Animal products besides serving as a big contributor for sustenance of farmers are also presumed to contribute as a rich source of protein for the Indian population¹. The meat quality of animals (buffaloes, sheep/goats, and rabbits) and poultry is often ruined by multifactorial causes, where extensive damage to edible organs (muscles and viscera) caused by parasites leads to losses in the form of condemnation of affected organs. The consumption of affected meat and meat products oten pose a potential zoonotic threat to human population². The parasitic diseases in animals may initiate with mild discomfort and may worsen to death if not controlled timely. The suggested resultant symptoms recorded in animals affected with parasitic conditions include weight loss, diarrhea, anemia, icterus, increased appetite, abdominal pain and finally death³.

The zoonotic significance of several parasitic conditions in animals viz. hydatidosis, amphistomiasis, trichnellosis etc. has already been established⁴. The main focus of the present study is to document the role of parasitic diseases on meat quality recorded during routine necropsy of meat animals.

The present study was carried out on the tissue samples collected from the meat animals including buffaloes, sheep and goat, rabbits and poultry from January 2017 to December, 2021 with an aim to investigate the incidence of commonly occurring subclinical or obscure pathological conditions of parasitological origin reported during necropsy examination (Table No. 1) done in the Department of Veterinary Pathology, DGCN COVAS CSKHPKV, Palampur. A thorough necropsy examination of the carcasses was done and the gross lesions recorded were photographed. The 0.5 cm thick representative tissue sections were collected in 10% neutral buffered formalin (NBF) to carry out the histopathological evaluation. The preserved tissue sections were dehydrated in alcohol, cleared in benzene, impregnated in molten paraffin, sectioned at 4–6 micron and stained with haematoxylin and eosin (H&E) stain as per the standard protocol⁵. The recovered parasites were collected and washed 3–4 times with phosphate buffer saline (PBS) for the parasitological identification. The cestodes and trematodes were flattened by putting between the two slides, pressed and stained in Borax carmine⁶. The nematodes were cleared in Lactophenol and identified on the basis of morphological characteristics.

In present study, the parasitic conditions recorded during necropsy examination of buffaloes included hydatidosis, cysticercosis, sarcocystis and fascioliasis. Hydatid cysts were evident in various organs including lungs, liver and mesenteries of the intestine. The lungs of the affected animals exhibited the presence of multifocal, lemon sized, transparent or containing calcified masses and dirty fluid containing cystic structures with hyperemic borders (Fig. 1). The histological evaluation of the affected lungs reflected the presence of diffuse proliferation of fibrous connective tissue causing compression of alveolar lumens (Fig. 2). The presence of multiple, grape like clear fluid filled cystic structures were also evidenced on the thoracic cavity and also involved the intercostal muscles. These parasitic cystic structures were finally declared as Cysticercus bovis (Fig. 3). The gross evaluation of heart muscles and muscles of tongue area in buffaloes has revealed the presence of whitish streaks. The affected areas on microscopic evaluation indicated the presence of oval to cigar shaped sarcocystic structures lying in between the muscle fibers, but did not exhibit any evidence of inflammatory reaction. The liver tissues collected from the buffaloes on cut section were found to show the presence of leaf like liver flukes inside the bile ducts along with necro-hemorrhagic areas (Fig. 4 and 5). The histological investigation of affected hepatic sections revealed the presence of areas of coagulative necrosis, hemorrhage, haemosiderosis, increased kupffer cell activity and mild bile duct hyperplasia.

Post-mortem examination of small ruminants (sheep and goat) revealed important parasitic conditions including dicrocoeliosis, verminous pneumonia, haemonchosis, tapeworms and cysticercosis. The animals affected with dicrocoeliosis exhibited the evidence of lancet like flukes within the bile ducts with diffuse areas of congestion (Fig. 6). The histological examination of stained tissue sections has shown mild bile duct hyperplasia along with engorged sinusoids and the presence of parasitic remnants inside the bile ducts (Fig. 7). The goats with the history of respiratory distress were thoroughly examined and were found to contain thread like whitish colored lung worms inside the airways along with froth mixed fluid. The histological examination of lung tissues collected from the affected goats depicted the presence of eosinophilic oedematous fluid admixed with mononuclear cells (MNCs) infiltration and the presence of parasitic eggs inside the alveolar lumens along with the alternate areas of atelectasis and emphysema. The goats with severe haemonchus infestation were found to reveal the evidence of fluid in the abdominal cavity, hydrothorax, oedematous and enlarged mesenteric lymph nodes and erosive to ulcerative abomasitis along with barbar pole like round worms (Fig. 8). Goats were also found to exhibit catarrhal enteritis associated with flatworms (Moniezia expansa). From some of the goats, parasitic cysts including hydatid and cysticercus tenuicollis were also retrieved.

A thorough examination of rabbits on necropsy indicated the evidence of intestinal and hepatic coccidiosis (Fig. 9), ear canker, flatworms and encephalitozoonoses (Fig. 10). The rabbits with fibrosed liver were found to show the presence of coccidian oocysts on microscopic examination of bile and intestinal contents. The histopathological evaluation of the stained sections depicted severe degenerative changes and the areas of necrosis along with the stages of coccidian protozoan parasite. Rabbits with dry and crusty lesions on the ear pinna were confirmed to be infested with a mite (Psoroptes cuniculi) causing ear canker. Some of the rabbits with the pitted appearance of kidneys and meningeal congestion were also reported during necropsy examination and suspected to be affected with a protozoan parasite encephalitozoonosis (Encephalitozoon cuniculi).

The poultry birds presented for necropsy examination were found to be infested with Ascaridia galli and intestinal coccidiosis. The birds with roundworms were found to show severe catarrhal enteritis with erosive to ulcerative areas (Fig. 11). The roundworms were also occasionally reported from the gizzard as a result of migration from the intestine after death. The birds affected with roundworms were emaciated depicting hide bound condition and prominent keel bone. The birds affected with intestinal and caecal coccidiosis revealed the evidence of diffuse areas of hemorrhages along with necrotic patches giving salt pepper like appearance (Fig. 12). The fecal smear examination of these poultry birds exhibited the presence of severe accumulation of sporulated or unsporulated coccidian oocysts. Microscopic examination of the intestinal sections have shown the presence of schizonts inside the epithelial cells and denuded and fused villi along with the infiltration of inflammatory cells especially heterophils.

The parasites can affect the gastrointestinal system of animals including hepato-biliary system (Strongylids, Eimeria spp., Nematodirus spp., Moniezia spp., Trichuris spp., Strongyloides spp., Fasciola hepatica, Protostrongylids, Ascaris suum and Trichuris spp. etc.) muscular system (Cysticercus, Trichinella etc.), circulatory system (Anaplasma spp, Babesia spp., Thelaria spp., Trypanosma spp. etc.) and other major vital organs (Echinococcus granulosus). The previous studies has shown that fascioliasis is one of the most important parasitic disease in domestic ruminants and found to produce pale, enlarged liver with multifocal areas of necrosis and hemorrhages and has parallel correlation with our study⁷. The sarcocysts formation was evident in the heart muscles, tongue and oesophagus in the present study. The microscopic evidences revealed the presence of cigar like oval structures entrapped in between the muscle fibres. These cystic structures present over the muscles oten shows zoonotic implication and the results of the present study reflected the significant concordance with a study conducted, previously⁸. The studies carried by Murrell et al.⁹ and Costa et al.¹⁰ have warranted the occurrence of Cysticercosis in human beings ater consuming raw and undercooked muscles of infected animals. The gross examination of the organs affected with Cysticercus bovis depicted the presence of multifocal, nodular, firm whitish colored lesions on various organs.

Echinococcosis is an important meat borne cyclozoo-notic disease evidenced to show multiple, soft or doughy and clear fluid filled variable sized cystic nodules in different organs mainly liver and lung. The similar necropsy lesions recorded in present study have parallel results to the earlier studies conducted by many researchers¹¹. Camara et al.¹² reported that dicrocoeliosis is one of the common parasitic disease found in ruminants causing cirrhotic changes in liver and scarring of the liver surface on chronic cases. The liver may become hard in consistency with the presence of lancet like flukes in the bile ducts as seen in the present study. In the present study, Hemonchus contratus, the barbar pole worm at ached to the abomasal mucosa was found to produce edematous abomasal mucosa along with the areas of petechial hemorrhages and erosions. The gross lesions were in accordance with the study conducted previously by Kumar et al.¹³. Muellerius capillaris is a one of the most commonly known lung parasites present in sheep and goat which causes verminous pneumonia. In this study the affected goats have shown multifocal nodules present in the caudal portion of the lungs along with lung worms and froth throughout the airways and trachea¹⁴. The presence of tape worms (Moniezia spp) in the intestine was found to produce catarrhal enteritis and has shown similar results as that of earlier studies¹⁵.

The pathological alterations caused by Eimeria spp. oten corresponds to management problems including poor husbandry practices, dietary issues and many other stress factors²². The intestinal lesions reported in poultry birds affected with coccidian protozoan parasites includes hemorrhagic to necrotic enteritis along with sloughed and clubbed villi¹⁶. Ascaria galli is the most commonly found round worms in the poultry birds causing heavy economical loss to the poultry farmers. The lesions concerned with ascaridiasis in poultry birds included severe catarrhal enteritis. The rabbits affected with hepatic coccidiosis were found to exhibit nodular appearance of liver with fibrosis. The present investigation has documented that the rabbits affected with coccidiosis were emaciated and weak¹⁷. In one of the study carried by the researchers have shown the pitted appearance of renal parenchyma along with interstitial nephritis in rabbits and confirmed to be caused by Encephalitozoon cuniculi¹⁸.

Parasitic infections draws an attention to researchers and veterinarians in-terms of production losses and zoonotic spill-over. Parasitic diseases can directly or indirectly influence the growth of animals and often pose a significant threat in terms of economic loss to marginal farmers or meat industries. The need of hour is to prevent the occurrence of parasitic infections in early stage via guiding the people or meat industry workers on proper management practices (hygiene, deworming, vaccination), seeking for early diagnosis, and timely treatment.

Authors are highly grateful to Dean COVAS and Head, Department of Veterinary Pathology for providing the necessary facilities to carry out this research work.

References