How did the ancestral HIV-1 group M retrovirus get to Leopoldville from southeastern Cameroon?

In previous papers in this journal, I have described and elaborated a hypothesis for the origin and evolution of a strain of HIV that has produced a lethal pandemic. Here I address the provocative question of how the ancestral HIV-1 group M retrovirus got to Leopoldville (Kinshasa, where the pandemic clearly spawned) from southeastern Cameroon (where the HIV-1 strains all seemed to originate from transfer of SIV(cpz) to humans). Consistent with the phylogenetic history of HIV-1 group M (e.g., by Korber et al.), I place the critical relocation of the ancestral HIV-1 in the timeframe 1920-1927. However, unlike other hypotheses, I believe that the ancestral retrovirus was already well adapted to humans and can be identified as HIV-1 Group M subtype A(pre)-1927. Based on documents from that time period (1920-1928), it can be shown that it was not unusual for native Africans to be brought as far as 500 miles for treatment at the Leopoldville clinic (national borders were no issue because health agencies had mandate to work throughout Cameroon and Congo-Brazzaville). Specifically, sleeping sickness (trypanosomiasis) was one of the diseases of most concern at the Leopoldville clinic; in the period 1926-1928 there was an outbreak of sleeping sickness in Cameroon; and one of the native African children in the pamaquine (plasmoquineTM) study that I believe selected for the major HIV-1 group M subgroups had trypanosomiasis. Thus, this child (or other patients/relatives from Cameroon) could have brought the ancestral HIV-1 group M retrovirus to the Leopoldville laboratory and spread it among the group of children who were undergoing treatment for malaria between February and August 1927. The diagnosis and monitoring of these protozoan diseases (trypanosomiasis and malaria) involved repetitive sampling of blood, which provides many opportunities for spreading the ancestral HIV-1 infection.