Prevalence of helminth parasites in sheep ( Ovis aries ) in Tangail district , Bangladesh

Prevalence of helminths of sheep in relation to age, sex, nutritional status, management system and flock size was studied at Tangail district, Bangladesh from July to December 2010 by fecal examination. A total of 190 sheep were examined of which 154 (81.1%) were positive for one or more species of helminth parasites. Seven species of helminths were identified, of them three species were trematodes, namely, Fasciola gigantica (8.4%), Paramphistomum spp. (44.2%) and Schistosoma indicum (3.7%); four species were nematodes, namely, Bunostomum sp (19.0%), Trichuris spp. (2.1%), Strongyles (62.6%) and Strongyloides spp. (9.5%). No cestodes were identified. Prevalence of helminths was significantly (p<0.01) higher in young sheep aged >1-2 year (92.7%) than adult aged > 2 years (83.3%) and lamb aged ≤ 1 year (63.6%). Higher prevalence was recorded in female than in male sheep. In relation to nutritional status and flock size, prevalence of helminths were significantly (p<0.01) higher in poor health and large flock sized animals. It is suggested that helminth infection is widely prevalent in sheep in Tangail district of Bangladesh. Keyword: Prevalence, Helminths, Sheep, Tangail District


Introduction
Parasitism is of supreme importance in many agro-ecological zones and still a serious threat to the livestock economy worldwide (Vercruysse and Claerebout, 2001).Sheep are known to suffer from various endoparasites of which helminth infection are of great importance.Helminth infections remain one of the major constraints to small ruminant production in tropics (FAO, 1992;Diaz et al., 2000).Infection with gastrointestinal nematodes is regarded as one of the important factor causing production losses of livestock.Tangail district situated in central region of Bangladesh is very prospective for sheep rearing due to its geo-climatic condition.But the sheep rearing is hindered by various problems of which parasitic diseases might be one of the major problems because the mild winter and the long summer including the rainy season create a favorable environmental condition for the survival of various parasites with their intermediate host such as snail (Islam, 1969 andHaq andSheikh, 1968).There is no precise report available on parasitic diseases of sheep in Bangladesh.Therefore, the present study was conducted to find out the prevalence of helminths of sheep at Tangail district and to determine the effect of age, sex, nutritional condition, management system and flock size of sheep, which would provide a basis for the understanding of different helminth parasites of sheep in formulating the control measures of the parasitic diseases.

Materials and Methods
The study was conducted for a period of six months from July to December 2010 at Tangail district of Bangladesh.Fecal samples of sheep were collected from the different areas of Tangail district and carried to the Laboratory for morphological examination of the parasites with their developmental stages.One hundred and ninety sheep were selected randomly irrespective of age, sex, nutritional status, management system and flock size.The age of the sheep were 5 months and above.Age of the sheep was determined by examining teeth as described by Rahman and Hossain (1997).According to age, sheep were divided into three groups, namely, lamb (≤ 1year), young (> 1-2 years) and adult (> 2 years).The nutritional condition of sheep was categorized into two groups, namely, poor health and healthy according to eye inspection and body condition (Rahman and Hossain, 1997).The selected sheep were reared either in semi intensive or free range grazing system.The flock size was divided into three groups as small flock consisting of sheep 4-8, Medium flock had 9-12 sheep and the large flock were >12 sheep.
After collection of all relevant information, sheep were restrained properly and all possible hygienic measures were maintained and feces were collected directly from the rectum.Some fresh fecal samples were collected from the ground immediately after voiding.A total of 190 samples were collected and about 5-10 gm of feces were collected from each sheep and kept in separate polythene bag, tied carefully, numbered properly and preserved in 10% formalin.The fecal samples were examined by Stoll's Ova counting technique and identification of egg of different helminths was performed by their characteristic morphological features as described by Soulsby (1982) and Rahman et al. (1996).Statistical analyses were carried out by using Statistical Package for Social Sciences (SPSS-11.5)technique using F test to detect the significant differences of mean values of eggs per gram of feces of identified helminths.Odds ratio of different parameters were calculated according to the formula given by Schlesselman (1982).

Nutritional status related prevalence of helminths in sheep
The prevalence of helminth infection was significantly (p<0

Management system related prevalence of helminths in sheep
Management system had a profound effect on the prevalence of helminth infection in sheep.The prevalence of helminth infection was higher in sheep reared in free range grazing system (82.8%)than that in sheep reared in semi-intensive grazing system (79.1%     Parasitism is of supreme importance in many agro-ecological zones and still a serious threat to the livestock economy worldwide (Vercruysse and Claerebout, 2001).Sheep are known to suffer from various endoparasites of which helminth infections are of great importance and remain one of the major constraints to small ruminant production in tropics (FAO, 1992;Diaz et al., 2000).
It was revealed that age of the sheep had significant (p< 0.01) effect on helminth infections.Young sheep (87.0%) were the most susceptible to infection followed by adults (83.3%) and lambs (63.6%), which supported the findings of Asif et al. (2007) who reported the higher prevalence of helminths infection in young animals compared to adult sheep in Pakistan (p< 0.059).But this result differed from that of Mazid et al. (2006) who reported higher prevalence of helminth parasites in younger (< 1 year) and old (≥ 2 year) than in young (≥ 1< 2 year) sheep in Mymensingh, Bangladesh.The higher rate of infection with Fasciola gigantica was in older sheep, which is similar to the earlier reports of Bhuyan (1970) in Bangladesh and Aydenizoz and Yildiz (2002) in Turkey.But the present finding is in contrast to the previous reports of Al-Bayati et al. (1991) who observed higher prevalence of fascioliasis in young (21.3%) than adults (12.0%) and lamb (7.3%) in Iraq.The findings of the present study is also similar to Lateef et al. (2005) in Pakistan with Strongylides infection, who observed higher prevalence in young animals but differ from Oka et al. (1999) in Cote d' Ivoire who stated that the highest infection was in animal below 1 year of age.This result is also dissimilar to Mazid et al. (2006) who reported older sheep were more susceptible to Paramphistomum infection than young (30.4%) in Bangladesh.The exact cause of this variation in the prevalence of helminth infection in different age groups of sheep is due to immunological status of animals.But it may be assumed that the differences in the methodology, management factors may be the reasons of this variation.
It was observed that the prevalence of helminth infections was higher in females (83.3%) than in male (79.3%) sheep.This finding is in agreement with the earlier study of Mazid et al. (2006) in Bangladesh who recorded higher prevalence of helminth infection in females than in male sheep (78.6%).But this report is in contrast to the previous report of Asif et al. (2007) who observed the sex-wise prevalence of helminths was higher in males than in females in Punjab, Pakistan.This result also differs from Okafor (1988) in Nigeria who observed that prevalence was not related to sex.The reason for higher prevalence of helminth infection in the females cannot be explained exactly but it might be assumed that the alteration in the physiological condition of the females during pregnancy, lactation and parturition as well as stresses leading to immunesuppression may be associated with this phenomenon.Higher level of prolaction and progesterone hormones makes the female individual more susceptible to any infection (Lloyd, 1983).
The present study revealed that nutritional condition of sheep had significant (p<0.01)effect with helminth infection.The higher prevalence of helminth infection was recorded in poor health (75.2%) sheep than that in healthy (64.2%) sheep.The present findings are in agreement with the earlier study of Lapage (1962) who found that malnourished animals are more susceptible to any infection as they are immunocompromised.The present study also agrees with the findings of Etter et al. (1999) who repoted that in immunocompromised animal the fecundity of parasites is usually increased.
The prevalence of helminth infection was higher in sheep reared in free ranged grazing system (82.8%)than that in sheep reared in semi-intensive system (79.1)sheep.It was observed that fluke infection was higher in free ranged grazing sheep whereas nematode infection was higher in semi-intensively reared sheep.The present findings can not be compared due to lack of available relevant literatures.It is assumed that regular and direct contact of animals to the contaminated pastures may be associated with this phenomenon.
It was revealed that the prevalence of helminths was significantly (p<0.01)higher in large flocked sheep (89.1%) than in small (81.8) and medium flocked (73.9%) sheep.The influence of flock size on the prevalence of helminths is difficult to explain exactly but it is assumed that crowding of animals, lower feed supplement and management practices may be associated with this variation.

Conclusion
The prevalence of helminth parasites of sheep at Tangail district, Bangladesh was highly susceptible to helminth infections.Age, nutritional status and flock size of sheep significantly (p<0.01)influenced the prevalence of helminth infections.Identification of the helminths down to species through ova detection is very difficult, and it may be better to isolate mature or immature helminths directly from the visceral organ of the sheep.Further study should be carried out to determine the economic losses due to helminthiasis of sheep and to develop effective control measures against it.

Table 2 . Age related prevalence of helminths in sheep in Tangail District
n = No. of sheep examined * = Total number of animals infected is less than the summation of individual infection because same animal was infected by more than one type of helminthes **= P<0.01 Figures in the 6th column having different superscript varies significantly (p<0.01).

Table 3 . Sex related prevalence of helminths in sheep in Tangail District
NS N = No. of sheep examined * = Total number of animals infected is less than the summation of individual infection because same animal was infected by more than one type of helminths NS= Not significant