Feline Neonatal Isoerythrolysis
The first year of life for a kitten can be a difficult time. Up to 27 percent of all kittens do not survive to celebrate their first birthday. There are a variety of causes of mortality, including birth defects, poor environment, low birth weight and cannibalism by the mother or other adult cats. An additional cause of kitten illness and death is related to mother and kitten blood types and is called neonatal isoerythrolysis (NI).
Neonatal isoerythrolysis refers to the destruction of the red blood cells (erythrocytes) within the kitten’s body system by the action of maternal antibodies, which gain access to the neonatal circulation. In cats, this entrance is through the colostrum.
As in humans, each cat is born with one of three primary blood types: type A, type B and type AB. Although the types are named similar to humans, they are not the same. In humans, type AB is a combination of type A and type B. In cats, type AB is a completely different blood type. In addition to the blood type, cats are born with natural antibodies against other blood types. For instance, type A cats are born with antibodies specifically made to destroy type B blood. The same occurs in type B blood. Type B blood has very strong anti-A antibodies, but type A has relatively weak anti-B antibodies. The anti-A antibodies in type B blood are so strong that even a small amount of type A blood given to a type B cat can result in serious illness and even death. No antibodies against other blood types are found in the very rare AB blood.
Neonatal isoerythrolysis occurs in kittens with type A blood born to type B queens. In the United States, the vast majority of cats are type A but about 5 percent of domestic shorthair cats are type B. Less than one percent are type AB. In the purebred population, certain breeds have a higher incidence of type B blood. The following is a list of breeds and the incidence of type B blood within their population in the United States. The incidence of type B blood varies in different parts of the world.
Not all kittens born to type B queens develop NI. The illness occurs only when the mother has type B blood and the kitten has type A or type AB. Also, while the mother is type B, the father is type A or type AB. If both the mother and father are type B, all the kittens will be type B. If the father is type A, about ½ of the litter will be type A since type A is dominant to type B.
During the first 24 hours of life, the intestinal tract of kittens is able to absorb large proteins and antibodies. This helps kittens absorb protective antibodies against various diseases and is the reason why babies need to nurse within the first day of life. After 24 hours, the intestinal tract changes and is no longer able to absorb large proteins. In type A kittens born to type B queens, this ability to absorb large proteins can be life threatening.
Type A kittens are born healthy and begin to nurse. Within the milk of their type B mother are antibodies specifically created to destroy type A blood. As the type A kitten nurses, he absorbs anti-A antibodies from his mother. These pass from the intestinal tract into the circulation and the red blood cells of the kitten are rapidly destroyed. This results in serious illness and death and most kittens die within the first 48 hours of life. The severity of signs depends on the number of antibodies ingested and varies from kitten to kitten. Even kittens that nurse for only a brief time may develop severe illness and die.
What to Watch For
A few kittens may not develop the fatal reaction. Some may develop small blood clots that may lodge in the tip of the tail, resulting in death of that part of the tail. Over time, the tip of the tail may slough. These kittens usually survive but the tip of their tail falls off.