Path-breaking study likens HIV to computer viruses

New findings by HIV specialists who teamed with network security experts at the University College London (UCL) suggest that the method that the killer virus uses to spread through the body is similar to how computer worms spread to infect multiple computers.

The study essentially concludes that HIV should be treated early to prevent full-blown AIDS.

World Health Organization (WHO) guidelines recommend that HIV treatment should only commence once the number of T cells in the bloodstream fall below a certain level. However, UCL's model forecasts that treatment should begin as soon as possible after infection to prevent AIDS from developing in the long term.

The experts at UCL have created a new model for HIV progression, from which they noticed that HIV spreads through the body using two methods - via the bloodstream; or directly between cells.

This is similar to how computer worms spread through both the internet and local networks to infect as many computers as possible.

The new HIV progression model for this "hybrid spreading" accurately predicted patients' progression from HIV to AIDS in a major clinical trial.

Detailed sample data from 17 London-based patients were used to verify the model, indicating that "hybrid spreading" provides the most suitable explanation for HIV progression and highlights the benefits of early treatment.

HIV infects CD4+ T cells - the cells that play a vital role in the immune system and protect people from diseases. As HIV advances, the number of active T cells in the body reduce until the immune system can no longer function properly - a state known as acquired immune deficiency syndrome or AIDS.

"The number of HIV cells in the bloodstream is always relatively low, and our model shows that HIV spread through the bloodstream alone would not be enough to cause AIDS," explains co-senior author Prof Benny Chain.

"It is likely that when HIV gains a foothold somewhere with a high T cell population, such as the gut, it uses a cell-to-cell transfer mechanism to efficiently spread directly between them. As such, if HIV has already spread to an area rich in T cells by the time treatment begins, preventing its spread through the bloodstream will not stop AIDS. Our model suggests that completely blocking cell-to-cell transfer would prevent progression to AIDS, highlighting the need to develop new treatments."

The inspiration for the HIV progression model came from similarities between HIV and computer worms such as the highly destructive 'Conficker' worm. Conficker was first detected in 2008, when it infected military and police computer networks across Europe. It is still active today.

Lead author Changwang Zhang, said, "HIV and Conficker have a lot in common. They both use hybrid-spreading mechanisms, persist for a very long time and are incredibly difficult to eradicate. Our model enables us to explain these important properties and to predict the infection process."

Changwang's supervisor, co-author Dr Shi Zhou, added, "Although the cybersecurity community organized an unprecedented collaboration to tackle Conficker, they still failed to eliminate Conficker from the Internet. HIV researchers face a similar problem. We hope that our new understanding of hybrid epidemics will help us to fight against Conficker and HIV."

Previous laboratory research led by co-senior author Dr Clare Jolly has shown that some drugs are better than others at stopping HIV from spreading directly between cells. However, as the spread occurs inside internal organs, it is unfeasible to measure cell-to-cell spread in patients directly.

"With this new model, we should be able to assess the effectiveness of drugs against different modes of HIV spread in real patients," explained Jolly.

"This could prove invaluable when interpreting the results of drug trials to understand what works and why. Using computer models to understand processes that we cannot directly observe is common in the physical sciences and supports many fundamental theories. Our model provides strong evidence that cell-to-cell spread is an important part of HIV spread. We hope to show this directly in future animal studies," she said.