Neonatal Isoerythrolysis

Neonatal isoerythrolysis (N.I.) is an immune-mediated hemolytic disorder of newborn foals due to absorption of colostral immunoglobulins which contain antibodies against red cell antigens inherited from the stallion. The problem is seen most commonly in multiparous Aa or Qa negative mares due to sensitization to blood group factors during pregnancy or blood transfusion. Other antigens may cause NI occasionally (Ua, Pa, Qc, Db). Recent reports indicate some donkey-mare matings have produced NI in mule foals. Ca antibodies may prevent NI through antibody-mediated immunosuppresion [1].

I. Clinical Features

1. Foal from high risk mare - Foals are normal at birth and only develop clinical signs after ingestion of colostrum.
2. Signs vary with rate and severity of erythrocyte destruction.
3. Progressively developing anemia, icterus or rarely hemoglobinuria leading to depression, anorexia, collapse, death.
4. Symptoms more severe and prognosis poorer in foals with obvious signs at 12 to 24 hours of age due to rapid loss of red cells. Significant signs may not be apparent until 3 to 4 days of age in foals with milder forms.
5. Neonatal isoerythrolysis in mule foals [2,3] A RBC antigen of some donkeys is not found in mares. Donkeys with this antigen mated to mares may sensitize mares to produce antibody to this antigen which may be inherited by the mule foal offspring of the mating. Typical NI reported in several mule foals. Test by screening serum of mares bred to donkeys when mares are in last trimester. If positive for antibody to donkey antigen, withhold colostrum from newborn and provide alternate source of colostrum to newborn mule.

II. Laboratory Features and Diagnosis [4]

1. Progressive hemolytic anemia.
2. Hyperbilirubinemia - Elevation of both direct and indirect bilirubin.
3. Blood typing (Serology Laboratory).
4. Hypoglycemia and acidosis may be present concurrently.
5. Coombs test
6. Flow cytometry
7. Serial tube agglutination test [5] (Jaundice Foal Agglutination Test- JFA-test)

1. Collect EDTA tube blood sample from the foal before it nurses.
2. Collect colostrum from the mare and filter though gauze
3. Set out 6 clean test tubes in a rack. Add 1 ml of normal saline at room temperature to each tube and label each tube.
4. In the first tube, add 1 ml of colostrum and mix well. This will be a 1:1 ratio.
5. In the second tube, a 1:2 ratio is established. This is done by pipetting 1 ml of the mixture of the first tube and mixing it in the second tube.
6. Pipet out 1 ml of the mixture of the second tube and put in the third tube to obtain a 1:4 ratio.
7. Continue this procedure down to the sixth tube until a 1:32 ratio is obtained. Pipet 1 ml from this mixture and save for further dilution if necessary
8. Place one drop of whole blood from the foal into each of the test tubes, mix gently and centrifuge at 1500 rpm for 3 minutes. The ratios should be:
   Tube #1 1:1        Tube #4 1:8
   Tube #2 1:2        Tube #5 1:16
   Tube #3 1:4        Tube #6 1:32

Interpretation of the Results:

Negative test: hold the test tube at a 30 degree tilt. A precipitate will form a streak which will stretch one inch and more.
Positive test: If the precipitate (plug) doesn't streak (or very little). If the test shows a strong positive at a 1:4 dilution but a weak positive at 1:8, let the foal nurse but watch very carefully!
If the result shows a strong positive at a 1:8 dilution, or greater, don't let the foal nurse!
If there is a positive reaction with foal's cells repeat with mare's RBC to validate procedure.

III. Treatment Blood Transfusion

Some of the signs of gastroduodenal ulcers in foals vary with the clinical syndrome.

1. Best results when administered prior to the onset of severe signs.
2. Indications

1. RBC <3 X 106/ul, PCV <14%, Hgb <5 g/dl.
2. Evidence of progressive decline in these parameters and hypovolemia.

3. Erythrocyte donor

1. Washed erythrocytes (0.5-2 L) from the dam. (Washed 1-3 times by centrifugation in isotonic (0.9%) saline under sterile conditions).

1. Administer shortly after washing because cells do not store well and risk of bacterial contamination is high.
2. Resuspend cells to make a 50% solution of red cells and isotonic saline (0.9% NaCl).
3. Administer 1 L/hour of this 50% suspension I.V.

1. Blood from an unrelated donor whose blood is compatible with the dam and the foal (may be difficult to find).
2. Do not use sire of foal as donor.

4. Monitor clinical and hematologic response. Repeat transfusion may be necessary.
5. Multiple transfusions associated with histologic evidence of iron-toxicity, development of liver failure and decreased survival rates[6].
6. Synthetic Hemoglobin products (Oxyglobin®, Biopure, Cambridge, MA) can be used if blood is not readily available (5-7.5 ml/kg).
7. Exchange Transfusion- to avoid kernicterus, practitioners in New Zealand often do an exchange transfusion on severe acute NI cases. Better success and long RBC life occurs when done with washed RBCs from the mare: 4-5 liters of washed maternal RBC is administered in one jugular vein and an equal amount of blood is taken from other jugular at the same rate into a collection vial that allows matching of volumes in and out. This removes bilirubin and anti-RBC antibody that would be active against remaining foal RBC inherited from sire.

IV. Supportive Care

1. Minimize stress, and exercise- stall rest is imperative.
2. Provide monitoring and supportive care depending on degree of clinical signs. N.I. foals need a warm, dry environment, adequate IV fluids, correction of hypoglycemia, or acidosis and monitoring for concurrent infection. Editors Comment - be careful with volumes of IV fluids - can drop PCV even lower.
3. Hyperbilirubinemia is a very serious complication and can produce permanent damage to basal ganglia region of brain (kernicterus). Mild cases have clinical signs of dysphagia and inability to suck and prehend food. Moderate and severe cases will develop coma and eventually die (usually if total bilirubin >20-30 mg/dl). (See Exchange Transfusion).
4. Sepsis due to partial failure of passive transfer of adequate antibodies, due to compromised hepatobiliary function, or due to tissue hypoxia and enhanced translocation. Administer antimicrobials to minimize the risk.
5. Liver failure can occur in severe cases. Several contributing factors have been proposed including hypoxia, immune complex deposition, cholangiopathy due to bile stasis and iron toxicity. Recent study has shown histologic evidence of centrolobular necrosis and increased number of siderophages within the liver supporting the theory of iron toxicity [6].

V. Management of the N.I. Mare

1. Observe foaling and do not allow foal to nurse mare.
2. Milk mare by hand.
3. Provide alternative colostrum from colostrum bank tested negative for alloantibodies.
4. Allow visual access to mare or muzzle foal until colostrum milked from mare. Allow a minimum of 18 hours to pass before foal nurses. Make sure that the foal has received adequate colostrum or plasma transfusion from another source and serum IgG indicates adequate passive transfer. Check milk via colostrometer and it may be possible to return the foal to the mare earlier.

VI. Prevention [5]

1. Screen mares to be bred by blood typing. Blood for typing and detection of the presence of antierythrocyte antibodies is collected and mailed to Serology Lab [a]. One clotted or serum tube and one whole blood tube with acidcitrate-dextrose (ACD) anticoagulant are required. Mares that are Aa or Qa negative are at higher risk delivering a possible NI foal.
2. Mares at risk:

1. Known to have had a previous foal with N.I.
2. Known to be Aa or Qa negative.

3. Evaluate antierythrocyte antibody titer in the last 2-3 weeks of pregnancy. Earlier blood tests may be negative because the antierythrocyte antibodies rise during pregnancy.

1. If hemolysin titer >1:4, withhold colostrum.
2. Anti Ca antibody not known to produce NI.
3. Provide antibodies to foal via alternate source of colostrum or plasma tested free of alloantibodies.

4. Breed to a stallion without A or Q antigens.
5. Anti-C antibody is found in mares with C negative blood type.

1. No documented cases of an anti C mediated N.I. disease.
2. If extremely high titers of anti C are found in a pregnant mare, should run the colostrum Serial Tube Agglutination Test (JFA test).

6. Serial tube agglutination test (Laboratory Features, Section G).

1. This field test has been used for many years by veterinary practitioners and appears to be an aid in determining if the foal should be prevented from nursing.
2. It is based on presence of agglutinins and not hemolysins. Agglutinins are believed present with hemolysins in all but Q system with R or S factors. The serial tube agglutination test will fail to indicate the presence of antibodies to these factors in the colostrum and regular serum screening for isoantibodies must be used.

Footnotes

1. Veterinary Genetics Laboratory University of California School of Veterinary Medicine One Shields Ave, Davis CA-95616, USA; +1 530-752-2211. www.vgl.ucdavis.edu