EVPC

Pathogenic Agent

Transmission occurs during crowding

Parainfluenzavirus 3 (PI-3), Adenovirus, REO virus, Rhinovirus, Coronavirus, ECBO virus, (BRSV, BVD/MD).

Secondary Agents:
Pasteurella hemolytica and multocida, Mycoplasms, Chlamydia, Staphylococci, Haemophilus somnus, Actinomyces pyogenes.

Etiology

Most of the viruses listed above cause only mild respiratory distress. An outbreak of disease occurs when a virus, host and environment interact in a specific complex way.Most susceptible to infection are calves aged two weeks to 6 months, and transmission of pathogens occurs most often during crowding on the farm or in transit. In general, high population density increases the risk of transmission. Possibility of infection depends on several factors. A calf's unique immune status will partly determine its susceptibility. It's immune status depends on the amount and diversity of maternal antibodies it acquired, and how well the calf has developed its own individual immunity. Prior infection with BVDV, or immunosuppressive treatments predispose calves to viral pneumonia. Certain environmental factors seem to reduce herd resistance to infection. Housing, climate conditions, and stress, caused by a variety of sources including weaning, transport, arrival procedures, handling, dehorning or nutritional changes can suppress immune response and disease resistance. Debilitation of the calf's defense system is another infection factor. The pulmonary defense system is compromised by viral infection, thereby allowing bacteria to gain access to the lower airways. Bacterial colonization of the lungs is followed by inflammation and results in severe bronchopneumonia.

Clinical Signs

Nasal discharge

During early stages of infection body temperature rises to 40 to 42°C (104 - 108°F). Infected animals become depressed and anorectic, their respiration is accelerated. The harsh, hacking cough in the beginning becomes moist and painful, and is accompanied by dyspnea.

Nasal discharge changes from serous to mucopurulent during the following days. Often there is mild diarrhea. Auscultation reveals crackles and loud and harsh breathing sounds over the affected areas. In case of pleurisy there are pleuritic friction rubs audible. Degree of clinical findings depends on the causative agents and the immune status of the calf. Cases of average severity recover in 4 to 7 days if there is no secondary bacterial infection.

Diagnosis

Fever, cough, results of auscultation and age of affected animals are easily recognized as signs of pneumonia. Collect samples of nasopharyngeal swabs, transtracheal wash or lung tissue post mortem to isolate the specimen involved.

Selection of antibiotics should be based on antibiotic susceptibility testing.

Differential Diagnosis

IBR, BRSV, bacterial pneumonia, lungworm pneumonia, aspiration pneumonia

Prevention

• feed at least 2 l (0,5 gal) of colostrum during the first two hours
• improve endogenous defense mechanisms prior to stressful events by paramunisation
• induce and improve acquired immunity of herds by vaccination (IBR, PI-3, BVDV, BRSV, Pasteurella, Hemophilus somnus
• revaccinate regulary to maintain vaccination status
• make sure calves are weaned well in advance of stressful events (transportation, changes in nutrition, cold seasons)
• vaccination, deworming and dehorning should be completed at least 3 weeks prior to shipment or entry to a feedlot
• cleaning and disinfection of animal houses and transporting equipment at regular intervals helps to prevent spreading of virus
• isolate new animals for at least a week and screen them for diseases
• optimize housing and management conditions (e.g.quarantine, hygiene, desinfection, vector control)
• rodent control
• fly control
• disinfection
• consider adopting the principle of closed herds

Treatment

Virus pneumonia does not respond to antibiotics. However antibacterial therapy is necessary because there is always a high risk of secondary bacterial pneumonia. Usually you have to start therapy before you know exactly what specimen is involved and to what kind of antibiotic it will respond. Therefore you should base your initial treatment on prior experiences with antibiotics in this area. If the animals fail to respond within three days of treatment change to broad spectrum antibiotics. Symptomatic and supportive treatment includes immunostimulating drugs, non steroidal anti-inflammatory drugs (NSAID), bronchodilatators and secretolytics.

Literature

• Blood, D.C., Radostis, O.M., Veterinary Medicine, 1989
• Dyer, R.M., The Bovine Respiratory Disease Complex: A Complex Interaction of Host, Environmental, and Infectious Factors, Compendium on Continuing EducationVol 4, No7, July 1982
• Fraser, C.M. et al., The Merck Veterinary Manual, 1991
• Hofmann, W., Rinderkrankheiten Band 1, 1992
• Mantey, S., Heifer Enemy No.1, Dairy Herd Management, December 1993
• Smith, B. P., Large Animal Internal Medicine, 1990