Pasteurellosis Outbreak Due to Pasteurella multocida Type A in Rabbits (Oryctolagus cuniculus)

Abstract

Background: Pasteurellosis is a common disease of cattle, pigs, and poultry, which rarely affects humans. In rabbits, the respiratory presentation of the disease is frequently reported. Clinical signs related to bronchopneumonia include sneezing, lung stertors, oculonasal discharge, dyspnea and cyanosis. Infection may lead to otitis, conjunctivitis, abscesses and sepsis. Furthermore, Pasteurella multocida infection may lead to sudden death without clinical manifestations. Reports of pasteurellosis in rabbits are scarce in Brazil. Therefore, the objective of this article is to describe an outbreak of pasteurellosis with high mortality in a rabbity in the State of Santa Catarina, Brazil.

Cases: Two adult rabbits were submitted for necropsy at the Veterinary Pathology Laboratory of the Instituto Federal Catarinense - Campus Concórdia, within an interval of twenty days. Herd was represented by 40 animals, of which six fattening rabbits and three breeders died.  Animals were kept in suspended cages with slatted floor. Clinical signs were represented by prostration, sneezing, and mucopurulent nasal discharge. In addition, wounds were observed in the distal portion of the limbs. Death occurred up to two days after the onset of clinical signs. Necropsies were performed and tissue samples were collected for histopathologic, immunohistochemical and microbiologic (bacterial culture and antibiogram) exams. At the necropsy, severe diffuse fibrinous exudate covering the pericardium sac, visceral and parietal pleural surfaces was noted, as well as multiple diaphragm adhesions. In addition, the lungs presented diffuse red coloration and showed multiple abscesses ranging from 0.3 to 1cm in diameter. The nasal sinus and the tracheal mucosa showed diffuse reddening (rabbits 1 and 2). Abscesses up to 2 cm in diameter were observed in the mammary glands (rabbit 1), heart and kidneys (rabbit 2). The urinary bladder was distended by cloudy urine and moderate amount of purulent exudate (rabbits 1 and 2). Histopathological evaluation revealed diffuse marked fibrinosuppurative pleuritis associated with severe multifocal suppurative bronchopneumonia (rabbits 1 and 2), as well as multifocal marked mastitis (rabbit 1), nephritis and myocarditis (rabbit 2). Also, intralesional bacterial aggregates and thrombosis were observed in both cases.  Pasteurella multocida type A was isolated through bacterial culture, and antibiogram showed sensitivity to all tested antibiotics. Immunohistochemistry showed mild multifocal positive staining for P. multocida in the visceral pleura in both cases.

Discussion: In the present case, P. multocida type A led to suppurative bronchopneumonia, pulmonary abscesses and fibrinosuppurative pleuritis in both rabbits. In addition, abscesses affecting the kidneys, heart and mammary glands were observed. These findings are typically seen in this condition in rabbits, and similar lesions may be noted in pigs. It is believed that nutritional, climatic and hierarchical changes may predispose to the development of the disease. In the present outbreak, the disease may have initially affected fattening rabbits, which are more exposed to stressful events, and then bacterial spread to breeders sharing the same facility may have occurred. Furthermore, contributing factors include concomitant bacterial infections, and the level of virulence of the bacterial strain involved in the outbreak. In the present study, the diagnosis of pasteurellosis in rabbits was based on the epidemiological, gross, histopathological, bacterial and immunohistochemical findings. It is believed that the present report will improve the understanding of the disease in rabbits in Brazil, since rare descriptions of the condition are currently available nationwide.