Notebook: Equine Respiratory System 3

These are notes taken on cases presented by Dr. Rose Nolen-Walston.

Diagnostic plan fever and abnormal lung sounds: rads, ultrasound, sample.
Rads: miliary pattern. Only a few causes: cancer (metastases), sepsis, fungal dz, silicosis. Nothing good that looks like this on rads! Probably not viral or bacteria.

Plan at this point: How to sample? Use BAL (not trans trach) because it's diffuse. Get fungal hyphae, indicates fungal pneumonia, which is rare. Can be primary or secondary (usually secondary doesn't cause a problem). If suspect primary, get a travel history. Treat with systemic anti-fungals. Tends to be $, and prognosis is poor. Best treatment: Itraconazole. (Case study presented in class resulted in full recovery).

Up to 70% of trach washes have fungal hyphae; THIS IS NORMAL! Do not treat with anti-fungals unless you see evidence of fungal pneumonia: i.e., large numbers of intra and extracellular fungal elements, consistent rad changes, or history.

Pneumocystis (and others) is an opportunistic bug (i.e., SKID foals, recent GI dz, other reasons for immuosuppression). Exactly the same diagnostics, but also test for immune function. Prognosis is poor.

Other possibility for miliary pattern: Interstitial pneumonia (pretty rare)
- present with severe clinical signs, i.e. cyanosis, profound respiratory distress, wasting away, cough, fever, pretty hypoxemic
- diagnose with rads (parenchymal disease)
-- pattern must be diffuse. Do BAL.
- Interstitial pnuemonia may be associated w/ viral dz (like flu), systemic inflammation (ARDS), equine nodular pulmonary fibrosis (may be associated w/ EHV5, pattern looks more nodular than miliary), silicosis: granulomas form around silicon, or ideopathic
- treatment is often futile. Euthanasia often elected if owner decides not to treat. (If you sit and wait, the horse may be fine!)
- prognosis is guarded to poor.

Case presented: foals with puffy joints, no lameness
- if foal w/ puffy joints is lame: septic arthritis (EMERGENCY)
- on ultrasound, see what may be neoplasia/ abscess/ granuloma
- rads pathognomonic Rhodococcus equi.
- Rhodococcus equi causes abscess-forming pneumonia.
- puffy joints but not lame: don't tap
- diagnosis: use cytology (pleomorphic cocci), culture, PCR
- on PCR, only VapA is really bad
- transmission: shed in feces
- use macrolides to treat b/c they go into the cell. Azithromycin stays at effective levels in pulmonary macrophages for 30 days! Treat with macrolides + rifampin.

- Rhodococcus is not the only thing that causes pneumonia in foals: top cause is Strep. zooepidemicus. Diagnose with imaging (rads/ US), sampling (trach wash). Put on broad spectrum (but not penicillin).
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Notebook: Equine Respiratory System 2

Treating pleural pneumonia Start with broad spectrum antibiotics (4 quadrant coverage): penicillin, gentomycin, metronidazole. Gas specks in lungs (on ultrasound) probably indicate anaerobic infections; also brown or red nasal discharge and stinky breath. These horses need to be put on metronidazole. Strep. zooepidemicus is the number one isolate; enrofloxacin doesn't get it! Oral drugs: TMS (nice but a lot of resistance), doxycycline, rifampin (not rifampin by itself!).

Will often put on anti-inflammatories (NSAIDs) to increase patient's comfort level. Remember to consider effects on kidneys and stomach. Use thoracic drains if necessary (if there's a lot of fluid). Support with calories very very early.

Increased pleural effusion decreases lymphatic drainage, leading to edema.

When do you stop the antibiotics? Recheck frequently with US (consolidation and abscesses), check fibrinogen and WBC counts, make sure afebrile for 4-5 days afterwards. May also re-check the tracheal wash (though a bit invasive).

Can do rib resection if you encounter "pizza pleura."

Epidemiology: Young racehorses being shipped are at top risk. Next is esophogeal obstruction in older horses, then post-anesthesia and recent viral infection.

Aspiration: When horses aspirate, it goes to the "triangle of death."

Prognosis is good for pleural abscess; horses with pleuritis -- prognosis is a lot worse.

Lympadenopathy, fever and nasal discharge is strangles (Strep. equi equi) until proven otherwise! Gets submandibular and retropharyngeal lymph nodes. Let the dz run its course; treat symptomatically; may want to use NSAIDs; drain abscesses when they're "ripe"; more severe cases will need tracheostomy; put complicated cases on penicillin. Prevention: isolate effected horses until they have a negative culture. May need to identify carriers if barn problems persist. Rare to get strangles twice. 2 vaccines available: new intranasal modified live vaccine is much more effective than the other vaccine. Always give it as the last vaccine because it is a modified live vaccine!

Bastard strangles: metastatic strangles. Lymph nodes in any part of the body are affected; can end up with problems in brain, liver, kidney etc. Diagnose with a titer for Strep. M protein. Treatment: long-term antibiotics. Penicillin works well.

Immune-mediated problems associated with Strep:
Purpura hemorrhagica is a vasculitis associated with the body getting confused by the Strep. Results in severe edema. Penicillin and corticosteroids; good prognosis. If outbreak, don't vaccinate horses that have possibly been exposed! Greater chance that they will develop purpura. Only vaccinate horses that you are really sure have not been exposed.
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