Читать книгу Farm Animal Medicine and Surgery - Graham R Duncanson - Страница 163

BRD is a syndrome affecting calves and growing cattle. Good animal husbandry is vital for its prevention and treatment. Vaccination and treatment with antibiotics and NSAIDs should always be secondary to changes in animal husbandry, particularly modifications to ventilation, prevention of draughts and lower stocking rates. Causative agents include the viruses and bacteria in the following list:

• Bovine herpesvirus 1 (BHV 1) will cause respiratory disease, particularly in older growing cattle, which is called infectious bovine rhinotracheitis (IBR). It will also cause the reproductive disease infectious pustular vulvovaginitis (IPV). The respiratory form of the disease manifests as serious pyrexia with an ocular and nasal discharge. Remarkably, the clinical course of the disease is much improved by injections of a combination of penicillin and streptomycin. The disease is readily detected by serology, which can be used in herd eradication schemes. There are good vaccines which are available either as live vaccination for intra-nasal or im use or as attenuated dead vaccination for sub cut injection. Care should be taken to use a marker vaccine if later eradication schemes are envisaged. See also ‘Bovine herpesvirus 1 (BHV 1)’ as a cause of abortion under ‘Diseases of the Reproductive System’ below.

• Bovine respiratory coronavirus (BRCV) has only recently been recognized as a serious potential respiratory pathogen. It now needs to be considered when investigating a BRD outbreak.

• Bovine respiratory syncytial virus (BRSV -or just plain RSV) is a very serious pathogen, particularly for young growing cattle – either suckler calves or concentrate-fed animals. It causes serious pyrexia, coughing, and nasal and lacrimal discharge. Dyspnoea and mouth breathing is a feature of advanced cases. Passive immunity helps but does not prevent the disease. There are good vaccines available.

• Bovine parainfluenza virus 3 (PI3) is a paramyxovirus which causes relatively mild disease signs but is a prime initiator for secondary bacterial infections. There are good vaccines available.

• Infectious bovine rhinotracheitis (IBR) is caused by BHV 1 (see above).

• Mannheimia haemolytica (formerly Pasteurella haemolytica) is probably the most important bacterial pathogen in the BRD complex. It can cause disease in its own right without a viral initiator. It is the main pathogen causing ‘shipping fever’. It is actually sensitive to penicillin in high doses even through it is a Gram-negative rod. However, there are a large number of other suitable antibiotics which are perhaps more effective and have a considerably longer action. NSAIDs are very useful. There are vaccines available.

• Pasteurella multocida is a bacterium that is also often found in the ‘shipping fever’ complex. It is also seen as a secondary to BRSV and PI3 infections in younger calves. It can cause pneumonia in its own right. Like M. haemolytica it is sensitive to high levels of penicillin, but more modern antibiotics and NSAIDs would be more appropriate for treatment.

• Arcanobacterium pyogenes is found at the end stage of a BRD case, i.e. it is a tertiary pathogen. Although it is sensitive to antibiotics in vitro the bacteria are infective in pus-filled abscesses. Euthanasia is the only option.

• Histophilus somni is a serious bacterial pathogen in its own right but is often linked with M. haemolytica. The bacteria can cause BRD on their own or be secondary to a virus. H. somni often occurs later on in the disease process and is difficult to treat with antibiotics. Changing the type of antibiotic used and NSAIDs are helpful treatments.

• Mycoplasma spp. include M. disbar and M. bovis. These are emerging pathogens in BRD. They synergize with other pathogens and cause fatal disease. Oxytetracycline is the antibiotic of choice. They will also infect the joints, causing acute lameness in young cattle which are already systemically ill. NSAIDs are very worthwhile treatment. The species are not included in any vaccines.

• Ureaplasma spp. may have a secondary role in BRD but it is not clear how important they are in respiratory disease. They are more important in reproductive disorders.