For decades, researchers have tried to develop an effective vaccine for Babesia bovis, a tick-borne disease that annually kills millions of cattle worldwide.
According to research recently published in the International Journal for Parasitology, scientists at the Agricultural Research Service-United States Department of Agriculture and Washington State University may finally know where to start.
USDA-ARS tick-borne disease experts Drs Massaro Ueti and Carlos Suarez and support scientist Carl Johnson, in collaboration with WSU's College of Veterinary Medicine, have identified which genes may be critically important to the survival and spread of the disease in ticks and mammals.
Dr. Ueti, a research veterinary medical officer at the USDA-ARS and adjunct professor in the WSU Department of Veterinary Microbiology and Pathology, led the work with longtime WSU tick disease expert Dr. Kelly Brayton.
"In order to determine a viable target for a vaccine, we have to know which genes are critical for the parasite's replication and survivability," Dr. Ueti said. "Now we have an idea which genes to target to prevent the disease's outcome in the blood and in ticks."
In addition to anemia, fever, abortion and death, Babesia bovis annually costs cattlemen millions due to loss in milk and meat production.
The disease is caused by a parasite that develops inside a tick's gut and is eventually spread to animals through the blood following a bite from larvae that hatch from the infected tick. Once in the target animals, the parasite invades the red blood cells and causes severe illness.
Dr. Ueti said the USDA-ARS and WSU research team used RNA sequencing to identify important Babesia genes. They specifically looked for genes encoding proteins that were active when the parasite was in the blood of a mammalian host or in the tick.
The study identified about 1,000 genes in the parasite more highly expressed in the mammalian host and about 900 genes that were expressed more highly when Babesia was in the tick.
Considering the gene's activity at the time of infection, Ueti and his team predicted these genes were critical for the survivability and replication of the disease.
While the disease is not prevalent in the United States, Ueti said neighboring Mexico has several outbreaks every year and a major outbreak in the United States could result in large economic losses for cattlemen. He said economic losses in Latin America from the disease surpass $20 million yearly.
"The goal is to prevent the disease from coming to the United States," Ueti said. In addition to Latin America, the disease is also widespread in Africa, Asia and Australia."
Now that the team has identified genes that could be viable vaccine targets, Ueti said the next step is to explore their functions and narrow the pool.
Ueti's research team at the USDA-ARS, which consists partly of WSU graduate students, plans to start with a few "promising" genes.
One gene identified in the tick particularly caught his eye - a gene that is exclusively expressed by the parasite during tick infection.
"There is currently no function associated with this gene because it is unlike any other known gene," Ueti said. "Perhaps, the gene is critical for the parasite to spread to the tick's ovaries."
Ueti said if researchers can stop the infection in the tick, the tick would not be able to spread the parasite, essentially solving the matter for the U.S. and global cattle industries.
