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Basics ⬇

Outline

BASICS

Definition!!navigator!!

  • Inflammation of pulmonary parenchyma occurring in foals <4 weeks of age
  • One of the most common sites of infection in neonatal foals

Pathophysiology!!navigator!!

Bacterial Septicemia

  • Most common cause of neonatal pneumonia, frequently as a sequel to bacterial septicemia
  • Low serum IgG concentration is highly correlated with incidence of disease
  • Pathogens implicated in neonatal septicemia are most frequently isolated, including Escherichia coli, Klebsiella pneumoniae, Actinobacillus equuli, Salmonella spp., Streptococcus spp.

Viral Infection

  • Can cause severe, refractory pneumonia in neonatal period
    • Foals may be infected in utero or shortly after birth
  • Most affected foals succumb quickly
  • Foals may be born preterm or aborted as consequence of maternal viral infection
  • Most common:
    • EHV-1 (less frequently EHV-4)
    • Equine arteritis virus
    • Equine influenza virus
    • Equine adenovirus (e.g. in Arabian foals with SCID)

Aspiration Pneumonia

  • Aspiration of milk and oral secretions occurs as a result of neonatal pharyngeal dysfunction and weakness
  • Risk factors include cleft palate, botulism, sepsis, nutritional myodegeneration, iatrogenic (syringe or bottle feeding), NMS

Systems Affected!!navigator!!

  • Respiratory
  • In foals with septicemic disease, other systems (e.g. musculoskeletal and gastrointestinal) may be concurrently affected

Genetics!!navigator!!

Arabian foals affected by SCID.

Incidence/Prevalence!!navigator!!

  • Affects up to 50% of neonatal foals examined at referral institutions
  • Case fatality rate is unknown but likely depends on timeliness of therapeutic intervention, etiologic agent, and immune status of foal, among other factors

Geographic Distribution!!navigator!!

No geographic distribution in incidence of disease; however, there may be geographic differences in bacterial isolates.

Signalment!!navigator!!

Breed Predilections

  • No breed predisposition
  • Exception is Arabian foals with SCID

Mean Age and Range

  • Neonatal foals (<14 days of age)
  • Most cases are <7 days of age at the time of presentation

Predominant Sex

No sex predisposition.

Signs!!navigator!!

General Comments

  • Foals may have severe pulmonary disease without overt clinical signs referable to the respiratory tract
  • Foals with pneumonia often display nonspecific signs of disease (lethargy, inappetence, fever, etc.)

Historical Findings

  • See Risk Factors
  • History of maternal disease
  • Prematurity
  • Inadequate colostral ingestion
  • Lethargy, depression, decreased nursing behavior

Physical Examination Findings

  • Often vague, nonlocalizing clinical signs
  • Weak, often increasingly recumbent
  • Decreased frequency of nursing
  • Fever, although may have increased, normal, or decreased body temperatures
  • Tachypnea/dyspnea
  • Pulmonary auscultation may reveal increased bronchovesicular sounds or absence of auscultable sounds over regions of consolidated/atelectatic lung, or may be normal (even in severely affected foals)
  • Cyanosis not common, and might not be noted in anemic foals
  • Cough and/or nasal discharge are not common findings in early disease

Risk Factors!!navigator!!

  • Failure of transfer of passive immunity is likely the single most important risk factor
  • Maternal risk factors:
    • Maternal illness (colic, respiratory disease, etc.)
    • Dystocia
    • Running colostrum/milk prior to parturition
    • Ascending cervicitis/placentitis
    • Maternal rejection of neonate
    • Agalactia/hypogalactia
    • Maternal age (very young or old mares—lower quality colostrum)
  • Neonatal risk factors:
    • Dystocia
    • NMS
    • Musculoskeletal disease preventing rising to nurse
  • Unhygienic environment in immediate neonatal period—ingested or inhaled pathogens
  • Prolonged lateral recumbency—vascular congestion, atelectasis of dependent lung may predispose to infection

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Anemia
  • Cardiac disease (e.g. congenital cardiac anomaly)
  • Hyperthermia
  • Idiopathic tachypnea
  • Trauma (rib fracture, pulmonary contusion)
  • Neurologic disease—abnormal respiratory patterns
  • Botulism—fatigue of ventilatory muscles

Laboratory Tests!!navigator!!

CBC

  • Segmented neutrophil count may be increased, normal, or decreased
  • Toxic granulation, vacuolation may be evident associated with sepsis
  • Viral infection may induce profound lymphopenia, but this is inconsistent
  • Elevated lymphocyte counts (greater than neutrophil count) in premature foals
  • Plasma fibrinogen, serum amyloid A often increased

Arterial Blood Gas Analysis

  • Ideal method to determine adequacy of gas exchange and pulmonary function
  • Best sampling sites include great metatarsal artery, brachial artery, or transverse facial artery
  • Patient should be standing or sternally recumbent for ≈5–10 min prior to sampling
  • Useful for monitoring response to therapy and assessing changes in patient's status
  • PaO2—values between 60 and 80 mmHg (normal >80 mmHg) may be associated with pulmonary disease or lateral recumbency at time of sampling. Values <60 mmHg indicate hypoxemia and poor pulmonary function
  • PaCO2—values >60 mmHg with concurrent hypoxemia indicate respiratory failure. Significant elevation is an indication for mechanical ventilation

Blood Culture

Likely to be helpful in identification of etiologic agent and antimicrobial susceptibility in septicemic cases.

Culture and Cytology of Samples of Respiratory Tract Secretions

  • Not recommended in dyspneic patients—patient should be stabilized first
  • Bacteria readily cultured, antimicrobial sensitivity helpful to guide therapy
  • Viral isolation may be performed on respiratory tract samples

Serum IgG Levels

Serum IgG level often <400 mg/dL in affected neonates.

Imaging!!navigator!!

  • Thoracic radiography
    • Useful for documenting extent and severity of disease
    • Hematogenous bacterial pneumonia—diffuse disease with an alveolar or interstitial/alveolar pattern
    • Aspiration pneumonia—cranioventral/caudoventral pulmonary fields (alveolar pattern)
    • Useful for monitoring response to therapy, resolution of disease (radiographic disease will typically lag behind clinical status of patient)
  • Thoracic US
    • Can visualize parietal abscessation, pulmonary consolidation, pleural effusion
    • Also useful for monitoring response to therapy
  • Thoracic CT
    • More sensitive than radiography, US for documenting pulmonary lesions

Other Diagnostic Procedures!!navigator!!

  • Endoscopy of the upper respiratory tract
    • May be useful for identifying cause in patients with aspiration pneumonia
  • Pulse oximetry may be useful as a continuous, noninvasive estimate of PaO2; results should be periodically calibrated against arterial blood gas measurements

Treatment ⬆ ⬇

Outline

TREATMENT

Aims!!navigator!!

  • Resolve infection within pulmonary parenchyma
  • Promote efficient gas exchange
  • Minimize inflammatory changes that may promote acute respiratory distress syndrome, systemic inflammatory response syndrome, and subsequent death of the patient

Appropriate Health Care!!navigator!!

Inpatient intensive management for severe disease.

Nursing Care!!navigator!!

  • Oxygen—humidified oxygen should be administered via nasal cannula(s) inserted to the level of the nasopharynx at a rate of 5–10 L/min
  • Thoracic coupage to mobilize; patients should be examined carefully for thoracic trauma (e.g. rib fractures) prior to instituting this therapy
  • Maintain sternal recumbency to minimize dependent lung atelectasis
  • Mechanical ventilation for foals in respiratory failure (hypoxemia with severe hypercapnia)
  • Judicious suctioning of respiratory secretions (use care—may cause pulmonary collapse and exacerbate hypoxemia); suction only as needed and for short periods (<2 s)
  • Fluid therapy to correct dehydration, electrolyte and acid–base abnormalities

Activity!!navigator!!

Should be minimized to decrease metabolic oxygen demands, especially in hypoxemic patients.

Diet!!navigator!!

  • Enteral nutrition via an indwelling nasogastric feeding tube, particularly in patients with pharyngeal dysfunction or weakness that has resulted in aspiration
  • Parenteral nutrition for foals that do not tolerate enteral feeding

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

Antimicrobials

  • Broad-spectrum bactericidal drugs should be administered prior to results of culture and sensitivity testing
  • Aminoglycoside/beta-lactam combinations are good choices for empiric therapy (e.g. amikacin 25 mg/kg IV daily and penicillin 22 000 IU/kg IV every 6 h)
  • Third-generation cephalosporins (e.g. ceftazidime 50 mg/kg IV every 6 h) are also good empiric choices, particularly if patient has renal compromise
  • Therapy may be adjusted based on culture and sensitivity results and should continue for 2–5 weeks
  • Antiviral therapy (acyclovir (aciclovir)) has been used for viral pneumonia; unlikely to affect clinical course

NSAIDs

  • Useful to minimize fever, inflammation
  • Ketoprofen (2.2 mg/kg IV every 12–24 h)
  • Flunixin meglumine (1.1 mg/kg IV every 12–24 h)
  • Use judiciously and with caution in neonates

Gastroprotectants

  • May be useful in foals receiving nonsteroidal medications
  • See chapter Gastric ulcers, neonate

Contraindications!!navigator!!

Aminoglycosides should not be used in azotemic patients.

Precautions!!navigator!!

Oxygen therapy may cause hypoventilation in hypercapnic patients.

Alternative Drugs!!navigator!!

Depending on results of bacterial culture/sensitivity, alternative antimicrobial drugs may be needed.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Attitude, respiratory rate, and pattern should be observed frequently until stabilized
  • Arterial blood gas analysis should be performed daily or when status of patient changes
  • CBC, fibrinogen every 3–5 days; when status of patient changes; prior to discontinuation of antimicrobial therapy
  • Thoracic radiography—weekly; when change in patient status; prior to discontinuation of antimicrobial therapy
  • Thoracic US may be performed daily or every other day

Prevention/Avoidance!!navigator!!

Ensure adequate transfer of passive immunity within the first 18–24 h of life.

Possible Complications!!navigator!!

  • Pulmonary abscessation
  • Pleural adhesions
  • Other septic foci (e.g. septic arthritis)

Expected Course and Prognosis!!navigator!!

  • Approximately two-thirds of foals with pneumonia survive to hospital discharge
  • Viral pneumonia is usually fatal
  • Effects on future athletic performance difficult to predict, but many go on to be performance animals as adults

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

  • Prematurity
  • Septicemia

Abbreviations!!navigator!!

  • CT = computed tomography
  • EHV = equine herpesvirus
  • Ig = immunoglobulin
  • NMS = neonatal maladjustment syndrome
  • NSAID = nonsteroidal anti-inflammatory drug
  • PaCO2 = partial pressure of carbon dioxide in arterial blood
  • PaO2 = partial pressure of oxygen in arterial blood
  • SCID = severe combined immunodeficiency
  • US = ultrasonography, ultrasound

Suggested Reading ⬆ ⬇

Bedenice D. Manifestations of septicemia: foal with septic pneumonia. In: Paradis MR, ed. Equine Neonatal Medicine: A Case-Based Approach. Philadelphia, PA: Saunders, 2006:99–111.

Bedenice D, Heuwieser W, Brawer R, et al. Clinical and prognostic significance of radiographic pattern, distribution, and severity of thoracic radiographic changes in neonatal foals. J Vet Intern Med 2003;17(6):876–886.

Reuss SM, Cohen ND. Update on bacterial pneumonia in the foal and weanling. Vet Clin North Am Eq Pract 2015;31:121–135.

Author(s) ⬆

Author: Teresa A. Burns

Consulting Editor: Margaret C. Mudge