FRANK J. MILNE STATE-OF-THE-ART LECTURE


quently, failure of passive transfer is listed as the leading cause of septicemia91–94 and the practice of assessing passive immunity has been associated with decreased morbidity due to septicemia.87 However, many (25%) confirmed septicemic foals have greater than 800 mg/dl IgG. Additionally, many foals with low IgG are sick at birth and have poor vigor and vitality. With good management, healthy foals with serum IgG of 200–400 mg/dl have only slight risk of acquiring illness.95 Efforts to raise IgG by various means seem not to have elimi- nated the problem of septicemia over the last 10–15 years. Well-conducted studies have indicated that low IgG per se is not a risk factor for disease and that foals with only 200 mg/dl IgG at 24 hours of age do not get sick on some farms.80,95 It is my opinion that this high rate of infection in this age group is best explained by delayed gut closure and bacterial invasion across the “open” gut rather than low IgG.


Predisposing Conditions


Predisposing conditions include: prematurity; de- layed access to colostrum; failure to ingest adequate quantity of colostrum and specific antibody; mater- nal risk factors—concurrent illness or fever, vaginal discharge, poor nutritional status, colic, endotox- emia, premature lactation, recent transport stress, agalactia, poor mothering; neonatal maladjustment syndrome (NMS); twins; and adverse environmental conditions. What all these conditions have in common is ex- posure to pathogens prior to colostrum ingestion.


Clinical Signs Clinical signs often cannot be differentiated from NMS. Early clinical signs are vague and include depression, lethargy, decreased mammary sucking, and a behavior change. Fever (102°F, 39°C) oc- curs in less than 50% of cases and hypothermia 100°F (37.8°C) is not uncommon. In advanced cases petechiation of pinnae and mucous mem- branes of the oral cavity and vulva is seen. It should be noted that episcleral hemorrhages are common after normal foalings from birth canal pres- sure. Other signs include anterior uveitis, diar- rhea, obtundation, coma, convulsions, respiratory distress, dehydration, poor pulse quality, and swol- len joints.


Clinical Pathology


Clinical pathology should be obtained as soon as possible. Serum IgG concentration of 400 mg/dl is common although some are within the 400 to 800 mg IgG range. Both neutropenia (4000/ul) and neutrophilia (12,000/ul) can occur (it should be remembered that premature, noninfected foals have neutropenia). Additional hematological findings include 50/ul band neutrophils and Dohle bodies, toxic granulation, or vacuolization in neutrophils. Fibrinogen concentration is frequently elevated 400 mg/dl indicative of inflammation. Hypogly-


cemia occurs in approximately 50% of cases (80 mg/dl) and arterial oxygen is 70 mmHg in 40% of cases. Acid-base status indicating a mild to severe acidosis is common. Blood culture is indicated in any suspected case of


sepsis and should be performed on all foals entering the intensive care unit. If blood culture medium is not readily available, the sample can be transferred in a yellow top tube containing anticoagulant citrate (ACD). Sampling should be performed before anti- biotics or at trough periods before next administra- tion. One blood sample should be collected initially upon admission and then repeated in 1 to 2 hours. Do not delay antimicrobial treatment of suspected septicemia to complete a series of cultures. Intra- venous antimicrobial therapy should be initiated if laboratory work does not rule out sepsis. Negative blood cultures do not rule out septicemia; over 50% of foals with E. coli septicemia have negative blood cultures.96 Organisms found most commonly are E. coli, Actinobacillus spp., Klebsiella pneumoniae, Pseudomonas spp., Citrobacter spp., Enterobacter spp., Salmonella, and gram-positive organisms such as Streptococcus, Staphylococcus, Enterococcus. Sepsis scoring is a method of attempting to predict infection based on history, physical exam, and clin- ical pathology designed by Brewer and Koterba, 1988. The system uses 14 historical, clinical and laboratory weighted variables to derive 14 scores, which are then added together to give the sepsis score. The sepsis score is reported to have a sensi- tivity of 93%, a specificity of 86%, positive accuracy rate of 89% and negative accuracy rate of 92%.97 Subsequent studies have suggested the sepsis score is less reliable than initially reported.98,99


Therapy Antimicrobials


Almost all systemic neonatal bacterial infections in- volve Gram-negative (often enteric) organisms, with or without accompanying gram positive organisms. The opposite is usually the case in adults. Septice- mic foals deteriorate rapidly and, therefore, antibi- otic treatment should be started as soon as cultures have been collected and later modified, if necessary, after culture and susceptibility results are available. Front line antibiotics should have excellent activity against Gram-negative bacteria and specific combi- nation therapy is rational to broaden the spectrum. The most useful antibiotics for initiating treatment of suspected or confirmed sepsis are the aminogly- cosides, e.g., amikacin or gentamicin, in combination with penicillin G, ampicillin, ticarcillin, or a cepha- losporin antibiotic. Depending on the susceptibil- ity of bacterial isolates, other antibiotics that may prove useful include trimethoprim/sulfonamide, 3rd-generation cephalosporins, or ticarcillin/clavu- lanic acid. Bactericidal drugs are preferred be- cause neonates have suboptimal defense mechanisms and most infected foals have total or


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