presence of canine influenza virus antibodies. 4 The most accurate method of testing for influenza virus requires paired acute serum samples (taken within 7 days of the onset of clinical signs, at which time there should be little to no circulating antibody present) and convalescent serum samples (taken 10 to 14 days later, during the dog’s peak immune response). A diagnosis of canine influenza is made based on a four-fold increase in antibody titer from the acute to the convalescent sample. 12 If an acute sample is not available, convalescent samples can indicate exposure but will not indicate whether that exposure was recent or historic. The primary disadvantage of serology is that results can rarely be used to guide treatment due to the need to wait for a convalescent sample; the value of serology results lies primarily in disease surveillance. 2 Still, the low cost
and availability of serology makes it a valuable test that can be utilized in dogs that are slow to respond to treatment. Serologic testing is available for both the H3N8 and H3N2 strains of canine influenza virus through a number of university and commercial labs. Suspected influenza cases should always be tested for both strains in order to rule out canine influenza infection. 12 Despite the fact that H3N2 is the strain that is more commonly depicted in the media at this time, H3N8 is still circulating within the canine population at low levels. When testing, however, keep in mind that dogs who have been vaccinated against canine influenza will likely demonstrate a titer against H3N8. 14
TREATMENT: MEDICAL THERAPIES; MILD CASES
Mild cases of canine influenza should be treated like any other mild upper respiratory infection (i.e. kennel cough), primarily with supportive care. Antibiotics are typically not recommended for young, healthy dogs unless there is evidence of bacterial infection, as antibiotics will not aid in clinical resolution of viral signs and may contribute to antibiotic resistance. 18 The primary secondary infection observed in these mild cases of canine influenza is a purulent nasal discharge, which is most often associated with Staphylococcus spp . or Streptococcus spp . Dogs with influenza who demonstrate this purulent nasal discharge can often be treated successfully with cephalexin (35 mg/kg every 12 hours). 3 There may be a slight benefit to cough suppressants in mild cases of canine influenza, but many practitioners have noted that the cough associated with influenza is poorly responsive to antitussives. In fact, this characteristic is often helpful in the diagnosis of canine influenza infection. Therefore, if cough suppressants are utilized in a suspected influenza case, clients should be warned that they may not see immediate effects. Additionally, antitussives should be avoided in dogs with a productive cough as the medication will interfere with the
clearance of secretions from the airways 3 and thus may further increase the lung damage associated with the disease. 1,19 Dogs that have other concurrent health issues, such as pregnancy, pre-existing lung disease (tracheal collapse, chronic bronchitis, etc.), or immunosuppression, may benefit from additional diagnostics or treatments even when only mild clinical signs of upper respiratory disease are noted. In these dogs, veterinarian should consider the use of antibiotics for any known or suspected secondary bacterial infections. 7 Ideally, these antibiotics should be selected on the basis of culture and sensitivity (performing a transtracheal wash for sample collection), but in the absence of culture and sensitivity results, a broad-spectrum antibiotic should be chosen. Many practitioners have found a combination of doxycycline (5 mg/kg every 12 hours) and clindamycin (5mg/kg to 11 mg/kg every 12 hours) to be beneficial in these cases. Also consider the use of fluids and nonsteroidal anti-inflammatory medications, if needed, to correct dehydration and reduce fever. 7 With supportive care alone, canine influenza virus is self-limiting in most patients and most cases will resolve within 2 to 3 weeks. 7
TREATMENT: MEDICAL THERAPIES; SEVERE CASES
Some dogs will develop a secondary pneumonia once infected with canine influenza. Clinical signs of pneumonia include increased respiratory rate or dyspnea, severe lethargy, weakness, and anorexia. 3 This pneumonia may be life-threatening and can require aggressive management. Intravenous fluids, parenteral antibiotics, and oxygen support should be used as needed. Oxygenation should be monitored using pulse oximetry or arterial blood gas and oxygen supplementation should be implemented if the SaO 2 falls below 94% or the PaO 2 falls below 80 mmHg SaO 2 . 3 Saline nebulization may be beneficial to aid in the breakup of bronchial secretions, while coupage and physical activity can also play an important role in stimulating coughing and aiding in the clearance of airway secretions. 3 Oral or parenteral N-acetylcysteine (150 mg/kg initially, and then 50 mg/kg every 4 to 6 hours via mouth or intravenous catheter, or 50 ml/hour for 30 to 60 minutes every 12 hours by nebulization) has been utilized for its mucolytic effects, though it may elicit bronchospasm if given via nebulization in patients with pre- existing bronchospastic disease. 3,20 Additionally, bronchodilators such as aminophylline (6 mg/kg to 11 mg/kg every eight hours), theophylline (6mg/kg to 11 mg/kg every 8 hours), or terbutaline (0.01 mg/kg every 8 hours) can be considered in cases of severe bronchiolitis. 3 Antibiotic therapy should be guided by culture and sensitivity, with samples obtained using transtracheal wash. If antibiotics must be selected empirically, consider broad-spectrum bactericidal antibiotics that will offer coverage against the most commonly-involved secondary bacteria. Common bacteria isolated in influenza-induced pneumonia include Pasteurella multocida, Klebsiella pneumoniae, E. coli,Streptococcus spp., Staphylococcus spp ., and Mycoplasma spp . 3,18 Mildly affected
adult dogs may be managed with doxycycline (5 mg/kg every 12 hours), while more severe cases of pneumonia may require fluoroquinolones, extended-spectrum penicillins (such as amoxicillin/clavulanate), or third generation cephalosporins. 3 Enrofloxacin (5 mg/kg every 12 hours) is often recommended if Bordetella bronchiseptica is suspected, based on in vitro efficacy and enrofloxacin’s excellent distribution to lung tissue. 3 There have been reports of canine influenza associated pneumonia cases that respond poorly to antibiotics. The pneumonia in these cases is often caused by a multidrug- resistant E. coli . Additionally, some severely affected dogs have negative bacterial cultures, suggesting that the virus itself may be contributing to severe alveolar disease and hypoxia. 3 Again, it is important to perform bacterial culture and sensitivity in all cases of pneumonia, if possible. Minimally, culture and sensitivity must be considered in any dog that is responding poorly to empirical therapy. The use of oseltamivir (Tamiflu™) in cases of canine influenza has been debated. Oseltamivir and other antiviral drugs have been tested and approved for human use only. There has been little study of the use of these antiviral drugs in dogs, and veterinarians who use these drugs are doing so in an off-label manner. 12 There is a potential benefit to using oseltamivir and other neuraminidase inhibitors, because influenza viruses do express neuraminidase, but no studies exist demonstrating a clear benefit. 18 Additionally, oseltamivir is most frequently used in humans early in the course of disease and dogs typically are not diagnosed with influenza until later in the course of disease, negating much of the benefit of oseltamivir and other antivirals. 3
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