Outbreak of paramyxovirus in Chestnut-bellied Seed-Finch (Sporophila angolensis). Transmission electron microscopy diagnosis / Surto de paramixovirose em curiós Sporophila angolensis). Diagnóstico por microscopia eletrônica de transmissão

Abstract

The Chestnut-bellied Seed-Finch (Sporophila angolensis) is a bird constantly sought after as a cage bird, which is the main threat and the cause of its disappearance from the most inhabited regions of the country. Paramyxovirus, present in most breeding sites and Ecological Parks, is the disease that most affects birds with a high mortality rate, causing significant losses, both economic and to nature. Avian paramyxoviruses belong to the family Paramyxoviridae, which includes 21 serotypes (APMVs-1-21). Serotypes 2 and 3 are the ones that most infect passerines. Type 2 causes respiratory disorders, while the disease caused by serotype 3 is characterized by pancreatitis, conjunctivitis, vomiting, diarrhea, dyspnea, dysphagia, pancreatitis, CNS symptoms, and death. Free-ranging birds can act as viral reservoirs and spread the disease when subjected to stress factors. During the period of 2009, during the illegal commercialization of Brazilian birds, 218 Chestnut-bellied Seed-Finch were apprehended and sent to the CRAS (Wild Animals Recovery Center) of the Tietê Ecological Park. Of these, 112 arrived dead and the rest died during the year. About 35 birds were sent to the Electron Microscopy Laboratory of the Biological institute, for research on viral agents. During the necropsy, it was observed that the intestines were dilated, containing yellowish and watery stools. Small intestine fragments were processed by negative staining (rapid preparation), antigen immunolabeling with colloidal gold particles and resin embedding. Under the transmission electron microscope, using the negative staining technique, pleomorphic, rounded or elongated, enveloped paramyxovirus particles containing helical herring-bone like nucleocapsid, measuring between 100 and 500 nm in diameter, were visualized in the samples of all birds. The antigen-antibody reaction was enhanced by colloidal gold particles. Ultrathin sections of the small intestine revealed the presence of nuclei with marginalized chromatin, containing intranuclear inclusions; amorphous intracytoplasmic inclusions, formed by helical nucleocapsids, complete particles measuring from 100 to 250 nm and incomplete ones, budding from the plasma membrane.