Table 56.1.
Comparing HIV-1 and HIV-2
| Characteristic | HIV-1 | HIV-2 |
|---|---|---|
| Epidemiological | ||
| Geographic spread7 | Worldwide | West Africa; rare elsewhere |
| Risk factors7 | History of STDs, laboratory evidence of STIs, multiple partners, history of commercial sex | Same |
| Age with highest prevalence | 20–34 years | 40–55 years |
| Epidemic trend | Variable | Stable or declining in most countries |
| Global number of cases7 | 40000000 | 2000000a |
| Transmission routes7 | Heterosexual, homosexual, mother-to-child, blood transfusions, needle sharing/incidents | Same |
| Mother-to-child-transmission4 | 20–40% | 1–4% |
| Sexual transmission8 | ⅓–¼ of that of HIV-1 | |
| Clinical | ||
| Median time to progression to AIDS5,6,22 | 10 years | >10 years |
| Kaposi's Sarcoma17 | Common | Less common |
| Proportion of infected subjects that develop | >99% | Unknown, but much lower |
| AIDS if not treated | ||
| Independent predictors of AIDS and mortality5,6,15 | High PVL and low CD4 | High PVL and low CD4 |
| Excess mortality (compared with uninfected adults)18 | 10-fold | 2–3 fold |
| Virological | ||
| Closest simian virus | SIVcpz | SIVsm |
| Homology to closest simian virus | Distant | 75–85% |
| Presumed timing of zoonotic event12 | 1930 | 1940 |
| Presumed number of zoonotic events | 1 (causing worldwide HIV-1 group M epidemic) several (causing sporadic N and M infections) | 8 (equal to number of subtypes) |
| Subtypes9,10,11,23 | Within group M: A, B, C, D, F, G, H, I, J, K, and several circulating recombinant forms | A, B, C, D, E, F, G, H |
| Genes | pol, gag, env, nef, tat, rev, vif, vpr | Same |
| vpu | vpx | |
| Plasma viral load3,5,14,19 | Usually high: 10 000–100 000 copies/ml | Usually low: undetectable to 1000 copies/ml; ⅓–⅕ of subjects have undetectable PVL |
| Proviral load (in asymptomatic subjects)13,14,16,24,25 | Similar | Similar |
| Use of co-receptors21 | CCR5 and CXCR4 | Broader: CCR5 and CXCR4 and several others |
| Sensitive to NNRTI20 | Yes | No |
| Immunological | ||
| CD4 decline14,26 | Fast | Slow |
| Immune activation27,28 | High | Low |
| Neutralizing antibodies | Efficient, broad specificity | Less efficient, narrow specificity |
| CTL29,30,31 | Common, mostly against gag | Same |
| Apoptosis of T cells27,32 | High | Low |
| Cross-reactive responses to other HIV29 | 46% of patients have CTL responses to HIV-2 peptides | 27% of patients have CTL responses to HIV-1 peptides |
STD, sexually transmitted disease; STI, sexually transmitted infection; PVL, plasma viral load; SIV, simian immunodeficiency virus; cpz, chimpanzee; sm, sooty mangabey; CTL, cytotoxic T lymphocyte; NNRTI, non-nucleoside reverse transcriptase inhibitor; PBMC, peripheral blood mononuclear cell.
a
Author's estimate.