A model for the sequential dominance of antigenic variants in African trypanosome infections

被引:32
作者
Frank, SA [1 ]
机构
[1] Univ Calif Irvine, Dept Ecol & Evolut Biol, Irvine, CA 92697 USA
关键词
parasitism; protozoa; Trypanosoma brucei; within-host dynamics;
D O I
10.1098/rspb.1999.0793
中图分类号
Q [生物科学];
学科分类号
07 ; 0710 ; 09 ;
摘要
Trypanosoma brucei infects various domestic and wild mammals in equatorial Africa. The parasite's genome contains several hundred alternative and highly diverged surface antigens, of which only a single one is expressed in any cell. Individual cells occasionally change expression of their surface antigen, allowing them to escape immune surveillance. These switches appear to occur in a partly random way, creating a diverse set of antigenic variants. In spite of this diversity, the parasitaemia develops as a series of outbreaks, each outbreak dominated by relatively few antigenic types. Host-specific immunity eventually clears the dominant antigenic types and a new outbreak follows from antigenic types that have apparently been present all along at low frequency This pattern of sequential dominance by different antigenic types remains unexplained. I use a mathematical model of parasitaemia and host immunity to show that small variations in the rate at which each type switches to other types can explain the observations. My model shows that randomly chosen switch rates do not provide sufficiently ordered parasitaemias to match the observations. Instead, minor modifications of switch rates by natural selection are required to develop a sequence of ordered parasitaemias.
引用
收藏
页码:1397 / 1401
页数:5
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