in senegal , livestock play both social and economic roles . it remains as the only source of livelihood for 30% of rural households . it is indeed a great potential for wealth creation in the sense that it represents 4.2% of the national gross domestic product and 28.8% of the primary sector ( gdp ) . nevertheless the enormous potential productivity of small ruminants is still weak , due to several constraints , including malnutrition , management , and diseases . in fact , diseases caused by parasites are also factors that contribute to reduction of the productivity of these animals around the world . gastrointestinal helminthes , with their toxic , mechanical , and absorptive actions , constitute a major constraint to health and productivity of domestic animals , especially in developing countries [ 47 ] . as far as we know , in africa , five species of anoplocephalid cestodes have been reported as major intestinal infections in small ruminants [ 8 , 9 ] . these are avitellina centripunctata rivolta , 1874 , moniezia expansa rudolphi , 1810 , moniezia benedeni moniez , 1879 , stilesia globipunctata rivolta , 1874 , and thysaniezia ovilla rivolta , 1878 , with a prevalence ranging from 6 to 92% [ 1019 ] . in senegal , these species have been confirmed , but their monthly and seasonal dynamics in ruminants have not yet been elucidated . the aims of present study were to determine the prevalence of the anoplocephalid cestodes infecting sheep and goats in senegal throughout the year and after performing scanning electron microscopic ( sem ) observations of specimens to put into evidence the characteristic of these species . small intestines of a total of 462 sheep ( ovis aries ) and 48 goats ( capra hircus ) were collected from the main slaughterhouse of dakar , senegal , from january to december , 2013 . sampling periods were characterized by a rainy season ( 500900  mm / year ) and a dry season extending from june to october and november to may , respectively . ruminant hosts were mostly between 2 and 5 years old , and they came from different localities in senegal . the cestodes were collected carefully from the intestines of small ruminants ( sheep / goats ) and identified after staining , using keys [ 2124 ] . staining was with iron hydrochloric carmine , destained in acid ethanol ( 100  ml 70% ethanol + 2  ml concentrated hcl ) , dehydrated in a graded ethanol series , cleared with eugenol ( clove oil ) , and mounted in canada balsam . stained specimens were examined and photographed under a leitz photo research microscope . to confirm detailed surface morphology , sem observations were performed . for sem , worms were isolated carefully from intestines and placed into a small amount of saline buffer . for living tapeworms , scolex , mature , and gravid proglottids of many specimens of each species were fixed overnight in cold 2.5% glutaraldehyde in a 0.1  m sodium cacodylate buffer at ph 7.4 . then , they were dehydrated in a graded ethanol series and dried using co2 in an emitech k850 critical point dryer . after being mounted on metal stubs , specimens were coated with gold / palladium in a quorum technologies sc7640 sputter coater and examined with a hitachi s-3400n scanning electron microscope at acceleration voltages between 3 and 20  kv in the  service d'etude et de recherche en microscopie electronique de l'universit de corse . the prevalence was calculated by dividing the number of animals harboring parasites by total number of examined animals . mean intensity was assessed by dividing the total number of parasites by the number of infected hosts . percentages ( % ) measure prevalence and chi - square (  ) association between prevalence of the parasite and species . in all the analyses , among the examined animals , 219 sheep and three goats were infected , corresponding to a prevalence of 47.4% and 6.2% , respectively . among sheep , the total number of parasites was 1304 and mean intensity was 5.9 ( range 140 ) . among goats total number of parasites was 7 , with a mean intensity of 2.3 ( range 15 ) . four species of anoplocephalid cestodes were recorded : avitellina centripunctata , moniezia expansa , stilesia globipunctata , and thysaniezia ovilla . in this study , 38.7% of sheep were infected by a. centripunctata , 15.4% by m. expansa , 16.7% by s. globipunctata , and 0.4% by t. ovilla . for goats , monthly and seasonal dynamics of prevalence were shown in figures 1 and 2 , respectively . the highest infection rates were recorded during may for a. centripunctata ( 54.5% ) , january for m. expansa ( 21.4% ) , and may for s. globipunctata ( 36.4% ) . the lowest value was noted in december for a. centripunctata ( 25.4% ) , april for m. expansa ( 7% ) , and march for s. globipunctata ( 6.5% ) . for each species , the differences on prevalence were not statistically significant between dry season and rainy season : p value = 0.94 for a. centripunctata , 0.64 for m. expansa , 0.28 for s. globipunctata , and 0.93 for t. ovilla . the mean intensity of infection for the tapeworms was 5.1 , 4.2 , 3.4 , and 1.5 for s. globipunctata , m. expansa , a. centripunctata , and t. ovilla , respectively , and was not statically different between dry and rainy season ( table 1 ) . single and associated species infections were evaluated among both sheep and goats . among sheep , the infections due to one , two , or three species were 56.2% , 37.4% , and 6.4% , respectively . for the infections caused by one species , a. centripunctata was the most prevalent with 39.3% followed by m. expansa ( 13.2% ) and s. globipunctata ( 3.6% ) . for the infections caused by two species , a. centripunctata and s. globipunctata were more prevalent ( 24.2% ) than a. centripunctata and m. expansa ( 11.4% ) , m. expansa and s. globipunctata ( 1.4% ) , and a. centripunctata and t. ovilla ( 0.5% ) . as for the infections due to three species , a. centripunctata , m. expansa , and s. globipunctata were more prevalent with 5.9% than a. centripunctata , m. expansa , and t. ovilla ( 0.5% ) . among goats , two of infected animals harbored a single species m. expansa , and the remaining harbored m. expansa and t. ovilla . a total of ten a. centripunctata , six s. globipunctata , six m. expansa , and six t. ovilla were examined . all avitellina and stilesia and four moniezia and thysaniezia specimens were collected from sheep ; two moniezia and thysaniezia specimens were collected from goats . the scolex is unarmed , spherical in shape , 1000 to 1600  m in diameter , and provided with four suckers located at its peripheral margin ( figure 3(a ) ) . each sucker shows a triangular opening from which the point of the triangle is directed towards the center of the scolex ( figure 3(b ) ) . the tegument of the scolex , suckers , and strobila of species are covered with acicular and capilliform filitriches ( figures 3(c ) and 3(d ) ) . the strobila has a threadlike appearance and is acraspedote , showing unilateral genital pores irregularly alternating . proglottids are wider than longer and weakly distinguished even in mature proglottids ( figures 3(e ) and 3(f ) ) . the scolex is unarmed , globular in shape , 400 to 600  m in diameter , and provided with four suckers located at its peripheral margin ( figure 4(a ) ) . each sucker shows a circular or subcircular opening ( figures 4(b ) and 4(c ) ) . the genital pores are paired in each proglottid and disposed laterally ( figures 4(e ) and 4(f ) ) . the tegument of the scolex , suckers , and strobila are covered with acicular and capilliform filitriches ( figure 4(d ) ) . the cirrus is entirely covered by capilliform filitriches ( figures 4(f ) and 4(g ) ) . the scolex is unarmed and is club - shaped , 300 to 600  m in diameter , and provided with four well - developed suckers ( figure 5(a ) ) . each sucker shows a circular opening ( figure 5(b ) ) . at the center of the scolex , the tegument of scolex , suckers , and strobila is covered with acicular and capilliform filitriches ( figure 5(c ) ) . strobila is craspedote , threadlike , and very spiral ( figures 5(d ) and 5(e ) ) . the scolex is unarmed and round , 300 to 450  m in diameter , and provided with four well - developed suckers ( figure 6(a ) ) . the tegument of the scolex , suckers , and strobila is covered with capilliform filitriches ( figure 6(c ) ) . the proglottids are wider than longer with unilateral genital pores irregularly alternating ( figure 6(d ) ) . from the genital pores , a rounded cirrus protrudes , which exhibits a cavity in the center ( figure 6(f ) ) . infections by anoplocephalid cestodes are common among sheep and goats [ 17 , 19 , 2629 ] . in senegal , five species of anoplocephalidae , a. centripunctata , m. expansa , m. benedeni , s. globipunctata , and t. ovilla , have already been described among ruminants [ 11 , 14 , 26 , 30 ] . in our study , all except m. benedeni were found among sheep , but among goats only m. expansa and t. ovilla have been observed . the overall prevalence of anoplocephalids was significantly higher among sheep than among goats , as previously reported in senegal by ba et al .   and ndao et al . other studies in west african countries such as gambia , burkina faso , and cte d'ivoire showed similar prevalence to those obtained in our study and confirmed that sheep were more frequently infected than goats [ 15 , 17 , 27 ] . the behavior of goats in pasture seems to limit their risk of infections and could explain also their low infestation intensity . goats consume longer pasture than sheep , making intermediate oribatid mite hosts less available ; another fact is that goats consume more ligneous food , rich in tannins , which are known natural anthelmintics and probably limit the infection . our study and others showed that infection in sheep is generally higher in western african areas compared to others : in north africa such as egypt ( 11% ) and in some european areas such as turkey ( 4.4% ) [ 19 , 32 ] . the prevalence among goats was slightly lower in turkey ( 6.3% )   compared to previous reports in senegal [ 14 , 31 ] . these differences can be attributed to climatic factors that are often highly variable from one area to another , such as the duration of the rainy season , which may affect the dynamics of intermediate hosts ( oribatid mites ) . also the soil kind , as oribatids , prefers acid soils and the type of farming in the different localities may therefore affect the prevalence of anoplocephalids . in the previous studies of prevalence of anoplocephalids among small ruminants , m. expansa was the most prevalent [ 26 , 31 ] . nevertheless in our work , these facts can be probably explained by the different age - group of ruminants examined in the studies , because it is known that a. centripunctata is the more common among adult ruminants and m. expansa is the highest among one - year - old ruminants [ 13 , 34 ] . another fact is that a. centripunctata better resists the immune system of hosts than m. expansa . sharkhuu   reported in mongolia that moniezia is common in goats and avitellina and thysaniezia are common in sheep . in present study , the prevalence of m. expansa among sheep and goats are similar to those reported in western ethiopia , but lower than in senegal [ 30 , 31 ] , cte d'ivoire , eastern ethiopia , and guinea . for a. centripunctata , the prevalence is lower than those reported in senegal , similar to cte d'ivoire , and higher than in senegal   and in cte d'ivoire . in our study , a. centripunctata was not found among goats as previously reported in cte d'ivoire [ 16 , 17 ] and mongolia   but in senegal ba et al . the prevalence in sheep in our study was similar to that in cte d'ivoire , but higher than in senegal . the same result was reported previously in cte d'ivoire , guinea , and western ethiopia . for t. ovilla , the prevalence was low , similar to the data from sharkhuu , but different from reports by nadge   who found t. ovilla from sheep in senegal , with a prevalence of 84% . . this reduction may be due to different control practices . since 1996 with the national plan for the development of animal husbandry ( npdah ) and its strategy of contributing to improving health and zootechnical conditions of livestock , a strategic deworming plan was generally proposed during the rainy season because of the heavy infestation of ruminants and at the end of the dry season for their weakness . other investigations have shown that climate is an important factor in determining levels of infection by anoplocephalids . generally anoplocephalids are more prevalent in the rainy season than the dry season [ 15 , 26 ] . oribatids are susceptible to desiccation and this fact may be a reason for little infection during the warmer months . however , our study revealed two peaks of prevalence both in the dry and in the rainy seasons unlike the previous reports . except for t. ovilla , anoplocephalids were present in small ruminants all the year . this lack of difference between seasons can be explained by deworming control methods applied in both rainy and dry seasons . also the mean intensity was generally low , due probably to the large size of these tapeworms exceeding generally one meter   and/or control methods by veterinaries services and breeders . no significant difference between dry and rainy season can be attributed to the longevity of the tapeworms , which exceed a year . in the present study , the infection with a. centripunctata and s. globipunctata was the most prevalent ( 24.2% ) , followed by a. centripunctata and m. expansa ( 11.4% ) . the multiple infestations play an important role in growth retardation and weight loss of small ruminants . more , it was reported that coinfections can be lethal among small ruminants [ 33 , 3639 ] . only a few scanning studies have been made on a. centripunctata , t. ovilla , and m. expansa , and these previous studies focused only on the scolex [ 19 , 40 ] . suckers have circular , oval , or linear openings , depending on the level of contraction . the proglottids are wider than longer ; they are craspedote for m. expansa , s. globipunctata , and t. ovilla and acraspedote for a. centripunctata . m. expansa and t. ovilla are large worms compared to a. centripunctata and s. globipunctata . they differ in the presence of paired genitalia in m. expansa and single and irregularly alternating genital pores in t. ovilla . the body of cestodes is fully covered by microtriches , presenting different forms and size among specimens . then standardized terminology was adopted to define the different kinds of microtriches . in our study , the microtriches observed among a. centripunctata , m. expansa , and s. globipunctata are acicular and capilliform filitriches . on the other hand , previous isoenzyme electrophoretic studies have shown that a. centripunctata , m. expansa , and t. ovilla are species complex [ 14 , 30 ] . but recently for moniezia expansa , a genetic analysis showed an intraspecific variation other than speciation , and further molecular investigation is necessary , in order to identify species in all of these genera . in small ruminants from senegal , four cestode species a. centripunctata , m. expansa , s. globipunctata , and t. ovilla were found among sheep . there were no statistically significant differences between dry and rainy season prevalence of anoplocephalidae among sheep . multiple infections of anoplocephalids were recorded and the double infection a. centripunctata and s. globipunctata was most prevalent with 24.2% .