Liver Fluke Infestation in Purple Heron (Ardea purpurea)

Infectious diseases have been serious threat for animal health and productivity in developing countries (Mehmood et al., 2017). Fasciolosis is the parasitic infection typically caused by liver fluke species Fasciola hepatica, which is popularly known as the ‘common liver fluke’ (Carmona and Tort, 2017). It is a parasitic trematode of the class Trematoda in the phylum Platyhelminthes. It infects the livers of various mammals and birds. Fasciolosis is often acquired through eating the metacercariae of the parasite. The life cycle of F. hepatica goes through the intermediate host (snails) and several environmental larval stages. The immature larval flukes migrate through the intestinal wall, the abdominal cavity and the parenchyma of the hepatic tissue, into the bile ducts, where they develop into mature adult flukes, which produce eggs. The pathology typically is most pronounced in the bile ducts and liver. Wild birds may pick up the infection from the snails.
       
Purple heron (Ardea purpurea) is a wide-ranging species of wading bird in the heron family Ardeidae. The scientific name comes from Latin ‘ardea’ meaning ‘heron’ and ‘purpureus’ for ‘coloured purple’ (Jobling, 2010). Purple herons are commonly seen in the lakes around Benagluru and feed on fish, snails and other fauna. These birds have gained importance worldwide due to their ability to adapt to different environments and aesthetic value. Parasitic diseases are the most common problems in herons in captivity. Parasitological surveys in wild and captive birds help in detection of serious pathological conditions. In this paper, we present fasciolosis in Purple heron at Bannerghatta Biological Park, Bengaluru that may allow the scientific community to identify the parasite in herons either based on the characteristics of the eggs detected through a simple faecal examination or by observing the pathological lesions during necropsy. This may facilitate ecological and systematic studies as well as increase the understanding of the epidemiology of this parasitosis in herons and other wild birds.

A carcass of Purple heron was submitted to Animal Disease Diagnostic Laboratory from Wild Animal Rescue and Rehabilitation Centre, Bannerghatta Biological Park (Fig 1). Systematic necropsy was performed and gross lesions were noted and photographed. Detection of fluke eggs was based on their morphology through microscopic examination of faecal samples using sedimentation method (Soulsby, 1982). The liver was dissected by following the main tributaries of the biliary duct for detailed examination, which involved visual examination and palpation of the liver so as to detect areas or spots for incision and finally the incision of the liver using a scalpel blade for scraping off infected portions so as to ascertain its pathology. The gall bladder was opened and turned inside out to examine for any visible worms. Representative pieces of liver, kidney were collected in 10% buffered neutral formalin, which were processed and sectioned at 5-6µm and stained with haematoxylin and eosin (HandE) for routine histopathological examination (Luna, 1968).
 

Upon necropsy and gross examination, liver was enlarged with whitish necrotic spots on its surface (Fig 2). Kidneys were pale with enlarged ureters (Fig 3). The microscopic examination of faecal samples revealed the presence of thin-walled, ellipsoidal, operculated golden yellow coloured eggs (Fig 4). Histopathology of kidney revealed diffuse degeneration of tubular structures and accumulation of uric acid crystal in the tubules (Fig 5). Liver exhibited proliferation of bile ducts along with fluke in the bile ducts with areas of ossification (Fig 6) and also showed desquamation of epithelium, cross sections of degenerating flukes and proliferation of periductular fibrous tissue (Fig 7A and B). Conclusively, the detection of eggs, gross and microscopic lesions of liver are suggestive of fasciolosis. As the Purple herons commonly feed on fish, snails and other flora/fauna in the lakes, it might have got an access to such intermediate hosts thereby being infected with Fasciola sp. It is reported that this infection normally comes through the ingestion of aquatic plants or intermediate hosts like snails containing the infective metacercariae.
 

 

 

 

 

 

 
The variety of mammals that can be hosts to Fasciola sp. highlights the immense adaptability of the parasite. A notable extension to this was the first report of liver flukes in the class Aves, with the description of two cases in Australian young farmed emus (Dromaius novaehollandiae) with gross hepatic lesions resembling subacute and chronic fasciolosis of ruminants observed at necropsy and histopathologic examination (Vaughan et al., 1997). However, in that study only one small adult was found and abnormal eggs were recovered, suggestive of an incomplete adaptation to birds as hosts. An adult fluke was also recovered from the liver of the emu and was identified as F. hepatica. The eggs of the fluke were irregular in shape and size that might be attributable to infection of an aberrant host.Two more recent reports of Fasciola sp. in farmed and wild populations of rhea (Rhea americana) provide evidence that a notable host-range extension to Aves has indeed occurred in South America (Soares et al., 2007; Martinez-Diaz et al., 2013). A coprological study of rheas across Argentina found F. hepatica-like eggs in the common rhea (R. americana) from two farms and one wild bird and also in Darwin’s rheas (R. pennata) from one Patagonian farm. The latter came from a farm where two adult birds died before the sampling and, according to the owner, presented liver lesions, but unfortunately were not kept for further analysis (Martinez-Diaz et al., 2013). The common rhea usually grazes together with cattle, sheep and horses in southern Brazil, Uruguay and the Argentinian pampas, while R. pennata is adapted to the Patagonia and altiplano regions, usually coinciding with sheep and guanacos. The presence of egg-producing parasites in rheas and herons as in the present study raises the question whether other bird species, for example herbivorous waterfowl, swans, geese, ducks living in endemic areas are also eventual hosts to liver flukes. Considering the migratory nature of some of these species, they might eventually contribute to the spread of the parasite. Hence, systematic studies are needed to throw better light in this direction.
       
Diagnosis of fasciolosis is made by examination of faecal sample and finding golden yellow or yellow-brown eggs. Current methods to control fasciolosis include the eradication of snails with molluscicides or separating birds from areas with snails, improving drainage systems to limit the habitat of the intermediate host and most commonly, the use of anthelminthic drugs. Hygienic practices and measures can be helpful in control and prevention of many parasitic diseases in the wild birds under captivity.

We thank Mr Range Gowda, Executive Director, Bannerghatta Biological Park for extending his support to carry out the study. We are thankful to all the staff of Wild Animals Rescue and Rehabilitation Centre and Wild Animals Disease Diagnostic Laboratory for their support during the study.