Parainfluenza-3 (PI-3) Virus

Family - Paramyxoviridae
Subfamily - Paramyxovirus

    Parainfluenza viruses are large enveloped viruses containing a genome that is a single molecule of single stranded negative sense RNA. 11

 Infections caused by PI-3 in cattle are common.5 This virus commonly causes a subclinical infection on its own although it is capable of causing a mild, self-limiting disease.  When the animal is infected with the other agents, such as Mycoplasma spp, and BRSV for example, or when adverse environmental conditions precipitate, clinical disease can occur.  PI-3 virus may persist for weeks following a natural infection and the presence of it may predispose the animal to respiratory disease by interfering with the host’s protective clearance mechanisms in the respiratory tract.  This allows for secondary invasion by bacteria or mycoplasmas.  It should also be mentioned that PI-3 virus is a predisposing factor in viral interstitial pneumonia, and pneumonic pasteurellosis (shipping fever) as well, but these diseases primarily affect older animals that are likely to be shipped off to the feedlot by the time these diseases become relevant.  1 

Clinical Signs:
serous nasal discharge
lacrimal discharge
increased respiratory rate
increased breath sounds

    PI-3 usually infects and contributes to enzootic pneumonia  in beef calves that are made susceptible by crowding, inadequate colostrum intake, and excessive infection pressure on newborns because of closeness to adults.  1


    Parainfluenza-3 virus is transmitted through the air and by direct contact, therefore increased crowding will increase the spread of the virus.  1


Morbidity and Mortality:
    The morbidity and mortality of PI-3 depends on the dose of the viral/bacterial exposure, because remember, all of these agents work in concert to cause enzootic pneumonia.  Morbidity can reach 100% in some cases, but mortality is usually less than 5%.  1

<>Risk factors in Developing Enzootic Pneumonia:
    Incidently, most of the pathogens that cause enzootic pneumonia are normally found within the respiratory tract of normal calves, so environmental risk factors play a role.  These include:

            -low ambient temperature (especially with rapid weather changes)
            -relative humidity
-increased population density

<>Several animal factors also play a role:
    -at 2-4 weeks, serum antibodies are at their lowest leaving the animal more susceptible
    -the occurrence of disease is higher in twin and male calves 1

    Most calves that recover from clinical enzootic pneumonia are resistant to disease caused by the same agents.1


<>Economic significance:
    If it occurs in nursing beef calves it can decrease weaning weights which leads to economic losses for the producer.1


    Subclinical viral pneumonia that is not complicated by secondary bacterial infections is not normally clinically significant.  The problem is that it can predispose the respiratory tract to these opportunistic bacteria.  1


-virus isolation
-indirect fluorescence techniques


    There is no treatment directed at PI-3 virus, however antibiotics are indicated to treat the secondary bacterial infections that arise.  Early treatment is advised to avoid the development of pulmonary abscesses, pleuritis, and bronchiectasis.  In some cases non-steroidal anti-inflammatories (NSAIDs) and bronchodilators may be indicated, but the efficacy of this is undetermined.  The most important thing to remember is to treat new cases of enzootic pneumonia quickly and vigorously.  1, 5


    Improving management is one way to help control the spread of this virus.  This can be done in the following ways:

-decrease overcrowding
            -improve ventilation if calves are kept in barns at any time
            -decrease exposure to poor weather
            -isolate any new calves for a few weeks before introducing them to the herd

    It is understood that these are somewhat impractical measures, therefore this should help to stress vaccinations as being an important tool in helping to control the spread of this virus and the spread of enzootic pneumonia in general.  In spite of ideal hygiene and maintenance, prevention of viral spread is not 100% possible because infection may already be in the herd or it may be brought in at any time. 1


<>     It has been recommended to vaccinate for PI-3 virus 2-3 weeks prior to weaning and 2-3 weeks prior to shipment to a feedlot as part of a preconditioning program to decrease morbidity and mortality from pneumonic pasteurellosis (shipping fever). 1 These vaccines are almost always combined with bovine herpes virus 1 (infectious bovine rhinotracheitis).  Both MLV and killed vaccines are available for IM administration.  There are also vaccines that contain temperature sensitive mutants for intranasal administration as well.  5  






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