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.

Equine neonatal isoerythrolysis

In foals, the condition results when a mare develops antibodies against the foal's red blood cells. This occurs when the foal inherits red blood cell antigens from its sireThe foal is unaffected during pregnancy because no blood or antibodies are able to cross the placenta. However at birth the foal ingests large numbers of antibodies in the colostrum, leading to severe haemolytic disease.

Clinical signs

Horses

Affected foals appear clinically normal at birth, and clinical signs develop from several hours up to a week after ingestion of colostrum. Foals with NI usually become progressively weak, lethargic and depressed develop icterus, tachycardia and tachypnoea. Although the signs are not pathognomonic for NI, a foal displaying haemoglobinuria and icterus born to a multiparous mare should be strongly suspected to have the disease. If the foal becomes severely hypoxic, seizures may occur. Death usually occurs if NI is not diagnosed and treated promptly.

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.

Diagnosis

In horses, a minor cross-match is performed using the foal's red blood cells and the mare's serum. A positive agglutination indicates a diagnosis of NI.

Treatment

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.

Prevention

The disease in horses is prevented by ensuring that mares are blood-typed before being mated. Mares who are negative for the blood antigens known for causing disease (primarily Aa, Qa, Qc and Ua) can be matched to stallions who are also negative.