Mosquitoes are the deadliest animals in the world. Diseases carried by mosquitoes kill more than 700,000 people annually, and one of the deadliest diseases carried by mosquitoes is malaria. Malaria is caused by the parasite Plasmodium falciparum; in 2021, there were around 247,000,000 cases of the disease globally. Furthermore, over 619,000 people died from the disease in that same year. Malaria is most prominent in tropical and subtropical climates, and approximately half of the world’s population is at risk of the disease. Recent discoveries have revealed that CRISPR technology, a genome-editing tool, may be able to significantly reduce the rate of malaria transmission in two principal ways—by minimizing mosquito populations and by altering the way the disease’s parasite is transmitted.
In order to create malaria-resistant mosquitoes, scientists can use CRISPR technology to insert gene drives into organisms’ genomes. While Mendelian inheritance states that alleles of the same gene are distributed evenly during meiosis (fifty percent to fifty percent), meiotic drive allows certain alleles to be distributed more often (i.e. ninety percent to ten percent). In this example, the allele that gets passed on ninety percent of the time would be considered the driving gene, and the latter the wild-type gene. CRISPR gene drives can be embedded in the organism’s chromosomes in a way that allows these genes to be passed onto offspring. The CRISPR gene drive removes part of the DNA in the chromosome and replaces it, allowing scientists to precisely modify an organism’s genome.
The first studied way of reducing malaria rates would be using CRISPR technology to drive malaria-infected mosquitoes to extinction. This method works by inflicting sterility on the mosquitoes with a driving gene. Through lab testing, the driving gene increased in prevalence among the mosquito population in all trials, demonstrating the effectiveness of the study. In one study, one hundred percent of mosquitoes eventually had the driving gene that caused sterility, and this led to the extinction of the population. While this method could be effective in removing malaria from local mosquito populations, questions have been raised regarding its long-term effectiveness. If malaria-infected mosquitoes are driven to extinction in one area, mosquitoes from neighboring areas could migrate over and reinfect the population with malaria. Furthermore, entirely eliminating local populations of mosquitoes raises ecological concerns, as they and their larvae serve as important food sources for fish, bats, birds, and other animals.
The second possible way of reducing malaria rates would be to lower mosquitoes’ ability to transmit the parasite that causes the disease. To achieve this, a drive gene could be inserted into a mosquito’s genome that would cause it to kill the malaria parasite which has infected the mosquito. As opposed to the method of driving mosquitoes to extinction, this approach would prevent a malaria outbreak from infected mosquitoes migrating to an area where the mosquitoes’ genomes were edited. This is because, as the migrant mosquitoes mate with the local population, the driving gene would prevail through generations, causing newly-born mosquitoes to be unable to transmit malaria to humans. This suggests that this method may be more effective, but neither method has been studied outside of laboratories.
Despite these promising advances, it is imperative to consider the ethical implications of using CRISPR genome editing. In the United States, two thousand cases of malaria are diagnosed each year. Compared to the global rate of over 247 million cases, this is low. Because of this, decisions regarding the use of CRISPR technology to fight malaria should be made by the populations most affected by the fatal disease. The wide introduction of genetically modified mosquitoes into wild populations may hold unforeseen environmental consequences and, thus, the input of local communities is essential. Finally, such a project would set a potentially dangerous precedent for acceptable use of genetic modification. At the same time, there is a moral argument against inaction. Given the massive death toll from malaria each year, some have argued that there is an obligation to use such technology to prevent further deaths as soon as possible. Striking a balance between ethical deliberation and the imperative to address this global health crisis is crucial as we navigate the path forward in combating malaria.
