HIV has become more virulent over time, not less, European study finds

The largest cohort study ever to look at CD4 count and viral loads in HIV-positive people around the time of diagnosis has found evidence that HIV, at least in Europe, has become more virulent over time. The average time taken to reach a CD4 count below 350 cells/mm3 has halved over the last 25 years, researchers calculate.

The study of 15,875 patients within the pan-European CASCADE cohort finds that the estimated CD4 count after seroconversion (a measure of how strongly the acute phase of HIV infection attacks the immune system) fell from 770 cells/mm3 in 1979 to 570 cells/mm3 in 2002.

The average ‘set point’ viral load – the rate at which HIV reproduces in the absence of treatment, after the initial burst of viral replication – increased from 11,200 copies/ml in 1980 to 31,000 copies/ml in 2002 (with a possible slight decline to 25,500 copies/ml by 2008).

The rate at which CD4 counts declined increased during the same time period. This meant that the average time taken for the CD4 count of a person who seroconverted in 1980 to fall below the current UK treatment-initiation threshold of 350 cells/mm3 was seven years; by 2002 this had halved to 3.4 years.


Contrast with African study

These figures differ strikingly from a recently published study (Payne et al.) which finds that HIV’s replicative capacity has declined over time, at least in southern Africa. This study received wide publicity in the world’s media after being reported by the BBC on World AIDS Day.

In this study, which was originally reported by Aidsmap from the HIV Vaccine Conference in 2013, researchers from the University of Oxford found that HIV from Gaborone in Botswana, where HIV prevalence peaked in the year 2000, reproduced 11% more slowly than virus in Durban, where HIV prevalence peaked in 2010.

In addition, the average viral load in the untreated population was 15,000 copies/ml in Gaborone and 29,000 copies/ml in Durban – though it appeared to have started falling very recently there too.

Lead researcher Philip Goulder also found that HIV in Gaborone had more resistance mutations against human immune system proteins. The research group therefore speculated that HIV, in trying to evade human immune defences, was mutating over time into a less virulent form.


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