Today's Veterinary Practice

JUL-AUG 2014

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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| Bordetella BronchiSeptica & CanIne Influenza VIRus (H3n8) Today's Veterinary Practice July/August 2014 34 DEFINITIVE DIAGNOSIS Bordetella bronchiseptica Definitive diagnosis of B bronchiseptica is based on isola- tion of the pathogen from aerobic culture of respiratory secretions. Sample Collection. For cytology and culture of bacte- ria, obtain airway samples via: • Transtracheal or endotracheal wash • Bronchoalveolar lavage (blind or bronchoscopy-guided). Patients with unresponsive focal pneumonia may require bronchoscopy-guided bronchoalveolar lavage fluid collec- tion to obtain a sample that accurately represents the caus- ative pathogen. Nasal, oral, oropharyngeal, and nasopharyngeal bacteri- al cultures are not recommended, as they yield growth of normal respiratory flora, making it difficult to determine the primary pathogen causing disease. In addition, deep oral swabs are not recommended in puppies with commu- nity-acquired pneumonia. 10 Mycoplasma species cannot be seen on cytology and are difficult to culture; consider submitting a mycoplasma polymerase chain reaction (PCR) or mycoplasma culture, when indicated. Sample Preparation. Following collection of an air- way sample, cytology should be performed as quickly as possible (ideally within hours) to reduce disruption of the cells. 11,12 Because many samples are fairly low in cellularity, a concentrated population of representative cells can be evaluated by a cytospin or line smear preparation or man- ual smearing of pelleted cells. If the clinician is planning to send the sample to a clini- cal pathologist for evaluation, the sample should be stored at 4°C and shipped overnight (ideally processed within 24 hours after collection). 12 Sample Evaluation. Evaluate the sample for the differen- tial cell count and presence of bacteria or other infectious organisms. B bronchiseptica has a characteristic cytologic appearance, with the coccobacilli adhering to respiratory epithelial cells (Figure 3). Canine Influenza Virus Definitive diagnosis of CIV is based on real-time PCR (RT- PCR) identification of CIV from respiratory secretions. RT- PCR (nasal or pharyngeal swabs) has replaced viral isola- tion via tissue culture or serology due to: 13,14 • Difficulty in obtaining samples for culture antemortem • Concerns about previous exposure clouding results of serologic testing. Definitive diagnosis is a challenge in some patients because viral shedding declines within approximately 7 to 10 days post exposure, often prior to onset of clinical signs, resulting in a false–negative RT-PCR. 5 ANTIMICROBIAL THERAPY Antimicrobial therapy can be important in patients with suspected B bronchiseptica infections or, if CIV or another viral respiratory pathogen is suspected, to treat secondary bacterial infections. Doxycycline Doxycycline (5 mg/kg PO Q 12 H or 10 mg/kg PO Q 24 H) is my treatment of choice for B bronchiseptica and most infectious respiratory diseases. Enamel Discoloration. Clinicians are often concerned about using doxycycline in young patients due to its poten- tial to discolor enamel of developing teeth; however, it is less likely to cause discoloration compared to other tetra- cycline antibiotics. Limiting treatment to < 10 days further reduces the risk. 1 Doxycycline Resistance. Some isolates of B bronchi- septica are doxycycline-resistant, and patients may require treatment with a fluoroquinolone (enrofloxacin or mar- bofloxacin), azithromycin, or chloramphenicol; however, management of these patients should ideally be based on culture and susceptibility of airway samples. Other Tetracyclines The current shortage of doxycycline has dramatically increased its cost; therefore, it is a less desirable option for owners with financial concerns. Most clinicians are using other tetracycline drugs, such as minocycline, in place of doxycycline for treatment of tick-borne disease, but the pharmacokinetics of minocycline for various disease con- ditions in dogs is currently under investigation. 15 Dosing for treatment of bordetellosis is currently unknown; recommended treatment of methicillin-resistant staphylococcal infections is 5 mg/kg PO Q 12 H or 10 mg/ kg PO Q 24 H. Other Antibiotics Other antibiotics to consider include: • Azithromycin • Fluoroquinolones • Amoxicillin-clavulanate • Cephalosporins. Figure 3. Bronchoalveolar lavage fluid cytology demonstrating characteristic cytologic appearance of Bordetella bronchiseptica; note the adherence of the coccobacilli to the ciliated respiratory epithelial cells (100×). Courtesy Tamara Hancock, DVM

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