Introduction

The disease echinococcosis occurs due to cestodes belonging to the genus Echinococcus (family Taeniidae). The important parasite species include Echinococcus granulosus, E. multilocularis, E. oligarthrus and E. vogeli (Rausch 1975; Thompson 1995). Carnivorous animals act as definitive hosts and shed eggs in the faeces. Ingestion of food or water contaminated with eggs leads to infection in the intermediate hosts (Thompson 1995). A number of herbivorous and omnivorous animals act as intermediate hosts. Numerous animal species such as animals belonging to families Bovidae, Cervidae, Suidae, Equidae, Camelidae, Giraffidae, Elephantidae, Hippopotamidae, Leporidae, primates and marsupials could act as intermediate and aberrant hosts (WHO 1984). Humans act as accidental intermediate hosts. Cystic echinococcosis (CE) is endemic in many countries across the world (Sakamoto et al. 1987; Ghorui and Sahai 1989; Uysaler et al. 1998; Yildiz and Tuncer 2005; Lahmar et al. 2009).

In intermediate hosts, the disease mostly remains asymptomatic and is usually detected at post mortem inspection. The hydatid cysts grow slowly and take several years to grow big enough and cause symptoms. The cysts are primarily located in liver and lungs but could be found in many other organs such as spleen, heart, kidneys and omentum etc. (WHO and OIE 2001).

However, the disease causes huge production and economic losses. CE due to E. granulosis is a serious economic concern in India (Singh et al. 2014) and the disease is endemic in most of the food producing animals such as cattle, buffalo, sheep, goat and pigs in the country (Singh et al. 2012). The present study was contemplated to understand histopathological changes associated with E. granulosus echinococcosis in food producing animals in north India.

Materials and methods

The present work was carried out in the Department of Veterinary Public Health, in collaboration with Department of Epidemiology and Preventive Veterinary Medicine, College of Veterinary Science, Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana, Punjab (INDIA). Samples for investigating hydatidosis of food animals were collected from a Municipal Corporation slaughter house Ludhiana (Punjab), private (individual) butchers’ places at Ludhiana (Punjab) and Saharanpur (Uttar Pradesh), or where livestock were slaughtered and at Post Mortem Halls at Ludhiana and Ladowal (Punjab). Due to ban on cow slaughter on religious beliefs and lack of organized buffalo slaughter houses, the animals dying of naturally/any other disease were also included in the study. The visceral organs of every animal included in the survey were examined visually, palpated and incised for the detection of hydatid cysts on post-mortem inspection. The organs infected with hydatid cyst were collected in plastic bags and transported to laboratory for further examination. Tissues comprising of pieces of liver and lungs were collected in 10 per cent formal buffered saline for histopathological examination. We examined carcasses of 4,130 food producing animals and collected 66 hydatid cyst containing livers and lungs. The formalin fixed tissues (liver and lungs) from 50 animals (10 cattle, buffalo, sheep, goat and pigs each) were selected and further processed by acetone benzene method (Luna 1968). The paraffin blocks were prepared and sections of 4–5 µm thickness were obtained on glass slides with rotatory microtome. These paraffin sections were stained with haematoxylin and eosin stain for routine histopathology (Luna 1968).

Results

We encountered numerous cysts embedded at different depths usually in liver and lungs of all the mentioned animal species (Fig. 1). The cysts were also found embedded in the spleen and heart of two pigs and one sheep, respectively. There was gross enlargement of infected organs. The cysts were surrounded by outer fibrous layer over the inner germinal layer and filled with clear hydatid fluid. The results re-confirmed that germinal layer is the primary site of parasite development. Echinococcal protoscolices were also noticed in some of the sections.

Fig. 1
figure 1

Hydatid cysts in lung of cow

Full size image

There was slight hemorrhage, leucocyte infiltration and mild hepatocellular degeneration in the liver (Figs. 2, 3). Due to pressure effects from developing cysts, adjacent hepatic paraenchyma showed atrophy, variable degeneration and lympho-mononuclear infiltration (Fig. 4). The parenchyma adjacent to cysts was markedly congested and showed multiple small haemorrhagic areas. In lungs, there was proliferation of fibrous connective tissue and infiltration of mononuclear cells (Fig. 5).

Fig. 2
figure 2

Section of sheep liver showing hydatid cyst with laminated wall and hepatic degeneration (10×)

Full size image
Fig. 3
figure 3

Section of sheep liver showing hydatid cyst with laminated wall and hepatic degeneration (40×)

Full size image
Fig. 4
figure 4

Section of liver showing hydatid cysts with laminated walls and cellular infiltration (10×)

Full size image
Fig. 5
figure 5

Section of hydatid cyst in lungs of sheep (10×)

Full size image

Discussion

The disease mostly remains asymptomatic in intermediate animal hosts (Eckert et al. 2001). Hydatid cysts have been commonly recorded in liver followed by lungs and majority of cysts are slow growing (Gemmell 1966). The results in the present study are in parity with many previous studies (Hussain et al. 1992; Ahmedullah et al. 2007). Barnes et al. (2011) reported that adventitial layer in the multilocular cysts was thick in sheep which could be restrictive to growth while simultaneously protecting the hydatid from the host immune response. Barnes et al. (2011) further reported that the acellular zone had an outer rim of viable granulation tissue in which there was a mild lymphoplasmacytic and histiocytic infiltrate, including scattered multinucleated giant cells, admixed with rare eosinophils. Occasional lymphofollicular proliferations or remnants of the peribronchiolar lymphoid tissue were seen in the outer part of the adventitia or adjacent lung parenchyma (Barnes et al. 2011). Rashed et al. (2004) also reported a case of severe hydatidosis in a liver of a Najdi sheep. Histopathological changes included the formation of fibrotic capsules around biliary tracts and portal vein and also leaky liver. Pre-malignant changes were also seen in the different foci particularly around the biliary tracts and portal veins. Joshi and Yamasaki (2010) also reported histopathological changes associated with CE in pigs in Nepal. Kul and Yildiz (2010) characterised multivesicular and unilocular hydatid cysts in cattle. They reported that severity of calcification; fibrous capsule formation and giant cell layer were similar for multivesicular and unilocular cysts. However, the severity of subcapsular inflammation, inflammatory cell infiltration into adjacent organ parenchyma and eosinophil leucocyte infiltration into the cyst lumen was higher in multivesicular cysts.