Texas harbors two species of mosquito that can potentially spread the Zika virus. AgriLife researchers target the “disease triangle” for stopping Zika and similar pathogens.
Before Zika cast fears over the 2016 Summer Olympics, before the disease appeared in headlines, AgriLife Research was already working to counter diseases like Zika.
For our work on insect-transmitted diseases, the Texas Legislature is granting our agency roughly $5 million in 2016–2017, and we are putting that funding to use. Two additional experts will join AgriLife Research in August.
Our state’s climate and location set us at risk for Zika and many similar diseases, which cost Texas hundreds of millions of dollars in lost productivity and in medical and veterinary expenses.
Texas harbors two species of mosquito that can potentially spread Zika. These mosquitoes can also spread chikungunya, dengue fever, and yellow fever. In Texas and beyond, insects and ticks transmit a wide variety of pathogens that strike humans, animals, and plants—causing malaria, Lyme disease, West Nile virus, Chagas disease, equine encephalitis, heartworm in dogs, the wheat streak mosaic virus, citrus greening disease, and more. AgriLife researchers are working to find solutions for each of these.
As treatments, vaccines, and other control strategies for Zika are sought, many questions about the disease remain to be answered.
The Zika virus did not cause much concern when it was first discovered in Uganda in 1947. Most people seem to have no symptoms at all during a Zika infection; others experience a low-grade fever, a rash, joint pain, and reddened eyes.
An alarming new set of symptoms appeared after the disease struck a large population with no immunity to it in Brazil in May 2015. Zika has now been linked to higher rates of miscarriages, stillbirths, and major birth defects in babies of women who are infected with the Zika virus while pregnant. Neither the range nor the rates of birth defects are fully understood. The virus has also been linked to an uptick in cases of Guillain-Barre Syndrome, a rare neurological illness that causes paralysis in adults.
More than 20 countries have now experienced Zika outbreaks. Two species of mosquitoes are known to spread Zika: the yellow fever mosquito, Aedes aegypti, and the Asian tiger mosquito, Aedes albopictus. As it happens, both species thrive in Texas.
It is not known whether mosquitoes in Texas have acquired the virus. If they do acquire the virus, it is not known exactly how large or persistent an outbreak our state might expect.
Targeting the disease triangle
A vector-borne disease outbreak requires three things: a vector carrying the pathogen (such as an Aedes aegypti mosquito infected with the Zika virus), a susceptible host population (such as humans with no immunity to Zika), and the right environment (not too cool). Controlling an insect-transmitted disease such as Zika involves targeting at least one point of the “disease triangle.”
“If you don’t have all three, you don’t have disease,” says Dr. David Ragsdale, AgriLife Research scientist and head of the Texas A&M Department of Entomology.
Accordingly, AgriLife researchers are studying how to stop Zika at each of these three points.
Among those focusing on the mosquito and the virus are Drs. Zach Adelman and Kevin Myles, who start work on August 1 as AgriLife Research scientists in the Department of Entomology. Long-time collaborators at Virginia Tech, Drs. Adelman and Myles are world-renowned for their work on viruses that replicate in mosquitoes and animals or humans. Dr. Myles is working to understand the basic biology of how these viruses replicate in mosquitoes. One of Dr. Adelman’s projects has involved creating mosquitoes that are resistant to viruses such as Zika.
Dr. Gabriel Hamer, also an AgriLife Research scientist in the Department of Entomology, is leading studies into how different environments help or hinder the transmission of diseases like Zika. One project in various parts of South Texas will capture mosquitoes near houses and test them for Zika, chikungunya, and dengue viruses. South Texas has seen small, sporadic outbreaks of dengue, Dr. Hamer says, and this new research will help determine the size of Zika outbreaks we may see in the future. The team will also study how often mosquitoes are biting people indoors and how conducive various landscapes are to the spread of diseases.
Among those helping is Dr. Patricia Pietrantonio, a Texas A&M AgriLife Research Fellow in the Department of Entomology. She and her students and collaborators have recently discovered a way to block certain taste receptors in female Aedes aegypti, making the mosquitoes fly away from sugar solutions. If these results can be expanded, the work may pave the way for new, specific types of mosquito repellent.
In addition, AgriLife Research is working with colleagues in AgriLife Extension and the Texas A&M Health Science Center to help protect people from Zika and mosquito bites. (See an AgriLife Extension page with brochures and videos or the Zika360 informational site from the Health Science Center.)
Zika is unlikely to invade and sweep through the United States, says Dr. Hamer. Air conditioning in homes and screens on windows keep mosquitoes out of houses and largely cut down on mosquito-human contact. But sporadic local transmission is certainly possible in many locations in the United States, he says. Zika may not cause large numbers of injuries or fatalities, he says, but we cannot trivialize the lives that the disease does affect.
The world’s experts have been compiling lists of severe mosquito-borne viruses for which to prepare, says Dr. Ragsdale. But before this year, Zika was not on any such list. Hundreds of mosquito-borne viruses have been discovered; untold numbers will likely emerge, he says.
In response to new, emerging, and well-known diseases, AgriLife researchers in a broad range of fields are learning how to combat an even broader range of human, animal, and plant illnesses caused by insects and ticks.
While advances are made in these disparate fields, collaborations across fields can help uncover solutions and new applications of standard research methods — such as the ability to predict the scope of an outbreak of a new disease, says Dr. Hamer.
His co-investigator for the projects in South Texas is Dr. Ismael Badillo-Vargas, who was hired this year as a vector entomologist at the AgriLife Research and Extension Center at Weslaco. Dr. Badillo-Vargas specializes in insect-borne plant diseases but is expanding his research portfolio as he works with Dr. Hamer.