Gastro-intestinal helminths of ducks : Some Epidemiologic and pathologic aspects

A total of 206 ducks were subjected to routine postmortem examinations from July 2007 to June 2008. Of the ducks examined, 167 (81.1 %) were infected by one/more species of gastro-intestinal helminths. A total of ten species of helminth parasites were recovered from gastrointestinal tract, of which four species were trematodes namely: Echinostoma revolutum, Notocotylus attenuatus, Hypoderaeum conoideum and Echinoparyphium recurvatum; two were nematodes, namely, Amidostomum anseris, Capillaria contorta; two were cestodes, viz, Hymenolepis coronula and Fimbriaria fasciolaris and two species belonged to acanthocephala such as, Arythmorhynchus anser and Filicollis anatis. Single double and mixed infections were found in 78 (46.7%), 46 (27.5%) and 43 (25.8%) ducks, respectively. Prevalence of gastrointestinal helminth was significantly (P<0.05) higher in female ducks (82.7 %) than male ducks (77.6%). Ducks above six month to one year of age were more affected (53.9%) than the ducks < 6 month (15.0%) and > 1 year of age (31.1%). Helminth infection was significantly (P<0.05) lower in rainy season (64.9%) in contrast to summer (75.7 %) and winter season (91.1 %). In heavy infections of E. revolutum haemorrhagic enteritis were noticed and parasites were firmly attached with the mucosa. E. recurvatum caused thickening of the serosal surface of intestinal wall. N. attenuatus produced catarrhal tryplitis characterized by thickening of the villi and formation of oeosinophilic granulomas. Massive infections with H. coronula produced inflammatory changes in the small intestine. Grossly petechial haemorrhages to ulcerative lesions were produced by A. anseris. In proventriculus circular ulcerative and necrotic areas with degeneration of the glandular tissues were seen. A. anser was also found in between the horney and muscular layer of the gizzard where they produced pin pointed haemorrhagic lesions and in severe case parasites were embedded into the mucosal layers of gizzard. For the control of helminths infections mass deworming is necessary.


Introduction
The duck population in Bangladesh is 35 million, which comprises about 10% of the total poultry.Ducks are commonly used for dual purpose (meat and egg) and mostly reared under traditional system (FAO, 1990).Parasitic infection is one of the major constraints in duck rearing in Bangladesh of which helminth infection is common.In fact, ducks are affected by different types of helminths (Anisuzzaman et al., 2005, Farjana et al., 2004, Islam et al., 1988), but very little attention has been paid to study the epidemiologic and pathologic aspects of helminth infections in ducks.Anisuzzaman et al. (2005) observed chronic active liver cirrhosis in ducks due to avian liver flukes infection.Das et al. (2008) observed sign of asphyxia due to tracheal fluke infection.The knowledge about the epidemiology of a disease/infection is essentially necessary to execute a control program successfully.Knowledge about the pathogenesis and pathology of a particular disease is a prerequisite in proper diagnosis of a disease.Considering these points, the present work was planned to study some epidemiology and pathology of gastro-intestinal helminths of ducks in Bangladesh.

Materials and Methods
A total of 206 indigenous ducks were examined during the period between July 2007 and June 2008.The ducks brought for diagnosis in a diagnostic centre or purchased from the households and local markets of Mymensingh district were examined.Before slaughtering, the vent area of the ducks was carefully examined to detect any soiling or other signs of diarrhoea.The slaughtered ducks were subjected to routine post-mortem examination following the procedure as described by Fowler (1990).Different parts of the gastro-intestinal tracts were cut and kept in separate petri dishes.Then the different parts of the gastro-intestinal tracts were opened to collect parasites and to detect gross pathological lesions produced by them.Collected trematodes, cestodes and acanthocephalan were fixed in alcohol-formol-acetic acid (AFA), stained with Semichon's carmine, dehydrated in graded alcohol, cleared in aneline oil, cleaned in xylene and mounted with Canada balsam.But nematodes were preserved in glycerin alcohol and morphology was studied by preparing temporary slides adding one drop of lacto phenol (Cable, 1957).The parasites were identified according to the keys and description given by Yamaguti (1961) and Soulsby (1982).
The gross pathological lesions were recorded and the affected organs were collected and preserved in 10% buffered neutral formalin.For histopathological study, suspected tissues were processed, embedded in wax, sectioned at six µ thickness and stained with haematoxylin and eosin (Luna, 1968).
To study the effects of the season on the prevalence of gastro-intestinal helminths, the year was divided into three seasons such as monsoon (July-October), winter (November-February) and summer (March-June) seasons.The ducks were divided into three age categories such as less than 6 months, 6 months to 1 year and more than 1 year of age.In ducklings, sexes were identified by the digital palpation of penis.The data were analyzed statistically by using chi-square test (Mostafa, 1989).Odds ratio and confidence interval were obtained by the formula according to the Schlesselman (1982).

Epidemiological aspects of gastrointestinal helminth infection in ducks
Exactly 167 (81.1%) ducks were found infected by one/more species of gastrointestinal helminths, which conformed to the findings of Ahmed (1969) who recorded 66% prevalence of H. lanceolata and E. revolutum infection.But the prevalence rate was much lower than that of Islam et al. (1988);Farjan et al. (2004) and Anisuzzaman et al. (2005) who reported 97%, 96.7% and 98.3% helminth infection.This disparity might be due to variations in the method of study, geo-climatic condition and husbandry practices.Farmers are now more conscious about the deleterious effects of parasites.So, most of them deworm the birds regularly.
During the study 67 male and 139 female ducks were examined.Among them 52 male (77.61%) and 115 female (82.7%) ducks were infected.Higher prevalence of helminth infection in female ducks (Farjana et al., 2004) may be due to their laying and eating habit.Due to lack of balance ration their immune status is questionable.Islam et al. (1988) reported that the prevalence of Tetrameres fissispina was higher in male than female.Betlejewska and Kalisinska (2001) did not find any difference in the prevalence of helminths in two sex groups.
Out of 167 ducks, 25(15.0%);90(53.9%);and 52(31.1%)ducks found infected in the age < 6 months, 6 months to 1 year and > 1 year, respectively.Higher prevalence of infection and density of helminths in older ducks were observed by Farjana et al. (2004).Islam et al. (1988) reported that Echistoma robusum was higher in younger ducks (2 to 20 weeks old).Pham et al. (2002) recorded that ducks of 2-4 months ages were mostly infected (80.7%) by worms.Prevalence of gastrointestinal helminths in adult ducks may be due to their free ranging system and loose management.Generally ducklings are kept confined to protect them from the predators.As a result they have relatively less chance to be exposed to the source of infections like various terrestrial and aquatic vectors/intermediate hosts of parasites.
The seasonal variation of helminths infection were observed and recorded in different seasons.The highest rate of infection was observed in winter season (91.1%) followed by summer (75.7%) and rainy season (64.9%).Seasonal fluctuatiion of helminth infection also observed by the earlier scientist.Anisuzzaman et al. (2005) observed relatively higher infection rate in rainy season (100%) followed by summer (98.1%) and winter (98.0%).Junkin et al. (2003) reported high prevalence of infection in rainy season but low in fall and winter.The highest rate of infection in winter may be due to pre-patent period and ability of parasites to remain in the host.On the other hand, in winter season ducks are reared in the stagnant water resulting the intermediate hosts like frogs, bettle, earth worms to get chance to infected the hosts.

Pathologic lesions produced by gastro-intestinal helmiths
E. revolutum produced haemorrhagic enteritis and parasites were firmly attached with the mucosa (Fig. 1).In histopathological examination, cross section of parasites were seen in the lumen of intestine along with some eosinophilic and lymphocytic infiltrations in the lamina propria of large intestine (Fig. 5).This finding conformed the observations of Forester et al. (1994) who observed haemorrhagic enteritis and thickened intestinal mucosa.They also detected extensive destruction and degeneration of the villi caused by the attachment and pressure of the flukes.E. recurvatum produces pathologic lesions as thickening of the intestinal wall, which was noticed from the serosal surface.After longitudinal incision, catarrhal inflammation was observed on the mucosal surface with many anchored parasites.Bhowmik et al. (1987) observed severe enteritis in turkeys due to E. recurvatum.Both the E. revolutum and E. recurvatum have spiny head collar and scaly cuticle (Soulsby, 1982).They remain firmly attached to the site of attachment and give irritation.Hypoderaeum conoideum produced catarrhal to haemorrhagic spots and in heavy infections it produced haemorrhagic enteritis.Parasites were firmly attached with the mucosa of small intestine.N. attenuatus produced catarrhal tryplitis characterized by thickening of the villi and formation of oeosinophilic granulomas (Fig. 8).This finding is in the agreements of the observation by Permin and Hensen (1998).Massive infections with H. coronula produced inflammatory changes in the small intestine which varied from catarrhal to haemorrhagic enteritis.Microscopically cross-section of scolex of parasite was seen in the mucosa of the intestine (Fig. 7).Permin and Hensen (1998) studied pathogenecity of H. lanceolata and found catarrhal enteritis, diarrhoea and death in chickens.Soulsby (1965) observed catarrhal enteritis leading to wasting, emaciation and death in geese.This parasite has rostellum armed with hooks and a large species measuring up to 130 mm (Soulsby, 1982).Possibly they induced inflammatory response by giving irritations.Grossly petechical haemorrhages to ulcerative lesions were produced by A. anseris.In most cases, they remained firmly attached under the horney cornified layer of gizzard (Fig. 2).In proventriculus, circular ulcerative and necrotic areas with considerable tissue reactions and degeneration of the glandular tissues were seen (Fig. 3.).Extensive leukocytic infiltrations and congested blood vessels were the common features.Petechial haemorrhages in the gizzard and ulcerative lesions in the proventriculus in A. anseris are reported by Anisuzzaman et al (2006); Soulsby (1982) and Lapage (1962) in ducks.These parasites deeply penetrate the horny layer of the gizzard and probably during penetration they cause haemorrhages.On the other hand, A. anser was found in between the horny and muscular layer of the gizzard.They causing thickening of the horny layer of the gizzard.In some cases, pin pointed raised dark haemorrhagic lesions were seen.The parasites were embedded into the mucosal layers of gizzard (Fig. 6) as observed by longitudinal sections.Anisuzzaman et al. (2005) first reported this acanthocephalan parasite from the gizzards of indigenous ducks in Bangladesh.However, its pathogenecity and pathology were not mentioned in earlier reports.This parasite posses thorny proboscis (Yamaguti, 1961), as they remain in between the horny and muscular layer of the gizzard that produces continuous irritation causing thickening of this layer.

Conclusion
It is suggested that ducks commonly reared in Bangladesh (Indigenous, Khaki Campbell, Jindin) are susceptible to gastrointestinal helminth infection irrespective to age and sex of ducks and seasons of the year.Pathological change due to Hypoderaeum conoideum infections are described, which are not reported before.Mass deworming is essntial routinely at definite interval with safety spectrum of anthelmintic.

Fig. 1 .
Fig. 1.E. revolutum firmly attached to the mucosa of the large intestine