Fading Kitten Caused by Feline Neonatal Isoerythrolysis (NI)
These antibodies are present in the colostrum and will be absorbed for up to the first 24 hours after birth. They destroy the red blood cells leading to anaemia. Affected kittens may die in the first two to three days. This problem is more frequent in certain breeds which have a high prevalence of group B individuals – such as British Shorthairs, Birmans and Devon Rex.
The AB blood group system: Thus far, only one blood group system with 3 blood types has been recognized. Although type A is by far the most common blood type, the frequency of type A and B in domestic shorthair cats varies worldwide and markedly among breeds.
The allele for type A is completely dominant over the allele for type B.
Thus, type B cats are homozygous for the B allele (B/B), whereas type A cats can either be homozygous (A/A) or heterozygous (A/B).
Type AB, the third feline blood type, occurs extremely rarely in domestic shorthair and purebred cats, and could be explained by a third allele.
Naturally occurring alloantibodies: In contrast to dogs, cats have naturally occurring antibodies against the blood type they are lacking in their plasma.
Type A cats have weak anti-B alloantibodies with titers typically only 1:2 and rarely reaching 1:32. However, all type B cats have very strong anti-A alloantibodies with hemagglutinin and hemolysin titers of 1:64 to 1:2064.
Neonatal kittens acquire maternal alloantibodies of the IgG class via colostrum during the first day of life and begin to produce their own alloantibodies between 6 to 10 weeks of age. These alloantibodies, particularly anti-A antibodies, are responsible for transfusion reactions and neonatal isoerythrolysis (NI).
Development
Colostral anti-A alloantibodies are responsible for NI, i.e., type A and AB kittens born to type B queens are at risk of developing NI during the first week of life.
Since all type B queens have high anti-A antibody titres, even primiparous queens can have litters with NI. No case of NI in a type B kitten born to a type A queen has been documented. The hemolysis may occur intra- as well as extravascularly and may cause anemia, nephropathy, as well as other organ failure.
Clinical signs
Kittens with type A or AB blood born to type B queens may develop signs of NI immediately following colostrum intake. The hallmark sign of NI is severe pigmenturia due to hemoglobinuria.
Other clinical signs include sudden death, failure to thrive (stop nursing), anemia, icterus, and tail tip necrosis.
Prevention
Despite removing the kittens from their queen as soon as the first clinical signs develop, the mortality rate is high. NI is best prevented by avoiding incompatible matings between type B queens and type A toms. In blood incompatible matings, kittens at risk for NI should not be allowed to nurse from their type B queen for the first 24 hours.
Cord blood could be used to determine the kitten's blood type or to perform a crossmatch with serum from the queen. Kittens with blood type B could be immediately placed back with their queen. Type A (or AB) kittens may safely receive milk or colostrum from a type A queen:.