Detection of Parapoxvirus in goats during contagious ecthyma outbreak in Ceará State, Brazil by transmission electron microscopy techniques

Abstract

Contagious ecthyma or contagious pustular dermatitis, is a viral skin disease that occurs in sheep, goats and wild ruminants and is characterized by the formation of papules, nodules or vesicles that progress into thick crusts or heavy scabs on the lips, gingiva and tongue, caused by a member of the Parapoxvirus genus. Humans are occasionally affected constituting important zoonosis. The disease not only has an economic impact on farmers worldwide but also has a considerable negative effect on animal welfare. In this study, a contagious ecthyma outbreak which occurred in one flock with 90 goats located in the Ceara State, Brazil, was described. Twenty-two goats older than 6 months were affected. The animals presented crusted lesions on the buccal region, tongue, udder and teats, which began with swelling in the mouth area. Dried crusts and serum collected were processed for transmission electron microscopy utilizing, negative staining (rapid preparation), Immunocytochemistry (immunolabelling with colloidal gold particles) and resin embedding techniques. At the Philips EM 208 transmission electron microscopy all the samples were analyzed by negative staining technique and a great number of parapoxvirus particles ovoid or cylindrical, showing two morphological forms, a mulberry (M) form with a distinctive crisscross filament pattern derived from the superimposition of upper and lower virion surfaces and a capsular (C) form caused by stain penetration and distention of the virion core, measuring 300 x 180 nm was observed. Antigen antibody reaction was increased by the colloidal gold particles. In the ultrathin sections of crusts, we verified the presence of three types of intracytoplasmic inclusion bodies, type A or Bollinger inclusion bodies, outlined by membrane, presented in it is interior, oval, mature or complete viral particles, measuring on the average, 225nm x 130 nm, showing an inner dumbell-shaped core, two lateral bodies and an external envelope, or cigar shaped core. In the type B electron dense inclusions bodies, were visualized parapoxvirus particles budding of dense and amorphous material. Fibrillar intracytoplasmic inclusions were also found located between the virions, consisting of groups of fibrils, arranged in groups or concentrically in the middle of the granular material. Intracytoplasmic vesicles outlined by membranes, measuring 560 x 420 nm, containing granular material in its interior were also observed. The nuclei showed an aspect deformed.