Septicaemia in the foal

Every breeder’s worst nightmare, foal septicaemia, and perinatal asphyxia syndrome (PAS), are two of the major diseases in foals which are responsible for 44 per cent of deaths in foals less than a week old.  They are very difficult to distinguish, particularly as assessment by published sepsis scores relies on some data not immediately available, especially if a vet is in the field or the practice doesn’t have advanced laboratory facilities.  The other problem is that a recent study carried out to evaluate how good the sepsis score is at predicting sepsis revealed that 45 per cent of the foals predicted not to have sepsis were actually septic.  This limits the clinical usefulness of attempts at sepsis scoring.

However, knowing which foals are septic and which aren’t remains important.  One of the reasons is that septic foals can cost approximately £650 more to treat than a foal with PAS, due to the higher levels of intensive hospital care, so owners need to be prepared for a higher bill. 

At a recent CPD meeting in Dublin on modern equine antibiotic therapy, hosted by animal health company Intervet UK, Kevin Corley BSc BVM&S MS PhD DECEIM DACVIM DACVECC MRCVS, specialist in medicine and critical care at Anglesey Lodge Equine Hospital in Ireland, provided delegates with an in-depth overview of foal septicaemia, its causes, clinical and laboratory signs and treatment.

Causes

Septicaemia is usually caused by bacteria, but the route of entry in most cases is not known.  Often it can be in utero infection, although it can be via the gastrointestinal tract. Contrary to popular belief infection is only occasionally through the umbilicus as there is no active blood flow to transport the bacterial infection into the body.  Approximately 70-85 per cent of septicaemia is caused by Gram-negative bacteria and Escherichia coli pre-dominates, followed by Actinobacillus.  This is something to consider when thinking about antimicrobial therapy.

Septicaemia can also result from fungal infection, usually caused by Candida, although this is more common in the USA.  In addition, viral septicaemia can be caused by EHV-1 and EVA.

History

Foals with septicaemia may present in different ways.  They can appear normal at birth, standing and nursing properly, but then become weaker, duller, depressed and unable to rise, or they may be abnormal at birth and continue to get weaker.  If the foal never stands, it’s likely to have been infected via the placenta.  About 25 per cent of foals referred with septicaemia are still standing on arrival at the referral centre. 

Failure of passive transfer is an important predisposing factor, but septicaemia should not be ignored in foals with good transfer of antibodies.  A foal can have a normal, high IgG, but still get septicaemia.

Clinical signs

In all cases, foals are depressed and can continue to deteriorate quickly, in some cases becoming comatose.  Sometimes foals experience seizures due to septic encephalopathy, although these are rare.  Often cardiovascular disturbances are seen, which may commonly be identified by injected mucus membranes and conjunctiva, although rarely oral petechiation may also occur.  It’s always important to look into the eyes and ears of septic foals to look for capillary leaks, hypopyon, and hyphaema, as well as erythema around the coronary bands.  Body temperature can be unreliable as foals may have fever, hypothermia or a normal rectal temperature, and this can undulate markedly during the day and may only spike above the normal range once or twice a day.

The internal umbilical remnants are a common site for infection and umbilical ultrasonography can demonstrate increases in the size or changes in the echo-density of the umbilical structures which suggests infection.  Synovial structures are also a common site of infection and it’s advisable to check for heat or effusion in all joints many times a day.  This enables joint infection to be detected early on, when the prognosis is still good.  Again ultrasonography can be helpful to demonstrate changes in the synovial echogenicity, synovial effusion and osteomyelitic lesions.  The lungs are also a common site of infection and can be investigated with ultrasonography or radiography.

It’s advisable to measure blood pressure, particularly in recumbent foals, to monitor any changes.  Low blood pressure is associated with sepsis and if identified early in the course of disease will enable vets to act quickly and treat foals for septicaemia.  Research at Kevin Corley’s practice amongst 111 foals revealed that if blood pressure was over 50mmHg on admission then 75 per cent survived, whereas no foals with blood pressure under 50mmHg on admission survived.  Foals have occasionally gone into rapid shock in the hospital with blood pressure under 50mmHg and have survived with intensive treatment, however the difference is that if they are admitted with the blood pressure this low then there is already irreversible organ damage and there is little benefit in going ahead with treatment.

Laboratory signs

The laboratory signs of septicaemia are non-specific.  Both low and high peripheral white cell counts are seen in foals with sepsis including immature neutrophils which are associated with Gram-negative sepsis.  Neutrophils with ring nuclei are typically seen in the more severe cases and plasma fibrinogen concentrations may be increased in sepsis.  If they increase in the first 24 hours of life, this suggests in utero infection.  Serum amyloid A is an acute phase protein that increases and decreases much faster than fibrinogen and several studies have shown that increased concentrations are a reasonably reliable indicate of sepsis in foals.

Treatment

Antibiotics are the mainstay of treatment for septicaemia.  However other medication may also be required, especially in more severely affected foals, and it’s important to ensure an adequate circulation prior to treatment with antibiotics.

The choice of antibiotics depends on a number of different factors including clinical signs and expense.  Broad-spectrum antibiotics are often used as treatment begins before bacteria are identified, but foals with low white cell counts are more likely to have Gram-negative infections, so therefore a broad-spectrum antibiotic with good Gram-negative activity should be administered. 

Maintaining the hydration status and circulation is extremely important.  Fluids and blood pressure support are titrated to the foal’s individual needs, based on arterial blood pressure, urine output and specific gravity, mentation, blood lactate measurements and, sometimes, central venous pressure and cardiac output measurements.  Foals do not handle sodium in the same way as adults and low sodium fluids, such as Plasmalyte-M are more suitable for maintenance fluid therapy than fluids such as Lactated Ringers’ solution.  The maintenance dose of fluids is generally 4-5ml/kg/hr in the foal, but this can vary.  The most commonly used products to support blood pressure are dobutamine and norepinephrine.  Vasopressin can also be used.

If joint sepsis is suspected, it is vital to treat this aggressively and early, so that the future athletic potential of the foal is not compromised.  Treatment includes needle flushes, arthroscopic lavage, local instillation of antimicrobials and region perfusion of antimicrobials.  The prognosis for athletic function decreases when more than one joint is involved and with each additional joint.

Prognosis
The prognosis for foals with septicaemia undergoing intensive care at referral centres is approximately 75 per cent, however the survival rate of septic foals managed in the field is probably much lower.  In a University of Leipzig report, only 30 per cent of foals with early sepsis (still standing and suckling) survived while the overall survival rate of septic foals was as low as 13 per cent. Over two years of racing, the earnings for horses that had septicaemia was equal to those that had no foal diseases. However, they earned less as two-year olds (and consequently more as three-year olds).  Prognosis for athletic function is reduced if more than two joints are involved.

Kevin Corley will be speaking at the Rossdale & Partners Foal Care Course, sponsored by Cephaguard^® IV, from 16-18 January 2008 at the British Racing School at Newmarket.  For further information, please contact 01638 577822.