There are three feline blood groups: A, B and AB. Group A is the most common, B is quite common in some breeds (see Table 1) but is rare in others, and group AB currently appears to be rare in all breeds.
Blood group is determined genetically and the gene for group A is dominant to the gene for group B. This means that a blood group B cat must carry two group B genes (ie, it is homozygous) and can only pass on a B gene to its offspring. A blood group A cat may have two A genes (ie, it may be homozygous), or it may have one A gene and one B gene (ie, it may be heterozygous). A heterozygous cat will pass an A gene to around half of its kittens, and will pass a B gene to the other kittens. This means that if a heterozygous group A stud cat is mated with a group B queen, a proportion of the resulting kittens can be expected to be group A. Blood group AB is inherited independently and the AB gene appears to be dominant to the B gene, but recessive to the A gene.
Type A is generally the most common blood type. Blood type A and B frequencies in domestic short- and longhair cats vary from country to country; some countries have only type A cats, whereas others may have as many as 50 per cent type B cats. Furthermore, blood type frequencies vary between breeds; for example the Siamese and some related breeds have only blood type A, while other breeds may have as many as half and half As and Bs (eg, Turkish Angora and Van).
Blood group incompatibility
Blood group B cats all have naturally occurring anti-A antibodies in their blood that are present in high levels from a few months of age and which can cause destruction of type A red blood cells. In the normal way this is quite safe because group B cats do not have any type A red blood cells. However, if a group B cat is given a blood transfusion from a group A cat then the transfused A cells will be rapidly destroyed and an immediate, dramatic, potentially fatal transfusion reaction is likely to occur.
Antibodies in the blood are also passed into the colostrum and milk, so if a newborn group A kitten suckles from a group B queen during its first day of life, it may absorb large amounts of anti-A antibodies, causing damage to its type A red blood cells – this is neonatal isoerythrolysis.
About one third of blood group A cats have some naturally occurring anti-B antibodies in their blood which will cause destruction of type B red blood cells. In most cases the anti-B antibodies are present in low numbers, enough to cause serious transfusion reactions, but not enough to cause neonatal isoerythrolysis.
Neonatal blood group incompatibility
Blood group incompatibility at birth, also known as ‘neonatal isoerythrolysis’ or ‘haemolysis of the newborn’, can be a significant cause of death in young kittens of certain breeds.
The problem arises if a queen with blood group B produces kittens that are blood group A or AB. The kittens are born healthy, but during their first day of life they absorb antibodies from the mother’s colostrum (first milk) which destroy their red blood cells causing anaemia and jaundice.
What to look for in affected kittens:
The kittens will all be normal at birth but, soon after they have suckled, any group A or AB kittens in the litter may start to show signs of disease. The severity of the signs is very variable.
- In some cases neonatal isoerythrolysis can cause sudden death, with no prior warning signs that the kitten is affected.
- In most cases the kittens will appear to ‘fade’ over the course of a few days: they will cease suckling and become weak; they often appear pale and if they survive may become jaundiced (yellow). They usually pass red coloured urine due to the presence of red cell breakdown products in the urine.
- Mildly affected kittens may show few signs of illness during the first week of life, but the tip of their tail may gradually die off.
- Some kittens remain unaffected and show no signs of disease at all.
These differences in the severity of signs are probably due to variations in the amount of anti-A antibody the queen passes into her colostrum; the amount of colostrum sucked by each kitten within the first few hours of life; and the amount of antibody the kitten absorbs from the colostrum.
Treatment of affected kittens
Once the kitten has absorbed the antibodies it is very difficult to treat the problem.
- If the problem is recognised within the first few hours of life the affected kittens must be removed from the queen to prevent further absorption of additional anti-A antibodies from the colostrum.
- It may be possible to give the kitten a blood transfusion of washed red cells from a group B cat (eg, the queen) in order to supply type B red blood cells which will not be destroyed by the anti-A antibodies. However, generally the problem is recognised too late for this to be helpful, and there are very real, practical difficulties in providing a blood transfusion to a newborn kitten.
Preventing the problem from occurring
As treatment is rarely possible it is much more appropriate to prevent the problem from occurring in the first place. There are a number of practical measures that a breeder can use to do this, as long as he/she knows the blood type of the cats involved.
Avoid using group B cats for breeding altogether: This approach certainly avoids the problem of neonatal isoerythrolysis, but it may limit the choice of breeding animals, which may be undesirable for other reasons particularly in small number breeds with a high prevalence of group B individuals. This approach will tend to reduce the proportion of group B cats within a breed. It is only practical in catteries with no other B cats, or in breeds where type B cats are rare.
Only mate group B queens with group B toms: This approach will also avoid the problem of neonatal isoerythrolysis, but again it will limit the choices for matings. All the offspring of such matings will be group B so this approach tends to gradually increase the proportion of group B cats within a breed.
Prevent group A kittens from suckling colostrum from a group B queen during first day: This method has been used by many breeders, but does involve some risk of losing kittens to neonatal isoerythrolysis (see ‘Home Care’ below).
Blood typing cats
Blood typing for cats is now readily available. A blood sample can be collected by your vet and submitted to a commercial laboratory for testing, or the practice may have blood typing kits to provide a more immediate result. A number of these kits are now available providing an accurate and inexpensive means to blood type cats.
Neonatal isoerythrolysis can be prevented if group A and AB kittens are prevented from suckling colostrum from their group B mother for the first 16-24 hours of life (the period during which they are able to absorb antibodies from the colostrum).
If blood typing kits are available then the kitten’s blood groups can be identified at birth, using a drop of anticoagulated blood from each kitten (or its umbilical cord). In this way only the group A and AB kittens need to be removed from the queen, but any group B kittens in the litter can be left to suck from the queen.
Once the kittens have been removed from the queen they must either be hand-reared for the first 16 to 24 hours of life, or they can be temporarily fostered onto a lactating group A queen, if one is available.
- Hand rearing the kittens has the disadvantage that the kittens miss out on the advantages of receiving colostrum, but in most cases this does not appear to cause clinical problems for the kitten except in catteries with high risk of infectious disease.
- Fostering the kittens to another group A queen will provide passive immunity to the kittens, even if the foster queen is no longer producing colostrum. Cats continue to produce relatively large amounts of protective antibodies in their milk throughout their lactation, and these antibodies will be absorbed by the newborn kittens, giving them some early protection from infectious diseases.
If no suitable foster queen is available, and the kittens are considered to be at risk from infectious diseases that are present in the breeding group, then some passive immunity can be provided using serum harvested from a blood sample collected from a donor cat. The blood sample must be collected and separated by a vet, and the serum can then be fed to the kittens or given by injection. While this is safe to do, it rarely appears to be necessary.
|Table 1: Estimated frequency of type B cats in various breeds
NB: For some breeds only small numbers of cats have been tested, so the figures may not be as accurate as they would be if results were available for larger numbers of cats. The proportion of group B cats within a breed may change with time, depending on breeding choices and patterns within that breed.
* Figures supplied by Dr Giger, University of Pennsylvania
^ Figures from a study of UK cats conducted by C Knottenbelt, University of Glasgow
† Figures supplied by Dr Addie, University of Glasgow
** Figures supplied by Professor D Gunn-Moore, Edinburgh University
Dr Urs Giger and Dr Diane Addie are internationally recognised specialists in feline medicine who have a particular interest in neonatal isoerythrolysis. Both have generously contributed their expertise to this information sheet.
Much of the information reported here is based on original work by Dr Giger’s group. Dr Giger has a transfusion laboratory where over 20,000 cats have been typed and many difficult blood typing problems have been studied and difficult incompatibilities have been reconciled. Dr Giger’s web site is www.vet.upenn.edu/penngen
Dr Diane Addie has also created a website which contains a lot of information about this disease and she has established a UK register of queens and stud cats of known blood groups to assist breeders in managing this difficult problem. The site is at www.catvirus.com
Updated November 2008
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