Neonatal Isoerythrolysis

Description

Neonatal isoerythrolysis is a disease of humans and domestic animals and has been observed in newborn cats, horses, pigs, cows and rarely in dogs. It is characterised by immune-mediated haemolytic anaemia due to ingestion of maternal colostral antibody directed against surface antigens on neonatal red blood cells. The maternal antibodies develop in response to specific foreign blood group antigens during previous pregnancies, unmatched transfusions, and from Babesia and Anaplasma vaccinations in cattle.

Pathogenesis

Feline neonatal isoerythrolysis

Although feline neonatal isoerythrolysis (FNA) is rare, the mortality associated with it is high. FNI develops when type B blood mothers mate with type A tomcats. Type B cats have naturally occurring anti-A antibodies without prior exposure. FNI affects the A, or AB blood type kitten, born from a B blood type mother by receiving anti-A antibodies when it ingests maternal colostrum.

Clinical signs

Horses

Affected foals appear clinicall normal at birth.

Cats

In a similar way to affected foals, kittens are born and nurse normally and clinical signs develop within a few hours or days. Clinical signs may include dark red/brown urine, icterus, weakness, anaemia.

Neonatal Isoerytholysis (NI)

First pregnancy from a stallion with incompatible blood type to the mare: Following mating of a mare and stallion with incompatible blood types, the neonate inherits the sire's blood type. At parturition, or because of placentitis, RBCs from the foal enter the maternal circulation. The surface of the foal's RBCs possess an antigen (usually Aa or Qa) that the mare's RBCs lack. The mare begins to mount an immune response towards the foal's RBCs. There are no antibodies against the foal's RBCs in the mare's colostrum as there has not been sufficient time to mount an immune attack and secrete them into the colostrum. The foal's intestine stops absorbing maternal antibodies after 30 hours (as previously discussed) and thus, when the alloantibody is secreted in the milk, it does not affect the foal.

Subsequent pregnancy from the same stallion or same blood group as previously exposed to

• Foal is born and suckles from the mare.
• Colostrum already contains alloantibodies against the foal's RBCs causing there to be RBC destruction or removal from the circulation (type II hypersensitivity reaction) leading to haemolytic anaemia and jaundice.
• When the foal's intestines are no longer able to absorb maternal antibody (approximately 30 hours post partum) it is safe to return the foal to the mare.