Western
Meeting of Poultry
Clinicians and Pathologists
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Clinicians and Pathologists
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Microscopic Metazoan Intestinal Parasites in Poultry A. Bickford, D.H. Willoughby, G.L. Cooper and B.R. Charlton California Veterinary Diagnostic Laboratory System
In the face of the multitude of emerging enteric diseases it may seem ludicrous to devote attention to a topic as archaic as intestinal metazoan parasites. However, even though most of these parasites were initially identified in the 1800’s, they still exist in poultry populations and may present as real diagnostic challenges to the clinician and diagnostician. The parasites considered in the report – larval Ascaridia Dissimilis in turkeys, Capillaria sp. (obsignata, columbae and caudinflata) in chickens, turkeys, pigeons and game birds and Davalinea proglottina in chickens – have occurred in California flocks in the past several years and frequently induced clinical effects which were not diagnosed without thorough work-ups. Summaries of our observations are as follows: 1. Larval Ascardai dissimilis enteritis: We have had numerous cases in turkey poults starting around eight weeks of age. Whatever the reason for submission, we find slightly ballooned intestines with thick mucus covering a thickened mucosa in the duodenum and jejunum. At this age we seldom find visible nematodes in the intestinal lumen. The same intestinal lesions may be seen in older turkeys, but starting at 10 to 12 weeks of age, visible, even mature, nematodes may be present in the lumen. In heavy infections microscopic evaluation of deep scrapings of the affected mucosa will contain typical ascardia larvae, but lighter infections may require multiple scrapings in several areas of the small intestines. Histologic evaluation of multiple levels of small intestine is also helpful in demonstrating migrating larvae in the mucosa and assessing the severity of the associated enteritis. Early changes in intestine include edema of the villous stroma with lymphohistiocytic infiltration of the propria but, particularly, eosinophilic infiltration deep in the mucosa at crypt level. In later stages dense lymphohistiocytic masses are noted in villous stroma and deep eosinophilic infiltrates persist. In a variable percentage of infected birds migrating larvae apparently gain entry into portal blood vessels and are carried to the liver where they induce eosinophilic granulomas or lymphofollicular reactive nodules. Beyond the diagnostic challenge, the economic significance of Ascarida dissimilis enteritis relates to suppression of weight gains (birds underweight at market age), liver condemnation at slaughter or promotion of more lethal intestinal disease such as necrotic enteritis.
2. Intestinal Capillariasis Capillaria worms are seen sporadically in floor or range-reared chickens and turkeys and more frequently in pigeons and game birds. These delicate thread-like worms are rarely visible because they burrow deeply in the mucosa entwining around villi. Affected birds are submitted due to unthriftiness and emaciation and, occasionally, significant levels of mortality. The affected intestine is thickened and edematous and, especially in pigeons, the muscularis may be thickened. In patent infections it is possible to demonstrate typical capillaria ova, (elliptical eggs with bipolar plugs), by fecal flotation. More reliable is microscopic evaluation of deep muscosal scrapings of affected areas of the small intestine. Capillaria worms are readily identified by the cellular esophagus and the presence of the unique ova in gravid females. Histologic examination of multiple intestinal sections is beneficial in that it confirms not only the presence of nematodes, but also the severity of intestinal damage. Prominent histopathologic findings in acute infections are villous edema or mucosal microulceration due to strangulation of villi by entwined nematodes. Some capillaria worms actually penetrate the epithelium and elicit substantial mucosal reaction including lymphoplasmacytic infiltration, fibroplasia and variable hyperplasia of the muscularis mucosa.
3. The Microscopic Tapeworm – Davainea Proglottina We have had five cases of this interesting intestinal parasite over the past five years and all have been in backyard "free-range" chickens. The intermediate hosts of this minute tapeworm are snails and slugs. It is not unusual for backyard chickens to have access to many other parasites and pathogens so 4 of the 5 affected flocks had a variety of diseases along with the Davainea infection. However, in the single flock where the tapeworm was the dominant pathogen, 10 of 13 chickens had died of a period of three months and affected birds were unthrifty and emaciated. While Davainea is a small tapeworm, (only 4 to 9 proglottids), it is not truly microscopic since it can measure up to 4mm in length. However, intermingled with intestinal villi, they are seldom grossly recognizable. The duodenum of affected chickens has a remarkably thickened "boggy" mucosa sometime with punctate hemorrhages and is often covered with thick mucus. Proglottis or entire tapeworms, including the scolex, can be found microscopically in deep mucosal scrapings and various portions of the worm are readily identified in histologic sections of the affected gut. The traction of the rostellar or acetabular hooklets causes the scolex to be drawn deeply into the mucosa and scolices may be found adjacent to the muscularis externa. The major histopathologic changes in the intestine are edema and proprial mixed inflammatory cell infiltration and fibroplasia.
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