Is this foal septicemic?

Septicemia, defined as the systemic reaction caused by the presence of microorganisms or their toxins in the blood, often is cited as the most common reason for illness and death in the neonatal period.

Thus, based on its definition, a positive blood culture usually is considered the gold standard of diagnostic proof of septicemia. However, the inherent delay in obtaining the results of blood culture precludes a timely diagnosis, which is vital for a successful outcome.

The purpose of this and the following article next month is to review physical findings and laboratory tests that can alert the practitioner working in the field that septicemia is likely.

The physical examination

Typically, the prodromal signs of sepsis are subtle and often are not recognized by the caretaker. Knowledge of normal foal behavior and physical parameters is essential to identify septicemia early on. Normal physical findings of the newborn foal are listed in Table 1.

Table 1: Some practical facts on normal newborn foals

In performing the physical examination, one should specifically try to identify potential primary routes of infection, signs of a clinical response to infection and signs of advanced infection into secondary sites.

Primary sites of infection

The skin, umbilicus and digestive, respiratory and genitourinary tracts should be carefully examined as potential sites of primary bacterial invasion.

Considering that gram-negative enteric bacteria, notably Escherichia coli, account for the majority of cases of septicemia in foals, it logically follows that the gastrointestinal tract is the most common primary site of infection.

Diarrhea is never considered normal in the first few days of life and may be the only important clue of colonization and invasion of the gastrointestinal tract. Bruxism, anorexia and colic also may be signs that indicate risk of bacterial translocation from the gastrointestinal tract.

Photo 1: Injected sclerae is an early sign of septicemia.

External evidence of omphalophlebitis may not be grossly apparent for several days to one to two weeks after initial infection. Occasionally, despite significant infection of the umbilical vessels or urachus interior to the body wall, there will be no obvious evidence of disease in the external umbilical stump. Clinical signs consistent with infection of the umbilical remnants include heat, swelling, patentcy, pain of the umbilical stalk or discharge or moistness from or around the stalk.

Surprisingly, even severe infection of the respiratory tract may not manifest clinical signs in neonatal foals. Often the only signs of respiratory-tract disease are the presence of unexplained tachypnea, nasal flare or dyspnea. Other localizing signs, such as nasal discharge, cough, pleurodynia or audible abnormalities, when present, are incriminating clues.

The clinical response to infection

The foal's response to sepsis can be highly variable, depending on the duration and intensity of the septic insult. The initial response to infection should evoke signs of decreased activity, malaise, increased periods of recumbency, inability to track the mare, decreased frequency of nursing and failure to gain weight.

Photo 2: Injection of the oral mucous membranes. (Photos: courtesy of Dr. Michelle Henry Barton)

All of these signs often are associated with the onset of fever. The cyclic nature of fever necessitates serial evaluation; otherwise it may be overlooked. As the inflammatory response to infection intensifies, other signs of systemic disease appear, including tachycardia, tachypnea, bilateral scleral injection (Photo 1), hyperemia of the coronary bands, unpigmented skin (Photo 2) and mucous membranes (Photo 3), petechial hemorrhages and edema. Petechiae in the pinnae (Photo 4) are a highly reliable indicator of sepsis in the foal and may develop as a result of either thrombocytopenia or vasculitis.

Identifying secondary sites of infection

If the innate immune system is incapable of controlling the infection as septicemia progresses, secondary sites of infection may develop. With the bloodstream serving as the conduit, essentially all tissues of the body are susceptible to secondary infection. Tissues that receive a large portion of the cardiac output and experience turbulent, slow or unique blood supplies, are targeted first and include physes, synoviae, the uveal tract, meninges, endocardium, liver, kidney and skin/muscle.

Photo 3: Petechial hemorrhages inside the ears is a reliable clinical sign associated with septicemia.

Any neonatal foal that has joint swelling, periarticular edema, lameness or prolonged recumbency should be carefully evaluated for sepsis. The cardinal signs of uveitis are blepharospasm, epiphora, miosis, aqueal flare, edema of the iris and hypopyon (Photo 5). These signs most often manifest bilaterally in septic foals, though unilateral presentation can occur.

Foals with meningitis often have an altered mental status, ataxia, seizures and a stiff, "guarded" neck and gait. Endocarditis is an infrequent complication of septicemia in foals. Tachycardia, tachyarrhythmia, lethargy, murmurs, jugular pulsation and dependent edema may be signs of endo-carditis.

Healthy neonatal foals commonly have a low-grade systolic murmur over the semilunar valves over the left heart base. However, loud murmurs over the semilunar valves, murmurs over the mitral or tricuspid valves or those that are accompanied by other signs of cardiac disease should be investigated further by echocardiography.

Hepatic, splenic and renal abscessation may occur secondary to septicemia, though secondary infection in these anatomic locations rarely cause localizing clinical signs.

When the systemic pro-inflammatory response to infection is uncontrolled and malignant, the clinical state of shock and MODS (Multiple Organ Dysfunction Syndrome) ensue.

Photo 4: Uveitis, characterized by cloudiness, aqueal flare or fibrin (arrow) in the anterior chamber, is a sign of advanced septicemia.

Septic shock is defined as hypotension accompanied by signs of hypo-perfusion (altered mental status, hypothermia, hypotension, shivering, cold extremities, mucous membrane pallor, bradycardia or tachycardia, poor capillary or jugular vein refill, poor pulse quality, oliguria and ileus) that is induced by the presence of sepsis, is the result of systemic vasodilation and persists, despite adequate fluid resuscitation.

The manifestations of MODS are vast and the signs reflect the organs that are predominantly affected. These may include mental deterioration, ataxia, seizures, oliguria, coagulo-pathy, dyspnea, tachypnea, tachycardia or bradycardia, colic and/or ileus. Ultimately, identification of clinical signs or physical findings of secondary infection, shock or MODS is significant. These conditions not only identify an advanced and improperly controlled disease state, but they also are associated with a poor prognosis.

Finally, when evaluating a neonatal foal for any reason, consider that any primary disease can induce a state of immunosuppression and/or cause loss of integrity of local protective barriers that subsequently welcomes infection. For example, other common diseases during the neonatal period, such as neonatal isoerythrolysis, neonatal encephalopathy, uroperitoneum, neonatal asphyxia syndrome, meconium impaction, diarrhea or any cause of colic, may be complicated by concurrent infection.

Photo 5: Basophilic cytoplasm, vacuolization Dohle bodies (arrow) in neutrophils, are reliable signs of bacterial infection.

Michelle Henry Barton is the Josiah Meigs Distinguished Teaching Professor at the University of Georgia's College of Veterinary Medicine, where she is a large-animal internist in academic practice. She received her DVM from the University of Illinois in 1985, her PhD in physiology at the University of Georgia in 1990 and became an ACVIM diplomate in 1990.