IN-DEPTH: NEONATOLOGY
given the hyperimmunized plasma appeared to have their manure become formed faster than the pa- tients not treated with the plasma. Bentonite clay can also be used for treatment
since it has been shown to adsorb Clostridium perfringens alpha, beta, and beta-2 exotoxins without interfering with absorption equine colos- tral antibodies.35 Numerous prophylactic measures can be insti-
tuted on farms with a history of C. perfringens– associated enterocolitis in foals. Optimal hygiene efforts to ensure cleanliness of the foaling stall and the mare (clean udder before and after birth, clean the perineal and hind-limb region) at parturition should be undertaken to decrease the degree of ex- posure of the foal to pathogens in the feces.36 Some farms have stopped their outbreak of foal diarrhea by foaling the mares out in pasture. Specific pre- ventative methods addressing C. perfringens in- clude immunizing mares with the use of a toxoid vaccine (aluminum hydroxide–adsorbed culture supernatant plus recombinant 2-toxoid). The vaccine strain is a C. perfringens Type A that carries genes for Alpha, 2, NetF, and CPE that has been developed (2007) by Hagyard Equine Medical Insti- tute. Other oral enteric protectants include the oral and/or administration of hyperimmunized plasma, which was previously mentioned. Specific immune treatments for C. perfringens types C andD do provide some protection against alpha-toxin, but it is generally believed that this protection would be inadequate against C. perfringens type A organisms.
6. Salmonella
Salmonella are gram negative, facultative, anaero- bic bacteria, which usually can access the intestinal tract via the fecal-oral route. Salmonella com- monly infects foals between 12 hours and 4 months of age. Young animals are more susceptible to Sal- monella infections maybe because of a less sophisti- cated or less well established microflora within the gastrointestinal tract. The most common source of exposure and infection in the foal is another horse. Often, the mare herself is an asymptomatic carrier. Mares have been shown to shed Salmonella at or shortly after parturition despite having as many as 19 negative cultures before foaling.37 Observations of foalings revealed that all mares defecate during stage 2 labor and that contamination of fetal mem- branes and the perineum/udder of the mare was possible if Salmonella was in the feces. During udder-seeking, the newborn foals will have exten- sive contact with the perineum and therefore may be at risk of Salmonella ingestion. Once Salmonella has overcome the host defense mechanisms (gastric acidity, intestinal flora, peri- stalsis, intestinal mucus, and lactoferrin) the bacte- ria migrate through the enterocytes and access the lamina propria where they stimulate an inflam- matory response. Both phagocytized and free Sal- monella organisms travel via the lymphatics to
regional lymph nodes where they persist in stimu- lating an inflammatory response. Salmonella can also reach circulation from efferent lymphatics. The neonate predisposition toward bacteremia and septicemia may be because of factors such as de- layed gut closure at birth, immature cellular im- mune response and decreased complement activity. Salmonella enterotoxins, cytotoxins, and general- ized inflammation within the bowel induces secre- tions of fluid from the intestinal epithelium.
Clinical Signs
Clinical signs of Salmonellosis are variable and can range from mild enteritis to severe septicemic shock. Diagnosis of Salmonella is demonstrated by a posi- tive fecal or blood cultures. The author has seen foals present with fevers of unknown origin with no signs of diarrhea that have had positive blood and fecal cultures for Salmonella. Intermittent shed- ding of Salmonella is common and therefore a min- imum of 3 to 5 consecutive 1-gram fecal cultures taken 24 hours apart are recommended.
Treatment
Treatment for salmonella is nonspecific and is aimed at maintaining hydration and electrolyte balance. Antibiotic therapy, even though it does not alter the clinical course of diarrhea or shedding of the organ- isms, should be initiated in foals to help prevent bacteremia. Polymyxin B (6000 IU/kg IV q8h) di- luted in1Lof fluids, flunixin meglumine (0.25 mg/kg q8h IV), and pentoxifylline (7.5 mg/kg PO q12h) all have been shown to reduce the effects of endotoxemia. Bismuth subsalicylate (1 to 3 mL/kg PO q4-8h) is also commonly used as a gastropro- tectant secondary to its endotoxic and antiprosta- glandin properties. J-5 plasma may also be given to aid in decreasing the systemic endotoxin level.
Prevention
Prevention of Salmonella consists of proper hygiene. Before the foal is able to nurse, the udder and peri- neal regions of the mare are to be thoroughly washed with dilute chlorohexidine or ivory soap and water. During an outbreak situation, foals should also be intubated with 6 to 8 oz of colostrum prior to contact with the mare. An experimental inactivated bacterin (Salmonella typhimurium and Newport) vaccine has been devel- oped by Hagyard Equine Medical Institute and Dr. John Timoney at the Gluck Research Center in Lex- ington, KY. This vaccine has been used on endemic farms since 2007.
7. E. durans (Group D Streptococcus)
E. durans is a gram-positive coccus in the alimen- tary tract that has been implicated as a cause of enteritis in foals, piglets, calves, and puppies. The author has documented E. durans as a cause of diarrhea in 5 of 7 foals that had developed diarrhea during the first 10 days of life.38 In one study con-
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