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Basics ⬇

Outline

BASICS

Overview!!navigator!!

Bacterial meningitis is an uncommon but serious sequela to septicemia in foals. Up to 5–10% of septic neonatal foals develop meningitis, resulting from hematogenous spread of bacteria to the central nervous system. The disease is rapidly fatal if untreated.

Signalment!!navigator!!

Neonatal foals, usually <2 weeks of age.

Signs!!navigator!!

Clinical signs vary widely but may include:

  • Lethargy/depression
  • Decreased nursing
  • Fever
  • Ataxia, weakness
  • Cervical stiffness/splinting
  • Hyperesthesia
  • Opisthotonus
  • Cranial nerve deficits
  • Anisocoria, abnormal pupillary light responses
  • Strabismus, nystagmus
  • Recumbency
  • Seizures, coma (late findings; poor prognostic indicators)
  • Clinical signs are usually rapidly progressive. Signs of other concurrent septic foci are frequently present (e.g. enteritis, arthritis)

Causes and Risk Factors!!navigator!!

  • Failure of transfer of passive immunity is the strongest risk factor
  • Bacterial isolates are similar to those implicated in neonatal septicemia
  • Infection may occur via the respiratory, gastrointestinal, cutaneous, or umbilical route

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Neonatal maladjustment syndrome
  • Congenital anomaly—hydrocephalus, hydranencephaly, other brain anomalies
  • Metabolic—hypoglycemia, hepatic encephalopathy, kernicterus, electrolyte and acid–base abnormalities
  • Nutritional myodegeneration
  • Tetanus
  • Trauma—external evidence typically present

CBC/Biochemistry/Urinalysis!!navigator!!

  • CBC—normal, increased, or decreased segmented neutrophils; toxic changes
  • Biochemistry—hyperfibrinogenemia, increased serum amyloid A; hypogammaglobulinemia

Other Laboratory Tests!!navigator!!

Serum IgG concentration—usually <400 mg/dL, often <200 mg/dL.

Imaging!!navigator!!

Radiography of the skull to rule out fracture, congenital anomaly.

Other Diagnostic Procedures!!navigator!!

  • CSF analysis—diagnostic test of choice. Fluid usually discolored (yellow, orange), turbid. Cytology—increased nucleated cell count (>6/μL, often >100/μL), predominantly degenerate neutrophils; intra- and extracellular bacteria often noted. Gram stain may identify the predominant bacterial population present
  • Bacterial culture and susceptibility of CSF is diagnostic
  • Blood cultures or cultures of other septic foci may be useful

Pathologic Findings!!navigator!!

  • Thickened, discolored, opaque meninges over cerebrum, cerebellum, brainstem
  • Meningeal vascular congestion

Treatment ⬆ ⬇

TREATMENT

  • Inpatient medical care and emergency stabilization are often required
  • Fluid therapy and nutrition
  • Padding and supervision to prevent self-trauma
  • Nasal oxygen or mechanical ventilation for respiratory failure

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

Antimicrobials

  • Broad-spectrum, bactericidal antimicrobial drugs that penetrate the blood–brain barrier
  • Third- and fourth-generation cephalosporins (cefotaxime 40 mg/kg IV every 6 h; ceftriaxone 25–50 mg/kg IV every 12 h; cefepime 11 mg/kg IV TID) are preferred
  • Penicillin, tetracyclines, and aminoglycosides do not reliably penetrate CSF

Anti-inflammatory Medication

  • Corticosteroids (dexamethasone 0.1 mg/kg IV or prednisolone 1–2 mg/kg IV)—recommend use early in the course of the disease, but no evidence that this treatment improves survival in horses
  • DMSO (1 g/kg as a 5–10% solution IV once daily)
  • NSAIDs (ketoprofen 1.1–2.2 mg/kg IV every 12–24 h or flunixin meglumine 0.5–1.1 mg/kg IV every 12–24 h) for analgesia

Seizure Control

  • Diazepam (0.2–0.5 mg/kg IV as bolus, can be given every 15–20 min)
  • Midazolam (0.06–0.1 mg/kg IV; 0.02–0.2 mg/kg/h as constant rate infusion)
  • Phenobarbital (10–20 mg/kg IV over 20 min, then 2–10 mg/kg PO SID–BID)

Contraindications/Possible Interactions!!navigator!!

Immunocompromise secondary to steroid administration is a concern in septicemic foals.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Serial physical and neurologic examinations
  • Recheck CBC, plasma fibrinogen concentration, ± repeated CSF

Prevention/Avoidance!!navigator!!

  • Ensure adequate colostral intake and serum IgG >800 mg/dL within first 24 h of life
  • Clean, hygienic environment

Possible Complications!!navigator!!

Persistent neurologic deficits possible in recovered foals.

Expected Course and Prognosis!!navigator!!

  • Rapidly fatal without treatment
  • Guarded prognosis with treatment; poor if signs progress to seizures and/or coma
  • At least 4–6 weeks of antimicrobial treatment recommended

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

Concurrent septic foci (pneumonia, arthritis, enteritis, uveitis, omphalitis, etc.).

Age-Related Factors!!navigator!!

Failure of transfer of passive immunity predisposes.

Zoonotic Potential!!navigator!!

Unlikely, but use caution if Salmonella spp. isolated from CSF, blood.

Abbreviations!!navigator!!

Suggested Reading ⬆ ⬇

MacKay RJ. Neurologic disorders of neonatal foals. Vet Clin North Am Equine Pract 2005;21:387–406.

Viu J, Monreal L, Jose-Cunilleras E, et al. Clinical findings in 10 foals with bacterial meningitis. Equine Vet J Suppl 2012;41:100–104.

Author(s) ⬆

Author: Teresa A. Burns

Consulting Editor: Margaret C. Mudge