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

Table 1: Some practical facts on normal newborn foals

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.

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.

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

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.

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

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

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.

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.