PATHOMORPHOLOGICAL STUDIES AND DETECTION OF RETROVIRAL ANTIGEN BY IMMUNOHISTOCHEMISTRY IN OVINE PULMONARY ADENOMATOSIS
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Date
2011-12
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Sri Venkateswara Veterinary University, TIRUPATI – 517 502,A.P
Abstract
ABSTRACT :
In India, sheep rearing is very popular amongst the backward and weaker sections of the society. Of late, sheep rearing has taken a turn of entrepreneurship in large scale because of their feeding habits, ease in management and housing, early returns and increased technical awareness. Though sheep rearing is less expensive in terms of housing, feeding and management one should always concentrate on health aspect of these animals as they are very much prone to many infectious diseases including tumors. Although tumors are less common in domestic animals, with an exception of sheep in which, two important tumors namely ovine pulmonary adenomatosis (OPA) and enzootic nasal adenocarcinoma (ENA) are common and OPA alone constitutes 70% of all tumors in sheep.
OPA (Jaagsiekte) is a naturally occurring retro virus induced lung cancer in sheep, having long incubation period of 2-4 years and caused by Jaagsiekte sheep retro virus (JSRV) of the family Retroviridae. JSRV induces tumors via the oncogenic properties of its envelope that is necessary and sufficient to induce neoplastic transformation of alveolar (ATII) and bronchiolar (Clara) epithelial cells. Clinically, OPA is characterized by progressive a febrile respiratory illness with loss of weight (inspite of good appetite), tendency to lag behind the flock when moved and appear to have been chased (“driving sickness”), tachypnoea and characteristic moist rales due to accumulation of fluid in the air ways resulting in spasmodic coughing; pulmonary fluid discharging from the nostrils, dyspnoea and eventually death.
The disease is worldwide in distribution spanning in South Africa, UK, USA and Asia including India but with an exception of Australia, New Zealand and Iceland. Perusal of the available literature revealed, only a few reports of OPA from Andhra Pradesh. Hence, keeping this in view, the present investigation was carried out to study the incidence of OPA in selected districts of Andhra Pradesh, gross and histopathological lesions, immunohistochemical detection of retroviral antigen and ultrastructural changes in the lungs of sheep affected with OPA.
The materials for the present study consisted of tissue samples of sheep lungs collected from suspected cases of OPA from various slaughter houses located in selected districts of coastal Andhra Pradesh, field mortalities and from postmortem examinations carried out at NTR College of Veterinary Science, Gannavaram. The duration of the study lasted from January 2010 to December 2010. A total of 3544 lungs of sheep of either sex, aged between 6 - 60 months were examined in detail and the lung samples were collected for the study.
On gross and histopathological examination, 36 (1.01%) lungs revealed definitive lesions of OPA in a total of 3544 sheep examined. West Godavari (13) district showed high incidence of OPA followed by East Godavari (8), Krishna (7), Vizag (4) and Nellore (4) districts with an incidence rate of 1.17, 0.99, 0.97, 1.01 and 0.76% respectively. Out of 36 OPA cases observed in the present study, 8 were males and 28 were females indicating higher incidence in females than in males.
Age wise incidence of OPA was more in sheep aged between 37 – 48 months (19 cases), followed by 49 – 60 months (7 cases) and 25 – 36 months (4 cases) and 3 cases each between 0 – 12 and 13 – 24 months. The youngest animal affected with OPA in the present study was a female lamb aged about 2 months.
Grossly the affected lungs revealed two different pathomorphological forms viz. classical and atypical. Out of 36 OPA lungs examined 25 (69.5%) revealed the classical form that was characterized by an increase in size and weight of the lungs and with lesions of grayish consolidated areas located in the cranio-ventral portion. The lesions were diffuse or nodular masses, light grey or purple in color and 0.5-6.0 cm in diameter.
The cut surfaces were moist with exudation of frothy fluid .The atypical form was observed in 11 lungs (30.5%) in the present study and it tended to be more nodular and appeared mainly in the diaphragmatic lobes. They were pearly white, very hard, 0.1-2.0 cm in diameter and the cut surface was dry with no exudation of frothy fluid in the air ways.
Histologically, both the forms revealed almost similar findings in all the 36 cases and was characterized by the presence of several foci of epithelial cell neoplastic proliferation in alveolar and bronchiolar regions with bronchioloalveolar, acinar and or papillary growth patterns. All these histopathological types were present in the same tumoral tissue. In addition, papillary and polypoid proliferation of bronchiolar epithelium that filled the lumen was noticed. Individual neoplastic cells were cuboidal to columnar with eosinophilic cytoplasm that was frequently vacuolated. Variable numbers of macrophages with vacuolated cytoplasm were consistently found surrounding the neoplastic alveoli. The neoplastic epithelial cells were supported by connective tissue stroma. In long standing tumors, proliferation of connective tissue was more characteristic. Nodular foci of myxomatous tissue were found admixed with tumor or in the intestinal tissue of affected areas. Lymphoid proliferation was seen around the bronchioles and within the alveolar interstitial tissue. No metastatic lesion was observed in the lymph nodes of any of the affected animals in the present study. Immunostaining for JSRV- MA was performed on 36 lung samples of OPA. Strong positive staining for JSRV-MA was present in all neoplastic cells, few macrophages and desquamated tumor cells. The neoplastic bronchiolar epithelial cells showed mild positivity for JSRV-MA. Strong positive immunoperoxidase staining for JSRV - CA was present in the neoplastic cells and in few alveolar macrophages. Immunostaining for JSRV-SU was intense and specific in the transformed neoplastic alveolar and bronchiolar epithelial cells, alveolar macrophages and desquamated neoplastic cells. The non - neoplastic cells showed no specific staining to any of the antiserum tested.
Ultrastructurally the neoplastic cells were categorized in to AT II cells, Clara cells and undifferentiated cells. AT II cells showed numerous cytoplasmic lamellar bodies, vacuoles, tight junctions between adjacent cells, microvilli, well developed rough endoplasmic reticulum (rER) and glycogen granules. The nuclei were oval to round with a prominent nucleolus and with deep indentations and heterochromatin was dispersed in peripheral and central clumps. In some cells, pyknotic nuclei, anisokaryosis and loose junctions between ATII cells were noticed. The neoplastic Clara cells were characterized by very well-developed smooth endoplasmic reticulum (sER) and electron- dense granules. The nuclei were round and usually without prominent indentations. Undifferentiated tumor cells were devoid of either lamellar bodies or electron dense granules in the affected alveoli and bronchioles. Neither complete virions
nor viral inclusions were identified in tumor or non-tumor cells in the sections examined. Non-tumor cells present included inflammatory cells such as neutrophils, lymphocytes, macrophages and plasma cells.
The present investigation revealed an incidence of 1.01% of ovine pulmonary adenomatosis in selected districts of coastal Andhra Pradesh. The pathomorphological lesions indicated the presence of two forms of the lesions and the immunohistochemical studies confirmed the presence of JSRV infection. The ultrastructural studies further aided in the diagnosis of OPA.
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Keywords
sheep ; OVINE PULMONARY ADENOMATOSIS; OPA; PATHOMORPHOLOGICAL STUDIES; RETROVIRAL ANTIGEN