With the Rio Olympics approaching, Zika – the virus confirmed to cause severe neuron damage to newborns – is understandably a worry. After all, the largest sporting event in the world is taking place in the heart of the latest outbreak, and there’s still so much scientists have yet to learn about this elusive pathogen.
With 2.2 billion people potentially at risk from the virus, things are looking grim. However, there may be a light at the end of the tunnel. According to a new model tracking the spread of the virus, it looks like the current outbreak in Latin America may burn itself out within just three years, and there won’t be another one for at least another decade. The Science study, sadly, does point out that the current epidemic cannot be contained using currently available methods.
This modeling, which collated all known available data about transmission rates and the epidemiology of the Zika virus, took into account something few have actually taken time to highlight – those infected by the virus are unlikely to be infected twice. This means that transmission rates between populations will inevitably slow down, and sooner than many have previously assumed.
Eventually, there will be too few people in large population pools to be able to effectively spread the virus, either through sexual transmission or by the more common mosquito vector, and diagnoses will drop off at a considerable pace. This is a process known as “herd immunity.”
“The current explosive epidemic will burn itself out,” Neil Ferguson, professor of mathematical biology at the faculty of medicine in Imperial College London’s School of Public Health, said in a statement. “We predict large-scale transmission will not restart for at least another ten years – until there is a new generation in the population who have not been exposed to the Zika virus.”
An artist's impression of the Zika virus. AutSpray/Shutterstock
Zika has a lot in common with dengue, in that both viruses belong to the Flaviviridae family and they are both transmitted primarily via the Aedes aegypti mosquito. This means that both spread in similar ways, and records of the proliferation of dengue, or other similar viruses, can be used to predict the spread of Zika. As a result, the team’s mathematical models suggest that the most likely scenario is that herd immunity will kick in by the end of next year, and Zika’s spread will rapidly be culled.
Counterintuitively, the team suggest that any efforts to slow viral transmission, like targeting the mosquitos themselves, may not be a good idea. “Slowing transmission between people means the population will take longer to reach the level of herd immunity needed for transmission to stop,” Ferguson added.
This study also suggests that any vaccines that are currently being trialed will not be able to be applied before the drop off begins to occur. In any case, whether you’re designing a vaccine or estimating transmission rates for the Zika virus, there are plenty of complications that may throw a curveball into proceedings, particularly when it comes to the effect the dengue virus may have on those at risk of Zika infection.
Previous research has revealed that if a person has been previously infected by the dengue virus, a subsequent Zika viral infection will either occur 12 times faster than it otherwise would, or it may not occur at all, depending on the antibodies produced by the host. At present, this effect is incredibly difficult to model.
“There are currently more questions surrounding Zika than answers,” Ferguson concluded. “Only through a coordinated global research effort will we find the answers we desperately need.”
Efforts to stop the spread of mosquitos carrying Zika may actually backfire, according to this study. Jung Rattanasiri/Shutterstock