Researchers at the University of Florida (U.F.) College of Veterinary Medicine say proteins common to multiple strains of Anaplasma marginale, a tick-borne pathogen could hold the key to developing an effective vaccine against the disease.
The disease costs the U.S. cattle industry an estimated $300 million a year. UF veterinary scientists sequenced the genes of multiple strains of the bacteria to identify common substances that could be candidates for vaccine development.
Anaplasma bacteria infect red blood cells making infected animals develop a fever, difficulty breathing and anemia. It's estimated that 30 percent of the animals that contract bovine anaplasmosis die.
“At the DNA level, we examined genes to determine how similar they are among various strains of the disease,” said Michael J. Dark, DVM, Ph.D., an assistant professor in the college’s department of infectious diseases and pathology. “If they show similarity, they are probably better vaccine candidates because they would presumably offer cross-protection against multiple strains.”
Attempts have been made since the early 1900s to develop a vaccine against Anaplasma marginale, but none have provided complete protection against infection with different strains of the bacteria, Dr. Dark said. Previous studies focused on two particular proteins, MSP2 and MSP3, which are known to protect against certain strains, but which have not provided universal protection.
The research team used pyrosequencing to compare multiple strains of Anaplasma marginale and determine which showed fewer DNA changes from strain to strain.
Maria B. Farias, UF HSC News
Anthony F. Barbet (left) and Michael J. Dark, researchers with the University of Florida College of Veterinary Medicine, pose next to genome-sequencing equipment at UF's Interdisciplinary Center for Biotechnology Research.
“No vaccine has been proven 100 percent effective against all strains, which is necessary for an effective vaccine,” Dark said. “Ideally, the perfect vaccine would also have other characteristics, such as not needing to be refrigerated; otherwise in places like Africa, you’d never be able to use it. You’d also want a vaccine to be effective quickly and long-lasting, hopefully for the life of the animal, or at least so that it wouldn’t need booster shots every year.”
But the disease is difficult to defend against, for several reasons.
“The biology of Anaplasma marginale is more difficult to protect against, because the organism has evolved in order to infect cattle for life,” Dark said. “Because of its ability to adapt and evade the immune system, this disease has made our lives that much more difficult in terms of trying to find a vaccine that is effective.”
Researchers say more is understood about the way in which Anaplasma affects the immune system than is known about many human diseases and even many other tick-borne diseases that affect livestock and other animals. Yet, despite that knowledge, a vaccine that protects against every strain hasn’t been developed.
“We are starting to get into more of the details as to what makes up the organism, but what is the difference between Anaplasma marginale in Florida and in Puerto Rico, and how can we use genetic information to determine where a disease comes from?” Dark said. “We have a lot of questions when we can look at all these organisms quickly at the genetic level and we can also get more information than we ever have before.”