Irrigation Practices and Intestinal Helminth Infections in Southern and Central Zones of Tigray

Background: Irrigation practices have impact on the distribution of schistosomiasis; so, identifying newly established schistosomiasis transmission foci allows for designing prevention and control strategy. Objective: To establish schistosomiasis prevalence and intensity in relation to development of water bodies for irrigation. Methods: A survey of stool specimens of 2000 school children using Kato thick smear method was carried out in Central and Southern Tigray between October 2001 and January 2002. Results: Among the 1012 males and 998 females examined, 29% males and 27.5% females were found positive for one or more parasite. The prevalence of S. mansoni was 27% in longstanding irrigated, 10.8% in recently constructed irrigation schemes and 1.8% in the non-irrigated rural localities. In the urban setting, its prevalence was 15.5% in areas with water body nearby and 0.5% in areas with no water body nearby (P<0.0001). New S. mansoni infection foci were detected in Tumuga with a prevalence of 87%; Dibdibo (41%), Mariam Shewito (25%), Adiha (23%) and Lekia (9%). Conclusion: The increasing risk of schistosomiasis mansoni in the irrigation sites is high. Hence, designing preventive and control strategies concurrent with the development of the irrigation projects will be required to reduce prevalence of schistosomiasis. [Ethiop.J.Health Dev. 2009;23(1):48-56] Introduction Parasitic worms adversely affect the health of humans in many parts of the world. Intestinal parasitic infections continue to be a public health problem globally, particularly among children in the developing countries (1). In many of the developing countries, the most prevalent and important helminths are those of the soiltransmitted nematodes. Chronic gut infection in humans commonly results from nematodes, particularly that of Ascaris lumbricoides, Trichuris trichiura and hookworms (Ancylostoma duodenale and Necator americanus) (2), and the blood flukes, schistosomes (3). Their distribution is influenced by sanitation, population movement, availability of water bodies, etc. For example, higher rates of ascariasis, trichuriasis and hookworm infection were constantly recorded among migrants from populations working in irrigation schemes in the Awash Valley than among nearby nomads or migrant populations employed in rain-fed agriculture in the semiarid Setit Humora area (4). The fact that hookworm, Ascaris and Trichuris larvae and ova require humid environments as in irrigation schemes indicates the role of such schemes in the transmission of these intestinal parasites (5). Lemma (6) also observed that the continuing large-scale agricultural use of rivers, the construction of highways and population movement lead to the spread of schistosomiasis. Various studies have been conducted on all intestinal parasites or only on Schistosoma mansoni infection in Tigray (12, 22 and 23). It is known that irrigation and the construction of dams with poor sanitary practice results in rapid spread of S. mansoni, since the aqueous environment provides suitable condition for intermediate snail host (7). Worldwide, in all endemic regions, the development of water resource plays an important role in the spread of schistosomiasis. For example, the introduction of irrigated agricultural scheme has been associated with introduction of S. mansoni in both upper and middle part of Awash valley (8). In Ethiopia, the introduction of irrigated agricultural schemes has been shown to be associated with the introduction of S. mansoni in both upper and middle part of Awash Valley (8). Currently, to reduce dependency on rain fed agriculture, construction of dams for irrigation is underway in Ethiopia. Tigray is one of the regions which have started a rural development program by an extensive construction of dams for irrigation. Although there is no national inventory of small dams in Ethiopia, there are more than 70 reservoirs in Tigray (Northern Ethiopia), ranging in reservoir water volume from 50,000 to 4,500,000 m (25 & 26). The majority of the dams are situated near human settlements at an altitude range of 1700-2700m. Dams serve many different purposes for the community, such as domestic and agricultural water supply, irrigation and fish culture. As a potential very negative side-effect, dams may create conducive environment for breeding sites of malaria and schistosomiasis vectors. Although increased economic benefit of expansion of irrigated agriculture is being realized, its public health impact is not fully understood. The present investigation was undertaken to establish the prevalence and intensity of intestinal schistosome and other helminth infections in relation to development of water bodies for irrigation. The information generated in the current study would help to identify new schistosomiasis foci and it can also be used as a baseline Irrigation practices and intestinal helminth infections in Southern and central zones of Tigray 49 Ethiop.J.Health Dev. 2009;23(1) data for mapping the distribution of schistosomiasis and future reference for designing and evaluating Schistosomiasis control strategies. Methods Central Tigray encompasses ten districts (Weredas) and has 265 primary schools. The population of Central Tigray was 1,132,112 and of this 88.8% are subsistence farmers (Fig. 1). South Tigray is divided into eight districts and has 256 primary schools. The population of South Tigray was 938,808, of which 85% are subsistence farmers. The study population was primary school children. They were selected because prevalence of infection in schoolage children can be used as an index for assessing community prevalence (9) and they are likely to accept the inconvenience of providing stool specimens. Sampling and sample size Comparing the results of pre-irrigation health data (especially for the recently constructed reservoirs) would have been important to explain the impact but such data are not available in the region. Thus, 10 representative schools were purposely selected from each of Central and South Tigray zones (Fig. 1). The selection comprises 3 schools from longstanding, 2 schools from recently constructed irrigation schemes, 3 schools from nonirrigated, 1 school from urban center with river nearby and 1 school from urban center with no river nearby. Hundred students from each of the 20 schools were selected using systematic sampling by using a random start. The total sample size was 2000 school children. Data collection was undertaken from October 2001 to January 2002. Parasitological examination Students were supplied with a piece of paper to bring about 3gms of faeces. Specimens were collected on-thespot. Teachers and school directors were assisting investigators in collecting the samples. Students who were not able to pass stool during sample collection were advised not to bring their friends stool, but to report that they could not pass stool. Those who reported were substituted by other students. In the field, the 2000 samples were processed by Kato thick smear (10) and transported to Mekelle University for microscopic examination. One slide was prepared for each sample and examined once by well trained expertise. All positive cases were treated. Those with S. mansoni were treated with Praziquantel 40 mg/kg body weight, single dose, while for others with helminthes (A. lumbricoides and T. trichiura and hookworm) infections were treated by Mebendazole 100mg BID for three days. Intensity of infection was estimated from the number of eggs per gram of faeces (epg). Based on egg counts, cutoff values for classification of intensity of infection were used. Intensity of S. mansoni is classified into: light infection (1-99epg), moderate (100-399 epg) and heavy (greater than 400 epg). Similarly, the classification for A. lumbricoides is: light infection (1-4999epg), moderate (5000-49999epg) and heavy (greater than 50,000epg). Intensity of T. trichiura is: light infection (1-999epg), moderate (1000-9999 epg) and heavy (greater than 10,000epg). Classification of hookworm is: light infection (1-1999epg), moderate (2000-3999 epg) and heavy (greater than 4,000epg) (11). In the result section, only intensity of S. mansoni was presented because the intensity in all others was light infection. Socioeconomic survey Data of socioeconomic factors was collected using a structured questionnaire specifically developed for this purpose. All questions were closed-ended in structure. One of the questions was filled by observation. Data was collected by one of the researchers. Data Analysis Data was entered into and were analyzed using SPSS version 10.1 software package. Results Prevalence A total of 1012 male and 988 female school children were examined. Out of these, 571 (295 males and 276 females) were positive for one or more helminths. On the whole, average intestinal helminth infection was 28.6% (range: 6% 92%). Considering irrigation practices, the overall prevalence of intestinal helminth infection in long-standing irrigation areas was 38.5% (range: 14 – 92%); in the newly introduced irrigation schemes, it was 20.8% (range: 6-47%) and in non-irrigated areas, it was 15.7% (range: 9-26%). Furthermore, significant difference (P<0.00001) was observed between prevalence in the urban centers (40.8% range: 15-88%) and rural communities (26.1% range: 9.5-50%) (Table 1). Of the 20 schools surveyed, 11 (55%) were positive for S. mansoni infection. The difference in the overall prevalence of S. mansoni infection with respect to irrigation was 17.5% in irrigated and 5.5% in nonirrigated areas (P < 0.0001) (Table 3). Further, the prevalence of S. mansoni infection was much higher (27%) in the longstanding irrigated locations than in the recently constructed irrigation schemes (10.7%) and 1.8% in the non-irrigated locations (P < 0.0001) (see Table 2). Similarly, urban centers with water body nearby had a much higher prevalence (15.5%) than urban centers with no water body nearby (0.5%). 50 Ethiop.J.Health Dev. Ethiop.J.Health Dev. 2009;23(1) Table 1: Proportion of students positive for one or more intestinal helminth species in South and Central Tigray, 2002 Setting South Tigray Central Tigray Total (ST & CT) Male Female Total Male Female Total Long-standing (Rural)dam 74/152 (48.7) 76/148 (51.4) 150/300 (50) 40/150 (26.7) 41/150 (27.3) 81/300 (27) 231/600 (38.5) Recent dam (Rural) 6/84 (7.1) 13/116 (11.2) 19/200 (9.5) 37/115 (32.2) 27/85 (31.8) 64/200 (32) 83/400 (20.8) No irrigation (Rural) 21/163 (11.5) 28/137 (20.4) 49/300 (16.3) 26/151 (17.2) 19/149 (12.8) 45/300 (15) 94/600 (15.7) Urban 59/96 (61.5) 52/104 (50) 111/200 (55.5) 32/101 (31.7) 20/99 (20.2) 52/200 (26) 163/400 (40.8) Total (Overall) 160/495 (32.3) 169/505 (33.5) 329/1000 (32.9) 135/517 (26.1) 107/483 (22.2) 242/1000 (24.2) 571/2000 (28.6) Key:1= values in brackets are %; 2 =in 50% of the urban area studied there are rivers nearby; ST= south Tigray; CT= Central Tigray Table 2: S. mansoni distribution in school children with respect to different irrigation practices and sex in South and Central Tigray, 2002 Settings Male Female Total