CD4 and infection: schweinfurthii chimpanzees in Gombe, Tanzania, that SIVcpzPts infection is associated with a 10 to 16 fold increase in age-corrected risk for death, reduced fertility in SIV positive females in terms of birth rate and survival of off-spring, and an AIDS (acquired immune deficiency syndrome)-like syndrome which correlated with low CD4 counts, revealed by post-mortem immunohistochemistry.