1. Introduction

Blood transfusions are lifesaving procedures. In dogs, because of the absence of naturally occurring alloantibodies, the risk of an acute hemolytic transfusion reaction at the first transfusion is negligible, but mismatched transfusions might produce alloimmunization. Safety of blood transfusion procedure depends on the knowledge of donor and recipient dog´s blood groups.

Dog blood group systems are defined according to species-specific antigens located on the surface of red blood cell membranes and are defined according to antigenic recognition. Each individual might express an antigen to a varying degree (positive blood type) or don´t express a specific antigen (negative blood type)^[1][2]. From the different blood groups systems reported in dogs, the Dog Erythrocyte Antigen (DEA) is the most studied with the DEA 1, 3, 4, 5, 6, 7 and 8 blood types recognized internationally after classification with polyclonal alloantibodies obtained from previously transfused dogs, or specific monoclonal antibodies^[1][3]. Since they are inherited as a complex autosomal dominant allelic system, dog red blood cells might co-express any combination of these blood types on its surface ^[1][4]. Within the DEA blood group system, the DEA 1 has a strong antigenicity and results in blood incompatibility reactions. Formerly the DEA 1 was proposed to have three subtypes: DEA 1.1, DEA 1.2, and DEA 1.3, but it was demonstrated that a single monoclonal antibody can recognize these antigens that are expressed from strong to weak positivity. This level of expression is genetically determined and the expression pattern remains constant^[5][6].

New dog blood groups have been described. The Dal blood type was initially described based on the identification of an acquired alloantibody in a Dalmatian dog^[7]. A high percentage of Dal negative Dalmatians and Doberman pinchers have been reported in North America and Germany^[8][9]. More recently, an investigation on the prevalence of two new blood groups, Kai 1 and Kai 2, produced by mouse hybridoma techniques found that most dogs in North America were Kai 1 positive/Kai 2 negative [10]. There is no proved relationship between Dal, Kai and DEA blood groups^[10][11]. The clinical relevance of Dal and Kai blood types in transfusion medicine is still unknown and testing is not currently routinely available. Blood incompatibilities related to other blood groups than DEA 1 can only be
evaluated by crossmatching [ 12 ].

Although dogs do not appear to have naturally occurring alloantibodies, and the first blood transfusion might be safe, a mismatched transfusions of DEA 1 positive to DEA 1 negative dogs produce anti-DEA 1 antibodies that might develop fatal, acute hemolytic reactions in subsequent incompatible transfusions^[12]. Nonetheless, there is still controversy about the clinical importance of the naturally occurring alloantibodies against DEA blood types other than DEA 1. Knowledge of dog blood types after blood typing can prevent and minimize the risk of blood transfusion reactions and the induction of alloantibodies against red blood cells because of blood incompatibilities. Therefore, it is of utmost importance to know the prevalence of blood types in the diverse breeds and locations. For clinical purposes, DEA 1 negative dogs are considered the preferred blood donors^[4]. However, in dogs, although the DEA 1 antigen has been shown to be very antigenicand capable of eliciting a strong and long-lasting immune response, there is no evidence that alloimmunization occurs in 100% of incompatible transfusion episodes. Therefore, caution should be exercised regarding the likelihood of a dog in the examined population developing alloimmunization and experiencing an acute hemolytic transfusion reaction following an incompatible DEA 1 transfusion.

Canine blood groups are known to vary between breeds and geographically^[13]. For the most part, the prevalence of DEA 1 in canines is around 60%^[6]. When looking to purebred dogs’, prevalences between 39.89% and 91.3% were found^[14], and in mongrels it can vary from 42.8% in canine blood donors from Italy and Spain^[15] to 91.3% in Brazil^[16]. In the Sub-Saharan Africa DEA 1 prevalence can vary from 78% in Zimbabwe^[17] to 47% in South Africa^[18], and 39.89% in Nigeria.

This work determined the prevalence of DEA 1 blood type in a canine population of Luanda province of Angola, a country on the Sub-Saharan region of Africa, and assessed the risk of alloimmunization and blood transfusion reactions after an incompatible blood transfusion.

To our best knowledge, this is the first description of dog blood types in Angola (Southern Africa). The blood typing results, and demographic characteristics of the population tested are presented on table 1. The calculated probability that a dog will become sensitized following a first-time mismatched blood transfusion was 24.9% and the probability of an acute hemolytic reaction following a second incompatible blood transfusion was approximatly of 6.21%.

Table 1. Demographic characteristics and DEA 1 blood typing results of the dogs tested.

In general, DEA 1 frequency was similar to that reported worldwide, but when compared to other Sub-Saharan African countries some differences were found. The risk of alloimmunization and acute hemolytic transfusion reactions in mismatched blood transfusions were higher than in other African regions. DEA 1 blood typing and/or crossmetching before blood transfusion is recommended. While blood typing tells us the blood group, crossmatching identifies blood incompatibilities that exist beyond the blood groups tested.

Also, results strongly support the idea that knowledge of breed blood types is helpful for building blood donor programs and recruiting donors during emergencies as well, especially if resources are limited for testing.

The results, and outcomes here expressed should be carefully extrapolated to other geographic areas of Angola.

This entry is adapted from the peer-reviewed paper 10.3390/vetsci11090449