Histopathological study of a natural outbreak of Peste des petits ruminants in goats of Tamilnadu
Introduction
Peste des petits ruminants (PPR) is an infectious disease specific for small ruminants. This disease was first reported by Gargadennec and Lalanne (1942)in Ivory Coast. The geographical distribution of the disease is widely increased and the first report of PPR amongst sheep in India was in 1989 (Shaila et al., 1989; Lefe'vre and Diallo, 1990). The principle host of PPR are sheep and goats, with goat being more susceptible to infection and subsequent disease (Ezeokoli et al., 1986).
The two important members of the Morbilli virus group affecting cattle and small ruminants viz. Rinderpest and PPR are especially distinguished between each other by their different range of pathogenicity and varied host range. Both Rinderpest virus (RPV) and PPR virus are two distinct but closely related viruses (Hamdy et al., 1976; Gibbs et al., 1979; Diallo, 1990).
Biochemical analysis of the virus showed variations only in the nucleoprotein (N) which codes for 525 amino acids (Diallo et al., 1989a). And since N is the major viral protein, cDNAs corresponding to the Ngene of PPRV and RPV can be labelled and used as a probe to differentiate the two viruses.
Though goats were referred most susceptible for PPR, in India, the disease was mostly recorded in sheep population. But the recent outbreak of the disease was seen to affect especially the goat population in India (Aruni et al., 1995) showing depletion of lymphoid cells in the peyer's patches, with villous atrophy and cellular casts in the crypts of Leiberkuhn.
The article deals with the first outbreak of PPR exclusively in goats among a mixed population of sheep and goat at Pasumpon Muthuramalingam District of Tamilnadu, India with its first recorded outbreak in the village Kalakanmai. More than 10 outbreaks occurred in goats affecting a flock of 50,000 goats in this area. Histopathological observations in correlation with clinical manifestations were studied from the affected animals.
Section snippets
Animal studied
A total of 48 animals which where found to be positive of PPR where studied from ten different outbreaks. Lungs, intestine, liver, spleen, lymph nodes from the affected animals were used in the histopathological study.
Secondary bacterial infection by pasteurella species was common only during terminal stages of infection. Isolation of mycosplasma, even though tried, were not given more importance.
Severely affected flocks were given more importance and autopsy was performed irrespective of age
Clinical signs
During the course of infection the goats between 3–12 months were seen severely affected, general clinical symptoms included purulent oculonasal discharge, severe cough and diarrhoea noticed at the terminal stages. Exfoliation of intestinal mucosa were noticed along with the diarrhoeal contents.
Gross lesions
Post mortem examination revealed presence of frothy exudate in the trachea with severely congested and consolidated, firm lung parenchyma. Purulent exudative areas were seen predominantly in the lung.
Lungs
The pathognomonic lesions were observed in lungs rather than intestines. Lungs showed evidence of pneumonitis. Bronchial epithelium exhibited squamous cell metaplasia (Fig. 1). In such sites where epithelium was hypertrophied, paucity of ciliated cells was evident. Epithelial giant cells with intra-nuclear inclusion bodies were observed. Alveolar septae were thickened and oedematous with mononuclear inflammatory infiltrate comprising of histiocytes, plasma cells and lymphocytes. Interstitial
Discussion
This article deals with an extensive study on histopathology of affected organs in goats by PPR virus. Following the first description of PPR it was postulated that the causal agent was a variant strain of rinderpest adapted to small ruminants (Mornet et al., 1956). This was confirmed by the present knowledge on the epidemiology of the two diseases which occur separately in the field.
The present outbreak of PPR was seen to affect only the goat population amidst a mixed population of sheep and
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