Texas Tech University

Environmental Toxicology Professor Gives Testimony on Zika Virus Before House Science Committee

Heidi Toth

May 24, 2016


(VIDEO) Steve Presley spoke to U.S. representatives about his labs’ Zika-related work and his role on the task force for the State of Texas response to Zika and public health protection.

"Science of Zika: The DNA of an Epidemic"

Video begins at 17:53


  • Dr. Kacey Ernst (29:20)
    Associate Professor, Department of Epidemiology and Biostatistics,
    University of Arizona
  • Dr. Daniel Neafsey (38:50)
    Associate Director, Genomic Center for Infectious Disease,
    Broad Institute of MIT and Harvard
  • Dr. Steven Presley (44:32)
    Professor, Department of Environmental Toxicology,
    Texas Tech University
  • Mr. Hadyn Parry (50:18)
    Chief Executive Officer,

  • Testimony is followed by Q&A. (56:20-2:11:22)

Steven M. Presley, a professor of environmental toxicology at Texas Tech University, gave testimony about his work related to the Zika virus in front of the U.S. House of Representatives Committee on Science, Space and Technology on Wednesday (May 25) in Washington, D.C.

Steven M. Presley
Steven M. Presley

Presley's testimony at the hearing, “Science of Zika: The DNA of an Epidemic” will be live-streamed. He was joined on the panel by experts from the University of Arizona, Harvard and Oxitec, an insect control company.

Presley, who is the director of the Biological Threat Research Laboratory and Bioterrorism Response Laboratory at The Institute of Environmental and Human Health (TIEHH), spoke to U.S. representatives about his labs' Zika-related work and his role on the task force for the State of Texas response to Zika and public health protection. Presley's lab is biosafety level three (BSL-3) and allows Texas Tech to be a public resource for the identification and confirmation of biological samples for outbreaks of infectious diseases and other public health emergencies.

In his work at TIEHH, Presley focuses on recognizing the risks and threats associated with infectious pathogens, with the goal of developing and fielding preventive measures against vector-borne infectious and zoonotic diseases. His lab collects and studies mosquitoes not only for Zika but also for West Nile virus, St. Louis encephalitis virus and Chikungunya. He is the chairman of the publications committee and on the science and technology committee of the American Mosquito Control Association and serves as regional director of the South Central United States for the Society for Vector Ecology.

Zika Latest in Chain of Mosquito-Borne Outbreaks to Affect U.S.

Environmental toxicology expert Steven Presley is testifying in front of the House Science Committee about his work with mosquito-borne illnesses and how to combat Zika.

Click image to enlarge.

Steven Presley has been studying arthropod-borne diseases for almost 30 years, looking for clues to sidestep the many serious and sometimes fatal diseases arthropods carry. He's made significant progress in the realm of West Nile virus, dengue fever, malaria and others, but new mosquito-borne illnesses still crop up, leaving him searching for answers in the growing Zika outbreak in the western hemisphere.

Presley, a professor in the Department of Environmental Toxicology at Texas Tech University, also directs the Biological Threat Research Laboratory at The Institute of Environmental and Human Health (TIEHH). This lab is the only place in West Texas equipped to test human samples for certain potentially infectious diseases and where samples of potentially infected mosquitoes go.

It also means Presley will be among the first to know when the Zika virus spreads to West Texas. Although his lab team has yet to test a positive sample, he's watching the mosquito populations closely. Zika worries him. The virus has been found in bodily fluids including saliva, blood, urine, amniotic fluids and semen and has been spread through sexual contact and from a mother to her unborn child in addition to mosquito bites. However, only one in five infected people are symptomatic, meaning 80 percent of those with Zika don't know they have it and aren't taking precautions to keep it from spreading, which is especially problematic in universities, cities and major hubs with travelers from throughout the world.

“Because there's not an intermediate amplifying host, and only one in five people is symptomatic with Zika virus, the transmission cycle is sped up, and people who are amplifying hosts of the virus may not be recognized,” he said. “You have these amplifying hosts out there promulgating the virus, and mosquitoes are biting somebody else without you ever knowing it's occurring in the area.”

Presley's research on mosquito- and other vector-borne illnesses

Prior to coming to Texas Tech, Presley was an active-duty entomologist in the U.S. Navy, including operational and field research on dengue fever and malaria control operations in Africa, Asia and South America. His studies also include:

  • Rift Valley fever (a viral disease that primarily affects domesticated animals and humans, found largely in sub-Saharan Africa)
  • Crimean Congo hemorrhagic fever (caused by a tick-borne virus but transmitted by ticks from animals to humans and through contact with infected bodily fluids; found largely in Eastern and Southern Europe, throughout the Mediterranean, Africa and parts of Asia)
  • Cutaneous leishmaniasis (a parasitic disease found in the tropics, subtropics and southern Europe caused by bites from sand flies; cutaneous leishmaniasis, one of the most common forms, causes skin sores).

Information from the Centers for Disease Control and Prevention

Since leaving the military, Presley has focused his research on diseases closer to home. He studies the effects of various infectious diseases on local wildlife, and his research team was the first to detect and identify the area vector species for West Nile virus in mosquito populations in the area in 2003. Since then they have worked with local and regional public health agencies to screen mosquitoes for pathogens.

The goal in Presley's research is the development and fielding of preventative measures against vector-borne infectious and zoonotic diseases. Because of that focus, he has taken an active role in the Texas Infectious Disease Readiness Task Force, particularly its newly formed Texas Entomology Consultation Group.

He has not studied other ways Zika can be transmitted, such as through sexual contact. However, Presley said he is working to establish a collaborative research relationship with a private company that has developed a high-tech, low-cost, user-friendly, portable handheld system to detect Zika virus and other mosquito-transmitted viruses in a wide range of human clinical and environmental sample types that could make diagnosis quicker, easier and enable researchers to get more accurate data about the number of Zika cases in the United States. An accurate number is hard to determine since so many of the cases are asympomatic.

The fears about Zika


Like West Nile fever, only about 20 percent of people infected with Zika show symptoms, and even most of those are mild cases. However, in a minority of cases, the effects are severe and devastating – microcephaly (below-average sized head and brain) among infants and Guillain-Barré syndrome in otherwise healthy adults. According to the CDC, Guillain-Barré is a rare disorder that causes a person's immune system to attack his or her nerve cells; it can cause muscle weakness and even paralysis. It typically lasts only a few weeks, though some people have long-term nerve damage.

Although the likelihood of either is small, Americans need to be aware of the danger Zika presents and take action to keep themselves safe. Because Americans are focused on the outbreak in Brazil and keeping mosquitoes out of their yard, they may miss the closer danger.

“I believe the major risk to most Americans is the potential for the Zika virus to be sexually transmitted from an asymptomatic person,” Presley said.

In light of the CDC's recent announcement that almost 300 pregnant women in the U.S. and its territories are being monitored for like Zika infection, having correct information is increasingly critical both for treatment, control and accurate reporting.

Combatting the virus and the fear surrounding it

This has to happen from multiple areas, Presley said, involving all levels of government, as well as neighborhoods and individuals. First, mosquitoes are still a risk, and people need to protect themselves from being bitten. People who are protecting themselves from the Culex tarsalis mosquito, which carries West Nile virus, may not be protecting themselves adequately against the Aedes aegypti (the yellow fever mosquito) and albopictus (the Asian tigermosquito) populations, which carry Zika.

Aedes aegypti
Aedes aegypti

“The biology and behavior of these mosquito species differs significantly from the principle mosquito species that transmit West Nile virus, St. Louis encephalitis virus and some other arboviruses in our area, and these differences pose unique challenges for controlling them and personal protection from them,” Presley said. “They prefer to live inside our houses, under furniture and beds and in closets.”

These species need only one to two ounces of standing water in which to lay eggs, making yards and garages even more of a breeding grounds. Additionally, Aedes aegypti and Aedes albopictus are day biters; they are most active after sunrise and just before sunset when it is cooler and relative humidity is higher. They also are “domestic,” meaning they prefer to reproduce and blood-feed near human habitats.

To protect themselves, residents and neighborhood associations should drain any standing water inside and outside the home, treat yards, surrounding vegetation and green spaces with insecticides (follow the instructions on the insecticide container) and wear long sleeves and pants as well as mosquito repellent when outside.

Culex tarsalis
Culex tarsalis

Governmental entities also can take action. Local governments should treat parks and green space, particularly if water collects there, with insecticides to keep mosquitoes from laying eggs. Presley also said more education is needed, both for public individuals and at the professional public health and health care provider level. Individuals and health care providers need to know how to recognize symptoms and how to reduce transmission between individuals.

Although the threat from Zika is new, the process society needs to go through to protect itself is similar for this and many other vector-borne illnesses common in the United States, he said. Such education is especially critical as the U.S. enters prime mosquito season.

“This rapidly evolving Zika virus threat in Texas and throughout the continental United States is just the most recent example of an emerging or resurgent mosquito-borne infectious disease to threaten the public health,” he said. “Last year it was Chikungunya, and there will likely be many more in future years.”