Section 8 Bovine Respiratory Disease (BRD)
- Louise Britton
- Research Officer, Central Veterinary Research Laboratory, Backweston, Celbridge, Co. Kildare, Ireland
Bovine respiratory disease (BRD) remains an important cause of morbidity and mortality in cattle. Good management practices, early detection of disease and appropriate treatment of infection are critical to avoid, minimise and control disease outbreaks. Clinical signs consistent with BRD may include but are not restricted to: depression, pyrexia, anorexia and loss of condition, serous to muco-prurulent ocular and/or nasal discharges with/without diphtheritic plaques, increased respiratory rate and effort with a variable abdominal component, stridor breathing and/or the presence of a cough, abnormal lung sounds ranging from an absence to the presence of crackles and wheezes, increased heart rate and abortion.
Following exposure, disease outcome depends on a range of pathogen, host and environmental effects. To cause BRD, pathogens must successfully manipulate or evade host defences, including the resident microflora, mucocillary escalator, antimicrobial peptides and proteins, and innate and adaptive immune responses (Ackermann, Derscheid, and Roth 2010, Caswell (2014)).
8.1 Bacterial Bovine Respiratory Disease
RVL submissions are an example of a passive surveillance system. In 2018, 542 submitted carcasses were diagnosed as BRD on post mortem examination. A breakdown of the number of cases, by agent and age group, can be seen in Table 8.1. Where two or more organisms may have been identified, the final diagnosis represents what would have been considered by the pathologist as the primary cause of disease.
Throughout 2018, bacterial agents were identified as the main cause of BRD in 64.3 per cent of submissions (Tables 8.1, 8.2 and 8.3). Reflecting the multi-factorial nature of the BRD complex, bacterial pathogens may also be identified in healthy cattle, but at a lower rate than those with acute disease (Timsit et al. 2017).
Mannheimia haemolytica and Pasturella multocida are Gram-negative commensals of the nasopharynx and an important cause of respiratory disease in cattle, sheep and goats. In particular, causing the cattle disease known as shipping fever or bovine pneumonic pasteurellosis/ mannheimiosis. Healthy animals can carry M. haemolytica as a commensal without developing clinical signs. When animals are stressed (e.g. at housing or during transportation), and/or become infected with viruses. When animals are stressed, for example at housing or during transportation, M. haemolytica can replicate and be inhaled into the lower respiratory tract. Other opportunistic pathogens can commonly invade following damage to tissue.
Figure 8.1: Characteristic cranioventral fibrinous bronchopneumonia (arrows) caused by Mannheimia haemolytica. Photo: Cosme Sánchez-Miguel.
During 2018, the most frequently detected primary pathogens associated with BRD were P. multocida, M. haemolytica (Figure 8.1) and M. bovis, which accounted for nearly half of all agents diagnosed on post mortem examination (see Table 8.2 and Figure 8.3). This is consistent with data from the immediately preceding years, with the exception of M. bovis which has increased (Figure 8.8).
| Organism Group | Calves | Weanlings | Adult Cattle | Total |
|---|---|---|---|---|
| Bacterial | 227 (69.2) | 76 (55.5) | 41 (54.7) | 344 (63.7) |
| Viral | 38 (11.6) | 35 (25.5) | 13 (17.3) | 86 (15.9) |
| No agent identified | 40 (12.2) | 5 (3.6) | 9 (12.0) | 54 (10.0) |
| Parasitic | 20 (6.1) | 20 (14.6) | 10 (13.3) | 50 (9.3) |
| Other | 1 (0.3) | 1 (0.7) | 2 (2.7) | 4 (0.7) |
| Fungal | 2 (0.6) | 0 (0.0) | 0 (0.0) | 2 (0.4) |
| Note: | ||||
| Calves:1-5 months old, | ||||
| Weanlings: 6-12 months old | ||||
| Adult Cattle: over 12 months old |
Mycoplasma bovis is associated with a characteristic cuffing bronchopneumonia and, in severe cases, multifocal pulmonary abscessation (Figure 8.2); it can also cause arthritis and otitis media. Mycoplasma bovis associated pneumonia can occur at any age. It has been associated with outbreaks in feedlot cattle and sometimes is followed by an outbreak of polyarthritis following the initial respiratory presentation. Mycoplasma bovis is capable of causing pneumonia on its own, or as part of the bovine respiratory disease complex where viral infections often cause the initial insult that damages the respiratory mucosa. This can reduce the activity of the cilia and weaken the immune defences of the respiratory tract. The animal’s immune status is important in the development of mycoplasma pneumonia; failure of passive transfer is a risk for the increased severity of respiratory disease in young calves.
Similar to the rest of the pneumonia pathogens, nonspecific respiratory defences can be compromised by many risk factors such as viral pathogens, changes in environmental temperature, heat or cold stress, overcrowding, transport, poor air quality and poor nutrition. Mycoplasma bovis is capable of persisting with or without causing clinical disease for variable periods of time making shedding patterns difficult to predict (Carty 2017).
Figure 8.2: Bovine lung. Rounded foci of caseous necrosis (green arrow) surrounded by a rim of granulation tissue and centered around the airways in a calf with Mycoplasma bovis}. Photo: Cosme Sánchez-Miguel.
Ante-Mortem samples
When choosing what ante-mortem samples to collect, the suspect pathogen, stage of disease and test to be employed are important considerations:
- BRD associated pathogens may be identified through bacterial culture, viral isolation or molecular techniques such as polymerase chain reaction (PCR) based assays.
- In addition to nasal swabs and blood samples, transtracheal washes and bronchoalveolar lavages may be used for agent identification.
- Samples should be collected from a representative population. Samples from untreated acute clinical cases are ideal for successfully identifying the primary cause of disease, particularly in the case of viruses. Chronic cases often have superimposed secondary bacterial infections. (Cooper and Brodersen 2010).
In 2018, other less commonly encountered organisms included Haemophilus somnus and Trueperella pyogenes (formerly Arcanobacterium pyogenes) (Table 8.2). H. somni (formerly Haemophilus somnus), causes septicemic infection with clinical presentations, including pneumonia, polyarthritis, myocarditis, abortion and meningoencephalitis. The respiratory system is usually the initial site of replication followed by spread to the CNS via the circulation. The CNS form is called thrombotic meningoencephalitis (TEME), previously called TEME. All age group of animals can be infected with H. somni, but 6 months to 2 years tends to be most frequent age of animals affected. Clinical signs include depression, high temperatures, dyspnoea, discharge from eyes and nose and some animals can display stiffness. When H. somni is involved in pneumonia it is often overgrown by Pasteurella spp. organisms. H. somni is an opportunistic pathogen that complicates viral infection and increases the severity of infection with other bacterial agents.
Trueperella pyogenes is an opportunistic bacterium related to various pyogenic infections in animals. A great variety of clinical manifestations has been attributed to T. pyogenes infections in domestic animals, including mastitis, pneumonia and metritis. Usually, it is a secondary pathogen in pneumonia where tissues have been previously acutely damaged by other pathogenic respiratory agents.
| Organism | No. of cases | Percentage |
|---|---|---|
| Pasteurella multocida | 96 | 17.7 |
| Mannheimia haemolytica | 83 | 15.3 |
| Mycoplasma bovis | 73 | 13.5 |
| No agent identified | 55 | 10.1 |
| RSV | 54 | 10.0 |
| Dictyocaulus spp | 51 | 9.4 |
| Others minor organisms | 36 | 6.6 |
| Histophilus somni | 32 | 5.9 |
| Trueperella pyogenes | 18 | 3.3 |
| IBR virus | 11 | 2.0 |
Figure 8.3: Relative frequency of the top ten pathogenic agents detected in BRD cases diagnosed on post-mortem examination, (n= 542 ).
| Organism Group | Calves | Weanlings | Adult Cattle |
|---|---|---|---|
| BHV4 | 2 (0.6) | 0 (0.0) | 4 (5.3) |
| Bibersteinia trehalosi | 1 (0.3) | 1 (0.7) | 2 (2.7) |
| BVD virus | 2 (0.6) | 0 (0.0) | 0 (0.0) |
| Coronavirus | 0 (0.0) | 2 (1.5) | 0 (0.0) |
| Dictyocaulus spp | 20 (6.1) | 20 (14.6) | 10 (13.3) |
| Fungal | 1 (0.3) | 0 (0.0) | 0 (0.0) |
| Histophilus somni | 22 (6.7) | 6 (4.4) | 4 (5.3) |
| IBR virus | 4 (1.2) | 1 (0.7) | 6 (8.0) |
| Mannheimia haemolytica | 61 (18.6) | 12 (8.8) | 10 (13.3) |
| Mycobacterium bovis | 2 (0.6) | 0 (0.0) | 1 (1.3) |
| Mycoplasma bovis | 48 (14.6) | 15 (10.9) | 10 (13.3) |
| No agent identified | 40 (12.2) | 5 (3.6) | 9 (12.0) |
| Other | 1 (0.3) | 1 (0.7) | 2 (2.7) |
| Others minor organisms | 24 (7.3) | 9 (6.6) | 3 (4.0) |
| Pasteurella multocida | 51 (15.5) | 36 (26.3) | 9 (12.0) |
| Pasteurella spp | 0 (0.0) | 1 (0.7) | 1 (1.3) |
| PI3 | 1 (0.3) | 3 (2.2) | 0 (0.0) |
| RSV | 28 (8.5) | 24 (17.5) | 2 (2.7) |
| Salmonella dublin | 5 (1.5) | 0 (0.0) | 0 (0.0) |
| Trueperella pyogenes | 15 (4.6) | 1 (0.7) | 2 (2.7) |
| Note: | |||
| Calves:1-5 months old, | |||
| Weanlings: 6-12 months old | |||
| Adult Cattle: over 12 months old |
Ante-Mortem samples (continued)
- Nasal swabs target upper respiratory tract pathogens (Cooper and Brodersen 2010) and help identify the presence of respiratory viruses (Caswell et al. 2012). Multiple nasal swabs from the same animal or multiple animals can be submitted and pooled for PCR analysis.
- Transtracheal washes and bronchoalveolar lavages are optimal for detecting lower respiratory tract pathogens and are preferable to identify the presence of BRD associated bacteria; they also facilitate cytological examination (Cooper and Brodersen 2010,Caswell2012).
- The humoral immune response can be identified through serological techniques such as enzyme linked immunosorbant assays (ELISAs) using blood samples; the presence of antibodies may indicate exposure, previous vaccination or passive immunity.
Bibersteinia trehalosi (previously known as Pasteurella trehalosi) is a commensal organism of upper gastrointestinal tract. It is thought that under stressful conditions the bacteria can multiply rapidly and spread to the lungs and other organs, causing an acute systemic infection. B. trehalosi is an important pathogen of sheep, typically associated with acute systemic infections causing death in growing lambs. It is comparatively infrequently identified as a pathogen in cattle; however, isolates are typically associated with bronchopneumonia.
Salmonella Dublin was detected as the causative pathogen in five calves diagnosed with respiratory disease. Enteric, septicaemic, and reproductive diseases are all possible manifestations of Salmonella infection, with pneumonia being a common manifestation of Salmonella Dublin infection in calves
8.2 Viral Bovine Respiratory Disease
Viral agents were implicated as the primary cause of 15.3 per cent BRD cases diagnosed on post mortem examination during 2018 (Table 8.1). A range of viruses are involved in the BRD complex and may lead to the development of broncho-interstitial pneumonia. As they are inhaled, gross lung lesions typically follow a cranio-ventral distribution and can vary from mild to severe. Often, two or more viruses are present simultaneously. Importantly, viral infection may in turn predispose to bacterial infection. Similarly to the period 2010 to 2017, during 2018 bovine respiratory syncytial virus (BRSV) and bovine herpesvirus-1 (BHV1) were counted among the most frequently identified pathogenic agents, found in 10 and 2 per cent of all of BRD cases diagnosed on post mortem examination, respectively (Table 8.2).
BRSV infections are associated with respiratory disease in young animals. Although capable of independently producing primary respiratory disease, it is an important component of the BRD complex affecting cattle younger than one year and ocasionally adults by predisposing animals to secondary bacterial infections (i.e. M. haemolytica). Initial exposure to BRSV can produce acute pneumonia, with subsequent exposure usually resulting in milder disease. The spectrum of clinical signs can range from mild to life-threatening in susceptible cattle. In outbreaks, morbidity tends to be high, and the case fatality rate can be 0–20 per cent. Fever, dyspnoea, anorexia and depression are typical clinical signs. Gross lesions can include a diffuse interstitial pneumonia with subpleural and interstitial emphysema along with interstitial oedema.
BHV1 can be divided into three subtypes by restriction endonuclease analysis; whereas subtype 1.1 and 1.2a are associated with the development of infectious bovine rhinotraceitis (IBR; Figure 8.5), subtype 1.2b is associated with infectious pustular vulvo-vaginitis and balano-posthitis (Raaperi, Orro, and Viltrop 2014). As implicated in respiratory disease, parainfluenza 3 (PI3), bovine herpesvirus 4 (BHV4), bovine viral diarrhoea (BVD) and bovine coronavirus (BoCo) virus were found sporadically but in very low numbers (Table 8.3).
Figure 8.4: Viral respiratory infections in carcasses. Monthly number of viral pneumonia diagnoses by primary microorganism.
Figure 8.5: The trachea (opened) of a bovine with severe suppurative tracheitis caused by Bovine Herpes Virus (IBR-BHV1). Photo: Cosme Sánchez-Miguel.
Sampling for virology
Nasal Swabs
- Select animals for swabbing carefully, for example those early in the disease which may only present with raised temperature or comrades which have not yet developed clinical signs.
- Use plain swabs, moistered with bottle water or saline solution.
- Swad as deep as posible but at least 1.5 inches, expecting resistance.
- Rotate and rub against nasal passage, targeting clear and/or milky secretions if present.
- Multiple swabs (e.g. 5-6) from suitable animals increase chances of detecting the virus, as sheeding can drastically decrease afte 5 days.
- Multiple swabs (e.g. 5-6) can be pooled for laboratory testing, minimizing cost while maximazing diagnostic potential.
Figure 8.6: Number of diagnoses of parasitic bronchopneumonia by month during 2018 (n= 51 ).
8.3 Trends
Figure 8.7: Trends in the incidence of parasitic pneumonia in the carcasses (all ages) submitted to the RVLs from 2010 to 2017.
Figure 8.8: Trends in the incidence of viral pneumonia in the carcasses (all ages) submitted to the RVLs from 2010 to 2017.
Figure 8.9: Trends in the incidence of bacterial pneumonia in the carcasses (all ages) submitted to the RVLs from 2010 to 2017.
8.4 Parasitic Bovine Respiratory Disease
From 2010 to 2017, the RVLs observed an increase in cases of parasitic bronchopneumonia peaking at 21 per cent of diagnosed BRD submissions in 2017 (Figure 8). During 2018, Dictyocaulus species were detected in 9.4 per cent of BRD submissions (Table 8.1). Lungworm infections are associated with cattle that are or have been recently at pasture and tend to occur in the late summer and autumn. Grossly, adult lungworms are usually found in the caudal bronchi (Caswell et al. 2012). However, animals in the acute prepatent stage can be difficult to diagnose as the adult lungworms will not be visible in the lungs and their eggs will not be found upon analysis of faecal samples (Caswell et al. 2012). Re-infection syndrome may occur in previously infected cattle which are partially immune to the parasites. It typically follows a subsequent challenge from heavily contaminated pasture, leading to the development of respiratory signs. However, the infection will not become patent; adult lungworms will not be found in the lungs and eggs will not be produced. Following six cases in January 2018, parasitic bronchopneumonia was not subsequently identified until June (Figure 8.4). Thereafter, it was diagnosed every month, with the largest numbers identified in August.
Figure 8.10: Adult Dictyocaulus viviparus in a bovine trachea. Photo: Cosme Sánchez-Miguel.
References
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Caswell, JL. 2014. “Failure of Respiratory Defenses in the Pathogenesis of Bacterial Pneumonia of Cattle.” Veterinary Pathology 51 (2). SAGE Publications Sage CA: Los Angeles, CA: 393–409.
Timsit, Edouard, Jennyka Hallewell, Calvin Booker, Nicolas Tison, Samat Amat, and Trevor W Alexander. 2017. “Prevalence and Antimicrobial Susceptibility of Mannheimia Haemolytica, Pasteurella Multocida, and Histophilus Somni Isolated from the Lower Respiratory Tract of Healthy Feedlot Cattle and Those Diagnosed with Bovine Respiratory Disease.” Veterinary Microbiology 208. Elsevier: 118–25.
Carty, C. 2017. “Mycoplasma Bovis.” Veterinary Ireland Journal. http://www.veterinaryirelandjournal.com/images/pdf/large/la_jun_2017.pdf.
Cooper, Vickie L, and Bruce W Brodersen. 2010. “Respiratory Disease Diagnostics of Cattle.” The Veterinary Clinics of North America. Food Animal Practice 26 (2): 409–16. doi:10.1016/j.cvfa.2010.04.009.
Caswell, Jeff L, Joanne Hewson, Ðurđa Slavić, Josepha DeLay, and Ken Bateman. 2012. “Laboratory and Postmortem Diagnosis of Bovine Respiratory Disease.” The Veterinary Clinics of North America. Food Animal Practice 28 (3): 419–41. doi:10.1016/j.cvfa.2012.07.004.
Raaperi, Kerli, Toomas Orro, and Arvo Viltrop. 2014. “Epidemiology and Control of Bovine Herpesvirus 1 Infection in Europe.” Veterinary Journal (London, England : 1997) 201 (3): 249–56. doi:10.1016/j.tvjl.2014.05.040.
A cooperative effort between the VLS and the SAT Section of the DAFM