Betinho contracted the virus from contaminated blood supplies he had to take regularly because of his haemophiliac condition. That same condition also meant that he almost died at birth in Minais Gerais in 1935, but he survived to go on to study at the local federal university and to embark on an academic career as a sociologist.
Although not a Christian, he was influenced by the radical theology being practised in Brazil in the early 1960s, and himself believed that sociologists should be involved not simply in the study of society but should attempt to change it. It was in this spirit that he set up the radical left wing Acao Popular, and pressed for revolutionary change in Brazil, one of the most unequal societies in the world.
This kind of activism was highly suspect for the military governments which came to power in Brazil in 1964, and by the end of the decade de Souza, like the current Brazilian president Henrique Cardoso, found himself forced into exile. De Souza went first to Chile, to participate in Salvador Allende's Popular Unity experiment with socialism, but in 1973 once again found the military on his doorstep pressuring him to leave. He took refuge in the Panamanian embassy, and after living in that country, went on to work in Canada, Sweden and France.
He still wanted above all to do "useful" work back in Brazil, and returned as soon as possible after an amnesty was announced for political exiles at the end of the 1970s. Betinho soon set up Brazil's first independent social research centre, the Brazilian Institute for Social and Economic Analysis, which he always adamantly kept free from political and government control. His own position was similarly independent, and, although he helped in the creation of new left-wing political parties that sprang up after the return of civilian government in the mid-Eighties, he never committed himself to any of them.
By this time, both Betinho and his two brothers, one a famous cartoonist who had lampooned the military government, the other a talented musician, had all been infected with contaminated blood. Betinho's brothers died in 1988 of Aids-related illnesses, but Betinho seemed to gain new energy. He set up the Brazilian Interdisciplinary Aids Association to control the health service's blood banks, and started educational campaigns about Aids. At a period when very few public figures were willing to speak about the disease, his courage and lucidity were vitally important in forcing the government to adopt measures to combat the growing problem.
Betinho used the public position these campaigns gave him in a more directly political struggle for ethics in public life when President Fernando Collor de Mello was accused of corruption in 1992. He followed this up by establishing what became known as his "Campaign Against Hunger". Horrified by surveys showing that 32 million Brazilians - almost a quarter of the population - suffered acute hunger, Betinho mobilised the middle classes, workers and others to collect food and money for the dispossessed.
He said: "I have never found any scientific reason why we can't feed our starving millions . . . the problem is that the Brazilian elites don't see the poor. It's a problem of the negation of other people."
The crusade against hunger led to his being proposed as a candidate for the Nobel Peace Prize in 1994. His position was undermined by revelations that, in order to secure finance for the Aids association, he had knowingly taken money from the racketeers running an illegal lottery syndicate in Rio de Janeiro. Betinho himself was philosophical about his fall from grace: "The good side was that it demystified my image. Saints don't exist. People take actions that are either right or not, and that's what matters."
Herbert Jose de Souza, sociologist: born Bocaivu, Minais Gerais, Brazil 13 November 1935; married Maria Nakano (two sons); died Rio de Janeiro 9 August 1997.