April 03, 2016

Research Roundup: Mosquitos and mice in the fight against Zika

Senior Program Assistant
Zika virus
Photo: CDC/Cynthia Goldsmith

Amid the Zika outbreak and with new vector control approaches in the pipeline, there has been much talk about the feasibility and potential risks and benefits of eradicating mosquitos. National Institute of Allergy and Infectious Diseases (NIAID) Director Dr. Anthony Fauci advocated for mosquito elimination in a recent STAT News article, joking that their only known role in the natural ecosystem is feeding birds. However, Dr. Andrew Dobson, a professor of ecology and evolutionary biology at Princeton University, argues that such an approach would be “naïve and foolish,” noting that there are more than 3,000 mosquito species, hundreds that bite humans, but just three that are responsible for the vast majority of human disease transmission. Further, Dobson suggests that we can’t predict the consequences of mosquito eradication on the natural ecosystem, and that it could lead to the development of insecticide-resistant mosquitos.

Meanwhile, NPR asked experts about the feasibility of eradicating even just one mosquito species and the resources required for it to be successful. First, global coordination mechanisms and high-level political will would be required, i.e., through the appointment of a United Nations mosquito czar. Next, financial resources are a must, with Pennsylvania State University Biologist and Entomologist Dr. Andrew Read estimating that US$250-500 million would be required to eliminate the Aedes aegypti mosquito—responsible for transmitting Zika, yellow fever, dengue, and chikungunya—a high pricetag but one that pales in comparison to the $1.5 billion pharmaceutical company Sanofi spent on developing a vaccine against just one of those diseases, dengue fever. With all the resources in place, the czar would then have to determine which vector control approach to take. As pathogens grow resistant to existing insecticides, both new insecticides and mutant mosquito interventions are under development. British biotech company Oxitec is currently testing its sterile-male mosquitos in Brazil. Oxitec’s mosquitos are released into the wild where they mate with female A. aegypti mosquitos, producing offspring that don’t live to adulthood and consequently can’t infect humans. The approach has resulted in an 82 percent decrease in the presence of A. aegypti larvae in the region in just nine months. Another intervention involves releasing mosquitos infected with Wolbachia bacteria, which then spreads among the mosquito population and can reduce the mosquitos’ ability to produce healthy offspring and to transmit viruses to humans. Finally, scientists are developing mosquitos using “gene-drive” technology, which involves releasing mosquitos genetically modified to be unable to lay eggs or transmit diseases.

A team of scientists at the University of Texas Medical Branch (UTMB) have created a genetically modified mouse that is susceptible to Zika virus, making it the first animal model that can be used to test drugs and vaccines against the virus. The study, published in The American Journal of Tropical Medicine and Hygiene, provides further evidence that Zika is sexually transmitted and that it impacts the nervous system, as the viral load in mice was highest in the spleen, brain, and testes. The team, led by UTMB Virologist Dr. Shannan Rossi, developed the model in just three weeks, an impressive feat for a process that normally takes several months. UTMB scientists are also using the model to test an antiviral drug, developed for dengue fever, against Zika. The mouse model will be invaluable to scientists, particularly in light of the dearth of research on Zika. However, the mouse amnion—in which fetal development takes place—varies significantly from the human amnion, and thus, scientists are continuing to look for animal models that can shed light on the impact of Zika during pregnancy.

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