Bovine Parainfluenza 3 (PI3) (presently Bovine Respirovirus 3) (-ssRNA, Paramyxoviridae, Respirovirus): Molecular diagnosis (RT-PCR)

The parainfluenza virus 3 (PI3) is a virus of the family Paramyxoviridae. This virus produces bovine infections, in which it causes a highly contagious disease called bovine parainfluenza 3 (BPI3). It is considered that this disease is associated with complex bovine respiratory disease (BRD). In addition, this agent is also involved in the enzootic pneumonia of calves. Parainfluenza 3 infection is common in many countries.

The parainfluenza viruses are enveloped viruses with a lipid membrane with glycoproteins spicules with hemagglutinating and hemolytic activity. The genome consists of a single strand of RNA of negative polarity (-ssRNA) with a size of 100 to 200 nm, with a nucleocapsid diameter of 18 nm.

Transmission of the parainfluenza 3 virus generally occurs by direct contact between the nasal or ocular secretions of diseased animals and the mucous membranes of the healthy animal, although transmission through dispersion in aerosols of nasal secretions or by objects or equipment is also possible. contaminated stressful events and situations in which a large number of animals are kept confined in confined spaces can increase the chances of contracting the disease. Once in the host organism, the virus starts its replication in the epithelial cells of the upper respiratory tract, where it produces morphological and functional alterations in the mucociliary apparatus. Subsequently, the virus invades the lower respiratory tract, affecting the cells of the alveolar and bronchiolar epithelium, mainly the alveolar macrophage, thus altering the defense mechanisms of the lung.

Infection by the virus causes a mild respiratory disease that involves nasal and ocular secretions, moderate fever, cough, expectoration and increased respiratory rate. Although the virus causes a mild initial bronchitis, as a consequence of its replication in the cells of the immune system (macrophages) it causes a decrease in the response against bacterial agents and predisposes the infected animals to a bronchiolitis that can spread to the alveoli, causing bronchointerstitial pneumonia, especially when exposed to secondary pathogens. This, together with traces of cellular lysis caused by viral infection, predispose to secondary complications with Mannheimia (Pasteurella) haemolytica and Pasteurella multocida. The pneumonias caused by these agents evolve in acute form with high mortality. In the severe form, the signs of the disease include intense dyspnea, mouth breathing, bowed head, respiratory moan and death.