Cdc: emerging infectious diseases are those infections that appeared recently in a population, or those that already existed but are spreading rapidly, in terms of both incidence and geographical distribution (grisotti and. These cases occur and are diagnosed, but doctors and health authorities ignore or fail to report them. (grisotti and avila-pires 2010: 68) Ultimate causes of disease emergence social / political / economic factors. Hiv: lentivirus, member of retrovirus family; 2 main groups composed of 5 different viral families : hiv-1 (m . 95% global cases, n, o types) and hiv-2 (a and b), largely confined to west africa. Producing defects in immune system: loss of lymphocytes, impairment of t cells. Subclinical infection with endemic diseases that tend to activate the immune system (eg, tb, malaria) appear to accelerate its expression. Results in opportunistic infections, pneumocystis pneumonia, kaposi"s sarcoma, cytomegalovirus, yeast infections, cervical cancer, tb, etc.