For the first time, researchers have shown that the number of parasites each mosquito carries influences the chance of successful malaria infection.
The new findings, from scientists at Imperial College London, may also explain why the only registered malaria vaccine, RTS,S, has had only partial efficacy in recent trials.
Not every infectious mosquito bite will result in malaria. To determine the intensity of malaria transmission, researchers and international organizations like the World Health Organization currently rely on a measure called the entomological inoculation rate (EIR): the average number of potentially infectious mosquito bites per person per year.
However, this does not take into account how infectious each of those bites may be – each bite is considered equally infectious. Previous studies using needle-injected parasites have suggested this may not be the case, but there have been no comprehensive studies using biting mosquitoes, which more accurately reflect real-world scenarios.
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Now, in a study funded by the PATH Malaria Vaccine Initiative and the Medical Research Council, published in the journal PLOS Pathogens, researchers have determined that the number of parasites each individual mosquito carries influences whether a person will develop malaria. Some mosquitoes can be ‘hyperinfected’, making them particularly likely to pass on the disease.
Study co-author Dr Andrew Blagborough, from the Department of Life Sciences at Imperial, said: “These findings could have significant implications for public health. We have shown that the concept of relying on the number of bites alone to predict malarial burden is flawed, and has probably hampered the successful use of control measures and the development of effective vaccines.
