HOW-TO SESSION: LIFE STAGE MANAGEMENT


Table 1. Ultrasonographic Grading of Pneumonia Grade 0


Description


No evidence of pulmonary consolidation. Pleural irregularities that appear as vertical hyperechoic lines and are described as reverberation artifacts.13


(Fig. 4)


1 2 3 4 5 6 7 8


9 10


Less than 1 cm in diameter/depth (Fig. 5) Lesions that are 1.0–2.0 cm in size 2.0–3.0 cm in size (Fig. 6) 3.0–4.0 cm in size (Fig. 7) 4.0–5.0 cm in size


5.0–6.0 cm in size (Fig. 8) 6.0–7.0 cm in size


7.0–9.0 cm in size. If pleural effusion is present then the lesion is assigned this grade regardless of whether you have lesser grades of consolidation or abscessation. 9.0–11 cm in size


The entire lung lobe is affected


BAL cells. Intramuscular administration of gami- thromycin at a dosage of 6 mg/kg IM in the semi- membranosus/semitendinosus muscles once a week


will not only improve prognosis for recovery but also reduces the treatment period (2 rather than 4–8 wk of antibiotic treatments). Treatment was discon- tinued when the ultrasound score achieved a grade of zero. The implementation of thoracic ultra- sonography on endemic farms seems to be highly sensitive because no foals that were diagnosed as a grade 0 developed clinical disease. The farms that implemented thoracic ultrasonography had no mor- talities and a marked reduction of clinical disease associated with R. equi. Thoracic ultrasonography is a practical, quick, accurate, and useful diagnostic modality when screening for R. equi. In addition, the pulmonary lesion grades should be routinely employed when monitoring treatments and commu- nicating the description of the lesions.


4. Treatment


Although control trials to evaluate optimal treat- ment are lacking, macrolides such as azithromycin and clarithromycin have been shown to have greater bioavailability, to be more chemically stable, and achieve high tissue as well an intracellular concen- trations, the pharmacokinetics of azithromycin has shown that 10 mg/kg by mouth every 24 hours for the first 5 days of treatment and then every other day achieve appropriate minimal inhibitory concen- trations (MIC) in bronchoalveolar cells, pulmonary epithelial lining fluid, and in polymorphonuclear leukocytes.8 On the basis of pharmacokinetic val- ues and MIC of R. equi isolates, clarithromycin at a dose of 7.5 mg/kg by mouth every 12 hours can keep


serum levels above the MIC90.8 Azithromycin or clarithromycin are commonly used in combination with rifampin because of their synergistic properties against R. equi. Another macrolide that has shown some promise for the use in R. equi infected foals is gamithromycin. Gamithromycin has been shown to achieve adequate levels in the neutrophils and


would maintain concentrations above MIC90 for R. equi for approximately 7 days.9,10 Because of mus- cle inflammation associated with the use of this medication, it is advisable to not administer a quan- tity greater than 4 mL in a single site. Practitio- ners have also administered flunixin meglumine at a dose 1 mg/kg IV before the administration of gami- thromycin to help alleviate any pain associated with the administration of this medication. Pharmaco- kinetic data of doxycycline in 4–8-week-old foals have shown that oral administration at a dosage of 10 mg/kg every 12 hours would maintain serum, pulmonary epithelial lining fluid, and BAL cell ac- tivity above the MIC of R. equi.8 Therefore, doxycy- cline or minocycline (4 mg/kg orally every 12 h) may be an option for foals that have adverse reactions to the macrolides. The author has used gentamicin (6 mg/kg IV once a day) in some cases of R. equi that do not respond to conventional therapy, usually along with a combination of a macrolide and rifampin. It is very important to obtain a proper diagnosis


and culture sensitivity when confronted with pneu- monia that has been presumptively diagnosed with R. equi. If the patient does not improve with con- ventional therapy then further diagnostics (TTW) should be explored because resistant R. equi has recently been documented. In a study documenting the prevalence of R. equi isolates resistant to macrolides or rifampin and out- come of infected foals, the overall prevalence of re- sistant isolates in Texas and Florida was 4% (12 of 328 isolates submitted).11 The survival proportion of foals infected with resistant R. equi isolates (2 of 8; 25%) was significantly (P  .004) lower than that of foals receiving the same treatment from which susceptible isolates were cultured (55 of 79; 70%). These results underscore the importance of culture and susceptibility testing in foals with pneumonia caused by R. equi.11 The overall prognosis for successful outcome (sur-


vival) has been reported to be approximately 80%. Foals that recover from R. equi pneumonia and make it to the racetrack have been shown to perform as well as expected.


Juvenile Hyperreactive Airway Disease


Juvenile hyperreactive airway disease tends to af- fect foals 4–7 months of age and is poorly under- stood. Juvenile hyperreactive airway disease is a syndrome of small-airway disease that has minimal response to antibiotics alone. The majority of the cases in the United States present between June and September.


Clinical Signs


Clinical signs are consistent. Foals present with a history of tachypnea with an exaggerated abdominal component, tracheal rattle, and flared nostrils with


AAEP PROCEEDINGS  Vol. 62  2016 439


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