Modeling the effect of protection by natural anti-A or -B antibodies on the virus transmission in populations
A deterministic SIR (susceptible, infectious, recovered) model of the transmission dynamics of SARS that takes into account the effect of the protection by anti-histo-blood group natural antibodies was developed. In this model, the whole population was divided according to the different blood groups (A, B, O, or AB) into four interacting subpopulations NA, NB, NO and NAB. For each subpopulation N = S(t) + I(t) + R(t) where S(t), I(t), and R(t) represent, for each blood group, the number of individuals susceptible, infected, or recovered at time t, respectively. Four different populations reflecting the variability in blood groups distributions were studied (Table I): Chinese from Hong Kong, Aïnu from Japan, Amerindians and white Americans from the United States.
Table I  Distribution of ABO blood groups in four different populations used to model the impact of the ABO effect on SARS transmission.
[O]  [A]  [B]  [AB]
Aïnu (Japan)  0.17  0.32  0.337  0.173
Chinese (Hong Kong)  0.422  0.178  0.333  0.067
Caucasians (USA)  0.45  0.40  0.111  0.039
Amerindians (USA)  0.79  0.16  0.046  0.004
The frequencies of each phenotype were obtained from Mourant (1983). Mathematical details are given in the appendix available as supplementary data; the program was written in C++, a 1-day step was used for all the simulations. In each simulation, changes in the number of infected individuals (cases) over time were determined.