In cattle, DDS develops when the septic process associated with digital infections extends locally to the phalanges, navicular bone, synovial structures, or flexor tendons.1–3 A variety of common causes of lameness can initiate DDS and result in infection and necrosis of essential weight-bearing digital structures.1,2,4–8 Surgical treatment of DDS is warranted unless the affected animal is immediately slaughtered or euthanized and typically involves local debridement to remove devitalized tissues and establish drainage or amputation of the affected digit in salvage animals.1,7,9 Because such treatments are very painful, RIVP of local anesthetic solutions is often used to provide analgesia. Additionally, RIVP of antimicrobials is an effective adjunctive treatment for infections of the distal aspect of the limb.10–15
Dissemination of bacteria from distal sites of infection has been reported following RIVP in both human and veterinary patients. In 1 study,16 4 of 15 human patients undergoing treatment for osteomyelitis developed signs of systemic sepsis within 4 hours after RIVP, and 1 patient was bacteremic, which resulted in a recommendation that patients be administered systemic antimicrobials prior to initiation of RIVP. In foals with septic tibiotarsal joints, secondary septic foci have been detected in the affected limbs after RIVP with antimicrobials.17 Caudal vena caval thrombosis was detected in a Holstein cow following multiple RIVPs and treatment of DDS, despite the absence of evidence of hepatic abscesses or another source of sepsis during necropsy.18 It is possible that the use of RIVP in cattle with DDS might cause local or systemic dissemination of bacterial pathogens, and the potential for development of bacteremia following a common treatment modality in cattle warrants investigation.
The objectives of the study reported here were to determine whether bacteremia of the pedal circulation develops following RIVP of a 2% lidocaine solution administered for examination with or without debridement of digital lesions in cattle with DDS and, if so, to determine which bacterial pathogens are most commonly isolated from the pedal circulation. We hypothesized that the probability of the detection of bacteremia in the pedal circulation of cattle with DDS following RIVP would be 25%, which we extrapolated from data regarding the likelihood of detecting bacteremia in the systemic circulation of neonatal patients with clinical sepsis.19 We also hypothesized that the most common bacteria isolated from the pedal circulation of cattle with DDS would be gram-negative anaerobes because those microorganisms are frequently associated with digital disease in cattle.20
Materials and Methods
Animals—The study included 2 groups of cattle; 1 group consisted of adult cattle with DDS (DDS group) and the other group consisted of healthy adult cattle without evidence of lameness or digital lesions (healthy comparison group). The cattle with DDS (n = 9) were all > 2 years old (range, 2 to 5 years) and consisted of 3 bulls and 6 cows that were client owned. Breeds represented included Angus (5), Gelbvieh (1), Limousin (1), Holstein (1), and Santa Gertrudis (1). Inclusion criteria for cattle in the DDS group included a history of lameness > 1 week in duration and clinically apparent infection of ≥ 1 of the following structures: third or second phalanx, distal sesamoid bone, distal interphalangeal joint, or proximal interphalangeal joint. Deep digital sepsis was diagnosed on the basis of the presence of radiographic changes characteristic of a septic process or processes or the ability to directly probe a bone or joint through draining tracts or wounds in the distal aspect of the affected limb or limbs. Cattle were excluded from the DDS group if they had been administered an antimicrobial within 48 hours prior to the examination or if a long-acting antimicrobial had been administered > 48 hours before the examination that was expected to maintain therapeutic concentrations of the drug in the systemic circulation during the 48 hours prior to the examination. Following initiation of the study, cattle were enrolled in the DDS group in the order in which they were evaluated. Each limb with DDS was considered independently. Owner consent was obtained for each animal in the DDS group prior to study enrollment.
The healthy comparison group consisted of 10 crossbred beef cows > 2 years old that had not been clinically lame within the 6 months prior to examination and had no evidence of digital disease at the time of sample collection. These cattle were owned by Oklahoma State University and were cared for and housed at a university facility prior to and following sample collections for the study. The study protocol was reviewed and approved by the Institutional Animal Care and Use Committee at Oklahoma State University.
RIVP and sample collection—Each animal was restrained in a hydraulic tilt chutea that was tilted so that the animal was in a lateral position. Additionally, each limb was individually restrained. Limbs affected by DDS were identified, and a rubber tourniquet (6 cm × 60 cm × 2 mm) was placed around the limb at the level of the midmetacarpus or midmetatarsus. Hair was clipped from the skin overlying the DCDV of the affected limb extending from the coronary band to the metacarpophalangeal or metatarsophalangeal joint. The clipped area was aseptically prepared by the use of sterile 4 × 4-inch gauze sponges, sterile saline (0.9% NaCl) solution, and chlorhexidine diacetate scrub. A sterile 19-gauge winged infusion setb was aseptically placed in the DCDV distal to the tourniquet, and between 6 and 8 mL of blood was collected into a syringe. The sample syringe was removed from the winged infusion set, and 20 mL of a 2% lidocaine hydrochloridec solution from a previously unopened bottle was infused into the DCDV. The infusion set was removed from the vessel. A sterile 18-gauge needle was placed on the syringe containing the blood sample and the sample was aseptically injected into a vial for bacterial culture.d,e This sample represented the pre-RIVP blood sample. A light pressure bandage was placed over the venipuncture site. For cattle in the DDS group, additional diagnostic testing, local cleansing, or debridement of the affected digit were performed as necessary for diagnosis with or without treatment of the lesions.
Thirty to 60 minutes after the tourniquet was applied (mean, 44 minutes; range, 34 to 58 minutes), the clipped area over the DCDV was again aseptically prepared. A sterile 19-gauge winged infusion setb was aseptically placed in the DCDV distal to the tourniquet at a site at least 0.5 cm away from the first venipuncture site, and 6 to 8 mL of blood was collected for bacterial culture in the same manner as that used for the pre-RIVP sample. This sample represented the post-RIVP blood sample. Immediately following collection of the post-RIVP blood sample, the tourniquet was removed. For cattle in the DDS group, the distal aspect of the affected limb was bandaged if deemed necessary and parenteral antimicrobial, anti-inflammatory, and analgesic treatments were administered at the discretion of the attending veterinarian. The animal was then released from the chute. For each study animal, the times at which the tourniquet was placed, the pre-RIVP blood sample was collected, the RIVP was administered, and the post-RIVP blood sample was collected were recorded.
For cattle in the healthy comparison group, a limb was randomly selected for RIVP and blood sample collection. Each cow in the healthy comparison group was matched with an animal in the DDS group in terms of the duration that the tourniquet was applied and the length of time between the RIVP and collection of the post-RIVP blood sample. Additional diagnostic testing, cleansing, and debridement of the selected digit were not performed, and no drugs were administered after sample collection to the cows in the healthy comparison group.
Bacterial culture of blood samples—Blood samples were submitted to the Oklahoma Animal Disease Diagnostic Laboratory for aerobic and anaerobic bacterial cultures in accordance with the laboratory's standard protocols within 1 hour after collection. The blood sample vials were incubated for 24 hours at 37°C, after which an aliquot was aseptically removed from each sample and plated onto blood, phenylethyl alcohol, and MacConkey agars for aerobic bacterial culture. The agar plates were incubated at 37°C and visually inspected for bacterial growth after 24 and 48 hours of incubation. For anaerobic bacterial cultures, an aliquot was aseptically removed from each sample and plated onto Brucella agar with 5% sheep blood, vitamin K, and hemin. Each anaerobic bacterial culture plate was incubated for 24 hours at 37°C in an anaerobic chamber with a packetf to absorb oxygen and generate CO2 and visually inspected for bacterial growth after 24 and 48 hours of incubation.
Aerobic bacterial isolates were identified with an automated microbial detection system.g Anaerobic bacterial isolates were identified with a rapid anaerobe identification systemh in accordance with the manufacturer's instructions. Bacterial isolates that were unidentifiable by those methods were sent for identification on the basis of 16S rRNA at the discretion of the microbiologist or on an investigator's request.
Statistical analysis—Data were analyzed with commercial statistical software.i A 2-sided Fisher exact test was used to compare the prevalence of bacteremia in the pedal circulation between cattle in the DDS and healthy comparison groups, and values of P < 0.05 were considered significant.
Results
Clinical findings for cattle in DDS group—One cow had a single claw affected on 2 limbs. Thus, 10 limbs with DDS were evaluated from 9 cows. The lateral claw of the hind limb was affected in 8 of 10 limbs evaluated.
The deep septic processes diagnosed included sepsis of the distal interphalangeal joint (n = 7; Figure 1), septic pedal osteitis (6), septic osteomyelitis of the second phalanx (3), sepsis of the proximal interphalangeal joint (1), and septic osteomyelitis of the first phalanx (1). Multiple septic processes were present in 6 of the affected limbs. Radiographs of the affected foot were obtained for 6 of the 10 limbs evaluated. In 2 of the affected limbs, the third phalanx was fractured, and the fracture was presumed to be secondary to sepsis in both instances. No complications or clinically apparent adverse effects of tourniquet application or blood collection were observed in any of the cattle prior to discharge from the hospital.
Photograph (A) and dorsoplantar radiographic image (B; lateral is to the left) of the right hind foot of a 2.5-year-old Santa Gertrudis bull that developed septic arthritis of the distal interphalangeal joint and septic pedal osteitis of the lateral claw subsequent to a laceration.
Citation: Journal of the American Veterinary Medical Association 245, 5; 10.2460/javma.245.5.565
Photograph (A) and dorsoplantar radiographic image (B; lateral is to the left) of the right hind foot of a 2.5-year-old Santa Gertrudis bull that developed septic arthritis of the distal interphalangeal joint and septic pedal osteitis of the lateral claw subsequent to a laceration.
Citation: Journal of the American Veterinary Medical Association 245, 5; 10.2460/javma.245.5.565
Photograph (A) and dorsoplantar radiographic image (B; lateral is to the left) of the right hind foot of a 2.5-year-old Santa Gertrudis bull that developed septic arthritis of the distal interphalangeal joint and septic pedal osteitis of the lateral claw subsequent to a laceration.
Citation: Journal of the American Veterinary Medical Association 245, 5; 10.2460/javma.245.5.565
Culture results—Bacterial growth was not identified in any of the blood samples obtained from the cows in the healthy comparison group. For the cattle of the DDS group, bacteria were isolated from the pedal circulation prior to RIVP in 1 cow and after RIVP and examination with or without debridement in that cow and 4 additional cattle. Cattle in the DDS group were significantly (P = 0.016) more likely to develop bacteremia in the pedal circulation than were cattle in the healthy comparison group.
Eight bacterial species were isolated. For the limb that yielded positive culture results in both the pre-RIVP and post-RIVP blood samples, 1 bacterial isolate was identified in the pre-RIVP sample and 2 bacterial isolates were identified in the post-RIVP sample. Two bacterial isolates were identified in the post-RIVP blood sample from 1 limb, and 1 bacterial isolate was identified in the post-RIVP blood sample from each of 3 limbs. The bacteria identified included Streptococcus spp (n = 3), Trueperella pyogenes (2), Moraxella osloensis (1), Escherichia coli (1), and Fusobacterium necrophorum (1). Of these 8 isolates, 5 were gram-positive facultative anaerobes, 1 was a gram-negative aerobe, 1 was a gram-negative facultative anaerobe, and 1 was a gram-negative obligate anaerobe.
Discussion
In the present study, RIVP with a 2% lidocaine solution in the DCDV and examination with limited debridement of digital lesions (ie, cleansing of external wounds, drainage of infection by means of hoof or sole paring, or lancing of SC abscesses) in cattle with DDS resulted in bacteremia in the pedal circulation of 5 of the 10 affected limbs evaluated. Although the type and severity of various septic disease processes and the duration of tourniquet application varied among the affected limbs evaluated, all cattle with DDS had a chronic history (ie, > 1 week) of severe lameness.
The number of post-RIVP blood samples from which bacteria were isolated in the present study could be falsely low. In foals with neonatal sepsis, bacterial culture of systemic blood samples yield false-negative results up to 37% of the time.19,21 False-negative bacterial culture results have been attributed to a small volume of blood obtained for culture, a low number of circulating bacteria, antimicrobial administration prior to sample collection, and type of culture system used.21–23 The use of molecular assays, including real-time PCR assay and broad-range conventional PCR assay, in conjunction with bacterial culture of blood might result in increased or more rapid diagnostic confirmation of bacteremia in human and equine patients.23–25 However, PCR assays detect nonviable as well as viable organisms, and use of that technology in the present study might have overestimated the prevalence of bacteremia in the pedal circulation.
In a study26 that involved human patients, bacterial culture of 2 or 3 systemic blood samples obtained during a 24-hour period for detection of bacteremia had a sensitivity of 85.7% and 100%, respectively. Because of concerns about adverse effects associated with restraining cattle in a lateral position as well as the application of a tourniquet to the distal aspect of a limb for a prolonged period, only 1 post-RIVP blood sample was obtained for bacterial culture in the present study. Culture of additional post-RIVP blood samples might have resulted in a higher prevalence of bacteremia in the pedal circulation than that reported for the cattle in the DDS group.
The use of a lidocaine solution for the RIVP might have also contributed to false-negative culture results. Results of some studies27,28 suggest that lidocaine has antimicrobial properties, which can inhibit bacterial growth. However, results of other studies indicate that lidocaine attenuates the immune response by a number of mechanisms including inhibition of leukocyte chemotaxis29,30 and suppression of toxic oxygen metabolite production30–32; thus, use of lidocaine might have facilitated the detection of bacteremia.
It is also possible that some of the bacterial culture results in the present study were false-positive results if the blood samples were contaminated with bacteria from the skin. However, we believe that contamination of the blood samples was unlikely. None of the blood samples obtained from the cows in the healthy comparison group and only 1 of 10 pre-RIVP blood samples obtained from the cattle in the DDS group yielded positive bacterial culture results, versus 5 of 10 post-RIVP samples that yielded positive bacterial culture results. Contamination of blood samples with skin bacteria in the present study would have been more likely for the pre-RIVP samples, which were obtained after only a single aseptic preparation of the venipuncture site, versus the post-RIVP samples, which were obtained after the venipuncture sites had been aseptically prepared twice. Had bacterial culture of all the digital lesions of the cattle in the DDS group been performed, we could have compared those results with those obtained from the bacterial culture of the blood samples collected from those cows. Similarities between the culture results of the digital lesions and blood samples would have helped to validate the presence of bacteremia as well as the clinical diagnosis of DDS. Unfortunately, bacterial culture of digital lesions was not performed because of economic constraints.
The main limitation of the present study was the small number of cattle with DDS that were evaluated, which prevented further investigation of several interesting questions raised by the study results. The correlation between the clinical and anatomic diagnosis of DDS and the likelihood of developing bacteremia in the pedal circulation or between a specific cause of DDS and the likelihood of bacteremia in the pedal circulation attributable to specific pathogens could not be determined. Similarly, the influence of lesion debridement following RIVP on the development of bacteremia in the pedal circulation could not be evaluated. Intuitively, it would seem that debridement of digital lesions would increase the likelihood of the dissemination of pathogens to the pedal circulation. The small number of cattle with DDS also prevented assessment of the relationship between the duration of tourniquet application and the likelihood of the development of bacteremia. One of the post-RIVP blood samples that yielded positive culture results was obtained from the limb that had the tourniquet applied for the shortest time (34 minutes). Also, the pre-RIVP sample that yielded positive culture results was obtained immediately after tourniquet placement, and the post-RIVP sample from that limb yielded positive culture results after only 36 minutes of tourniquet application. These observations suggested that, although duration of tourniquet application might be associated with the development of bacteremia, it is likely not the only risk factor for bacteremia in the pedal circulation of cattle with DDS. Further investigation is necessary to clarify the questions raised by the present study and to assist clinicians in determining which patients with DDS are at greatest risk of developing bacteremia in the pedal circulation so that judicial and appropriate antimicrobial treatment can be administered.
Although T pyogenes and F necrophorum are commonly associated with digital infections and DDS in cattle, some of the other bacteria isolated from the pedal circulation of the cattle in the DDS group of the present study were less expected. The E coli isolate was likely an environmental contaminant that obtained access to the pedal circulation via an open fracture of the third phalanx, and the Streptococcus spp were likely opportunistic secondary pathogens that gained access to the pedal circulation via similar open wounds or fractures. In the present study, cows might have been exposed more frequently to environmental streptococci than were bulls because those bacteria frequently colonize the vaginal vault, and most of the DDS-affected limbs were hind limbs, which are more likely to be exposed to urine that can become contaminated when it passes through a vaginal vault colonized by streptococci. In a study33 conducted to identify the aerobic bacteria that comprise the vaginal flora of cows, Streptococcus spp were cultured from 23 of 135 (17%) vaginal swab specimens obtained from healthy cows in various stages of the estrous cycle and gestation. In the present study, all of the Streptococcus spp isolates were obtained from blood samples of cows with external lesions or wounds associated with DDS. Similarly, M osloensis is a saprophytic bacterium of the skin and could have been shed in urine if present in the vaginal vault. The blood sample from which M osloensis was isolated was obtained from a cow that developed DDS secondary to a draining and contaminated sole ulcer.
For the cattle in the DDS group that had post-RIVP blood samples with positive bacterial culture results, the precise mechanism for the development of bacteremia in the pedal circulation following RIVP is unknown. Regional IV perfusion creates gaps between the endothelial cells of the vascular wall,34 and bacterial translocation across the endothelium into the circulation may ensue. Application of a tourniquet to a limb causes acidemia and hypoxia distal to the tourniquet, which can result in tissue compromise and an increase in vascular permeability, conditions that may predispose the area to bacteremia. The lidocaine solution used in the RIVP might have had an immunosuppressive effect on leukocytes in the region that contributed to the development of bacteremia. Alternatively, the debridement of the digital lesions could have dislodged bacterial emboli and facilitated their entrance into circulation. To investigate that supposition in this study, we would have needed another group of cattle with DDS in which a RIVP of lidocaine solution was performed without subsequent debridement; however, this was not done because it was not considered clinically applicable. It is also possible that multiple sites of sepsis within a digit or within both digits of the same limb increase the likelihood of bacteremia. In the present study, the only animal in which DDS affected both digits of the same limb had a culture-positive post-RIVP blood sample. Ultimately, a combination of these factors was likely responsible for development of bacteremia in the pedal circulation following RIVP of cattle with DDS.
The systemic consequences from bacteremia in the pedal circulation of cattle have not been elucidated. Four human patients with osteomyelitis in a limb who were treated with an antimicrobial RIVP developed clinical evidence of sepsis16; however, clinical signs of sepsis were not evident in any of the cattle of the present study following RIVP of a 2% lidocaine solution. The collection of systemic blood samples immediately after RIVP and the release of the tourniquet and at specific time points thereafter for bacterial culture along with extensive follow-up of patients to document clinical evidence of bacterial dissemination or distant colonization would help clinicians elucidate the possible systemic consequences of bacteremia in the pedal circulation.
In the present study, bacteria isolated from the pedal circulation in 5 of 10 cattle with DDS consisted of both gram-positive and gram-negative bacteria as well as both aerobes and anaerobes. These findings suggested that administration of systemic or local antimicrobials might be warranted for the treatment of cattle with DDS prior to or concurrent with RIVP of local anesthetics. Given the variety of bacteria isolated in these cases, we recommend administration of broad-spectrum antimicrobials with bactericidal activity against aerobes and anaerobes. Of course, administration of antimicrobials to cattle with DDS prior to or concurrently with RIVP of a local anesthetic should be judicious and has economic implications in regard to the costs associated with the subsequent milk and slaughter withdrawal intervals required for treated cattle.
Concurrent administration of local anesthetics and certain antimicrobials via RIVP has been associated with severe complications that necessitated euthanasia in cattle.35,36 Additionally, human patients with osteomyelitis of a limb have developed systemic bacteremia following administration of regional antimicrobials,16 which suggests that regional antimicrobial administration may not be sufficient to prevent bacteremia.
Results of the present study indicated that approximately half of the cattle with DDS developed bacteremia in the pedal circulation following RIVP with a 2% lidocaine solution and examination with or without debridement of the digital lesions. Thus, systemic administration of broad-spectrum antimicrobials may be warranted prior to or concurrently with RIVP of the affected limb in those patients. Additional studies to determine local and systemic sequelae to bacteremia of the pedal circulation in cattle are warranted.
DVM Tilt Chute, Flying W Livestock Equipment, Watonga, Okla.
Surflo winged infusion set, 19-gauge 0.75-inch thin walled needle with 12-inch tubing, Terumo Medical, Somerset, NJ.
Lidocaine 2% injectable solution, The Butler Co, Dublin, Ohio.
BBL SEPTI-CHEK, Becton, Dickson, and Co, Franklin Lakes, NJ.
Oxoid SIGNAL blood culture system, Oxoid Ltd, Basingstoke, Hampshire, England.
AnaeroGen sachet, Oxoid Ltd, Basingstoke, Hampshire, England.
Trek, TREK Diagnostic Center Inc, Cleveland, Ohio.
Rapid Anaerobe ID, B1017-2, Siemens AG, Erlangen, Germany.
SPSS Statistics 20, IBM Corp, Armonk, NY.
ABBREVIATIONS
| DCDV | Dorsal common digital vein |
| DDS | Deep digital sepsis |
| RIVP | Regional IV perfusion |
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