Infectious Disease Postdoc/Clinician
Department of Pediatrics, University Hospital, Syracuse NY
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Alex Russell is wrong on several counts, although he does bring up a cogent point: that a large proportion of the heterosexual HIV cases in the UK are in newly arrived immigrants or from sexual contact overseas. I fail to see though how this detracts from the premise that HIV is sexually transmitted: by its very nature, sexual contact is selective in the populations to which it would spread.
The idea that retroviruses are always vertically transmitted stems sounds strikingly similar to words written by Prof P Duesberg in "Inventing the AIDS virus". A better title would be "Inventing an argument against the AIDS virus." It is a falsehood. It is true than endogenous retroelements are transmitted in a Mendellian fashion, but exogenous viruses are not. Duesberg argues his case conveniently ignoring the infant mortality due to untreated perinatal HIV infection, which destroys all logic of HIV being a harmless passenger virus with maternal transmission. HIV is the rule, not the exception!
ATL was first diagnosed in 1977. HTLV-1 was not discovered until 1980. AIDS was described in 1981, HIV was not discovered until 1983. The disease pre-dated the discovery of the causative agent in each case [1-4]. It took a further 2-3 years after the discovery of each virus to formally give a causative role in their respective diseases [5-6].
Mr Russel is right in that the retrovirologists were hoping to find a disease: acute cancer. Animal models of retroviruses were highly biased towards acutely transforming infections leading to cancer. No such human pathogen has been found, despite the initial hopes. The human pathogens are more closely related to lentiviruses such as Maedi-Visna Virus of sheep - an example of bias failing utterly to affect the outcome. This bias is clear if one reads the work of Duesberg (a prominent investigator of Rous Sarcoma Virus) and his arguments against HIV causing AIDS (one being that "retroviruses always cause acute infections" and another being that "retroviruses never kill infected cells").
New diseases are always being found, and old diseases are diagnosed with better efficiency. Such is progress! The recent appearance of HIV at least correlates nicely with the timing of the invasion of the African area home to the Central Chimp (pan troglodytes troglodytes) which by no mean feat carries the closest relative to HIV-1. Post-WW2 logging and transport, coupled with forced alterations in the native lifestyle and the bushmeat trade, made for a bad combination of exposure and travel factors that facilitated the spread of a blood-borne, sexually transmitted infection.
Retroviruses as a species have been around for far longer than a few hundred years. Humans and apes have amylase in their saliva in addition to their normal pancreatic secretions due to an ancestral retrovirus- induced mutation - not true for old world monkeys, never mind any other animal. The mamallian placenta utilises an envelope protein of an endogenous retrovirus to form the syncitiotrophoblast layer. No doubt great plagues of retroviruses swept across the world tweaking evolution as they integrated into the various germlines - it's just that we happen to be around and technologically aware enough to see this one.
From an academic viewpoint, it's interesting to ask whether in a few hundred thousand years' time the active CCR5/CCR3/CCR2 receptors will have been purged from the human genome... Due to the fact that to do so every carrier of those genes would have to have been killed prior to procreation, one rather hopes not!
1. Uchiyama et al Adult T cell Leukemia: clinical and hematological features of 16 cases. Blood. 1977;50:481-492
2. Poiesz et al. Detection and isolation of type C retrovirus particles from fresh and cultured lymphocytes of a patient with cutaneous T-cell lymphoma. Proc Natl Acad Sci U S A. 1980 Dec;77(12):7415-9.
3. CDC Pneumocystic pneumonia - Los Angeles. MMWR 1981; 30:250-252
4. Barre-Sinoussi et al. Isolation of a T-lymphotrophic retrovirus from a patient at risk for acquired immune deficiency syndrome (AIDS). Science 1983;220:868-871
5. Popovic et al. The virus of Japanese Adult T cell leukemia is a member of the human T cell lymphotrophic virus group. Nature 1982;300:63- 66
6. Coffin et al. Human immunodeficiency viruses. Science 1986;232:697
Competing interests: None declared