Adela Chavez, Texas A&M AgriLife Research entomologist and assistant professor in the Texas A&M College of Agriculture and Life Sciences Department of Entomology, Bryan-College Station, grew up in a farming family in Honduras and learned at a young age how ticks can impact animal and human health. Her experiences around beef and dairy production and as a child at play shaped her interests in science and continue to fuel her passion to provide scientific breakthroughs that can prevent or treat tick-borne diseases like Lyme disease and human granulocytic anaplasmosis in humans and Texas cattle fever, bovine babesiosis, in livestock.
“I’ve seen cows unable to stand up because of severe anemia, and so I was interested at a very young age to do something to solve this problem,” she said. “I would go outside and play and come home covered in ticks, and back in those days there wasn’t much information about tick-borne diseases.”
Her sister developed a serious fever after an outing, and the diagnosis was a mosquito-borne virus, but Chavez now suspects it was linked to a tick bite.
A career to solve both human and animal diseases
Chavez focused her early education and career on agriculture and animal health. Since then, she has been committed to finding scientific solutions and creating tools to fight against tick-borne diseases that cause significant problems for humans and animals as well as economic losses around the globe.
Now she is on the front-line in the battle against diseases spread by these parasites. And as the nation and world continues to deal with the physical and economic toll of COVID-19, the importance of researching diseases passed from animal to human has moved to the forefront.
Her latest research was recently published in Nature Communications, and she was also named to a multidisciplinary group of 50 junior scientists from around the country who are focused on various global threats related to animal-borne diseases’ impacts on human health.
Chavez’s efforts are now more important than ever because the chance of pathogens being transferred from parasite to host has risen with tick populations over the last two decades, according to the Centers for Disease Control and Prevention. Total tick-borne disease cases have more than doubled to 50,865 in 2019 compared to 22,257 in 2004.
Lyme disease, the most common tick-borne disease in humans, is estimated to affect 476,000 Americans annually, based on insurance records. This results in costs between $712 million and $1.3 billion, according to John Hopkins Bloomberg School of Public Health. In animals, bovine anaplasmosis, a disease caused by a bacterium transmitted by several tick species, alone is estimated to cost livestock producers $300 million annually. Nevertheless, the overall impact of ticks on livestock operations is likely to be even higher, because it is difficult to measure the parasites’ impact on cattle weights, reduced milk production, aborted calves or other health problems that reduce production.
Chavez said the number of people infected by vector-borne pathogens carried by ticks is also likely much higher than CDC estimates due to misdiagnosis and low report rates in mild cases. Bites can lead to major health issues for healthy hosts and can lead to bad health outcomes for the immunocompromised.
Winning the war against ticks
The bite site is Chavez’s new focus. Her research showed that changes occur on the molecular level as ticks feed and impact the host’s immune response and ability to fight pathogens.
Feeding for ticks can be a long process that can last several days, she said. At some point during feeding, ticks pass along the pathogen as they repeat a cycle of injecting saliva and sucking blood.
This transmission sequence is where Chavez believes micro-RNA and proteins from the tick are transferred to the host to manipulate the immune response in a way that allows the tick to feed. Reduced immune response prevents body responses like blood coagulation, wound closure and any direct immuno-counterattack against the parasite.
“These pathogens are doing more than just taking a ride in the tick,” Chavez said. “The pathogens and ticks have a symbiotic relationship that dates back more than 100 million years.
“It’s an arms race, really,” she said. “The tick bites, and the host’s immune response wants to kill the tick, and there is a fight. The pathogen that has adapted to utilize the tick as a vessel works with it in a symbiotic way in this fight to disrupt the host’s immune response and allows the tick to continue feeding.”
By learning which particular cell types or immune signaling pathways are activated during the response to the tick’s bite, Chavez and other scientists hope to enhance the immune response to stop or treat the infection by tick-borne pathogens.
“The final product would be a vaccine that would make the host immune to the tick and kill the tick before it passes a pathogen,” she said. “My goal is to find tools that prevent disease and are affordable for individuals and small farming operations in the U.S. and around the world.”
Reducing the impact of ticks
Hundreds of tick species exist, and ticks can be found on every continent. All ticks are blood feeders, but there is great diversity among species, including their feeding processes and the diseases they carry.
Available vaccines target some tick species of economic importance in livestock, but the efficacy can be limited when controlling ticks from different strains, Chavez said.
The U.S. Department of Agriculture and its Animal and Plant Health Inspection Service are funding a project focused on developing better vaccines. Chavez started working on that project in 2019 and is purifying material that she expects to begin trials at USDA facilities in October/November.
Chavez and fellow Texas A&M AgriLife entomology scientists are also looking into epigenetic similarities and differences in tick populations. By determining epigenetic markers found in local ticks, health officials can track characteristics, behaviors and pathogens in those populations.
For example, how and where the tick locates itself on vegetation while waiting for a host, or “questing,” appears to be inherited from the tick’s parents. Different tick populations from southern parts and northern parts of the country quest differently, Chavez said.
The difference in questing is one hypothesis as to why Lyme disease is not as prevalent in Texas as it is in northern parts of the country, including Minnesota where partnering scientists exchange data found through tick surveys.
“Lyme disease is present here and throughout the South, but ticks don’t go as high on the vegetation as strains of the same tick species do in the Midwest,” she said. “They don’t transmit to humans or acquire pathogens as much.”
Investigating these epigenetic markers could also be critical to prevention, she said.
Research focused on ticks is increasingly important, Chavez said, because species are expanding their range due to warmer weather patterns and higher numbers of potential hosts like deer. These efforts are also critically important to prevent invasive tick species, like cattle fever ticks found in parts of southern Texas and is especially deadly for cattle, from inflicting catastrophic losses in the U.S.
“Ticks are not a new problem, but there has been more attention on them over the last 20 years, especially on their effects on humans,” Chavez said. “But whether it’s affecting sources of food, or livelihoods or human health, it is important that we learn more about ticks to reduce their impact.”
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