of 20 to 40% (Muhoho et al., 1994). At the end of the program, in 1994, gravity-fed water supply was provided to the village. Although the water facilities were damaged by flooding in 1998, new and further expanded gravity-fed water supply facilities consisting of 7 standpipes were introduced in 2000. The follow-up survey done in 1999 revealed reduced prevalence and intensity of infection, I.e. 23.0% and 1.2 eggs/ 10 ml of urine (unpublished data). The present study was carried out in 2006, 6 years after the last mass-chemotherapy. Urine examination showed that the prevalence and intensity of infection had return to 52.2% and 7.4 eggs/10 ml, nearly the same level as the pre-treatment level. The results of our study demonstrated that, over the long-term, the gravity-fed water supply facilities had little impact on the overall prevalence and intensity of infection in this village. However, analysis of the spatial pattern of infection, observation of human water contact at the river and a questionnaire on water use shed light on the possible impact of water supply on human water contact. The younger people (5-19 years old) with easy access to the standpipes showed a lower prevalence and intensity of infection, while the relationship was not clear in other age groups. The result of the questionnaire indicated that the long distance from household to standpipe was the major factor limiting the use of the communal tap water. Most of the villagers who used piped water as the main source of water lived within 800 m of the nearest standpipe, and villagers who used river water exclusively lived beyond that distance. Observation of water-related activities at the communal water facilities also indicated that the residents who lived near standpipes used the piped water more frequently. The frequency of total visits to river water sites did not differ between residents who lived near and far from the standpipe. However, water contact in the form of playing, the highest risk behavior, was observed exclusively among children who lived far (>250m) from standpipes, although the number of observations was small. The present study demonstrated that the water facilities had little effect on the dispersed population but might have a beneficial effect on some villagers given easy access to standpipes