Chronic pneumonia and polyarthritis syndrome in a feedlot calf

Abstract

A feedlot heifer was diagnosed with chronic pneumonia and polyarthritis syndrome (CPPS), which was confirmed on postmortem examination. The syndrome is caused by Mycoplasma bovis; however, available data support the theory that other pathogens play a role in predisposing to this disease. Continued research on CPPS focuses on pathogenesis, treatment, and prevention.

A fall-placed heifer calf from the chronic pen of a feedlot was humanely euthanized and necropsied. The animal had a history of lameness and respiratory disease for 1 mo. The heifer had been in the feedlot for approximately 5 wk, having entered with a group of 350 heifer calves at an average weight of 225-kg. Upon arrival, the animals were processed (ear-tagged and branded), treated with ivermectin (Ivomec Pour-on; Merial, Baie d’Urfe, Quebec), 0.5 mg/kg bodyweight (BW), topical, and implanted with testosterone/estradiol (Component E-H; Elanco Animal Health, Guelph, Ontario). The heifers were administered a Mannheimia hemolytica and Histophilus somni vaccine (Somnu-Star Ph; Novartis, Mississauga, Ontario); a 4-way viral vaccine for Infectious bovine rhinotracheitis virus, Bovine viral diarrhea (BVD) virus, Parainfluenza-3 virus, and Bovine respiratory syncytial virus (StarVac 4 Plus; Novartis, Mississauga, Ontario); and a 7-way clostridial vaccine (Vision 7; Intervet, Whitby, Ontario). The heifers were also administered oxytetracycline (Tetra-Dure LA 300; Merial, Baie d’Urfe, Quebec), 5 mg/kg BW, SC, upon entry to the feedlot as a prophylactic measure.

At 3 and 6 d on feed, this heifer was pulled from its pen by the feedlot medical crew and treated for lameness. Ceftiofur (Excenel RTU; Pfizer, Kirkland, Quebec), 1 mg/kg BW, IM, and dexamethasone (Rafterdex; Alfasan, Woerden, Holland), 20 mg, IM, were administered on day 3, and enrofloxacin (Baytril 100; Bayer, Toronto, Ontario), 10 mg/kg BW, SC, and flunixin (Banamine; Schering Canada, Pointe-Claire, Quebec), 2.2 mg/kg BW, IM, were given on day 6. At 13 and 19 d on feed, the heifer was pulled from its pen because of signs of respiratory disease. On these days, her temperature was measured at 40.5°C and 41.1°C, respectively. The heifer was treated for bovine respiratory disease (BRD) with tilmicosin (Micotil; Elanco Animal Health, Guelph, Ontario), 10 mg/kg BW, SC, on day 13 and florfenicol (Nuflor; Schering Canada, Pointe-Claire, Quebec), 40 mg/kg BW, SC, on day 19 and placed in a hospital pen. The lameness and respiratory disease did not improve, and the heifer was euthanized 2 wk later.

The postmortem examination revealed moderate broncho-pneumonia of the cranioventral lung lobes. Several small, firm, raised, nodular lesions containing a dry, caseous material and measuring approximately 2–10 mm were disseminated throughout the lungs. The associated lung parenchyma was dark red and firm. The capsules of the stifle joints were bilaterally distended with an increased amount of viscous synovial fluid and a large amount of thick yellow fibrinous material. The abomasum and proximal portion of the duodenum contained several large trichobezoars. An abscess, measuring approximately 4 cm, was identified on the right lateral aspect of the neck. This was assumed to be an injection site with bacterial contamination.

The postmortem findings, in combination with the clinical picture and history of poor response to treatment, were characteristic of the chronic pneumonia and polyarthritis syndrome (CPPS) seen in feedlots in recent years: CPPS has become an important concern for the feedlot industry as the syndrome has evolved (1,2, Shahriar FM, Clark EG, personal communication). It is characterized by pneumonia that is nonresponsive to antibiotics and, sometimes, a concurrent polyarthritis. The major organism recovered from these CPPS cases is Mycoplasma bovis (1–3, Shahriar FM, Clark EG, personal communication). Ideally, further diagnostic tests, such as bacterial culture of lung samples, bronchoalveolar lavage, polymerase chain reaction, or immunohistochemical staining, would have been carried out on this case to identify M. bovis (Shahriar FM, Clark EG, personal communication), but that was not possible in this situation.

Mycoplasma spp. are unique microorganisms associated with several disease manifestations, including this pneumonia-arthritis syndrome (1–4). Mycoplasma are intracellular organisms that lack a cell wall. They are generally host-specific and induce chronic disease with high morbidity and low mortality. In addition to CPPS, M. bovis also causes mastitis, otitis media, and reproductive disorders in cows and bulls (3, Shahriar FM, Clark EG, personal communication).

The lesions of CPPS are distinct, and the syndrome is commonly diagnosed on gross postmortem examination. Lung lesions include a chronic cranioventral bronchopneumonia with nodular, firm, yellow lesions throughout the lung lobes, often projecting above the pleural surface. These lesions vary from 1–2 mm to 1–2 cm in size and contain caseous necrotic material (Figure 1). Affected joints are swollen due to increased synovial fluid with fibrinopurulent exudate. The infection commonly spreads into the tendon sheaths, bursae, and joint capsules (2,3, Shahriar FM, Clark EG, personal communication), causing severe lameness (Figure 2). The chronic pneumonia and polyarthritis syndrome must be differentiated from other important disease syndromes, including M. hemolytica, H. somni, and Pasteurella multocida pneumonia and acute or chronic BVD. In contrast to the chronic bronchopneumonia of CPPS, P. multocida and M. hemolytica cause an acute fibrinous bronchopneumonia, usually in the first 2 wk of the feeding period. Histophilus somni causes an acute suppurative pleuropneumonia at approximately 45 d (4). Although eradicated from North America, contagious bovine pleuropneumonia (caused by M. mycoides subspecies mycoides small colony type) is also a differential diagnosis.

Figure 1.

The characteristic caseous necrotic lung lesions of chronic pneumonia and polyarthritis syndrome.

Figure 2.

A feedlot calf in lateral recumbency due to severe lameness, like that of chronic pneumonia and polyarthritis syndrome.

While M. bovis has been consistently associated with CPPS, the exact role of the organism in this syndrome has not been defined and is made difficult due to isolation of Mycoplasma spp. from both healthy and diseased animals (2,5). Mycoplasma bovis has been reported to approach a prevalence of 100% by 2 wk after entry into a feedlot (5). Animals with disease associated with M. bovis are chronically ill and fail to thrive, similar to those with chronic BVD virus infection. Bovine viral diarrhea virus induces immunosuppression and increases susceptibility to disease caused by M. bovis (1). However, a recent study suggests otherwise. While BVD virus infection is more prevalent in calves with bacterial pneumonia (as compared with those with either viral or no pneumonia), the prevalence of BVD virus infection is not different in calves with lesions indicative of mycoplasma pneumonia from that in calves with lesions indicating bacterial bronchopneumonia. This suggests that while the immunosuppression of BVD virus predisposes to bacterial and mycoplasma respiratory disease in general, there is no specific correlation between BVD and CPPS (3).

The role of M. bovis in CPPS may be as an opportunistic or secondary invader. Mycoplasma bovis can be cultured from 80% to 100% of pneumonic lungs in the feedlot (6), suggesting that the presence of the organism in culture is not sufficient to prove M. bovis as the exclusive causative agent. It is probable that other organisms are present and play some role in the pathogenesis of CPPS (2,6). In addition, increased severity of clinical signs has been reported for mixed infections of M. bovis and bacterial pathogens, including M. hemolytica and P. multocida (2,7), supporting the theory that some relationship exists between M. bovis and bacterial pathogens. Evidence exists to support the hypothesis that M. bovis colonizes and perpetuates the lung lesions initiated by common bacterial pathogens (M. hemolytica, H. somni, and/or P. multocida). This suggests that M. bovis is a secondary invader, and the key to prevention of CPPS may ultimately lie in controlling these bacterial pneumonias (3,6).

Treatment of CPPS has proved especially challenging. Mycoplasma bovis is inherently refractory to many antibiotics, as it lacks a cell wall. The organism is also resistant to certain antibiotics, including tetracycline, tilmicosin, and spectinomycin (7). Although some clinical improvement may be noted with certain antibiotic treatments, the organism will not be eliminated from the animal. Continued isolation of M. bovis has been reported following treatment with several antibiotics (including tilmicosin and spectinomycin), despite improvements in the clinical picture of the treated animals (8). The value of antimicrobial treatment for M. bovis infections should be questioned. While the antimicrobial therapy may be eliminating bacterial pathogens that initiated the disease, it is not effective against M. bovis in a chronically ill animal. This underlines the welfare implications of CPPS, including chronic lameness and respiratory distress that induce pain and suffering.

Research into new antibiotic compounds is focused on producing a product that is effective in treating M. bovis infection. Tulathromycin (Draxxin; Pfizer, New York, New York), a new macrolide antibiotic that is not yet licensed in Canada, has been reported to be effective in the treatment and prevention of the respiratory signs of BRD, including those of M. bovis infection (8). However, its efficacy needs to be proven in clinical trials. Vaccination against M. bovis has been investigated, and good levels of protection, decreased clinical signs, and no adverse effects have been reported for a M. bovis vaccine containing saponin as an adjuvant. Saponin has been shown to boost immune response, especially against mycoplasmas, and its successful use in vaccines has previously been demonstrated for other mycoplasma infections in small ruminants (9). However, currently, no vaccine against M. bovis is commercially available in Canada.

Chronic pneumonia and polyarthritis syndrome has become important and of concern. Recent data suggest a strong correlation between common bacterial respiratory pathogens and M. bovis in causing the CPPS and dispute the previously reported synergism between BVD virus and M. bovis. Continued research will allow further insight into, and understanding of, the syndrome and its pathogenesis, prevention, and treatment.