This story comes to us from the USDA Agriculture Research Service’s AgResearch Magazine by ARS’s Sandra Avant.
The economic impact of cattle fever ticks, including the southern cattle fever tick, Rhipicephalus (Boophilus) microplus, was so severe in the late 1800s that the U.S. Department of Agriculture started an eradication program in the early 1900s to eliminate the deadly disease bovine babesiosis, which is transmitted by this parasitic pest. Although cattle fever ticks were declared eradicated in the United States in 1943, today they are still common in Mexico and can hitchhike on stray livestock, white-tailed deer, and other wildlife that cross the Rio Grande River into Texas.
At the Agricultural Research Service’s Tick and Biting Fly Research Unit in Kerrville, Texas, scientists are looking for ways to get rid of this pest for good. A new vaccine may help.
Insect physiologist Felix D. Guerrero and his colleagues made a significant discovery while sequencing the complicated, huge cattle tick genome, which contains about 2.5 times the DNA of the human genome. Sequencing the genome allowed them to determine the exact sequence of the entire set of tick proteins.
“We identified several proteins that might be good targets to exploit to try to disrupt the cattle tick’s function, and in doing so would likely kill it or at least impact its survival,” Guerrero says. “One of those proteins was aquaporin.”
Aquaporins are water channels that assist the tick in excreting the large amount of water it ingests with a blood meal, he adds. Aquaporins are present in all higher organisms, including arthropods and mammals.
Guerrero and his fellow scientists developed a recombinant tick aquaporin protein vaccine and partnered with the Brazilian Agricultural Research Corporation (Embrapa) to test the vaccine’s ability to protect cattle against infestation. Molecular biologist Renato Andreotti and his team at the Embrapa National Center for Beef Cattle Research in Campo Grande, Brazil, put animals infested with a known amount of cattle tick larvae into two pens. One group was vaccinated with the aquaporin vaccine and the other group was not vaccinated. Researchers compared the number of adult ticks produced on each vaccinated and unvaccinated cow.
“In two trials, we saw a 75-percent and 68-percent reduction in the number of ticks on vaccinated 1-year-old Holstein calves,” Guerrero says. “This demonstrated that the aquaporin protein shows promise as an antigen in cattle vaccines to help prevent cattle fever tick infestations.”
Only a limited number of acaricides (chemicals that kill ticks) are available to cattle producers, and ticks have developed resistance to most, including pyrethroids, organophosphates, and amitraz, Guerrero says. Vaccines provide an alternative to chemical acaricides for tick control. “Presently, only one anti-tick vaccine is commercially available, and it’s produced in Cuba. Our work aims to provide new vaccines for the cattle industry,” he adds.
Although Texas ranchers follow eradication program guidelines and treat their cattle, infested wildlife can keep a cattle fever tick infestation going, Guerrero says. Cattle fever ticks transmit the agents that cause bovine babesiosis (a malaria-like illness) and anaplasmosis (which causes severe anemia), which kill cattle.
“Our research goal is to provide tools for U.S. ranchers to help control cattle fever ticks and prevent reinfestation of the United States,” Guerrero says. “This new vaccine is one more step toward meeting that goal.”
ARS has received a patent on the aquaporin protein vaccine and on another tick vaccine tested at the same time in Brazil. The agency is working with an animal health company, looking at the feasibility of producing a commercial aquaporin vaccine.
I contacted Dr. Felix Guerrero, the Project Leader, for this research for more information. I’m posting his reply here in the comments for all the folks who had questions:
Thanks for running the article and for publicizing the research that my
lab at the USDA-ARS laboratory in Kerrville, TX is doing to give cattle
ranchers scientifically documented and approved alternatives to chemical
pesticides for cattle tick control. I am glad that your readership has
concerns relating to off-target effects, such as those about the spiders
and dung beetles. That concern shows they look at the entire ecosystem.
I am a molecular biologist working with a team of veterinarians, animal
scientists, entomologists, and vaccinologists to see if we can take a
scientific discovery from my lab to the agricultural community with the
assistance of an interested animal health industry partner. We are just
beginning the testing of our vaccines to see if they would be an effective
treatment for cattle ticks, so I cannot give a definitive answer yet about
effects on spiders. I assume your reader was concerned about spiders that
bite cattle? I am not a spider expert and so am not sure what spiders have
a lifecycle that would expose them to blood from vaccinated cattle.
Since this vaccine would be given to an individual bovine as an
injection, such as existing vaccines given to prevent bacterial or viral
infections, unless an organism bites the bovine and ingests a lot of
blood, there should not be any effect. We do not expect there will be
vaccine-derived material on the surface of the bovine or in the manure.
But safety studies should take a look at such possibilities. So we do not
foresee effects upon dung beetles or spiders. However, those safety
studies will look for off-target effects such as you describe.
Even if a spider bites the bovine, I doubt they ingest blood. Only blood
feeding organisms are expected to be affected by a vaccine against cattle
ticks. This vaccine utilizes a cattle tick aquaporin and any company that
decides this vaccine is worth pursuing as an animal health product will
have to work with regulatory agencies to get approval for use in cattle.
I hope this information helps you answer the questions of your readers.
Do not hesitate to contact me if there is any other information you think
would be helpful to you!
Sadly any tick immunization will suffer from our totally incomplete understanding of tick born infections. Ticks carry and infect hosts with multiple organisms at the same time with little if any effective testing available. Use of genetically modified vaccines have great potential value but also pose real risks for unintended effects. The drive to get a vaccine to the market overshadows the need for long term testing to be sure that side effects do not surface months or even years latter. Buyer beware. The best thing to do is to maximize the immunity of your cattle with good pastures and trace minerals and no crowding.
Have there been studies into whether this vaccine will effect other arthropods or insects in addition to attached ticks? This needs to be taken into account if we are to maintain healthy ecosystems.
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