The Conficker worm has existed since 2008 and through five distinct versions. Its authors remain unknown and the malware itself exists with something like impunity. Users acquire and spread it without knowing and, by 2009, Conficker had spread to nine million computers, according to f-secure.com. As described in a new paper from researchers at University College London, that power can be explained in part by what it shares with another seemingly impervious infection: HIV. The connection is in an ability known as hybrid spreading.The comparison goes like this. HIV develops with help from both cell-to-cell transmission and through bloodstream transport, which the UCL researchers—led by computer scientist Changwang Zhang—compare to Conficker's ability to spread via both the internet (bloodstream) and local networks (cell to cell). The group crafted a model based on this dual-mode propagation and found that it accurately predicted the development of HIV into full-blown AIDS, e.g. when the immune system can no longer properly function and deadly opportunistic infections arise."Hybrid spreading of HIV is well documented experimentally but its importance to HIV progression has been unclear," Zhang and co. write in PLOS Computational Biology. "In this paper, we introduce a mathematical model of HIV dynamics that explicitly incorporates hybrid spreading. The model output shows excellent agreement to two sets of clinical data from a treatment naive cohort and from the Short Pulse Anti-Retroviral Therapy at Seroconversion trial. The model demonstrates that hybrid spreading is an essential feature of HIV progression, a result which has significant implications for future therapeutic strategies against HIV."
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Both HIV and Conficker navigate a balance between cell-to-cell/computer-to-computer transfer and long-distance internet/bloodstream-based spread. Cell-to-cell transmission has the best chances for success, but the range of potential targets is much smaller. Meanwhile, efforts at spreading the virus globally are able to access a larger pool of targets, but with lower chances of success per target. Earlier this year, Zhang published a paper finding that hybrid spreading is necessary to explain the large outbreak of worms (like Conficker) across the internet."Our results show that the Conficker epidemic is an example of a critically hybrid epidemic, in which the different modes of spreading in isolation do not lead to successful epidemics," Zhang wrote then. "Such hybrid spreading strategies may be used beneficially to provide the most effective strategies for promulgating information across a large population."One potential implication of Zhang's work is in how and when HIV is first treated. Common protocols delay antiviral therapies until the patient's T-cell (immune cell) levels fall below a certain threshold. The UCL researchers argue that their model gives support to a protocol involving "Short Pulse Anti-Retroviral Therapy at Seroconversion" (SPARTAC), which is pretty much what it sounds: As soon as an HIV infection is detected, antiviral therapy is administered."Notably, the model predicts that cell-to-cell spread becomes increasingly effective as infection progresses and thus may present a considerable treatment barrier," Zhang and his group write. So, the longer the gap between infection and antiviral administration, the better positioned the virus is to spread via its most potent cell-to-cell further down the road."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," notes the study's senior co-author, Benny Chain, in a statement. "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."Our model suggests that completely blocking cell-to-cell transfer would prevent progression to AIDS.