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Title: Diagnosi di campo del complesso della malattia respiratoria bovina (BRD) nel vitello
Other Titles: Field diagnosis of bovine respiratory disease complex (BRD) in calf
Authors: Franzoni, Alessandro
Issue Date: 15-Oct-2020
Publisher: Università di Parma, Dipartimento di Scienze Medico-Veterinarie
Document Type: Master thesis
Abstract: Abstract: Bovine respiratory disease (BRD) is a multifactorial disease with both short-term and longterm economic impacts on bovine production. In veal and dairy operations, the peak of clinical incidence of BRD occurs during the first two months of life. Accurate diagnosis of BRD during this time is therefore necessary for two reasons: 1. to establish an appropriate treatment plan and avoid the subsequent negative outcomes caused by not treating affected animals; 2. to avoid unjustified and inappropriate use of antimicrobials due to falsepositive test results. However, a distinction between active pneumonia (i.e. infection of the lower airway with signs of inflammation) and nonactive pneumonia (i.e. upper airway BRD, scarring, fibrosis of the lung) is essential to establishing an appropriate treatment plan (Berman, J., et al.,2019). The BRD complex is a medical challenge in veterinary medicine because clinical diagnosis is difficult, especially because of a lack of gold standard diagnostic tests. Being able to find a gold standard test for early diagnosis and prognosis of BRD remains a major challenge for dairy cattle industries (Buczinski, S., et al.,2014). Different strategies have been implemented to assess active pneumonia in pre-weaned calves. For producers, diagnosis of active pneumonia is typically based on visual signs of respiratory disease (e.g. anorexia, depression, nasal and ocular discharge, cough, and ear position), associated or not with an increased rectal temperature. In recent years, a systematic scoring method has been developed. The calf respiratory scoring system is now widely used in North America, and is a method that can be easily applied by producers to screen calves for active pneumonia. However, this diagnostic approach is only moderately accurate for identifying sick (sensitivity [Se] = 62.4%; 95%; Bayesian credible intervals [BCI]: 47.9, 75.8%) and healthy animals (specificity [Sp] = 74.1%; 95% BCI: 64.9, 82.8%). For veterinarians, diagnosis of active pneumonia is typically based on the presence of visual signs of respiratory disease and abnormal lung sounds, such as increased bronchial sounds, crackles, wheezes, or the absence of respiratory sounds, on thoracic auscultation (AUS). But the accuracy of AUS, like that of the CRSC, is questionable, with a moderate Se (Se = 72.9%; 95% BCI: 50.1, 96.4%), and quite poor Sp (Sp = 53.3%; 95% BCI: 43.3, 64.0%). Thus, these two tests are imperfect, and supplementary tools are necessary to establish an accurate diagnosis of active pneumonia. In the past few years, thoracic ultrasonography (TUS) has been developed and used to diagnose BRD in calves. Among the lesions that can be detected with TUS, depth of lung consolidation was one of the abnormalities most closely associated with a clinical outcome (e.g. euthanasia or death) in a case-control study involving feedlot 2 calves, and was, above all, the easiest parameter to measure. Moreover, inter-observer agreement for identifying calves with this type of lesion was substantial. Ultrasonographical evidence of lung consolidation is apparent when inflammatory and infectious processes affect the lung parenchyma, resulting in a non-aerated lung. When pulmonary consolidation is present, lung tissue appears hypoechoic, and its echo texture may resemble liver parenchyma. This differs from normal lung tissue, which is anechoic due to its gas content (Berman, J., et al.,2019). One of the most interesting assets of thoracic ultrasonography is that it can be easily performed calf-side and gives an immediate result, in contrast to other techniques like radiographs. For these reasons, it could be potentially useful in the field when examining a calf with suspected BRD (Buczinski, S., et al.,2013). TUS can be performed with a portable rectal US machines (already in use by bovine veterinarians for reproductive examinations). When combined with respiratory scoring, systematic TUS allows the differentiation of BRD into specific practical subtypes, including upper respiratory tract disease, clinical pneumonia, and subclinical pneumonia, all of which can be performance limiting (Ollivett, T. L., Buczinski, S.,2016). Different reaserches have try to investigate the accuracy of TUS. Two different studies reported similar accuracy values for TUS to detect active pneumonia: a Se of 0.79 (95% BCI: 0.66, 0.91) and Sp of 0.93 (95% BCI: 0.87, 0.97) (Buczinski, S., et al.,2015); Se of 0.77 (95% BCI: 0.60, 0.89) and Sp of 0.93 (95% BCI: 0.87, 0.97) (Buczinski, S., et al., 2016). The study that reported the higher accuracy value in TUS investigation was conducted by (Berman, J., et al.,2019). It reported a sensitivity of 0.89 (95% BCI:0.55, 1.0) and a specificity of 0.95 (95% BCI: 0.92, 0.98), respectively. Other intersting tecniques, useful for field diagnosis, are bronchoalveolar lavage (BAL) and transtracheal aspiration. In practice, transtracheal aspiration (TTA), and bronchoalveolar lavage (BAL) have been used for sampling the respiratory tract. Transtracheal aspiration samples the bronchial bifurcation, but has the disadvantage of being more time-consuming, expensive, and invasive, while at the same time holding a certain risk (e.g., hemorrhage, emphysema, infection) for the animal. BAL can be performed with a reusable sterilized BAL catheter without endoscopic guidance. This makes it easier for large numbers of animals to be sampled at the lung level in a short time frame and with a low cost per calf. However, an important point of criticism is the nasal passage of the BAL catheter, which may inoculate the BAL sample with either respiratory pathogens of the nasal cavity or commensal microflora (Van Driessche, L., et al.,2017). Also, the accuracy of BAL was calculated, data suggest a sensitivity (Se) of 81% (95% CI, 56–94%), and a specificity (Sp) of 75% (95% CI, 36–95%) (Ollivett, T. L., et al., 2015).
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