VIRAL FACTORS THAT INFLUENCE LEVEL OF VIREMIA

One potential factor that influences level of viremia is viral fitness. There are several examples of specific strains of HIV that are associated with less virulent infection. Early data for this were found in simian models.

The Sydney Blood Bank Cohort is a group of eight blood transfusion recipients who acquired HIV from a single donor, the ninth member of the cohort. These patients were described in 1992 after infection with HIV-contaminated blood products administered between 1980 and 1984. Despite documented HIV infection, disease progression in the majority of these individuals was noted to be very slow, leading to the theory that the virus with which they were infected was somehow attenuated.⁹ Sequence analysis revealed that their virus harbored a deletion of 150 base pairs in the Nef-LTR (long terminal repeats) overlap region as well as duplications and rearrangements of the Sp1 transcription factor binding site and the nuclear factor κ-B binding site within the LTR.¹⁰ Twenty or more years after their HIV infection, the living members of this cohort continue to have averted any AIDS-defining illnesses. One of the nine patients died due to Pneumocystis jerovecii pneumonia. It is unclear, however, if the immunocompromise that led to this opportunistic infection was secondary to HIV infection or other therapies for systemic lupus erythematosus. Two of the nine died of causes unrelated to HIV infection. Three recipients and the donor have low but detectable viremia, with slowly declining CD4⁺ counts. The other two recipients have undetectable viral loads but still demonstrate slowly declining CD4⁺ counts.¹¹ Other examples of HIV mutations that attenuate virulence have been described but are beyond the scope of this chapter.¹²